xr200r rebuild/oil blowby/rookie 1st rebuild

Hey ya'll, I have an '82 xr200r that died awhile back, and on teardown found multiple probs., two broken gears, and the cam and bushing were scored badly. I scored a 200 from an atv 200 that had new bearings, crank, piston rod, piston, bearings, etc., story was it wouldn't shift and he gave it to my cousin in disgust. Basically I used my gears and cylinderhead, and bought a new cam and bushing. Upon reassembly, it starts with one kick, but smokes alot and there seems to be alot of black oily blowby...I did lube the cylinder with white grease before inserting the piston, and thinking about it now, the piston went in easily...maybe too easy? Questions now occur as to piston size differences in a like-year model atv 200 and my xr200r piston. Anybody got any suggestions on my next move with this thing?

Upon a little searching around in the forum, I found this quote:

ENGINE: The greatest improvement to the XR200R engine is a big bore kit. Here are the 2 most common kits:http://www.powroll.c...HONDA_XR200.htm 
Other options include porting and polishing the head, high compression pistons, hotter cams, etc. The more you do, the more reliability is reduced, but it is a trade off for power. Another option is an ’83 -’85 ATC200X cylinder head. It has a .5mm smaller bore, so it would need to be bored to 65.5mm, however, it has much larger cooling fins. For motors that are constantly being run in extreme temperatures, this is an option to consider.

IF this engine came from a like year atc (I am seeking confirmation) and I used the new piston it came with in my xr200r cylinder, could it provide enough starting compression, yet not enough to prevent blowby?


here's a pic:

Screen shot 2012-10-06 at 3.44.37 PM.png

well you are going to need to confirm which cylinder and piston used. if you used the ATV piston at 65mm and installed your xr cylinder at 65.5mm then we have just found your problem. the xr piston will not fit in to a stock bored atv cylinder. the rings on the atv engine should seal up enough to give enough compression to start the engine with the XR cylinder but they wont be nearly tight enough to do there job correctally and the oil control ring wont have enough cylinder pressure to "clean" the excess oil off of the cylinder so then it burns with the air fuel mixture, the other problem with the rings being expanded outside of the piston is theydont have the support that they need and can flex and break causing all your new parts to become scrap . next problem is you shouldn't use grease as an assembly lube. it can cause all kinds of weird stuff to happen and wont allow the rings to "bed" in to the cylinder correctally. I typically just use engine oil on assembly alough specialized assembly lubes are usually recommended in the manuals.


I am also building an engine similar to what you are doing, but I am using my XL bottom end with a rebuilt crank and an atc200m top end with a atc200x piston, to get the CR up to where it should be at for the bike engine.


so pull it out and tear it back down and measure stuff correctally and you will find your problem.


hope this helps, im by no means an expert just trying to help

Edited by steve_1987

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