I'm curious about the option proposed by soupbone as well.

Chris

Knife edging would do little or nothing as would lightening.
With out counter weights it becomes very difficult the balance this big lump of *****.
Best bet. Don't build an engine with a 964 crank and try to spin it.

Does the 993 or GT3 76.4mm crank have counter weights or the same? What are the alternatives for this case if one wanted to spin it?

Thanks

Henry, Appreciate the feedback. What is the safe limit for long life with the 964, 7K RPM?

Chris

Forum:
1. What does Porsche say about this?

2. Do you have links discussing other 964 problems?

Henry: thanks for the empirical evidence, as a picture is worth a thousand words.

Regards,

Out of curiosity, could a disimilar metal case through bolt cause this during uneven temperatures at cool down/ heat up. It would seem that if you put enough compressive force on those webs from disimilar metal temps with different strains, then add some vibration from the crank into the fire, and assuming the case through bolts are very strong it could indeed have enough magnitude to crack.

Something to think about is the fact that with the 964/993 cases, the case through-bolt torque spec. was inreased by about 10 lb./ft. (so was the head nut torque)

correct me if I'm wrong, but isn't the 964 crank used in the 993 RSR & GT-2?? NOT the 993 crank?

Do those engines run harmonic balancers?

Sorry, I don't have any empirical experience to add. AND I appreciate Henry's free advice and input (along with other professionals.) Henry's experience and base of knowledge is notable.

Thank you,

Doug

That's roughly 39% increase in clamping force. Now either that larger crank has so much vibration that that extra force is needed to keep the case closed with a safety margin, or it doesn't need it and that extra torque is causing the case to crack with time (fatigue in brittle material maybe). I have no experience with this, just chiming in to give some new opinions on this phenomenon.

Exactly.

Clearly the two are related, but I wonder which is the cause of the cracks. Maybe both contribute.