Chamfered case through bolt holes

[lindy 911]

My 78 SC engine has chamfered through bolt holes on one half of the case but not on the other. I'm having a tough time getting the non-chamfered side to seal up properly. The o-ring on the bolt is getting squeezed out when tightened.

My first go round was with the blue o-rings and RTV as per Waynes book and they leaked badly where ever there was a bolt in a pressure circuit. I pulled the engine, tore it down to where I could get the bolts out and re-o-ringed them this time with the preferred green o-rings with a light coating of silicone grease. Same results; o-ring getting squeezed out after tightening on the non-chamfered side.

I know the factory put this engine together without leaks the way it is with the non-chamfered holes. I am making sure the bolts do not turn when I tighten the nut. My engine runs really well short of this final oil leak.

This past weekend I pulled the carbs, fan shroud, oil return tubes and air deflectors so I could get at the bolts. I loosened the nut and pushed the head of the bolt out as far as it would go until it hit the base of the cylinder. The o-ring was destroyed so I removed what was left, cleaned the area with carb cleaner and applied a liberal amount of Permatex aviation hardening gasket maker. It leaked after one minute of idling.

Any ideas?

[Flat6pac]

You havent mixed the head washers with the cross bolt washers so there is no where for the rubber gasket to set in the concave area of the through washer?
Bruce

[MBruns]

Lindy, we run into this all the time, you need to chamfer those that are not, there is not enough room for the "O" ring without destroying it, a simple countersink and a hand drill will do the job if its big enough ie. 5/8 ", test it out for speed and pressure on some of your outer holes first where the perimeter hardware goes to get it figured out.

Mike Bruns

[lindy 911]

Bruce;

No, I used all the original hardware for the through bolts after cleaning them up. All the washers have a countersink but only one half of the case has a countersink on the holes. Besides, I have Supretec studs which use a very different style washers from the through bolt type.

Mike;

Are you saying the countersink bit should be about 5/8" ? Can you reference a source for the bit? I think this is exactly what I need to do.

How did the factory get these to seal up with no counter sink?

[MBruns]

Lindy the original "O" rings were a silicone and were not near as tough to compress as the viton, so it basicly became a packing, whereas the viton has nowhere to go and shreads on the sharp edge. PM me an e mail address and I will send you a pic of what I use for the free hand method.
Mike Bruns