Case Through O-Ring trouble??
 

I was working on my engine assembly today after being away from the project for a month and I noticed some little bits of the Viton O-Rings showing around the edges of the washers on the case through bolts. These bolt heads never turned while I was torquing the nuts, the rings were lubricated with the 3M goop from Henry's kit, and I have nothing showing on the nut side, only on the bolt head side.

You guys think I need to pull these bolts and install new seals?
Or is a little squeeze out on these things normal?


http://forums.pelicanparts.com/uploa...1375635060.jpg

I had a few like that on my rebuild and I redid them one at a time.

That happens on the case half that does not have a relief/chamfer cut in the bolt bore. Mike Bruns gave us a nice tip to buy a countersink for aluminum and cut the bores yourself with a hand drill on slow speed.

http://forums.pelicanparts.com/911-engine-rebuilding-forum/646102-chamfered-case-through-bolt-holes.html

I bought a c-sink from McMaster and it was very effective at cutting the case material w/out any chatter or mess. I chose the middle of the selection and got a 90 deg cutting angle McMaster-Carr

Needs more lube. If you see any bits of o-ring at all come out then the ring has failed during assembly and should be replaced.

http://i458.photobucket.com/albums/qq302/aagvt/P911/IMG_3361_zps2958f588.jpg

KTL is absolutely correct. No chamfer equals no seal due to failed o-ring. The Viton O-rings are not the same as the original stock O-rings and don't squeeze down around the bolt. They are too hard to do that. You can either chamfer the hole or find the original O-rings (impossible). No amount of lube will cure this problem.

I disagree and have no such failure with proper lube.

Hey Andrew, good for you. On what year engine are you having no failures? Probably not a '78 or '79 as those are the only years with the chamfer problem. A thin coat of lube is all that is needed if there is a chamfer which is likely in your case.

'74

There you have it. You have a chamfered through bolt hole which explains your success. A case without a chamfer through bolt hole, like the one posted above, has little chance of sealing without a chamfer or an OEM O-ring.

Thanks guys.
I plan on pulling them one by one and resealing next weekend.
I will definitely look to see if my case has chamfered holes.

That's strange... my case holes are not beveled but the washers are.

http://i458.photobucket.com/albums/qq302/aagvt/P911/IMG_3354_zps1eae5b24.jpg

Is that what you mean?

Maybe on Andrew's '74, with the coarse threads on the thru-bolt nut side, the coarse threads allow more squish of the o-ring?

Incidentally I chamfered the one side of my case that was not. Cut it to a chamfer depth similar to the already chamfered case halve. Measured it by the precision of my sharp eye of course....

Had no leaks but still found the nice Viton o-rings mangled upon disassembly. All washers were watched to avoid spinning during tightening and plenty of Dow 112 paste was used to install them. Engine was disassembled shortly after rebuild due to oiling problem. So more chamfering (or thinner/softer o-ring) is in order to avoid wrecking the o-rings. Yep, my washers are beveled underneath too.

Speaking of case thru-bolts, i'd be interested to see what the washers in the spendy ARP thru-bolt kit look like. I wonder if they made sure to bevel their washers?

Speaking of o-rings, I think I found an alternative to the DPH Viton o-rings. Sourced a bag of 25 from McMaster but haven't put them to the test yet on the engine rebuild.

McMaster-Carr 2.4mm-8.3mm Viton Rings

Size of these is apparently better to be a bit on the small side to avoid excess squish, as well as plenty of o-ring paste to facilitate damage avoidance. I'll check the dimensions of my McMaster o-rings to the typical Vitons and see how they compare.

Whatever the case, I just can't bring myself to use RTV as a belt & suspenders solution in this location. That stuff is such a PITA to clean up both during assembly and down the road at disassembly.

Not all lubes are equal either. I use Krytox by Dupont exclusively. Pricey but by far is the best in my opinion.

Andrew,

I can't tell for sure from your picture but it does look like a small chamfer on the edge of that hole. Did you have the O-rings squeeze out like the original poster? The SC case I have had chamfers only on one side.

-Andy

My dilemma is that the portion of the thru bolt that comes out thru the case hole in question is threaded. How can any o-ring seal against a threaded surface?

With the Krytox and Viton seals I do not have any squeezed seals. The previous owner/mechanic had used red seals (original?) but had left powdercoat on the case surface where the ring was to contact. I would approximate greater than 80% failure rate of those red seals when disassembling. Chamfer/bevel/lube/technique all contribute for sure. Case is not beveled but I did remove the powdercoat with sandpaper by hand. I would suggest to use a papertowel plug technique which is a ramrod from behind with the bolt and hold your thumb over the hole to make a nice seal with a small chunk of towel. This would also work well for when beveling the case holes to keep debris from entering the case/oil galleys.

Some better pictures:


http://i458.photobucket.com/albums/qq302/aagvt/P911/IMG_3344_zps1a560e24.jpg

http://i458.photobucket.com/albums/qq302/aagvt/P911/IMG_3348_zps15641f63.jpg

http://i458.photobucket.com/albums/qq302/aagvt/P911/IMG_3347_zps96435e8d.jpg

http://i458.photobucket.com/albums/qq302/aagvt/P911/IMG_3363_zpsc476ef34.jpg

Papertowel plug in place:
http://i458.photobucket.com/albums/qq302/aagvt/P911/IMG_3357_zps2ae3bc99.jpg

Same here - good o-ring grease does the job.

Check the case for proper chamfer. The lube ("goop") provided with the Supertec case sealing kit is actually Dow 55 o-ring lubricant. It's hard to find an o-ring lube with better properties for this application.

Thanks for the comments Henry. I sent you an Email.

Andrew - The beer cups are a nice touch :-)

Which flavor? I use Krytox 226 on bearings. It is expensive $150+ for a cartridge, but it does work well in certain applications. It is Fluorinated grease.

It is good for around 500°F, but I prefer o-ring grease for o-rings.

I believe in using whatever works for you.