Problem with case bolts + viton o-rings

4sd911 · 05:11 PM

I'm having the same issue with the through bolt viton O rings as shown in this thread below. Basically some of the bolt side O rings can be seen and measured with a feller gage as the washers aren't seating against the case. Anyone else have this issue, I'm thinking of replacing them with the blue ones. I didn't see a resolution in the other thread. I used dow corning 111 grease on the rings.

Problem with case bolts + viton o-rings

Walt Fricke · 03-27-2010, 06:23 PM

As you may have noticed, there are some accomplished engine builders who swear by the Vitons, and at the blue ones.

Not knowing any better, I have used the blue ones. Yes, they tear some even if you are careful to hold the bolt end when tightening. My main gripe is that this means only one out of 20 or so can be reused, and I am cheap and like to reuse things. I bought a largish (for a home brewer) amount of the blues a while back, before being educated (or confused) by this fine forum's contributors.

But my engines have not leaked here. Other places (the chain box to case seal is my bete noire, and RSR rings don't seem to keep the rocker shafts from weeping) do, naturally, a bit.

I'd be more concerned, as you are, about getting a critical and permanent clamping force than I would about the disadvantages of blue seals. For this reason I gave up using the CV joint gaskets - I think often the initial torque is not enough to get enough CV metal to hub metal clamping. But those you can easily retorque after running. Not so for the case bolts.

But if you are patient, perhaps Steve or Henry or one of the other guys who do lots and lots of engines can opine. A washer gap would freak me out, too.

MBruns · 03-28-2010, 05:22 AM

Take a look at the case where the seal goes and be sure there is a chamfer, without this the o ring has no room and the viton seals could hold the washer off, the lack of chamfer on the mag cases is common and also the movment on those cases will even create a hi spot and make the problem worse, I have seen the lack of chamfer even on the SC and later cases, we have a piloted tool to chamfer them the proper dia. and depth and that takes care of it.

Mike Bruns JBRacing.com

4sd911 · 03-28-2010, 01:18 PM

Correct there is no chamfer on the mag case, and there is a high spot at some of the holes as you point out. I changed out all the seals one bolt at a time to the blue ones and all washers are now seated to the case. The Dow corning 111 keep the all but one seal from squeezing out at the washer.

There needs to be a warning with the viton through bolt seals about this issue.

MBruns · 03-29-2010, 08:25 AM

Without a chamfer there will still be an issue, the silicone o rings are softer and seem OK . The viton is a better seal.

4sd911 · 03-29-2010, 09:30 AM

Thanks for the info, I would think that one of the two machine shops that had this case for repair should of brought this up. I can see now why the blue seals squeeze out from under the washers on my 912/911 builds. The 911 case is together now and I plan on running it with the blue seals, if this case is split in the future I'll have this addressed.

mcguiver7 · mcguiver7's Garage

I too used the blue ones, but noticed they squeezed out after torquing down. It made me too nervous so i removed them and installed the green ones. Though upon inspection of removing the blue ones it appeared they would have been fine with the massive amounts of rtv. I still think the green ones along with the corning lube is much cleaner and probably safer.