A very pretty 2009 Suzuki V Strom 650 came into the shop last week. She looked showroom fresh, with less than 2k miles on her. Needless to say, she had been parked for years...and sadly, with a half full tank of gas...which, predictably, turned into a tank full of rust.
The owner had already cleaned the tank and replaced some or all of the fuel pump assembly, which lives inside the tank itself, but despite these ministrations, she would bog down under load. She idled like a champ, but just wouldn't pull when the rider cranked on the throttle. Very frustrating for the owner.
There are a number of esoteric possible causes for that behavior, but the most obvious thing to check is fuel pressure, which is a proxy for looking at fuel flow. This is a fuel injected bike, so fuel pressure is supposed to be pretty high, around 60 PSI. Fuel injectors just won't work right if the pressure gets too low. And if the fuel pump assembly cannot keep up with the fuel demand from the engine (as the engine control computer tries to get it to make more power), then the fuel pressure in the fuel supply line is going to drop.
Because spraying 60 PSI gas around your shop is a bad idea, selecting the right fuel pressure test rig is important. Fortunately, bike manufacturers have largely selected standardized fuel line fittings when they design their bikes. In this case one of the mid-size quick disconnect fittings was just the ticket and that allowed disconnecting the fuel line from the tank, plugging in the tester T-connector, reconnecting the fuel line to the Tee and then hooking up the pressure gauge to the open end of the Tee. The results can be seen at the links below...
Start and Blip Throttle and Advance to Higher RPM
What you see here is a significant drop in fuel pressure as engine RPM is increased...despite the fact that the bike is just sitting in the shop in neutral, not even spinning the back tire. So even with zero load on the engine, the fuel pressure drops...a lot. You might even notice in the second video that you can hear the RPM begin to drop (despite increasing throttle) when fuel pressure gets near 20 PSI. It is significant that the pressure drop is smooth. Pressure rolls off steadily as RPM increases. It does not, for example, spike low intermittently and then pop back, which might suggest an intermittent electrical connection to the (electric) fuel pump. Nope, this sure looks like plain old low flow. The fuel pump assembly just cannot keep up.
Now why say "fuel pump assembly" and not "fuel pump"? Because inside the tank there is not only a fuel screen / filter, there is also a pressure regulator, as well as the pump itself. Poor flow could be caused by problems with any one of them, not to mention the possibility that the fuel pump assembly components themselves may have been misassembled and are leaking fuel from the pressurized lines inside the tank into the low pressure area inside the tank itself. That would not produce a fuel leak that is visible outside the tank, but it could cause a pressure drop in the fuel line when fuel demand increases.
So, how did this all turn out? We don't know yet. Now that he has a solid answer on the fuel pressure question, he and his bike are back home awaiting the arrival of a new Suzuki OEM Fuel Pump assembly, which he will install after taking another good look inside that tank...to see if another cleanup is in order before installing the new pump. Stay tuned!
What does every mechanic want most? New wrench set? A better set of screwdrivers? Nope. In the middle of just about every job, at some point we say "Damn, I need one more hand!"
Well, when it comes to changing tires, it couldn't happen more often. Fortunately, some bright guy came up with a way to add and extra "hand" and a very strong arm, to a tire changer.
The need is pretty simple. To demount or mount a tire, the sidewall needs to be pushed towards the center of the wheel. Some tires make that VERY difficult, particularly, low profile, high performance tires...the sort you might find on large, powerful bikes. With the advent of "helper arms" on tire changers, jobs that are very difficult with conventional tools become far easier...if not downright easy.
The helper arm, the black mechanism shown above, swings an air ram that is attached to a plastic foot, over a wheel and tire that has been clamped to the turntable. With the press of an air valve, the ram presses the foot down onto the sidewall as far as necessary to put the bead into the "drop zone" (the smaller diameter inner section of the wheel) which now gives enough clearance for the tire to be shifted sideways on the wheel, allowing the bead to be lifted over (demount) or pressed past (mount) the opposite side of the wheel. The arm is double jointed and the foot pivots, allowing the air ram to maintain pressure on the tire, even as the wheel is rotated on the turntable. Pretty nifty.
CLICK HERE to see it in action!
See that burned wire?
When this 2002 Honda VTX 1800C heavy cruiser came into the shop, she had been parked for 5 years with an electrical bug. Over the months preceding her last ride, she had run worse and worse until finally an attempted restart resulted in smoke curling up from under the seat and fuel tank. The owner wisely gave up trying to start the engine so, thankfully, a fireball was avoided. The owner had some wrenching experience, so he pulled the seat and tank and found burned wires but no blown fuses. Nobody seemed to have any clues about what to do, so the bike just sat.
When the VTX came in, other than being partially disassembled, she was pretty as a picture...but missing her battery and had a third of a tank of rusty gas. Some of the smoked wires were visible and the story was that she had run very badly at low RPM before she finally died, and that part of the difficulty before the bad running developed, was that attempted starts often failed because the starter motor often wouldn't turn. Some mechanical pundits had suggested a bad battery, others suggested a bad starter, others suggested a bad starter relay, all of which had been replaced on various occasions to no avail. Very interesting.
Step one was a deep dive into the bike schematic to see how a GROUND wire in the harness could burn up without blowing any fuses. Interestingly, the bike did have a Honda Service Bulletin for an electrical issue... The VTX-1800C, for a time, rolled out of the factory (a USA factory) with the far end of the main ground wire from the battery connected to the wrong place on the frame of the bike. But that fix, putting the ground lug where it belonged, had been long since done. Something else was amiss.
