Topic: Head gasket sealing

[Coldsmoke]

Hi all,
 I'll be replacing the head gasket on my 350F soon and I want to make sure it gets done Right the first time as ive seen new gaskets leak like the old ones were after a few hundred miles which I certainly dont have time or patience for.

I plan on resurfacing the head and cylinder mating surfaces and using a Honda gasket. Has anyone found some adhesive compound to be benificial to long term/proper sealing? Yamabond or the permatex rattle can sealer come to mind. Thoughts?

Thanks!!

[dave500]

dont use any sealant on it.

[Dimitri13]

Some will recommend copper gasket spray.

[crazypj]

Not on a genuine gasket. They have heat activated sealer applied.
Don't know about 350 but all the 4's leak from the cam bearing oil feed eventually, 550 seems to be worse than most (probably because they get ridden harder?)

[HondaMan]

Like they said ^^^ if it is a genuine Honda gasket. Those have an excellent sealer in them to prevent the problem. Just be sure to bring the engine up to hot when doing the initial startup (no fan, please) so the sealant can get started doing its thing.

If it is an aftermarket gasket, you may have to improve on it. On the 750 aftermarket gaskets, I often add 2mm thick O-rings inside the oil passage holes where there is room (or punch the gasket out, if not) to help seal them, as they don't seal well for oils. I also add some of the Permatex non-hardening sealant around the oil drain holes: this will NOT help around the oil feed holes, though. Make sure any of the seals around those feeders have the right thickness of O-ring or rubber: many aftermarket kits today do not have the right ones (often too thin) as Honda had many custom-sized O-rings made (and they still do in Japan) for these bikes.

[Duanob]

I sprayed my OEM head gasket with permatex copper spray. No leaks yet after a year and a half. I would do this again.

[Coldsmoke]

Thanks guys...this is a gold mine of info. I'm sure many will benefit from this thread.

Cheers!!

[Coldsmoke]

I should ad that the Honda head gasket that I plan on using came in a complete gasket kit in a green package. It's definitely old but in perfect condition, I'll guess from the 80's. Might this "old" gasket not be the sealing type? or should I just buck up for a brand new modern one??

Again, I Need this to be done correctly the 1st time.
Thanks

[HondaMan]

I should ad that the Honda head gasket that I plan on using came in a complete gasket kit in a green package. It's definitely old but in perfect condition, I'll guess from the 80's. Might this "old" gasket not be the sealing type? or should I just buck up for a brand new modern one??

Again, I Need this to be done correctly the 1st time.
Thanks

The "good" Honda ones have a dull, rubbery-like thin coating on them, hard to miss. That's the mystery sealant we're talking about.

Is that piston in your avatar from a 250-6?

[Coldsmoke]

I should ad that the Honda head gasket that I plan on using came in a complete gasket kit in a green package. It's definitely old but in perfect condition, I'll guess from the 80's. Might this "old" gasket not be the sealing type? or should I just buck up for a brand new modern one??

Again, I Need this to be done correctly the 1st time.
Thanks

The "good" Honda ones have a dull, rubbery-like thin coating on them, hard to miss. That's the mystery sealant we're talking about.

Is that piston in your avatar from a 250-6?

Oh! Very helpful info...my NOS Honda gasket has no such layer on it, it's plain graphite. Ok then, a new gasket will be on the way..Thank you!!

And yes, that piston/rod is out of an RC166 250cc-6 cyl. 41X31 are the #'s. How come we didn't get the roller cranks?!-lol

[HondaMan]

I should ad that the Honda head gasket that I plan on using came in a complete gasket kit in a green package. It's definitely old but in perfect condition, I'll guess from the 80's. Might this "old" gasket not be the sealing type? or should I just buck up for a brand new modern one??

Again, I Need this to be done correctly the 1st time.
Thanks

The "good" Honda ones have a dull, rubbery-like thin coating on them, hard to miss. That's the mystery sealant we're talking about.

Is that piston in your avatar from a 250-6?

Oh! Very helpful info...my NOS Honda gasket has no such layer on it, it's plain graphite. Ok then, a new gasket will be on the way..Thank you!!

And yes, that piston/rod is out of an RC166 250cc-6 cyl. 41X31 are the #'s. How come we didn't get the roller cranks?!-lol

Wow! Do you have one of those RC bikes? Those are the coolest!

[Coldsmoke]

Yes, the old Honda factory racers were and still are super cool and nothing short of amazing.....I do Not have a beast of that nature in my collection, just a neat little pic as my avitar:) The remaining vintage Honda racers are in museums and considered part of Japans national heritage...so unfortunately.. Unaccessible   

Thanks again...Everyone, for your time and knowledge on this thread!!!!!
Dave

[Clasico]

My mech is telling me to change tha gasket but not to resurface head or barrel.
He is specialised in classic bikes and claims that there is no need for resurface if a good gasket is use, of course without any aditional sealant. According to him the key is the quality and "fresnesh" of the gasket.