Questions and Answers

Moving Crankshaft Q. Not sure if you can help me. Would like a suggestion if you wouldn't mind. I have a 1974 Chevy Nova. The motor is a 350 bored 60 over. Flat top pistons, standard crank and rods, high output cam.

Also have turbo 350 trans with 2500 stall. Stall is new. Trans and motor were rebuilt. Crank keeps moving forward approx. 0.100. The first time was about 5 hours of run time, the second time at around 450 miles. Motor guy says transmission is creating too much pressure. Trans guy says it's the motor. Could you give advice, or tell me what to check?

P.S. The drive shaft is same as always, it has been checked for proper clearance.

A. 0.100, that's way over the max limit of 0.006.

There are two measurements you should do before mating an engine and transmission. The transmission end play and the crankshaft end play. The crankshaft end play is checked while the engine is assembled, after the crankshaft is installed and before the connecting rods are installed. End play should be 0.002 - 0.006. The crankshaft thrust bearing is what determines the end play.

The transmission end play is checked after it's rebuilt and before it's installed. Personally I think this is where the problem is. When a transmission is rebuilt and new "hard" parts, such as hubs and pistons, are installed there are differences in size. Once the transmission is fully assembled, the end play is checked and if it's excessive, adjustments can be made installing or removing shims or spacers or a different turbine shaft. Generally 0.005 - 0.036 is the spec for transmission end play.

Either way, you're going to have to pull the engine and transmission to determine which is the problem. If it's the transmission, you'll have to replace the crankshaft thrust bearing and then check the crankshaft end play.

Information provided courtesy of ALLDATA