Close reading of the schematics and tracing out where all the ground wires went didn't offer much help. Everything in the schematic looked pretty normal. The fun started when the bike wiring itself was compared to the schematic.
The bike itself was missing a ground lug connection...THE ground lug connection...the main ground junction in the wiring harness where all the smaller ground wires from all over the bike come to a single ground lug that gets solidly bolted to the frame. The result was that ground current from every device on the bike that was not itself grounded directly to the frame (such as the Fuel Injection System and the Starter Relay) was being routed through a very small wire that ran about two feet long from the harness ground junction under the seat (shown in the photo at the top of the page), under the gas tank, to a small secondary grounding lug adjacent to the radiator at the front of the bike. Yep, you guessed it...the very wire that had gotten so hot it melted and/or burned away its insulation.
Other high current items like the spark plugs, the starter motor and the radiator fan motor were all grounded directly the the frame itself...which was connected back to the battery with the big fat battery ground wire via the now repaired battery cable main frame lug. But there was still lots of stuff sending current back to the battery by way of this poor little, now smoked, green wire.
How could this happen?
The missing harness ground lug was so bizarre, customer modification of the bike was the most likely explanation...but a call to the local Honda dealer techs confirmed that the connector with the burned wire but no lug, was indeed a stock Honda connector. There is only one explanation, this was a birth defect. The Product Engineer(s) responsible for the manufacturing of the bike at the factory had screwed up TWICE, first by allowing the battery wire frame lug connection error to enter production (resulting in a Service Bulletin), but also by allowing the elimination of the main harness frame lug. Clearly, the bike design team knew the lug was needed to handle return currents from all over the harness. It was right there in the schematic...but not on the bike. That is on the Product Engineering team. That ground lug should not have been eliminated. In fact, it is likely that the missing lug has actually been the primary problem that has plagued VTX 1800s all along...and that the Service Bulletin cured an inconsequential problem but missed the real issue.
So why don't all VTX 1800s burn up the little wire that runs from the ground junction to the secondary ground lug? Obviously, the little ground wire was good enough to work kind of ok, at least for a while. Lots of bikes rolled out that door that way without immediately catching fire.
One of the things that happens with overloaded wires, even if they are not overloaded badly enough to burn immediately, is that the heat in them slowly bakes the insulation around the wire, causing it to become dry and brittle, eventually causing the insulation to flake off and expose the copper conductor inside. If it is a power wire and that bare copper touches a grounded frame member, sparks fly and fuses blow. However in this case, if a ground wire touches a grounded frame member...nothing happens. It's a ground wire. That is where it is supposed to be connected. So in this case, that is not too big a deal. But because the wire was buried inside the big wire bundle that runs from the front of the bike back to the battery and the computer, making contact with an adjacent power wire in the bundle was a real possibility. Testing revealed that, fortunately that had not happened. The next problem is that the wire's connection points can overheat and carbonize, slowly offering more and more resistance to current flow. At first, that might seem ok too...more resistance results in less current flow and less heat. Sounds perfect. Well, not quite.
Passing current through a resistance results in a voltage drop across that resistance. That is how they make electric heaters...the ones that get red hot and keep your feet toasty in the winter. Just how hot it gets is a function of power (watts) and the volume within which that power is being dissipated. If the volume of the conductor where that current is flowing is small, then all the power, all the watts, are being concentrated in that small space...and the temperature in that spot can become VERY high. (That is exactly how an Arc Welder works.) As a result, what may start as a small problem can get worse and worse (a little heat degrades the connection a little, but as time goes by, resistance in the connection gets higher and higher until it finally burns up). But on the way toward that fiery end, all the other items in the circuit served by that connection are being starved for voltage. If it is a 12 volt circuit and 3 volts are being dissipated across the resistive connection, then only 9 volts remain to serve the load device...say the Engine Control Computer, for example.
Now we have a plausible explanation for what happened. The overtaxed ground wire slowly got worse and worse, stealing voltage from the engine computer...which controls both the fuel injectors and spark plug pulses. Is it any wonder this bike was running worse and worse until it finally gave up the ghost? And guess which electrical component on the bike that uses the harness ground junction, is the one that consumes the most current when it is operating? That's right, the starter relay; the relay that gets activated when you punch the start button. It was during attempted starts that the overloaded ground wire finally sent up smoke signals.
The solution? Rewire the main ground junction to a new frame lug to conform with the schematic...and replace the fried wire that ran from the harness ground junction to the secondary frame lug at the front of the bike. And just to be double-dog sure this NEVER happens again, do a complete overkill on the job and use 8 gauge stranded copper wire to do it.
So...with the ground wire and ground lugs fixed, everything should be perfect, right?
Yea...not so much.
Now with the wiring fixed and a brand new battery installed, attempted starts are a complete crapshoot. Sometimes they work and sometimes the bike does absolutely nothing when the starter button is pressed. Jeez now what?
A trouble light connected to the relay coil quickly proved that the relay was getting juice every time the start button was pushed, which was no surprise since you could hear it click every time the starter button was pressed. The problem was the starter relay, the one the customer reported was fairly new (as a result of an earlier failed attempt to cure the hard start problem). Fortunately, it is a quick* fix. Yank out the old one and bolt in the new one, reconnect the battery and off she goes. (* Quick, not cheap. A replacement OEM relay was ~$40. Aftermarket relays that looked exactly the same could be had for less than $10...but buyer review reported very high failure rates...so Honda got the order.)
But a bad relay is a bit of a mystery. Generally they are either good or bad. This one showed wildly different contact resistance measurements every time it is tested. So (naturally!), an autopsy was in order. After ripping it apart and looking at all the parts, nothing seemed to be wrong with it . Sure, the internal contacts looked a little pitted...but can that be so bad. Well, it turns out, YES!
