M96 crank locked

[JE 17]

In process of rebuilding a 3.2.

All new mains, polished journals. Clearance is about .002

I’ve gone to ARP bolts for the bearing cage. The directions say line honing may be indicated. When torquing, all is well, going in three steps. But at the specified torque, 50 ft-lbs, the crank will not rotate. It’s fine at the second step, 33ft-lbs. 

And of course, I’m in the Porsche wilderness where the local machinist who decked the cases and heads has no fixture to hone the cage. Ideas?

[JFP in PA]

Something does not make sense here; if the difference between the crank journals micrometer readings and the bearing "cage" internal diameters with the shells installed and torqued to spec is 0.002, there is no way the crank should lock up unless the crank carrier is warped by the new bolts or one of more bearing shells are installed incorrectly.

 

If it does need to be line honed, you should try LN Engineering in Momence, Illinois; they are one of the leading machine shops for these engines.

[JE 17]

Thanks, it doesn’t make sense. I may end up there. Rapidly realizing there’s a reason no one rebuilds these at every shop!

[JFP in PA]

There are very few rebuild shops for the M96/97 engines, even fewer good ones, due to the lack of credible published internal specs and the incredible number of specialized tooling required and a total lack of oversized bearings for cut cranks.

 

Normally, when the internal and external journal and shell bore diameters are good, the only way that the crank locks up upon assembly is either the crank or the carrier do not align true (one of the other is bent).

[JE 17]

I’ve been super lucky to be offered a chance to work with someone very experienced and associated with one of the premier M96 gurus to assemble the rotating assembly. So I can come in from the wilderness!

[JE 17]

Our attempt didn’t go well. The crank locked for him too. So he sent out my crank to get checked (as well as my spare.)

Both are good, so at this point it appears the bearings are issue. So we are going to try another set of factory bearings.