Missing pilot bushing?
 

I had the 923 trans in my 912 rebuilt by a shop.
In the process, while they were in there, I had the flywheel lightened.
Ever since they put the drivetrain back together, the trans has been very noisy.
I have replaced the coupler bushings.
I have also replaced the shifter tower and guts several times, going from factory, and aftermarket short shifters, and finally to a stock configuration.
I even replaced the throttle rod bushings in the tunnel, thinking the rattling was the throttle rod hitting the tunnel walls. They were toast, but it only reduced some of the noise.

The shop thought it sounded like a ring and pinion problem, so they pulled it the last time I had a corner balance. They found zero metal shavings, bits, dust, or ugly wear patterns, and pronounced it healthy and buttoned it up.


Still a lot of gear whine.

Other than the noise, the car drives great. This weekend, I drove to non-stop to Watkins Glen and back, (5 hours each way) with zero problems.

My question, could all the noise be from not installing the pilot bushing in the flywheel before mating to the engine?

Thanks for your insight.

Bill K

Any recent changes to engine/trans mounts?

Any difference between clutch in or out? A pilot only makes noise when the clutch is disengaged I believe--otherwise it's rotating same as everything else.

Would the omission of pilot bearing make it somewhat difficult to center the clutch during reassembly ?

Negative, I was going to replace the trans and engine mounts, but the products listed on Pelican are the wrong ones for the 923 trans, and the engine mounts need the whole rear clamshell housing of the 914 motor to be undone.

....."Would the omission of pilot bearing make it somewhat difficult to center the clutch during reassembly ?....

I'm thinking not if you have one of those handy-dandy wooden centering spools.

....Any difference between clutch in or out? A pilot only makes noise when the clutch is disengaged I believe--otherwise it's rotating same as everything else......

As a matter of fact - yes. I was chalking it up to replacing the clutch package with an aluminum Sacks RS package was causing the take-up/release differences.

The centering tools fit into the pilot bearing, that's how they work. No bearing, nothing to center on, and the tool can't locate the center.

What kind of noise is it making, anyway?

Is the pilot bearing mounted in the crankshaft or the flywheel? I was under the assumption that it was mounted into the crank similar to other makes. Am I incorrect on this assumption? If it is crank mounted removal and replacement of the flywheel would have no relevance to the existence of the pilot bearing.

The other thing that comes to mind, and I dont know how relevant this might be to the problem being experienced, but IF the pilot bearing is not there, what is keeping the transmission input shaft centered in place ? ?

That's part of my question. The main shaft might be rattling around on the bearing races in the case, rather than spinning inside the pilot bushing.
I can make the noise go away by putting a little forward pressure on the shift lever, but is comes right back after a few miles. Noise is a combination of whine, rattle, and a sack of blue stone. Most noticeable on deceleration, or coasting to a stop in gear.

Thanks to all for the input.

Bill K

I have some friends who race an older BMW who had an issue with the wrong size pilot bearing being installed at some point. Basically the input shaft was unsupported at the flywheel/crank, similar to what you are suggesting. The symptom was rattling noises and vibration during operation. Apparently not as bad as I would have thought you’d see for such a case. It did cause damage to the trans, but I don’t recall the details offhand.