cool head dillema

[Mechanix311]

I have a 1986 motor in my 250r. I had the cylinder at 67.25mm and i bumped it up to a 72.95mm or 310 kit. I had a cool head on it when it was at 67.25mm but i am wondering if i have to have a special cool head for the new bore size. It is a stock honda resleeve no a pro x. Can i have the dome cut wider maybe? Any help would be appreciated. THanks

[Honda5]

you will want to open it up a little if not you are going to have some high psi. you should be able to get another dome or get yours cut.

[BLACKeR]

i would check into a big bore head. i assume that was a re-sleeve? if so the o-ring seal on you dome might not sealed to anything. i learned the hard way once on a 404 banshee with a coolhead. both of the dome o-rings droped into the cylinder and all my coolent went bye bye

[zedicus00]

i used a non o-ring cool head for a stock bore on a bigbore resleeve once, it JUST BARELY fit. my pump gas dome just barely let me run pumpgas too, so if yur a lucky person give it a go. or do like i did and measure everthing and do a compression test.

[beerock]

well, you can run a stock head and take a dremel and make the inner diameter of the gasket match the bore size but you might have problems you really need the cylinder machined and have a special metal ring made for it. mac dizzy has done it for his 270's
the biggest you can go with a stock cyl is a 295 and most big bore 310's are 295, search on mac dizzy site for it

[zedicus00]

the last bore on a resleave is like 305 cc's i believe. my stock head is milled so much the gasket area is flat with the dome anyways, and thas how the non oring coolheads are. you dont NEED the wire ring installed, my engine builder doesnt use them, but it doesnt hurt by any meens either.

cometic makes a big bore resleeve gasket, not that cometic makes the best gaskets but add a lil gasket seel and an extra torc to the head bolts and you should b o.k.

[xlr810]

It will work fine with the right gasket. I have a few Cometic 72mm gaskets I may be willing to part with.

[Mechanix311]

I have a stock head that has been cut wider to allow the piston to clear. What i am wondering is do they make a dome that has a larger diameter where it seats on the cylinder or can i get the one i have cut. With the 295 resleeve cylinder off, If i install the cool head with the dome for 67.25mm bore and i look down the bore of the cylinder their is a lip because the dome isnt widened for the bigger bore. Is this ok. Sorry for being so vague. Thanks for all the responses.

[xlr810]

You should be fine.

The piston shouldn't extend beyond the top of the cylinder-- definitely not beyond the cylinder + head gasket. You can bench test it to check.

The main potential issue to worry about is if there is enough of the inner dome remaining that it will seal the head gasket and cylinder. If the entire removable dome is smaller than the bore it isn't going to work. Again, pretty easy to bench test before assembly.