Connecting the main terminals to an ohm meter and then placing the contactor across the gap (just as it would be when the relay has activated), results in the meter reading "0L" or Over-Range, meaning Infinite Resistance...no circuit, no current flow. no go. These are all solid copper pieces. How can this be? Clearly the carbonizing and pitting shown above on the left is enough to kill current flow in the picture above on the right. Now we have the cause of the no starter reaction when the starter button is pressed...and sure enough, with the new starter relay installed the bike fires right up...
...most of the time. Well, dang. Now what?
Sometimes when the starter button is pressed, the starter motor just cannot make the engine spin. And sometimes, it moves it just a bit...and then stalls, like it suddenly got stuck in glue. What's up with that?!
Now we finally know why this VTX burned up its overtaxed harness ground wire. It has a failing (or failed) compression relief valve in the engine.
Engines with big cylinders (and this 1800cc Twin has some of the biggest they make) have a compression relief system that reduces the air pressure inside the cylinder when the engine is spinning a very low RPM, such as when it is trying to start. Why? Because it is very difficult to get the engine to turn in the compression stroke...when the intake air and fuel vapor charge that the spark plug is about to ignite is being compressed toward the spark plug. If the bike has a kickstarter, a light weight rider might not be able to kick start a big bike without a compression relief system...and if it has an electric starter motor, a successful start without a compression relief system might require both a larger starter motor and a larger battery, which would take up more space, add weight and expense to the bike.
But a compression relief system, like any system, can fail and it can fail in at least two different ways: It can fail active and it can fail inactive. In other words, it can fail to relieve pressure when it should or it can get stuck and always relieve pressure, even when it should not. In this case, it looks like the compression relief cam (a spring loaded movable cam surface built into the valve camshaft mounted on top of the cylinder head on each cylinder) is failing to deploy when the engine stops, such that when a start is attempted, IF the engine has stopped right at the start of one cylinder's compression stroke (Reminder: The four strokes of a 4 stroke engine cycle are: Power Stroke, Exhaust Stroke, Intake Stroke, Compression Stroke), then even a perfectly healthy starter motor might not be able to spin the motor.
In this engine, the movable cam cracks the exhaust valve open on the Compression Stroke, wasting a little fuel/air mix, but allowing the engine to spin more easily...and therefore faster, to start more easily. Once the engine fires and quickly spins up to idle speed (about 1000 RPM) the cam retracts and full compression is restored, allowing the engine to run at full power. If the cam fails to retract, the fuel waste and reduced compression both conspire to reduce engine power output.
So what does this have to do with an electrical failure? Here it is. When the engine is asked to start in a high compression state, the electric starter motor stalls. The starter motor consumes a tremendous amount of current in this condition...over 100 amps. The rider may continue to keep the start button mashed in, or may release it, only to hit it again. The contacts in starter relays are pretty tough, but they are not designed to handle the kind of current flow for more than a fraction of a second. (That current flow drops considerably when the starter motor starts to spin.) Nor are they designed to handle lots of restart attempts in a short period of time. Each start attempt heats the starter relay contacts...and enough start attempts in a short period of time could start to burn the contact surfaces. So the pitted / failed starter relay contacts are not a big surprise at this point. But what about the melted ground wire?
As mentioned earlier, the starter motor current does not pass through the wiring harness at all. (See the schematic above.) It leaves the battery, goes through the main lugs of the starter relay, flows through the starter windings, into the bike engine case and frame, and from there, through the main battery wire ground lug, through the battery ground wire and back to the battery. It never goes through the wiring harness at all...BUT...the current that activates the starter relay, that flows through the starter relay windings, that current does go through the harness ground junction...and the starter relay has a big honking winding, that consumes multiple amps of current when it is activated. Bingo. That is where the intermittent high current flow, that eventually fried the overloaded ground wire, was coming from.
So...here's the sequence. The spring-loaded, centrifugally released, compression relief cam on the exhaust valve overhead cam lobe (at least occasionally) fails to deploy when the engine stops, making the next start much more difficult. Repeated attempts to start the engine against full compression causes lots of current draw, arcing and pitting of the starter relay contacts, making starts even more difficult...and encouraging the rider to keep the start button engaged for excessively long periods and/or in excessively rapid succession. The high current draw of the active starter relay coil adds to the already excessive current flow through the soon-to-be-fried secondary ground wire as it heads for the secondary harness frame ground lug, because the primary harness frame ground lug is missing...and the wire starts to smoke, creating a general sense of alarm in those around to witness the smoke rising from under the fuel tank.
So...what's next? If the fix were free, then determining which of the two camshafts (one on top of each cylinder) has the bad compression relief cam would be next...and it could be fixed or more likely, replaced. However, for the owner, who is not made of money, there is an alternative, at least for now. Live with it.
Because the engine does not always stop at exactly the same spot in its cycle, the problematic piston is not always the one that is up to bat. And perhaps the defective mechanism does not get stuck all the time. The fact is that the bike starts just fine somewhere between half and three-quarters of the time. So it falls to the rider to address the problem properly when the problem occurs.
Assuming the failing compression relief system does not get any worse, the owner should be able to operate the bike without too much trouble, saving the near $1000 repair bill that would likely be waiting for him at the end of a camshaft replacement project. Not bad; huh?
Now, what about that rusty gas?
