CR Gaskets question

[troybilt]

What do you guys/gals know about running CR gaskets on the jug and head for a mostly stock 250R?

...and yes, I tried searching first and didn't see anything previously.

Thanks!

[BKex]

If you want one. you need one from an 89 cr250. Its the thinnest gasket compared to the trx and the atc. Will bump up the compression a bit and give you a little more bottom end power

[troybilt]

Thanks!

Is there something to running 2 gaskets on the jug? My buddy is rebuilding his motor, see (cratered engine help) thread, and has CR gaskets already. It is an 86 motor, any difference there either?

[All250R]

The CR head gasket is equivalent to one of the outside layers on a stock TRX head gasket (about .25mm). Like BK said it will bump your compression and should give you a little more power across the board. It narrows the extremely wide stock squish clearance a bit which helps power too - though it's still too wide. Stock TRX head setups from Honda were very unoptimized. Not surprisingly the CR of the same year made signifantly more power so the TRX needs fixing.

If the bore is around stock, rings are healthy and the head is unmodified it will pick your compression up to around 205. You'll want to run at least 100 octane. It's a litlte more expensive of a setup that way, but you'll appreciate the little bump in power you get for it.

*by the way you can separeate a stock TRX gasket and use the outer layers. Use some copper gasket spray since there is no coating on the bottom of the separated layer.

*the CR gasket needed I believe runs years 89-91

[bluetrx]

Originally posted by troybilt
Thanks!

Is there something to running 2 gaskets on the jug? My buddy is rebuilding his motor, see (cratered engine help) thread, and has CR gaskets already. It is an 86 motor, any difference there either?

the only logical reason to run 2 baseplate gaskets is if your compression is slightly too high, and you dont want to shave material out of the combustion chamber. max cylinder pressure for a motor with some good longevity is around 230psi. at 245psi even 110 octane is at risk of detonation.

the '86 motor is diffrent from '87-'89 the bore and stroke are the same, but the rod length is diffrent and the wrist pin height in the piston is changed to accomodate. i cant remember which is the long rod someone else jump in here.

[bluetrx]

this might be a little off the subject, but i just reviewed your cratered motor help thread and was wondering if youve already got that bottom end back together (probably, being that youre asking about cylinder gaskets). if not heres a sweet trick for assembly. put your crank in the freezer, and your crank bearings in the oven, the crank shrinks and the bearings get bigger. slide the bearings on the crank with ease, then put the crank and bearings in the freezer before joining the case halves. this trick work great for pinion bearings and carrier bearings too if you happen to set up rear ends in cars.

[8686]

The 85-86 are short rod. The 87-89 are long rod.

[troybilt]

Originally posted by bluetrx
this might be a little off the subject, but i just reviewed your cratered motor help thread and was wondering if youve already got that bottom end back together (probably, being that youre asking about cylinder gaskets). if not heres a sweet trick for assembly. put your crank in the freezer, and your crank bearings in the oven, the crank shrinks and the bearings get bigger. slide the bearings on the crank with ease, then put the crank and bearings in the freezer before joining the case halves. this trick work great for pinion bearings and carrier bearings too if you happen to set up rear ends in cars.

Yeah, I wondered if anyone tried this. Thanks for the tip. I'm an engineer for Caterpillar and I have some experience using a cryo freezer for things like this.

Just have to be careful you don't overheat w/oven, stay less than 400 degrees F. At 400 you are close to the annealing temperature of the steel and could possible change the grain structure... i.e. weaken the part.

For anyone that cares, the rule of thumb for 1" Diameter steel alloy parts is roughly, 154 degrees temperature differential per 0.001" press. So if you have a 0.001" pressfit and a 1" shaft, and the ambient temp is 70 degrees, cooling the shaft to -84 F there would be a 1-1 fit.

[mineralgrey01gt]

man my compression on mine is low then, last i checked it was around 150's I think. I may try this CR250 gasket trick

[beerock]

Originally posted by mineralgrey01gt
man my compression on mine is low then, last i checked it was around 150's I think. I may try this CR250 gasket trick

if your comp is that low you need a new top end

[beerock]

also, only the left side case needs to be heated(IF AT ALL) i just press in the left side bearing and crank and then press in the right bearing.

the right side of the crank will actually slip onto the right side case right onto the bearing if it doesnt then something isnt right.

[mineralgrey01gt]

Originally posted by beerock
if your comp is that low you need a new top end

the new top end probably doesnt have 15 hours on it, it runs strong as is, but i think it has a thicker gasket on it than normal for an 85 engine, what is the stock compression suppose to be? Also to note: you can sit on the bike and crank it, i know that isnt suppose to happen

[beerock]

should be around 170-180 Im not sure but 165 might be stock been a while.

if you can sit on the bike and crank it over with your foot it sounds TOO LOW

maybe the install was bad and it popped a ring I dunno that def sounds low. get 2 diff comp testers and see what the readings are.

[mineralgrey01gt]

Originally posted by beerock
should be around 170-180 Im not sure but 165 might be stock been a while.

if you can sit on the bike and crank it over with your foot it sounds TOO LOW

maybe the install was bad and it popped a ring I dunno that def sounds low. get 2 diff comp testers and see what the readings are.


ill have to check it out and see. It may need another top end, if it does, im going to throw on a 310 and roll with it