i've used the rotary aviation teflon coolant seals (both inner and outer, although i don't think the black outer rings are teflon encapsulated), and i have no complaints. i also used their viton oil control o-rings. the outer rings are a little big, but with some coaxing and some patience they will slip into the groove. just be careful not to tear them.

 

Mcmaster-carr also has bare silicone, as opposed to teflon encapsulated silicone O rings. I think I might try these instead. I've used the teflon ones three times now and they always get pinched on the inside edge somewhat, like they are a hair too small. The ones rotary aviation sends with their kits always need to be stretched a little.

So anyhow, I just ordered part number 9396K199, which is AS568A Dash Number 176, 3/32" round red silicone O ring in 9 1/4" inside diameter. It's basically the same cross section as the teflon ones, but one size larger diameter (1/4" larger dia.).

They're $3.19 apiece. I "rebuild" this engine so often due to stupid mistakes that it won't hurt to see if bare silicone will work too. If I could get the square cross section like stock, I'd do that but they don't list any of those.

I'll report back my results, wish me luck!

 

Petrol destroys silicone.Viton is much more suitable.

 

True. I figured the stock rings are silicone so we'll see.........

 

The stock ones are silicone,protected by a strip of teflon.Even these will fail when an engine is left flooded with fuel.Viton is unaffected.