Worn input shaft, due to siezed Pilot Bearing
 

Hey all,

Thanks to our 6 month winter "pause" up here in Canada, I have a 1988 Carrera Coupe with a G50 apart at the moment to do a top end refresh and replace bad valve guides.

While the motor was dropped I took the opportunity to check the clutch and transmission. The clutch had been making an occasional noise only at the moment when the clutch made contact with the flywheel. Therefore no noise when clutch was fully engaged or when fully released.

It turns out the pilot bearing had completely seized and the shaft was rotating within the bearing, wearing down the tip of the input shaft in the process. Unfortunately it looks like even though the clutch and flywheel had been upgraded to the 930 style by the PO, the bearing had not been changed? Unfortunate.

The end of the pilot shaft is now coarse and copper colored. When the new bearing is placed on the end, there is some minute play which causes me to worry. My fear being that the shaft will now want to rotate within the center ring of the bearing.

Questions:

1. Not being completely familiar with the stresses in this example, am I right to worry? Or will the new pilot bearing work fine on the worn shaft?

2. Does this occur frequently enough that there is some fix? Either a resurfacing and treating of the shaft, or a different bearing?

Any suggestions are welcome other than my mechanics suggestion of a new input shaft at a cost of $2,500 just for the part alone. Many Thanks!

Jase.

http://forums.pelicanparts.com/uploa...1486606816.jpg
http://forums.pelicanparts.com/uploa...1486606816.jpg

When I was a kid, my dad would have polished that with a little crocus cloth and put a little Lubriplate on the inside of the new bearing.

Did anybody even mic that ?

I just had the same issue with my '88 Carrera - upon change of the clutch it turned out that the pilot bearing was in bad shape and seizing. Luckily the shaft tip was still smooth and without thermal discoloration, but according to my (very trustworthy and Porsche experienced) mechanic it wasn't a minute too soon, as a worn shaft would inevitable call for replacement.

Brgds
Alex

God, that doesn't sound good.

At this point I'd rather weld the new bearing onto the shaft! LOL

Jase.

Clear, close-up, well lit picture please.

kk, will do.

Better?http://forums.pelicanparts.com/uploa...1486669588.jpg
http://forums.pelicanparts.com/uploa...1486669588.jpg
http://forums.pelicanparts.com/uploa...1486669588.jpg

Thats not bad. its not super critical. crocus cloth to smooth it up a bit and use it. This is why I always use a bushing instead of a needle bearing. It happens alot! A bushing will only wear out not seize up and ruin the shaft

I'll mic it tomorrow. But I don't like the fact it's gone to copper... or is that just heat?

Using this ruler on the far right, I'd guess it's one half blonde c-hair off :)

http://forums.pelicanparts.com/uploa...1486686929.jpg

Is a bronze bushing an option with our cars?

I would mic it first. Looks reusable to me.

How important is this bearing?
Its only a support when the clutch is engaged (edit: with that I mean depressed), right?

As far as I know, it sits in the end of the crank and it's importance is three-fold: It acts as support, it acts to align the transmission, and when the clutch is depressed the bearing comes into play to handle the difference in speed of the Crankshaft and the input shaft.

Align, yes i would see that being a use. But you don't have much force that you need support for, or is my thinking flawed?
Is there a transition when you are slipping on the clutch where there is a force acting on the bearing?

I wouldn't say so. The mechanic is just worried that the input shaft will spin INSIDE the sleeve of the bearing, rather then the bearing spinning itself... thereby causing heat and more damage to the input shaft.

Personally, there's no way in hell I am buying a $2,500 part and THEN cracking open the trans to install it and everything else inside the case. I am inclined to say hand polish, grease and button the thing up. It's got to be better than the seized bearing that was in there for over a year and a half.

I just wanted to get all your opinions first :)

Jase.

So, the mic measure at the unworn tip of the shaft is 14.91mm. The mic measure at the worn part is 14.88mm, making it out by 0.03mm.

I told the guy to make her smooth and grease her up.

Thanks for all your input!

Jase.

Have a question related to this. All clutch parts of my '88 are being replaced, including pilot bearing. I have the correct grease for the input shaft splines but should any grease go on the end of the input shaft that goes INTO the pilot bearing? my thought is no since the bearing will obviously rotate but just wanted to check.

Just grease the bearing. Optimoly or the like.

Thanks John but the bearing appears to be totally sealed and spins freely. Not sure how to add grease to it. It looks just like the one in there before that seemed to be in good shape but I replaced it anyway. Are you saying add grease to the "inside" hole of the bearing...the part that rides on the end of the input shaft?

I see the discoloration all the time, don’t worry about that. Buy a new bearing and see how much it rocks on the shaft, I think you’re ok.