Cylinder head modified for "O" rings?
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I've seen that done on liquid cooled engines (stock and aftermarket) but I'm not sure how the o-ring would survive on an air cooled head. Obviously, the head "surface" (the part you can touch) doesn't get THAT hot but the mating surface between the head and cylinder might get that hot....
As I always say, more research is needed!
Viton o rings would be up to the task of handling the heat, you would just have to keep some on hand because they usually need to be replaced once opened up because they will expand.
a lot of the a/m pipes use viton o-rings
a lot of the a/m pipes use viton o-rings
According to DuPont, Viton has a "stable" temperature up to 400°F.
Obviously, the surface of the head never gets that hot but I'm not convinced (at least on gasoline
) that the top of the deck doesn't get that hot on a blaster engine....
i coulda swore i read that someone was using them on head o-rings, but i'm not 100% positive.
OP, shoot an email to a Pro-Design, they make the cool head to work with O-rings, see what they have to say
OP, shoot an email to a Pro-Design, they make the cool head to work with O-rings, see what they have to say
The cool head is using viton o-rings but it also has 170°F coolant on the backside drawing the heat away from the o-rings. Blaster's don't have that luxury....
That 1993 YZ250 I have has a viton and one Buna-N oring on the head. The inner "compression seal" oring is viton and the outer "coolant seal" oring is regular rubber but again, viton definitely can survive up to 400°F which isn't a stretch on a well designed liquid cooled head. Not so sure on a blaster air cooled head...
It's completely possible that it would work great and never get hot enough to bother it at all but I'm not SURE that will...
Blaner
Your Friendly South African Ambassador
the idea of the copper gasket is to transmit heat to the head where the cooling fins distribute it. Copper is a good heat conductor, whereas O rings do not, so heat from the top region of the barrel wont ever be transferred to the head, causing build up of heat in the barrel, which I dont believe is finned enough to handle that.
This would be true if the "O" ring were sandwiched between the surfaces, but I am looking to put it in a groove.
Most of the combustion heat goes to head and piston, with the piston and exhaust ports then conducting heat to the cylinder. Usually the head is hotter than the cylinder and conduction across the head gasket joint is helpful in keeping everything balanced out. An "O" ring that just sits in its groove forms a seal against pressure loss. There would still be all that aluminum against aluminum contact to conduct heat. The head would be 0.035" closer to the piston, which is something we need in these motors, and the main reason I am thinking of doing it. Trying to get the plug closer to the piston than its stock 3/4". Looking to have a flatter combustion chamber shape after some machining.
Blaner
Your Friendly South African Ambassador
yes, but would it be as effective at heat transfer as a copper gasket? me thinks not, these motors were designed with the copper gasket for a very good reason.I see the merits of squish band clearance in its removal but I for one would put my trust in Yamaha for this one
With a 12" swing lathe with a tapering rest, you can shave as much of that head off as you want to. If you feel inclined, you could cut as far down as removing the bottom cooling fin off of the head to correct the combustion chamber.
I'm not sure that the gasket's purpose is to transmit the heat of combustion to the head. It *MAY* just be that yamaha designed them all in the late 70's with copper gaskets so they just kept on that way.... without some experimentation it's hard to say whether an o-ring would work well in a gasoline fueled blaster head or not. I'm sure in an engine that produces less heat (fueled by ethanol, methanol, or nitro) the o-ring wouldn't affect the heat transfer as much which probably would make this discussion mute....
I think Paulie B had his 400 grooved for copper o-rings ... I don't believe there would be such a difference in heat transfer as to cause a problem ... the groove size for the viton o-ring is critical, I got a just bit sloppy regrooving after decking a yz250 jug and had a leak problem ... hope someone's ambitious enough to give it a try
I think Paulie B had his 400 grooved for copper o-rings ... I don't believe there would be such a difference in heat transfer as to cause a problem ... the groove size for the viton o-ring is critical, I got a just bit sloppy regrooving after decking a yz250 jug and had a leak problem ... hope someone's ambitious enough to give it a try
I had a V8 Ford 289 grooved for copper "O" rings many years ago.
Not entirely successful in my opinion. They seemed to relax their seal over time, not very good for a street driven engine.
I have been a bit sour toward them ever since...
My KTMs run composite gaskets on the early engines and Viton "O" rings on the newer stuff, but they are water cooled so 220f max.
The "O" rings are very durable and seal very well, I just don't know how they would do with air cooled.
Groove size and tension is extremely critical for the copper rings, Viton (or rubber) a bit more forgiving.
Copper is an interesting choice for a gasket. It was an old favourite many years ago because of its softness and ease of shaping. Soft aluminum and steel sheet was also used. I think that heat transfer rate of these metals might have just been incidental to their softness.
Asbestos cored composite gaskets pretty much supplanted copper after WWII because of superior performance and material costs.
The search for asbestos substitutes caused a lot of the head gasket failures that were so common in the 1980s and 90s.
The less durable cores would rip, buckle and relax from head to block expansion movement.
Multilayer steel shim seems to be the favourite these days, relying on a Viton coating and the spring of the cupped steel edge to seal.
I appreciate all of your advice. It looks like someone has to jump in if we are going to find out what the water is like!
My son is putting together his stroker motor. If he gets a head turned (we are talking about a toroidal chamber design) we may try an "O" ring design.
