Through bolts and why they leak on 993's

[84toy]

OK, a torn o-ring at the through bolts cost me dearly since I had an oil leak on my fresh engine and now it's out and totally disassembled again. I hate an oil leak!

I was very careful during installation and I used the green viton o-rings. Teardown showed a cut o-ring. After fooling around and some trial and error I figured out why. The step on the bolts are just too sharp and when pulled through, it tears the o-ring. Looking at them you would never think they would but the sharp edge has to go!

The cure is simple.....I took each bolt ion the lathe and chamfered the sharp edge back about 1/16th with a file and finished with a little sandpaper. I then kissed it with my buffer for a nice smooth finish. This does not effect where the o-ring sits just the entry of the bolt through the o-ring.

When I pushed the bolt through, it went in with about 75% less force. Very easy to assemble. I'm confident they won't leak or get torn.

I also made a tool out of Delrin that centers the tool on the outer step before inserting the o-ring. It also centers the bolt. Using the tool assures that the o-ring goes in straight and eliminates cutting.

And finally, I used some heat shrink tubing for a protective sleeve. Cut an extra long piece, slide it over the threads, heat it and then dunk in water. Works perfect and it's very thin so it won't stretch the o-ring

pics...

[cgarr]

You might also try torquing the case all down without the o-rings then remove one bolt at a time and add the rings, less twisting on them rings, an old 912 case trick.

[TimT]

and when pulled through

Looks to me like your fixing something that isnt broken..

I (we) have built many,many engines.......and dont recall ever having a though bolt leak..

Am I missing something?... lube up the bolt with vaseline or dow 111 .. lube up the o-rings and pre-assemble the lot..

...

[84toy]

Originally Posted by TimT

Looks to me like your fixing something that isnt broken..

I (we) have built many,many engines.......and dont recall ever having a though bolt leak..

Am I missing something?... lube up the bolt with vaseline or dow 111 .. lube up the o-rings and pre-assemble the lot..

...

Tim, I'm really glad you have had such good luck. The case was not disassembled and only one bolt at at time was removed. I lubed with silicone grease and after numerous trial runs and rechecks, it would consistently peel a sliver from the inside of the o-ring. After the mod, the bolts slid into the o-rings much easier and no peeling. Perhaps it was broken.....The early engines with the acorn nuts and no blind hole are not as touchy.

I talked to numerous 3.6 engine builders and all have at one time or another peeled an o-ring on a 3.6 on those bolts and all had there own tricks to resolve it. This was my solution. For those that do have a problem, I hope this solution works for you.