99 CR 250 Engine Rebuild

Loc
Posts
69
Joined
5/24/2017
Location
DE
1/17/2021 12:34pm Edited Date/Time 1/17/2021 2:09pm
bought a used 99 CR some time ago. cylinder was in much better condition than the head and power valve assembly. after analyzing part numbers, I found out that the previous owner replaced the cylinder with a 96 one. fits the description from these, as strong power, mostly mid to top, endless overrev, even with a short PC silencer on....

anyway, engine ran good, a little spooge maybe. but lately the transmission has become hard to shift and made some strange noise. this was enough for me to split cases:




tolerances were good and everything in spec, but almost no oil left (replaced it only a few hours). so it must be the crank seal. in the process I replaced all gaskets, crank seals and bearings with OE/koyo//proX and a hot rods kit for the transmisson.










to save space and weight, honda R&D placed the power valve mechanism inside the resonance chamber. this is sub optimal, to say the least, but it's easy tune able because of it's simplicity. this is a simple way of chancing the opening position of the PV. I also sealed the PV stopper bolt with teflontape and both actuation shafts with grease to increase internal compression.







cleaned the carb with ultrasound. set float to 16mm




finally engine back in. feels good to have it back together



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sandman768
Posts
5958
Joined
3/21/2014
Location
Saratoga Springs, NY US
1/17/2021 2:09pm
Well done...I like the heat freeze method also..it’s a good thing the gears were ok, many of the high wear gears are NLA. I”m rebuilding a 94, that the previous owner had a flat top piston installed with the dome top head... 😂
2
Loc
Posts
69
Joined
5/24/2017
Location
DE
1/18/2021 10:17am
it was the first time I've done this. splitting cases was awesome.

the freezing method is stupid easy (pre heated cases to about 230F). they just dropped in place. had to really use the press for only one bearing, the needle bearing which was a real bitch to remove..

and yes, almost all transmission parts are out, you can only buy the small stuff like special bolts, washers. glad that everything was in excellent shape. now its operating perfectly smooth. the odds are that it was just low trans oil levels paired with worn out bearings.




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