Head gasket/ coolhead question

[Qracer]

I picked up an extemely low hour 85 atc 250r motor & I want to install my cool head. What should I use for the gasket, the 85 fiber style or the newer shim style. What size dome should I use? I have a 19cc & 21cc.

[deathman53]

I would use a stock 85/86 ATC head gasket(thin fiber sandwhiched between 2 thin metal riveted together) or a cr gasket(paper thin metal) and the 19cc dome. You are using race gas right? With that kind of compression, you will need to.

[86 Quad R]

depends on where ya want to run the compression at as to what dome/gasket combo to go with.

[Qracer]

I tried the fiber 85 style gasket with the 21cc dome & I got 155psi of compression( same as the stock head & gasket. When I filled the rediator, coolant started seeping around the head. I tried retorqing the head a few time, but it didn't help. I ended up using 1 of the thin shims from a 87-89 trx gasket with the 21cc dome. Compression is now at 192psi & no more leaks.

[deathman53]

your compression should be higher than that, stock the compression is between 180-190, with a thinner gasket and smaller dome it should be up near 220. I had a cool-head w/ 18cc dome and trx gasket, making over 200 psi, with a thin gasket it would have been near 240 psi.

my 85/86 atc250r shop manual says 170.7-199.1 psi(this is on the honda manual, so its bone stock specs). Also the head nuts get torqued to 17-21 ft/lbs.

[Qracer]

The engine was a new take out from a 85 ATC. I put about 5 hours on it last year & checked the compression, I only got about 155 with the stock head & gasket. The piston looks great, still has a perfect crosshatch on the bore. I have checked it with 3 different testers & they all read within 5psi.

[deathman53]

Did you test the compression with the motor warm and throttle wot?? Maybe that is why your results are off, if you didn't do so. The numbers seam pretty low.