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Cylinder head O rings

12K views 12 replies 7 participants last post by  Auggie 
#1 ·
Are theese Buna or Viton O rings that cat use for the head gaskets?
 
#7 ·
Buna-N (nitrile) O-rings are rated for about 275 degree-F tops. Viton O-rings are rated for about 400 degrees F. But, the head temperature should never get over 300 degrees anyway, so it would seem that Buna-N o-rings would do it, right?

Not so. Heat isn't the whole issue, its heat and chemical attack on the o-ring. Because the coolant in our sleds is a 50/50 mix of water and polypropelene glycol, and glycol contains ethers. The water/glycol, at temperatures over 180 degrees, WILL soften and swell Buna-N material over time. Once the o-rings softens, it may not maintain a seal. If the seal is lost, coolant may get into the combustion chamber (leans it out) or oil may get into the coolant. So, Viton is the choice for the coolant seal. Viton does not react to ethers in glycols at higher temperatures.

This is not the place to go cheap. If you can get a large O-ring in Viton from a hydraulics supplier that's fine, but don't use Buna-N. I know this because I have worked as a field engineer in hydraulics for Parker Hannifin for 15 years. I have seen the results of chemical incompatibility and heat attack on synthetic rubber components.
 
#9 ·
<div class='quotetop'>QUOTE (omercityman @ Mar 13 2010, 07:19 AM) <{POST_SNAPBACK}></div>
I think because you can get them from a hydraulic reduilder for about 1/3 the cost and there stronger. Ron.[/b]

Exactly! I had to replace a piston this winter. The old outer O ring has "grown" to the point of being un usable which lead me to belive it was Buna in which case you can buy them for about a buck apiece from a cylinder shop. I purchased the sled used so who knows if it was an OEM o ring. If in fact the OEM rings are Viton then the prices are somewhat more justifiable. Either way Viton is the way to go in theese applications.
 
#10 ·
The O-rings from a hydraulic shop are not necessarily stronger. There are a number of factors to consider. For one, Buna-N is not stronger that Viton. Also, even as Buna-N material, there are different durometer values of the Buna-N to consider. Most o-rings for hydraulics are a 90 Durometer, which is strong, but the Viton o-rings are of the same rating.

Viton has the higher heat capability, and Viton is more compatible with a wider range of chemicals.

In a pinch, the Buna-N o-rings will work. Lets say your sled blows a head o-ring on a weekend and all you can get is a Buna-N ring, it would work. But I wouldn't leave it in there.
 
#11 ·
I didn't mean that hydraulic shop rings were stronger but that a guy can get good Viton rings at a cheaper price at a hydraulic rebuilder. Also put your oversize ring in the freezed for a couple hours and then install quickly. It will shrink up a little in the freezer. Ron.
 
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