which head gasket?

[EXtreme-]

sorry fellas, I tried searching till my eyes fell out. Working on an 86 shorty. I see numbers for 3 different trx gaskets.... 12254-HB9-003, 12254-HA2-770, 12254-HA2-771. Which one to use with a cool head 21cc? Why 3 choices? I thought the jugs were all interchangable (long rod coversion included)?

[440ex dragger]

I imagine that its for the TRX250R, ATC250R, and CR250R.
That is all I could think of.

[Rich250RRacer]

None of those are gaskets for a CR, this can be determined by the 3 middle digits of the part number. What you want to use is one thin piece from a stock gasket. This will require taking the gasket apart. Don't use the center piece, just one of the outer pieces. As far as the part numbers are concerned, the one with HB9 in it is the '86 gasket (the thickest). The HA2 gaskets that you have listed are for 87-89 models. One supersedes the other. This is somewhat strange since HA2 is the product code for an 85-86 ATC. Honda usually doesn't go back to an older product code like that. Just for reference, the ATC gasket is listed as 12254-HA2-000. My bet would be the 770 and 771 are just superseded versions of this. The only way to tell is to measure thickness of each one.

[EXtreme-]

much better info. Why go thru the trouble of splitting the gasket vs. getting a cr gasket (thinner right?)? I realise compression will increase...but how much greater by doing a split? Or, why not use, if applicable, a newer superseeded trx gasket without splitting it?

trying to learn a few things and fix the quad at the same time!

wouldn't your average Joe just buy one and throw it on?

[Rich250RRacer]

Originally posted by EXtreme-
much better info. Why go thru the trouble of splitting the gasket vs. getting a cr gasket (thinner right?)? I realise compression will increase...but how much greater by doing a split? Or, why not use, if applicable, a newer superseeded trx gasket without splitting it?

trying to learn a few things and fix the quad at the same time!

wouldn't your average Joe just buy one and throw it on?

Sorry to leave you hangin'. Most of the CR gaskets that I've found are multi-layer, like the stock TRX and ATC gasket. In fact, I normally run a CR gasket (12254-KS7-881), which I split also. The outer layers are the same (or very close) no matter which gasket you buy. The center piece is where the difference is. Back to your question, If you want to run a full gasket, then go with the CR it will give you the highest compression with out splitting one. But with your 21cc dome, I would split the gasket, which means it doesn't really matter which one you buy.

[matt250r21]

Try this gasket, 12254-KZ3-000, 89 STYLE CR 250 head gasket. No spliting involved, one picece and real thin. I always had to use copper spray on gasket maker to help it seal though.

[Rich250RRacer]

Originally posted by matt250r21
Try this gasket, 12254-KZ3-000, 89 STYLE CR 250 head gasket. No spliting involved, one picece and real thin. I always had to use copper spray on gasket maker to help it seal though.

That's true the 89 gaskets were just one layer, I think 90-91 are also, but you may want to check price first. The 89 gasket is only $1.00 cheaper than the multi-layer, and with the multi-layer you end up with two gaskets for about the same price as one. No-brainer there.