Much better... This is the result of about one gallon of gas left in a three gallon tank for five years. The nasty object above is the in-tank fuel pump and integrated fuel filters. That is pretty easy to fix. All you need is $500 and the time to remove it, rebuild or replace it, and reinstall a few bolts. Not cheap, but pretty easy. (Sure, you need to drain and remove the gas tank, which may require a pump and lots of disassembly time...and then you need to put it all back together correctly, but that isn't rocket science either.) The inside of the tank itself is a bigger problem.
The rehabilitation of rusty fuel tanks seems to be a religious matter. Doctrine ranges from "Don't...just replace it", to "Clean it and coat the inside with (insert the name of some sort of paint-like product here) ." And recommended methods for cleaning are all over the map too, ranging from "Rinse out the chunks and call it done." to "Fill it with (wood screws, abrasive, BB's, etc.) and (shake it, tumble it, vibrate it, etc.) . I have tried some alternatives and today I generally take a middle of the road approach. I will say, if I had a big tumbler system or high powered ultrasonic wand that I could insert, I might do differently, but I don't. So I keep it simple.
I do not paint / epoxy tank interiors. I believe it is risky (the paints can degrade / flake off) and that fuel filters are really pretty good. Sure, keep a weather eye on your fuel filter(s) after you start riding again. If they start filling with rust then further intervention may be needed. But if you care for your tank with two final steps, that is not likely to become necessary.
Step 9 - Fill your tank all the way on your way home from each ride.
The water in the tank does not (mainly) precipitate out of the gas. It mostly enters your tank in the form of humid air. Once inside, the water condenses out of the trapped air in the tank and falls to the bottom of the pool, where it does its dirty work. If there is no air space at the top of your tank, there is no water vapor to condense inside, and your rust problems are considerably reduced. Naturally there are other alternatives. You can drain the tank absolutely dry. That works too.
Step 10 - Ride often. (Or at least run the engine for a half hour each week...and then top up the tank with new, not stored, gas.)
But here's a word of caution regarding that full gas tank. Modern Ethanol-mix fuel harbors bacteria that eat ethanol and piss Acetic Acid...which will eat everything metalic in your fuel system, especially aluminum parts. Yes, I know I just recommended filling a rusted tank up with 30% Acetic Acid, but I also said get it all out when you are done. The bacteria in your tank are kinda slow growers, but if a tank has been sitting for a month or so, even a completely full tank, the bacteria bloom is underway and will accelerate exponentially over time until the bugs die in their own piss. If you have ever seen and/or smelled green fuel in a tank, you have seen the aftermath of a bloom for yourself.
If you are not going to keep fuel rotating through your tank (burning up the blooming bacteria and re-filling with fresh gas) then at least use a fuel preservative product like Stabil, to keep the buggers at bay for a few months. If it is going to be longer than that, drain that tank...completely dry.
(Full disclosure: water does come into the tank mixed in solution with the ethanol in the fuel. Water does not mix with gasoline, but it does mix beautifully with alcohol, as your bartender can readily confirm. And any batch of ethanol-gas you get may have water trapped in the ethanol. If you get a tank with high water content, the next tankfull is likely to dilute the concentration of water in the tank. Just another reason to keep using the gas in the tank regularly.)
So...either drain that tank dry or fill it full and burn some off every week. Don't give rust a chance. Like Neil says, better to burn up than it is to rust.
Internal combustion engines need three things to run. Fuel, Fire and Compression. If the correct amount of fuel (and air) is in the cylinder, and the mix is properly compressed (to somewhere near 1/9th of it's uncompressed volume), and it gets a spark, the mix will explode. Physics. It cannot do otherwise.
Granted, lots of things need to happen properly in an engine for all that to come together and happen at the right time in the piston cycle, but that remains the core principle of internal combustion engines. To troubleshoot an engine that is not running, or not running properly, those are the three main issues to consider.
Lots of things can cause a loss of compression, but they all come down to the cylinder having a leak. Mechanical wear, blown gaskets, defective seals, dirty / leaky valves or bad valve timing can all cause a loss of compression. Fortunately, serious compression loss is fairly rare...and that is good, because it is always the most expensive problem to solve. Engines are built, first and foremost, to continue to hold compression through their service life. The good news is that if you have verified fuel and fire, checking compression is among the easiest test to do on an engine. Still, it is rarely a sensible place to start your troubleshooting. Failures in the fuel supply and ignition systems are far more common.
Outside of flat running out of gas, ignition failure is by far the most common cause of an engine failing to run. And that is great, because it is the easiest problem to check directly and is often the cheapest problem to fix. The easiest ignition check is to unplug a spark plug wire, remove the spare plug, reconnect the plug wire, ground threads of that plug to the block, and crank the engine. If you can see a nice blue-white (or even reddish) spark you can PROBABLY say ignition is ok and move on. I say "probably" because if you do see a spark, you still do not know if the spark happening at the right time. If you don't see one, you do not yet know why. Maybe the plug is bad, or maybe other ignition components are bad and you still need to track that down (or maybe the kill switch is turned on!). But at least you know the next path to follow. But, there is actually something that is even easier to check, if only indirectly. And since we are trying to zero in on the main problem area quickly, easy counts for a lot. And the easy test involves the third leg of the stool...and is often a great place to start your troubleshooting.
So, we have already assumed you are not out of gas...but on a small engine, you better make sure the fuel valve (often called a "petcock") is open and fuel is actually flowing. Next up on smaller machines, including most motorcycles, is the carburetor, which regulates the amount of fuel that is supplied to the engine under various throttle and load conditions. Larger, more sophisticated, less polluting, engines get their fuel via a fuel injection system. Let's start with carbs.
