atomic_fungus (atomic_fungus) wrote,
atomic_fungus
atomic_fungus

#3915: It'd be nice if I could, y'know, RIDE my dirt bike.

The dirt bike continues to vex me.

Okay: it's 41 years old and never had the best of maintenance. It had the same set of tires on it from the factory until 2010, which was 38 years. My brother used it as daily transportation his first year of medical school (1985) and it has never, never, ever had any serious work done.

Really, that speaks well for the job Suzuki did building the thing. It hasn't exactly seen daily use (but for 1985) yet in 41 years, the past year is the first time anyone has even tried to do anything to get the bike into top shape. It's the first time anyone's needed to.

You may recall that the bike was missing a piston ring. You may further recall that, last year, I had discovered that the piston was verfuckled to the point that I could not just put new rings on it and call it good; I needed a new piston.

There was a deal on ebay--0.55 mm oversize piston, cylinder (needs honing), rings, wrist pin, small end bearing, $50. Sailor V bought the auction for me on the 4th of July and had it shipped here; and as you may recall it turned out that the cylinder had been bored by a maniac and could not be honed to the right size. It would have to be bored 1 mm oversize and a 1.00 oversize piston (and rings for same) bought if I wanted to go that route.

Seemed simpler to have the old cylinder bored and honed 0.5 mm over. Right? Fresh cylinder, new piston, new rings--what could be wrong with that?

When I finally got the cylinder back in OCTOBER I had other fish to fry and the whole project languished.

Fast-forward to today, when I decided to work on getting the dirt bike functional so my wife could practice shifting gears and using the clutch on a bike small enough that her feet can touch the ground. I cleaned up the cylinder as instructed by the machinist, and was glad to see that I was able to get it so clean I could spray WD-40 into the ports, wipe it with a clean paper towel, and get only oil out. That's clean.

Pulled the old piston off the engine, got the new piston and started putting on the rings--

Wait, WTF? Why don't these fit? Oh--these are the standard size ones, right. Where are the 0.5 mm oversized? (Search box) Here! Ah. Well, let's go, then.

One ring went on fine and fit perfectly. The other--not so much. The two rings from the oversize set have identical markings on them, but one of them simply will not fit. Double-checked the manual and it told me what I knew already: markings side up, both rings are the same (are supposed to be the same, at any rate) and either one will fit in either ring groove. The manual cautions you, in fact, that if you re-use the rings, to make sure they get back into their original grooves.

The ring that fits will fit fine into either groove without any trouble whatsoever. The ring that does not fit will not fit either groove. I can't compress it; it will physically go into the groove but there's no springiness. I should be able to compress it so that it sits flush with the piston surface, and it won't.

My next brilliant idea was to lap the ring: take some fine sandpaper (I used 600 grit) and some WD-40, lay it on a flat surface, spray the sandpaper with the WD-40, lay the ring atop it, and move it around in a figure-eight motion to reduce the thickness of the ring. This almost worked; I got it to the point that I could slide the ring around the piston a lot easier than it had been when I started. But then I compared the good ring with the bad one and saw how much more material I'd have to remove to get the thing to fit right, and realized that there's no way in f-ing hell this is going to work. It's one thing to lap a few thousandths off a piece of metal; it's another thing to have to cut it down by a visible amount. I have no idea what that would do to the metallurgy of the thing, and I don't want to find out by jacking up a freshly bored and honed cylinder. ($0.05 says that Og sends me an e-mail: "600 grit? That's for pussies! Cut it down with 400 grit and then polish with 600, you pansy. It'll be fine!" I wish I knew only as much about machinery and metallurgy as he's forgotten....)

I made sure the ring groove was clean. I sacrificed the ring on the old piston (I have a spare set of rings for that one, anyway) to make a ring groove cleaning tool the old fashioned way, and then scraped out the groove. It was clean as a whistle before; it was equally clean afterwards. No go.

It looks to me as if the ring has suffered from a manufacturing defect. It should have a square profile, like the good one, but instead it has a bevel on the bottom outside edge. That's my problem, and that's what's got to come off. *sigh*

So I put everything away and came inside.

Just now I checked the part numbers, and the boxes sitting on my desk have the right part numbers on them. It's possible that the parts in them are wrong, but I don't think that's so, either. Everything I see here says that Suzuki either put one wrong ring in the box with one right ring, or else a bad one slipped past QC. Either way, I'm stuck until I figure out what to do about this.

More and more, it's looking like I should just have done what I first thought to do when I discovered that the original piston was messed up: go to Ace, buy a drill bit in a size just slightly smaller than coat hanger wire, drill a hole in the ring groove, and drive in a 1/4" piece of coat hanger wire to hold the top ring in place. That was my first idea, but nooo, I had to decide to make the repair the correct way....

* * *

So I'm looking at the verfuckled piston sitting on my desk, and I'm realizing that if I ever make a rat rod I have the perfect shift knob here. (Rat rod, sand rail, WTF-ever.)

* * *

It turns out that someone did, long ago, try to do a wheelie on the dirt bike and failed, smashing the shit out of the taillight etcetera.

My brother complained that the thing had left a stripe up his back when he rode it to school every day in 1985. Well, it turns out that when I inherited the thing I discovered that one of the crankcase housings was cracked, with a chunk knocked out; I took it to the family mechanic, who TIG welded it back together. I never had a problem with it. That was the source of my brother's stripe, not a leaky output shaft seal.

* * *

Ah, the life of the home mechanic is fraught with peril.
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