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.

1. Rinse out as much of the junk as you can with plain tap water.
2. Fill the tank with a gallon or more of Industrial vinegar. (This stuff is available from the big box hardware stores like Lowes. It is different from household white vinegar because it has a much higher Acetic Acid content than food grade vinegar.)
3. Agitate the tank (shake it vigorously) to coat all the inner surfaces with the vinegar.
4. Let it sit for a while, and agitate again, perhaps tilting the tank to a different angle so a different part of the tank interior can be covered with the pool of vinegar, and
5. Repeat...until you are satisfied with what you see inside (either because it is not getting any better or because it is perfectly clean...or because you are just bored with this step).
6. Drain the tank and rinse with clean tap water MANY times, even a few times after the water runs clean. Get all the chunks and all the vinegar out.
7. Dry the tank interior with forced air (air compressor, blower, hair dryer, etc.) and let it sit, preferably out in the sun, until absolutely dry inside.
8. Call it quits.

What you see in the photos above is the same spot inside the tank. The BEFORE photo was taken AFTER lots of plain water rinsing. The AFTER photo was taken after the tank sat overnight with industrial vinegar inside. There has been no brushing, no wood screws shaken inside, nothing but vinegar. It did not come out looking like new, but as you can see, it was tremendously improved.

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. 

COMPRESSION
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.

FIRE
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.

FUEL
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.

TIRE PROFILE

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.

TIRE COMPOUND

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. 

GOOD ENOUGH?

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?

DEFLATION 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.

SUMMARY

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. 

ENHANCEMENT PROJECTS
There were just a few more items to cover. 

• Lower the suspension 1 inch front and rear.
• Install engine guards.
• Install accessory power outlet.
• Install phone mount.
• Replace broken clock with a DC Voltage panel meter.

Both the engine guards and the lowering links (for the rear suspension) required jacking up the bike and/or engine assembly to allow removal of critical structural bolts and installation of the new pieces.  Not difficult if adequate care is exercised. Everything fit. No problems. The front suspension is lowered by slipping the fork tubes 1 inch further into the triple-tree. Piece of cake.

The outcome? See for yourself. Looks like a pretty happy customer to me.

Some things were just obvious. The battery was missing. She was covered with dirt and chaff from sitting in an open pole barn on a farm near Taylor for a few years. Her tires were flat and her ignition switch was gone...and her model number indicated she was pushing 40 years old. But when I reached in and grabbed the output pulley, and tried to turn it by hand, her engine would move...so off to the shop she went and the search for parts got underway.

She had fuel in the cylinder. The spark plug was sparking. The compression was ok. What the heck?! All you need is Fuel, Fire (at the right time) and Compression and an engine will run. It must run. The starter spins the motor like a demon, but it won't start. It won't even pop once. It is definitely NOT running. What's happening?!

Have you guessed yet?

Yep. Ignition Timing. Spark really does need to happen at the right time.

This engine has a three-phase alternator integrated into the flywheel and the top of the engine case. It is so simple it doesn't even have a voltage regulator. It keeps the battery charged...barely. But that's it. It has nothing to do with the ignition system.

In addition to the magnets that form the alternator, there is one more magnet mounted in the perimeter of the flywheel and it swings past a coil of wire that is connected to nothing except the spark plug. When the magnet comes by, it generates a pulse that sparks the plug and fires the charge in the cylinder. Simple. No points to set. No condenser to short out.  Foolproof...except for one little detail. Recognize these shiny little aluminum rectangles? They are Woodruff Keys.  

The position of the flywheel on the crankshaft is critical because the ignition magneto must cause a spark at exactly the right time in the engine cycle. One of these little woodruff keys fits into a slot cut into the crankshaft and a matching slot cut into the hub of the flywheel, so that when the flywheel is mounted on the shaft, it is certain that the alignment is exactly correct...unless...

Sometimes something happens...a backfire...and violent engine stop...a loose flywheel bolt...and the flywheel rotates on the shaft anyway, shearing the poor little soft aluminum key (but absorbing energy that might otherwise do more damage), and screwing up the ignition timing. The solution? Pull the flywheel, realign it with a new key, torque the mounting bolt to spec and try again.

And she fired right up. Ran like a top. Two days later she was back on the job, roaring through grass like a 20 year old! Way to go Deere!

Disconnecting those items from the engine quickly proved it was the engine that was locked. Bummer. This little Honda may have cut her last blade.

With nothing to lose, we pulled the head and took a look. Although covered with tar-like oil, the valve train looked ok. The piston was stuck almost at TDC (Top Dead Center), so we couldn't see the cylinder walls. After applying a big dose of acetone and Automatic Transmission Fluid (the hot ticket for penetrating oil applications), and considerable muscle, the piston broke free and would turn by hand. More oil and more turns revealed no untoward noises and the cylinder walls did not show any scars.

She blew a little smoke at first but ran like a top!

Next up was the transmission, which was stuck in high gear. After removal from the mower (which requires removing everything connected to the rear wheels) it was disassembled and cleaned. Inspection showed normal wear but nothing broken, so she got a full load of gear oil and went back together with no leaks (to my complete amazement). 

Back in the mower, with the control cables adjusted to spec, the trans shifted like a dream and the little Honda that almost went to the dump is back home and cutting grass like like a champ. Yes, she smokes a little on start-up...but heck...she's 30 years old. I think that's allowed.