Carbs have tiny passages in them, through which tiny streams of fuel flow, that ultimately get mixed with the air coming into the engine. Just a little schmutz in any of those passages can put a carb out of commission. A failed fuel pump or clogged fuel filter can also stop the music (in fuel injected motors too). If your machine has been sitting for a few months with fuel in it, there is a very good chance your carb is plugged up and needs to be cleaned. But let's not jump to conclusions.
While you can look at spark plug and get a pretty good idea of whether or not it is sparking, you cannot just look into a carb and see whether or not it is working properly. Fuel injection systems in gasoline engines are almost always computer controlled, and with proper diagnostic tools, can often tell you if and why they are sick. But for a carbureted engine that has no blinky lights, it is not so easy. What to do?
Well, obviously, you cheat. (And the cheat actually works on fuel injected engines too.)
One of the products you will find on the shelf at every auto parts store is a can of "starting fluid" or "starting spray". The can will contain a cocktail of flammable chemicals, usually including ether, which vaporizes easily and happens to burn like crazy. A spray can of starting fluid is a great diagnostic tool. Remove the air cleaner so you have a clear shot at the intake, give it a one second blast of ether, and immediately crank the engine. If it fires and runs for a few beats (perhaps for a few seconds), you now know that you have reasonably good ignition, firing at (at least approximately) the right time. You know you have at least marginal compression. And you know that you just supplied the missing element...fuel, more specifically, vaporized fuel. (Engines do not run on liquid fuel. They run on vaporized fuel.) Now you have a pretty good idea where to look...the fuel delivery system. Ignition may not be perfect, but it was good enough to fire the ether. Compression may not be perfect, but it was good enough to explode the ether. So right now the fuel delivery system is the prime suspect. Conversely, if the engine did not fire with ether, you PROBABLY have an ignition problem and should at least do the easy ignition test (pull a spark plug and check for good spark).
If you see good spark AND the motor will not fire on ether...well, now you are in for an education. It is time to dig deeper.
So...you aren't supposed to talk about religion and politics in gentele company, right? Well, I am going to put on my big steel-toed boots and stomp right into the middle of a hot religion topic in motorcycling...using car tires on motorcycles.
"What kind of lunatic puts a car tire on a motorcycle?", you might ask. I cannot say with absolute certainty, but the evidence suggests to me that they are, at their core, shortsighted cheapskates; the sort who try to seal up a cavity in their tooth with superglue to avoid paying a dentist, only to reap an abscess and need dental surgery later.
Why would someone even consider this insane idea? Well, motorcycle tires are not cheap, particularly not good motorcycle tires. And the labor charges to install them are often almost as much as the tires themselves. So it can cost almost as much to put two tires on a bike as it costs to put four tires on a car. That, understandably, rubs some folks the wrong way. Worse still, motorcycle tires may last 10k miles or even less, so they get changed much more often than car tires. In short, tires represent a significant cost of ownership to a motorcycle rider.
Nobody who has followed my work will be surprised I say that those who are not willing to pay what it costs to operate a bike safely, shouldn't own or ride motorcycles. But what are the safety issues? They all come down to the key mission of the tires...keeping the bike stuck on the roadway rather than sliding over/off it. Car tires present two obvious significant challenges to that mission.
So this is kind of a no-brainer. Bikes lean when they turn. They must lean to turn. The rounded cross section of a motorcycle tire produces a near-uniform contact patch (that part of the tire surface that is in contact with the roadway), no mater what the lean-angle of the bike. The car tire, in contrast, has a rectangular profile and typically, very stiff sidewalls, so as the bike leans, the contact patch of the of the tire shrinks as the main body of the tire lifts off the roadway. Not good.
The other big issue is the tire's grip on the road...traction. Traction and tread life are the core tradeoffs in tire design. Hard rubber wears off slower than soft rubber, but soft rubber grips better than hard rubber. You may be able to visualize soft rubber oozing into the tiny pits in a paved roadway, while a harder rubber only makes contact with the tops of the roadway texture. Some motorcycle tires, particularly those for touring bikes that do lots of highway miles, finesse this issue with a multi-compound design. The center of the tread area is made with a harder rubber for good wear when the bike is rolling straight ahead, but the outer portions of the tread surface, between the center area and the sidewalls, are built with a softer compound that provides better grip when the tire is leaned into a turn. Car tires, which are not only designed for a heavier vehicle (and so have a harder tread compound for suitable wear in their intended application) but are also designed for a vehicle suspension system that is designed to keep the tire upright in a turn, making a multi-compound approach less useful.
BUT WAIT, THERE'S MORE
Or perhaps, there is less. In this case, less contact with the bead seating surface. "Bead" may be an unfamiliar term in the context of tires but here it is in a nutshell. It is the part of the tire that seats against the wheel and provides both the air seal that keeps the tire inflated but also provides the structural connection between the tire and the bike. The bead on car tires are designed to seat / seal / hold to the rims of car wheels (duh). The bead of motorcycle tires and seating profile of motorcycle wheels are different. Perhaps they did not need to be, but bikes weigh much less than cars and the cornering forces placed on car tires are different from those put on motorcycle tires, so the tire seating region is smaller than is found on car wheels. Or to consider it from the other perspective, a car tire expects a different, larger bead seating region on the wheel, and therein lies the rub...or perhaps the lack of a rub. The seating surface on a motorcycle wheel is not right for a car tire.
You may hear someone say, "But it works fine!". Well, that depends on your definition of "fine". Yes, as a rule, a car tire can be induced to hold air when mounted on a motorcycle wheel. And depending on the bike and the car tire selected, the tire will clear the surrounding suspension structure of the bike so the bike can roll. Let's even say that we are willing to accept the traction and handling compromises introduced by a car tire (I cannot imagine why you would, but let's say so, for the sake of argument.) What else is there to consider? What about emergencies?
