86 250r cylinder head help!!! PICS ADDED!!!

[200x newby]

So I went the cheaper route and had my stock cylinder re-sleeved to the 310 kit. Well I baught a cool head also, so heres my question! my cylinder was decked and the head is flat and not warped. I keep blowing head gaskets left and right and they are the big bore head gaskets. Is the reason I keep blowing head gaskets because the cool head is for a (close to stock) bore cylinder and not for a big bore cylinder? Anyone ever had/ heard of this problem? would like to ride again soon! It's been 3 months since I blew the last head gasket and want to ride again!

Any help would be great! Thanks!

Alex

[TeamGeek6]

Pictures! Howd it blow?

[Red Rider]

Is the reason I keep blowing head gaskets because the cool head is for a (close to stock) bore cylinder and not for a big bore cylinder? Anyone ever had/ heard of this problem?From what I've read on resleeving to a bigbore, when you do that, you need to get the head rechambered also, and it sounds like you're just using an off-the-shelf, unmodified coolhead.

[200x newby]

From what I've read on resleeving to a bigbore, when you do that, you need to get the head rechambered also, and it sounds like you're just using an off-the-shelf, unmodified coolhead.

yes it is its for the stock sleeve cylinder. i have heard that there are big bore heads for the stock cylinders is this true? there is one on ebay but is it real?

[Red Rider]

yes it is its for the stock sleeve cylinder. i have heard that there are big bore heads for the stock cylinders is this true? there is one on ebay but is it real?Other than the Pro-X heads, for use on the Pro-X bigbore cylinders, I've never heard of, or seen any "bigbore" heads, unless it's a stock head that's been modified for a bigbore cylinder.

[RedRider_AK]

Maybe the stock combustion chamber is too small? Too much compression?

[jason85atc250r]

what cc dome do you have in the cool head also.

[200x newby]

19cc dome! you think the compressin is to high? when i put the gasket on the head it doesnt seem to have alot of area that it seals to.

[x.system]

Can you get pics of the head with the dome in it? Did you ever do a compression check with that dome? Does the dome sit flush with the cool head? May need to get a different dome meant for the larger bore size. Any other markings on the dome besides 19cc?

[200x newby]

took some pics of the head. the first pic is of the whole bottom side and the second pic is of the VERY small sealing surface.

[Dirtcrasher]

Wow, that sealing area appears small, like 4mm or so....

[200x newby]

Wow, that sealing area appears small, like 4mm or so....

I thought it was very small also.

[Somekindofjerk]

Try doubling your torque specs and see if that helps... Allso try GENTLY scoring the sealing surface with fine grit sand paper to create for lack of a better word "traction"

[200x newby]

Try doubling your torque specs and see if that helps... Allso try GENTLY scoring the sealing surface with fine grit sand paper to create for lack of a better word "traction"

Oh I've tightend them so much past torque specs it actually started to tighten the actual stud again and I sand blasted the head and dome before use( that did not cause any problems).

[x.system]

Get a piece of glass, marble or any perfectly flat surface and wet sand both the head and dome as one piece. Use 300/400 grit wet paper, sand in one direction back and forth and you should be able to see the sand scratch's fairly quick. If you have any of that blue dye it would help show any low areas but you can do it without the dye.

You may need to do the same thing with the top of the cylinder.

[rich250rracer]

You MUST have the Cool Head dome rechambered to work on a sleeved big bore. And you have to run the big bore gasket, or have it o-ringed.

[200x newby]

im running the BIGBORE gasket! the head IS NOT he o-ring style. do you know of anyone who rechambers these heads?

[Red Rider]

do you know of anyone who rechambers these heads?Whoever installed the bigbore sleeve should have rechambered the head also. If you bought the cylinder that way, try contacting LA Sleeve, as they sell/install bigbore sleeves, and should be able to rechamber the head for you.

[200x newby]

i took the cylinder to my local honda dealer and they shipped out to Dayton, Ohio. i did not have the head at the time. wait a minute doesn't yamahondaman do work with heads? anyone know if he could rechamber it for me?

[honda250sx]

Yes indeed he does rework heads. I believe i have seen a few guys post 250r heads hes done. He has done tri-z's for me.