Viton o-ring as head gasket?

[TZ350]

i had the idea of machining a groove in the head to fit a viton o ring they are good for 400 degrees, it wouldn't be to hard for me to make a groove in the lathe with a 4 jaw chuck, but thinking as its air cooled it may be no good?

I originally read about using Viton O rings for head gaskets in an article posted by Dale Alexander. But I don't know of any main stream performance air cooled engine manufactures that use O rings for head gaskets but I do know a few of the Bucket boys have used Black (ordinary) Viton O rings in their air cooled 2-Strokes.

For me they have proved very reliable with very few failures. And all the failures that I have seen, mine and others could be traced to pulled studs or the cylinder loosening off in some way.



I myself am looking to move back to composite head gaskets as they thermally isolate the head from the cylinder and the head runs quite a bit cooler than the barrel that way.

I think the bulk of the heat in a 2-Strokes cooling system enters via the exhaust port tract and the upper reaches of the transfer ducts at high rpm when they are exposed to hot combustion gases that enter them before the blow down process is complete.

Below are from the Team ESE thread which is gaining a reputation for very informative 2-Stroke tuning content. http://www.kiwibiker.co.nz/forums/sh...post1130543255

Attachment 263916

Got the head off tonight.

Attachment 263917

Doesn't look to bad in there.

Attachment 263918

Carefully re checking the squish.

Attachment 263914

And it looks like 1mm.

So the trick is to figure out how to take 0.4mm of the top of the barrel for 0.6mm static squish.

Attachment 263915

Also checked the timing to see whats needed to get the Ex opening 80 ATDC and the main Trans opening 116 and sec 114 ATDC.

Ok I got the chance tonight to find out what went wrong on the dyno last night.

Attachment 254567 Attachment 254568

Blown head gasket ("O" ring) as I suspected.

Attachment 254570 Attachment 254569

The piston has been just touching the head

Attachment 254571

The piston itself looked good and the ring was still free in the grove.

Attachment 254566

The culprit is the hand made gasket on the right, it compressed down to much, I expect its compress-ability allowed the combustion pressure to spit the "O" ring out. I replaced it with an alloy plate which should give a more reliable stack for setting the squish clearance and give something more solid for the head to pull up against.

[F5 Dave]

. . . but I do know a few of the Bucket boys have used Black (ordinary) Viton O rings in their air cooled 2-Strokes.
. . .

Erm, Black is usually Nitrile & is just fine for outer gallerys. You might get away with them but all the Viton o-rings I've seen are dark green or brown.

[TZ350]

Erm, Black is usually Nitrile all the Viton o-rings I've seen are dark green or brown.

Properties of O rings. http://www.sealanddesign.com/categor...Rings/462.html

The common ones, Viton Nitrile and EPDM can all come in black as carbon is the filler of choice, other colors mean different fillers have been used to give the O ring particular properties.

The standard commercial V1000 Viton O ring is black. http://www.marcorubber.com/viton.htm also lots of other useful info like groove design and material selection.


Page 2 of ProMinents tec sheet talks about "the bounce test" which is the easiest way to tell black Viton and EPDM O rings apart.

ESE imports, distributes and supports the full range of ProMinent water treatment equipment throughout NZ. http://www.ese.co.nz/