The car tire shown in this article came into the shop mounted on a motorcycle wheel. It did something very interesting when it was deflated. It spontaneously dismounted itself from the motorcycle wheel. That is to say, the tire bead became unseated from the wheel without any additional force being required. OMG!
If you have never mounted new tires on car or motorcycle rims, you may not be aware that, once seated on the wheel, removing that tire from the wheel requires considerable side force. Getting the tire unseated from the wheel is the main mechanical challenge in any tire change job, followed by the challenge of getting the tire off the wheel after it is deflated and then, finally, by the difficulty of getting the new one onto the wheel. That may not sound surprising...but the first item on the list is critical from a safety point of view.
If we do not know anything else about tires, we know that they sometimes go flat. But we also know that they rarely come off the wheel just because they have lost air. Yes, a massive blowout can shred a tire and leave you with a bare wheel, but that is rare and virtually never happens to tires until they are used long past the end of their service life. On a car, a tire dismounting from a wheel causes damage to the wheel and perhaps the bodywork. It could even cause a loss of control and an accident. However, on a motorcycle, it WILL cause a loss of control, and that, for motorcyclists, is often deadly.
Of all the hazards a car tire presents to a rider, the most insidious is the risk of a low pressure spontaneous dismount of the tire. Because car tire sidewalls are made for much greater loads than motorcycles offer, an inattentive rider may be on an under-inflated tire without realizing it. The tire may not "go flat". However, at some point, as inflation pressure continues to fall due to a small leak, the tire may no longer keep its grip on the motorcycle wheel. That dismount event is most likely to occur when the rider enters a curve...and is most likely to occur when entering a high speed curve. How's that for a nightmare scenario?
Granted, motorcycle riding is not an enterprise for seriously risk averse folks. But it is an enterprise that tends to weed out the reckless. Using a car tire on a motorcycle may not get you killed, but it absolutely lowers your chances of survival. It's not worth it to me. Make your own call. (But I will never mount one for anybody in my shop.)
OMG, she is so cute! She is a red Vespa GT4 / 150, a hot little Italian number who just wants to have fun. (Does that make me an Italian Lover?)
Well, she wanted to have fun, but she was in a coma when she came in. Her battery was DOA, her tires were far too old to be ridden safely, she needed fresh oil in her engine and transmission, and obviously new brake fluid...but her carb. Oh dear. Her carb betrayed her.
Like so many gasoline powered machines, she had been sitting in a garage for quite a while with ethanol-mix fuel in her tank, going nowhere. And while she sat, her carb got more and more filled with gunk (that's a technical term)...but worse, while she sat the carb was discontinued by the manufacturer. Worse still, all support (i.e. repair parts) for the carb were discontinued. What could have been a reasonably inexpensive clean / rebuild became a more expensive carb replacement job. The good news was that the same manufacturer had a substitute carb that fit perfectly and worked perfectly as soon as it was installed.
But how do you get all that bad gas out? Well, the fuel hose gets disconnected when you pull the carb, how about pointing it into a bucket and letting it flow? Not so fast, Lover Lips. The tank has a gallon of old gas in it and noting is coming out. What gives?
Motorcycle fuel tanks on carbureted bikes have a petcock (a valve) between the tank and the carb. In many cases the petcock is bolted into the tank. In other cases, it hangs below the tank. In any case, the valve controls whether or not fuel flows from the tank into the carb float bowl. The carb has a float valve that is supposed to allow fuel into the carb when the fuel level in the bowl gets low...and stop fuel coming in when the bowl is full enough. You see float bowls in the photos above. They are the bowl shaped pieces bolted to the bottom of the carbs. But the float valve is just a weak and tiny thing and bike manufacturers tend not to trust the valve to prevent every little drip from getting through. You can imagine if it sits for a week, letting just one drop of fuel get in every hour, it is not long before you have a flooded engine. Not good. So the float valve is backed up with an upstream petcock (an upstream fuel valve).
Many bikes have a manual petcock. You may have noticed a motorcycle rider walking up to his bike, reaching under the fuel tank for some odd reason, and then turning the key and firing up the bike. That rider was opening the petcock. However, some bike have an automatic petcock. In very rare cases it may be electric on a carbureted bike. In most cases, if automatic, it is vacuum operated. When the engine turns over, the cylinder sucks air in through the carb...and when it does, it creates a little low pressure area (a little vacuum) right at the carb inlet. And that is where a tube is attached that carries that vacuum to the flexible diaphragm in the petcock, that gets sucked back under vacuum, and pulls the fuel valve open, allowing fuel to flow.
So...sitting on the lift not running, this little Vespa would not allow any fuel to flow from the tank, into the fuel line that connected to the carb. No vacuum, no fuel flow, no draining the tank. Hmmm. What we need here is something that sucks.
Not much sophistication is required. An ordinary syringe provides all the suction required to open the valve when connected to the vacuum port on the bottom of the petcock. A little white plastic fitting was used to connect the fuel hose to a longer piece of scrap hose leading into a disposal bucket and è fatta (it is done).
The rest of the work is pretty normal stuff, except that Vespa uses the oddest collection of nuts and bolts imaginable. It is a tiny, lightweight machine, yet it has some of the largest nuts and bolts you will see on a motorcycle. The front brake caliper bleed screw was half as big as the entire caliper. I suppose Italian lovers are know for having a few idiosyncrasies...
