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DT125 : Unsticking a Simple Beauty

To get the DT125 running again, a nearly forgotten two-stroke needed gentle persuasion instead of brute force. There’s a lesson in all this.

 I had to resort to an old-time fix for an old-time bike. It was enjoyable. It’s a long story, time-wise anyway. About 20 years ago I bought a Yamaha DT125 Enduro from a friend. It was one of those things where it had to leave his garage because he had to leave the house—splitting up is not fun. 

Anyway, the deal was I pay for the engine rebuild parts and cylinder hone and the bike was mine. Good deal for me but after assembling the engine I never got around to getting a battery. 

Forward 20 years, I was cleaning out the breezeway and found the little DT125. I had not completely forgotten it but it has been pushed so far back on my project list there was little hope of it ever running under my ownership. Thinking swap meet, I figured, better see how it had fared. It was pretty much all there (even the throttle slide is free), but it wouldn’t kick over. 

After surveying the roached seat, rotten front tire and rusty spokes the first question people will ask, “Is the engine stuck?” Better see if I can fix it. Penetration oil in the sparkplug hole and a sit overnight might work. Nope, the piston was sitting low enough to uncover the exhaust port; the pipe is full of oil now anyway. 

Here is where things can go badly, because it’s very tempting to force the kicker. If you do it’s quite likely to break inside the case, and if that happens a bike that might be worth a few hundred bucks now might bring 50 or less.

The thing to do is take off the head; this is beautiful simplicity. Four bolts, the head gasket is copper (that means it can be reused) you don’t even have to take off the gas tank. 

Once the piston was in view I could see a very light dusting of cylinder wall rust. Using a soft hammer handle on the piston and hitting it with another dead blow resulted in the piston moving down. Once down a bit of a wipe with some Scotch-Brite got everything back to looking new. (It actually is a new piston with rings.)

It kicks over like a champ now, some vigorous kicker action and most of the extra oil is pumped out of the crankcase. The Dt125 engine will likely run now, I concluded.

Standing back it struck me: no cam chains to mess with, no lifters or shims or valves, the old two-strokes were so simple there is a beauty in how they work. The tank smells like bad gas and it still needs a battery and front wheel, but it might be a fun bike for the right person, someone who can appreciate why we used to love little bikes like the DT125 so much.  

by Rich Burgess Canadian Biker Issue #315


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