1982 KDX250 Engine Rebuid

[ohgood]

Hello everyone, I recently picked up an air cooled 82 KDX250 and I have decided to completely rebuild it this winter and I need advice. The bike had a good spark when I picked it up, but it did not run. I also checked compression and it was decent at 130 PSI and after I cleaned the carbon out of the exhaust port and cylinder it tested at 155 PSI. After ultrasonically cleaning the carb and setting the float height I got it to run well for a week or so. While out riding one day the bike developed a lean condition, which lead to a runaway engine. Luckily I got the engine killed before any major damaged occurred. I think the crank seal on the flywheel side is a dry air seal, so I figured that was causing the runaway engine because I do not think it would've been anything else and no other variables changed.

Assuming the crank seals were bad, I completely disassembled the engine except for splitting the cases because I do not have a crank case splitter. When I got the top end off I poured the crank area full of premix and checked for leaks, but I do not see any. The crank does have a little play in it from side to side and I have already ordered bearings and seals. A new piston, rings and gaskets have also been ordered.

I am a little weary about splitting the cases and replacing the bearings and seals, however, I would like to learn this process instead of paying a shop to complete the work. I need guidance from someone who has completed this process. I know it is possible to freeze the bearings and heat the cases to get the bearings to complete this. Anyone know of a write up with a step-by-step guide?

see this video, and several of the suggested (right side of youtube) videos that accompany it.



i used parrallels and a 2 jaw puller to press out the crank. no special tools needed.

for installing the crank, i froze the bearings and heated the cases, then froze the crank, and heated the bearing (heated slug method) and it was very easy.

when reassembling the transmission (final assembly of both case halves) make sure everything is free and you have good alignment. you'll see what i mean about this when you have it all apart.

take pictures during disassembly, of all those parts, the shifter forks, clutch assembly, spacers, etc

take your time. it's easy but time consuming. :)

[brawlingkhan]

Thanks to previous post in this thread I was able to assemble the cases and transmission pretty easily. My issue now is that the shift mechanisms are not allowing the bike to shift back down through the gears after shifting up from 1st gear. It appears on of the ratchet pawl springs in the shift pawl is stuck and not allowing the transmission to shift properly. Does anyone have a picture of the shift pawl and shift pawl springs so I can compare it and see if my springs need to be replaced?

[KDX Geoff]

I'll get pics loaded later today (Australian time)

[KDX Geoff]

I'm hope these will help.

[brawlingkhan]

Thanks for posting the pictures, they helped a ton. The transmission is now fully assembled and I plan on putting the stator, flywheel and top end back on this weekend. Any advice on timing this machine? The service manual indicates you need a tool to find TDC in the stroke and then you align the timing marks... I do not have this tool and I am not sure if it is needed to complete this task... Has anyone done this without this special tool?

[Tedh98]

Never heard of that for a 2 stroke.

[brawlingkhan]

I have never reassembled a two stroke, so I have no idea just going by the manual. Do I simply align the timing marks on the round stator plate and engine? Also, the flywheel has markings on it and I assume they need to aligned as well?

[Tedh98]

Does your crank have a woodruff key to position the flywheel?

[brawlingkhan]

Yes, there is a woodruff key on the crank that positions the flywheel. Do I simply align the flywheel so the woodruff key fits and align the timing marks on the stator?

[Tedh98]

Do I simply align the flywheel so the woodruff key fits and align the timing marks on the stator?

That is the procedure for all the different bikes I have owned.

The service manual indicates you need a tool to find TDC in the stroke and then you align the timing marks

I've never had a KDX250, but I don't understand why the manual is having you do this. Maybe wait for KDX Geoff to reply since he has one of these bikes.

[KDX Geoff]

Yes, there is a woodruff key on the crank that positions the flywheel. Do I simply align the flywheel so the woodruff key fits and align the timing marks on the stator?

That's what I'd do (as per the manuals directions). You could get a dial indicator (to locate TDC) to check the static timing if there's a problem after its running.

Its a good habit to put your own marks parts like these on disassembly so you can put things back exactly where they came from.

[brawlingkhan]

Hey everyone, this are the final pictures of the bike. Just finished it this week and had time to post pictures and wrap up this thread. Thank you KDX Geoff and everyone else who posted responses and pictures, I could not have finished this project without your help. Surprisingly, the lighting coil re-winding worked and all the lights are functional. The bike usually starts within 2 kicks and is a blast to ride. Gonna go get a tag for it soon so I can ride it around on the street.

Has anyone put a modern disc brake front end on one of these old air-cooled bikes?