Her brake fluid was nasty and low, but cleaned up nicely. Removing her rear wheel requires first removing the exhaust manifold and muffler (not unheard of). Getting to the front brake master cylinder required removing the headlight faring (weird). But, her rear brake shoes and front brake pads were just fine. The front wheel is attached with five little lug screws, allowing the brake disk and caliper to remain untouched when removing the front wheel, just like your car does (very cute). Tires were a little bit of a battle. A normal larger motorcycle wheel is a bit easier to mount because the curve of a 17 inch wheel is much gentler than the curve of a 10 inch wheel. The amount of flex require to mount each tire is about the same, but it is a much larger percentage of the tire diameter when the wheel is 10 inches in diameter. A little tougher...but certainly within reason.
So there you have it. The hot little Italian number is back home doing what she does best, making big smiles. What more can a WrenchMonster ask for?
The only thing that stands between your engine and death is oil. Did you know (I was shocked when I leaned), that the major turning loads in your engine are NOT supported by ball bearings, or roller bearings, or anything else that rolls? All the main loads are carried by a round part stuck into a round hole, with room for just a microns-thin film of oil between the shaft and the hole. That's it. A thin film of oil. And how those parts suffer if there are bits of dirt or metal in that oil. And may the engine gods have mercy on your engine's soul if the oil is gone. Metal rubs on metal, heat builds up, the metal expands and soon the gap is gone and the shaft welds itself into the hole...and that's the end. So...dirty oil and low oil...bad, bad, bad. But what happens if there is too much oil? Mechanical sickness and engine death are ready and waiting for you there too. Let me count a few of the ways...
Why do I bring this up? This year I have had three over-oiled machines come into the shop. One wouldn't turn at all. One wouldn't run. The third, fortunately for the owner, had already died and the engine had been over-filled in a misguided attempt to revive it, so it was never re-started with too much oil, fortunately for him.
The basic problem is that excess oil goes places it shouldn't. More on that in a moment. The other problem, is that with most engine designs, excess oil gets splashed excessively...to the extent that it becomes foamy... foamy oil doesn't flow, and cannot go where it is needed...which is just as bad as having too little oil. How does this happen? The connecting rods that connect the pistons to the crankshaft travel down into the upper reaches of the oil pan at the bottom of the engine. If they hit the oil, it splashes and becomes filled with air bubbles...it foams. So, too much oil puts oil was where it was not supposed to be (too high in the oil pan) and foamy oil is the result.
You recall I mentioned the over-oiled engine that would not turn? That engine had a horizontal cylinder. It pointed sideways rather than mostly up. It was a lawnmower and most lawnmowers are designed that way. In that case, while the engine was off, the excess oil seeped past the piston rings and filled up the cylinder. The cylinder is not supposed to have anything inside it but air and a few molecules of fuel. When the owner went to start the engine, the piston could not rise in the cylinder because the cylinder was full of oil. Air will compress; liquids, including oil, will not. The piston might as well have been welded to the cylinder walls. It would not budge...until we pulled out the spark plug and drained out the oil stuck inside the cylinder. After that, we drained the oil down to normal level, cleaned, dried and reinstalled the spark plug...and fired it right up. The next guy was not so lucky.
The next engine would turn, but wouldn't run. The plug was completely fouled (caked with residue burned carbon from burning too much oil), the air cleaner was soaked with oil and the exhaust was dripping oil. In this case, the cleanup required was a little more extensive, but in the end, the result was the same. After draining out the excess oil, getting a new clean filter and a clean plug, she fired right up. She smoked like crazy as the excess oil in the exhaust burned off, but after running for five minutes, the excess oil had cooked off, the smoke stopped, and she ran like a top.
So, how does one prevent this ugly problem? First, read. Read the manual. These days, a little Google searching will turn up reliable documentation on your engine that will tell you how much, and what sort of oil your engine needs. Next, check the dipstick. Most engines have a dipstick, and those that do not generally have a sight window that allows you to see the oil level from outside the engine.
After the engine has been off for at least a few minutes, sitting on level ground, pull the stick, wipe it clean, (like the one you see above), stick it back where it came from, and pull it out again. When you do, you should see oil on the stick, somewhere between the ADD and FILL marks. Too low on the stick, add oil. Too high on the stick, like you see in this next photo, (You see the stick is wet right up to the L's in FULL, way past the point of the FULL arrow)...
...then it is time to get rid of some oil. Drain some or use something to suck it out (something besides your mouth, like a plastic tube and a turkey baster!). Once your oil level is right, your mechanical life can go back to normal.
Here is a 1989 Honda Hawk GT. It is a mid-size (650 CC) street bike that had a short manufacturing run but still enjoys a strong following. The Hawk has a very elegant single swing-arm rear suspension and a very cool eccentric rear axle carrier that allows for simple chain tension adjustments and obviates the usual sprocket alignment adjustment. The fuel tank is secured with a removable bushing up front. The rear tank mounting bolt is used to extract the bushing from the frame when removing the fuel tank (so cool). The only fly in the ointment on this design is a difficult to access front left spark plug. This is the second Honda V-Twin I have encountered that makes access to the front left plug so difficult that it requires a special tool. Fortunately, the Hawk comes with the required tool and the owner of this Hawk still has the stock tool kit that came with the bike.
The Hawk came in able to idle but wouldn't rev up and run. Having been parked with fuel in the tank for a few years, being a carbureted bike, that was not surprising. She had tires with good tread but rotten, cracked sidewalls (very dangerous) so they had to go. Her oil was old, her chain was rusty, her coolant and brake fluid were low and dirty. On top of that the turn signal switch wouldn't work worth a darn. Very sticky.
