failing and fixing

so, as you may have read, i added a kit to my puch magnum. i was pretty proud of myself, although it still needed some adjustment to get it working perfectly. mainly it needed to be properly tuned. this meant determining if the air to fuel ratio was too rich (too much fuel) or too lean (too much air). running too rich isn't efficient as it wastes fuel and can also adversely affect performance (i.e. bogging). running too lean is not good at all. this condition causes the engine to run too hot and can cause serious damage to the engine (i.g. seizing the piston). ideally you want to be right in the middle of those and perhaps erring a bit on the side of rich, just to be safe. there are several factors that affect the air/fuel mixture (main jet, idle jet, throttle needle position, air filter, air leaks, altitude, etc). the most important of these when operating at wide open throttle (wot) is the main jet. the main jet is just a little piece of brass with a hole in it and allows fuel to flow into the carburetor where it mixes with air. there is a number stamped on the jet that indicates how large the hole is (and therefore how much fuel it will let in). to figure out what the fuel mixture is you have to do something called a plug chop. it's basically running the moped at wide open throttle for about a mile with a fresh spark plug and then taking it out and checking the color. if it's black then it's running too rich and if it's white it's too lean. tan to chocolate colored is just about right.

anyway, i did a couple plug chops and found a spot where it was brown, but probably on the lean side. i was running an 86 jet and wanted to try an 88, but didn't have one. i was going to order one, but this was right as i was moving. i figured i was close enough that i wouldn't hurt it. i had to make it 19.2 km (thanks google earth) from my old place to the new house. i made it 16.3 km. i pulled over and sure enough the engine was seized... oops! that's a first. so, i locked it to a pole and walked the remaining 3 kilometers (this is part of the fun of moped ownership). the next day i picked it up with a friend's truck and brought it back to the house. i also managed to blow out all three lights on the bike. that wasn't necessarily a surprise, but it's still a pain. this was caused by the bike going faster than it was originally designed to, which caused a spike in the voltage coming from the magneto, which blew everything up. i'll have to fix that too.

the first step was to take it apart and figure out what happened. i thought the piston had siezed, which is bad, but sometimes you can pound it loose with a hammer and a piece a wood and just keep riding it. it might require a new piston ring, piston, or cylinder if it's really bad. anyway, i took off the head and the cylinder and it turned out the piston was moving freely. that meant whatever went wrong happened in the crank case. i've never taken a crank case apart, so let the adventure begin.

first, it turns out they used flat head screws to hold the two halves of a E50 engine case together. this made disassembly a major hassle as many of the screws did not want to turn. i barely got it apart as i nearly stripped the heads on a couple of them. i made a note to replace them with socket head cap screws. so, i finally got it apart and this is what the crank looked like:



as you can see, the bushing that goes between the connecting rod and the wrist pin was mangled (although a lot of the mangling in the photo is from me trying to rip it out). i also cooked the bushing between the connecting rod and the crank. you can see all the heat marks around the area. this is what seized my engine. i could have tried to replace those bushings, but i decided to take the opportunity to replace the whole assembly with a higher performance crank. i also decided to replace the bearings and seals while the thing was torn apart (they sounded pretty worn out anyway).

by the way, i used this tutorial for rebuilding an E50 engine, which was a huge help.

here is engine pulled apart with the crank missing and just the gear that connects the clutch to the drive sprocket:

here are the two halves of the engine case. i decided to clean everything while it was in pieces:

this is the one of the old bearings coming off. i had to use a gear puller, which isn't shown:

then we skip all the way to the case reassembled, because i did a terrible job of taking photos. essentially is was straight forward. i had to take the old bearings and seals off, put new bearings and seals on the new crank, seal the case with silicon and then bolt it back together (with the new socket head cap screws). i also decided to put new heavier springs in the clutch while i had it apart (which also required buying a clutch puller). this means the engine revs higher before the clutch engages the wheel, which improves acceleration. you can see the new crank has needle bearings instead of brass bushings:


check out those sweet socket head cap screws:


the verdict: total success. it is really gratifying to have the whole engine in a bunch of little pieces laying around the garage, and then a few hours later i'm rocking down the street. i put in the 88 main jet and did another plug chop. it looks better, but i am going to try the 90 and see how that works. i got a voltage regulator which should minimize blowing out lights. although i'm not 100% how it works. i thought it was just supposed to to inline, but one of the leads is grounded, so that means the light doesn't work at all. right now i have it hooked up as a shunt. i am assuming when the voltage goes over a certain point it starts dumping power. i dunno? so far my headlight still works. i still have to revisit the electrical stuff and then comes the cosmetic improvements. first step: new lower handlebars.