964 Case Crack - - Experience ??
 

Well, we are not going to make it to the NASA Championships this year at Laguna Seca - - Caca Pasa - -

Found a crack in the case at the #7 Crank journal too late for Ollie's to get it repaired. . .
Also, had to find a replacement crankshaft after inspection by Ollie's - Troy at EBS Reno had one and sent it to Ollie's for oil passage drilling, etc . . . all looked good until our engine builder found the case crack - but Ollie's has a technique to replace the journal and then will shuffle pin the case and line bore and clean the oil passages - but since Tim will be having knee surgery the case won't be ready for another month or 6 weeks - hence not racing at Laguna . . .

Photo of case and marked the location of the crack - - Do any of you have any experience with this??

Thanks in advance for your feedback . . .

Regards,
Roy T

Edit: See Post 21 for assembly update

http://forums.pelicanparts.com/uploa...1659223599.jpg

We have a new case on the shelf, ready to ship. 993 and 964 cranks ready to go as well. Cross drill in house.

Don't shuffle pin the case. 3.6 cases need the material in the webbing. Do this instead:

http://forums.pelicanparts.com/uploa...1659233405.jpg

I think Mike Bruns did this one. JB Racing does this too.

The 964 case cracking is caused by crank imbalance. 964/993 street cranks are crap. Race engine builder often remove the dual mass flywheel and dual front pulley so the cranks create a huge harmonic that cracks the case. A GT3 crank and light weight rod/piston combination will help but running these engine a full throttle for prolonged periods creates an engine life that is at times very short. 50-100 hrs if you're lucky.The rod and piston combination on two valve high comp. engines is too much for sustained high rpm.

BTW: Although # 7 is the most common journal to crack, the journal you have marked is actually # 2 not #7.

One more thought: If you're running solid mounts, throw them in the trash. There is no lap time in solid mounts and they tear up everything. More importantly, they create driver fatigue. A tired driver is the biggest deficit to lap times, even more than tyres.

Henry,
Thank you for the help - -

Question: will the Wevo Semi solid mounts work ok - I will be glad to replace the
solids we now use ?? I will talk to Ira at Tarett tomorrow about the switch over.

Question: Because we have replaced the front dynamic pully and the flywheel
changed to Patrick's 3.6L - 915 conversion - Does the total balancing of crankshaft,
flywheel, rods and pistons alleviate the imbalance problem of the 964 crankshaft??
The balancing this time around is done by Ollie's . . .

Thanks in advance for your reply.

Regards,
Roy Turner

Scott,

Thank you for your help - I have asked Tim at Ollie's to do this procedure instead of
shuffle pin. It will take a while for Ollie's to get this work done because Tim is having
knee surgery soon.

We also discussed the "Fly cut procedure" - but for now I will pass on this because we
are looking for durability not more power -- what do you think??

Regards,
Roy T

What's the fly cut procedure?

As Henry pointed out, that's the #2 main. The #7 mains commonly crack through the weak point, more in the earlier cases. All due to the crank movement. Adding a damper solves this.

Also as an alternative to the dowels we offer this as a solutionhttp://forums.pelicanparts.com/uploa...1659359844.jpg

Bolts, nuts and stepped washers are titanium to lower weight. Head of the through bolts are marked to give the correct orientation to allow the oil flow through and past the bolts.

Dampers and Alt pulleys are available as well. http://forums.pelicanparts.com/uploa...1659360229.jpg

Both require machine work. The through bolts when installed in earlier 911 cases require a counter bore both sides for the stepped washer to be fitted, (like 944/993) but the machine work through the case parting line can be done with the case assembled, holding the line bore correctly.

The damper fitment can only be done when the engine is rebuilt as the #8 bearing requires some machine work. A thinner front seal is fitted and moved back into the bearing housing so the damper has the correct overlap onto the crank nose.

I'm not sure I have the terminology correct - but it's the removing material from the
bottom of the web and the piston skirt to allow better flow of air inside the case -
mostly used in high RPM and HP engines.

Regards,
Roy T

Neil,
Thank you for your added information.

Ollie's will only do the Shuffle Pin procedure - we will do this in addition to the Web fix
- etc. . . .
This 964 engine has lasted very well in our 911 race car for 10 years - my son loves
to drive the old school 911 with the improvements we have done - we expect to get
10 more years of racing less often because of son raising 2 girls (who play competitive soccer) . . .

Regards,
Roy T

Of all the places I would not expect a crack, that is one of them. Unless something else is the cause. The #2 would be the main web with the least amount of movement with the #1 well supported with the thrust shell. You always see wear on the thrusts from the clutch but the shells that show the most wear are typically at the other end of the crank.

The back side of the shell will tell a story of what could be going on. Very strange. Some what surprised that the shell did not lose its fit and the crank grab due to loss of clearance.

You were very lucky to find this.

unusual crack
 

I have never seen a problem back there.I would suspect a flywheel imbalance or incorrect quality control on a clutch replacement.Most of the fatigue cracks happen around the #6 or #7 main web.The achillies heel of the 935 era.80 hours time for a new case.Water cooled heads helped a lot with that problem.I would agree with Neil about the cranks from that era as well.Mr Harveys damper is a great design and worth the money.Lots of thought go to some of these improvements.No one person can no it all. I can not.But through a collaboration of posts here we all get more insight.Thanks Pelican.

Roy, Ollie's is not the only vendor to work on cases.....

An added bit of information :
This is part of a larger project - the clutch pressure plate failed and a piece stuck in the starter hole locking up the engine and transmission on the race track - son/driver pushed in the clutch put the trans in neutral and coasted to a safe place behind a tire barrier. We thought the engine had seized - but after disassembly found the pressure plate failure. It's possible in the split second of the lock up there was a large enough shock to the driveshaft to cause the web crack (but who knows if this occurred) . I think all of you are correct in that the 964 crankshaft harmonic vibration over 10 years of racing caused this web crack . . .

Regards,
Roy T

http://forums.pelicanparts.com/uploa...1659463906.jpg

http://forums.pelicanparts.com/uploa...1659463906.jpg

Scott,
Thanks for your help - we like to keep our $$ in Arizona :D -
- and I like to drive over and talk to them face to face (and CMS also) . . .

We will miss the NASA National Championships at La Guna this year - but we have
plenty of time and other opportunities to get back on the track - hope to see you there someday . . .

Regards,
Roy T

Roy,

I get that. I am all for supporting local shops when it makes sense.

But doing the shuffle pinning weakens the webbing. Kind of the opposite of what you want to be doing based on the problem you have.

If Ollie's does not have the ability to do what other shops can do, does it make sense to do the wrong procedure just to keep the work local??

I have been using the JWE Clutch setup and it is less failure prone than your current setup:

https://rennlist.com/forums/attachme...e-img_0771.jpg

https://rennlist.com/forums/attachme...e-img_0773.jpg

https://rennlist.com/forums/attachme...e-img_0775.jpg

https://rennlist.com/forums/attachme...e-img_0777.jpg

Scott,
Thanks for the clutch info - we won't be putting a Sachs clutch back in the car when it
finally gets to that point in time . . . the JWE looks really robust and sturdy.

Regards,
Roy T