CV-19 made getting OEM parts really slow and difficult, but in the end, everything but the fork rebuild kit showed up. We will get to the forks later. The carbs cleaned up well. The rubber carb mounting boots were original, cracked, and hard as rocks, so they got replaced. The new Michelin tires look great. The replaced brake pads and new DOT4 fluid are working fine without having to rebuild the master cylinders. There were some non-metallic particulates in the old coolant but the flush cleaned all that out. The very elaborate air filter was dirty and got replaced. Some plastic parts, like a fuel line tee and a small foam filter in the pollution control system, simply crumbled when handled, and had to be replaced. That was not surprising for a bike that is over 30 years old. And dismantling the turn signal switch, giving it a good scrub and lube has it working like new. So overall, almost nothing but ordinary maintenance was needed to bring this Hawk back to life.
She did need some new bar ends (one, it seems, went missing some time back). But that was obvious. What was not obvious until the test ride, was the voltage regulator was dead as a stick.
Motorcycles have alternators. As a rule, they generate 3 phase AC that gets fed to a rectifier / regulator that converts the AC voltage, which may go higher than 60 volts as the engine revs higher, into DC and holds the voltage supplied to the battery to anywhere from 12 to just less than 15 volts (i.e. normal charging voltage for all our cars, motorcycles, scooters and lawn tractors). Most automotive alternators have the voltage regulator built into the alternator housing. But as a rule, motorcycles have a separate regulator that plugs into the wiring harness of the bike. It often looks a lot like the one on the Hawk.
It will have three (usually yellow) wires that accept the three phases of AC current from the alternator and two or more wires that deliver the DC current (often +12V Red and Green Ground).
That makes diagnosing charging problems pretty easy. If you unplug the regulator and still have AC voltage coming out of all three phases of the alternator (specifically, from the Stator windings) but do not have good charging voltage when you plug the regulator back in, the regulator is bad...and so it was with the Hawk.
When the new regulator arrived, it took a little effort to dig the old one out of its hiding place in the bike, but the new one fit like a glove and worked like a charm.
This little Hawk GT rides like a dream and I predict will run another 100k miles...and will probably generate almost that many smiles.
This is a 1997 BMW F650ST, also known as a Funduro. A client had just bought it and brought it in to be made roadworthy again. It had been sitting parked for a few years...and had a few problems...most of which the seller did not disclose. Some were obvious (like, it wouldn't start!). Some only became apparent after it was running again.
Once the carbs were cleaned, rebuilt and re-installed, the bike got new spark plugs and fresh gas and then fired instantly, (Yay!) Unfortunately, there are some things that just cannot be known until the engine starts running and test rides get underway.
THE NEWLY OBVIOUS
The radiator went to a repair shop, which fixed it successfully...full flow, no leaks. Then the thermal switch that controlled the fan was proven dead and was replaced. The radiator cap was replaced just for good measure, a step that was way overdue. The upshot? No more overheating!
The battery was still running down. Some quick testing showed that the alternator was producing 3 phase AC voltage (> 50 VAC per phase at 3k RPM), just like it should, when it was unplugged from the rectifier / regulator assembly...and was not when the regulator was plugged in...and the regulator was not producing charging voltage (~14V DC) when the bike was running. So...a clear case of bad regulator. In addition, in the course of troubleshooting the electrical problems, we discovered a couple of spots in the wiring harness (between the alternator and the regulator) that had gotten so hot at some point years ago that insulation was burned off. It was pretty plain that connectors had become corroded and gone ohmic (partially open), resulting in overheated connectors that burned the wires. The bad connectors were cut out of the wiring harness and replaced. We tried a cheap knock-off regulator, but it too failed within minutes of installation. A couple of days later we had a genuine BMW unit installed and the charging system was cured. Like magic, the bike produced 14.4 VDC to the battery @ 3k RPM. Perfect.
The previous cursory inspection of the engine oil drain plug had revealed it had been installed with no crush washer, so a leak was no shock. But when a new crush washer failed to stop the drips, it was clear that a closer look was needed...and the sight was appalling. The drain had been manhandled by a neanderthal on multiple occasions. For starters, at some point, someone had screwed the plug in so tight that they cracked to block. (Note: This bike uses a "dry sump" oil circulation system, meaning, it does not have an oil pan on the bottom of the engine. Instead, oil is scavenged off the bottom of the crankcase and pumped into an oil storage tank, from which it is pumped back into the engine. The design is better for off-road bikes that would go into oil starvation if oil were splashing around in a big oil pan when the bike was bouncing around off-road. So...the engine oil drain plug is screwed into the block itself...not into a replaceable oil pan. ) So...yikes!
The good news turned out to be that the crack had previously been repaired. Somebody drilled out the case and installed an insert that was tapped for a new plug, which effectively sealed the crack. The bad news was that some other moron had since over-tightened the plug again (without a crush washer) and had chewed chunks out of the mating surface where the washer was supposed to land. There was no way it would ever seal. Well, desperate situations call for desperate measures. Judicious application of fine grit wet/dry sandpaper and a flat sanding block whittled the drain hole outer surface down to flat...at least flat enough for the sealing washer to fill any gaps. It worked. No more drips.
There were just a few more items to cover.
The broken analog clock in the dashboard would have cost a king's ransom to replace. It fits into a standard 2" round meter hole, so swapping in a standard 2 inch $20 DCV panel meter, which is infinitely more useful, was a no-brainer. And the power outlet and phone mount went onto the handlebars with minimal fuss.
The outcome? See for yourself. Looks like a pretty happy customer to me.