thrust bearing issue

[runningman]

Hi All

Can some one please clarify.

If the crank thrust bearing needs replacing, is it a straight forward job or does the crank need to be removed to do it. I going to look at a 928 this morning with the interest to buy and just want some knowledge. I will get round to buying a workshop manual eventually.

Ive replaced them years ago on old British cars and it was as simple as removing the bearing cap and spin the old one out and spin the new one in.

Regards

[Pete R]

You could possibly do rod bearings with out crank removal but to do the main bearings (of which the trust bearing is one, you have to split the block and remove the crankshaft.

[JK McDonald]

Hey Runningman - I hope we haven't scared you off from buying a 928 with some of our precautions and warnings of things to look out for. There are lots of good ones around when you have a heads-up of what to look for. The 928 Porsche thrust bearing problem is only an issue on an engine that has not had a simple crankshaft end play check during it's routine maintenance. It is most often the result of a previous non-informed or uncaring owner.

Although it is recommended that the associated pinch/bolt coupler/adjustment-crank shaft check be part of any pre-purchase inspection, it's the later (higher HP) model cars that are most often found with the thrust bearing problem. Both my 1984 and 1985 were fine even though I suspect that this potential problem area had never been checked on either car. Since the problem is torque related it is the slippage or creep of the pinch coupler that allows the drive shaft to lengthen slightly against the flex-plate and push the crank shaft against the internal thrust bearing. If caught before there is any damage, there are several easy solutions that will fix the problem including a newer design for the pinch coupler.

Here is good explanation and over view: http://members.rennlist.com/v1uhoh/928TechFlexPlatearticleTH.pdf

Good Luck with your search, Michael

[stepson]

Originally Posted by JK McDonald

Although it is recommended that the associated pinch/bolt coupler/adjustment-crank shaft check be part of any pre-purchase inspection, it's the later (higher HP) model cars that are most often found with the thrust bearing problem. Both my 1984 and 1985 were fine even though I suspect that this potential problem area had never been checked on either car. Since the problem is torque related it is the slippage or creep of the pinch coupler that allows the drive shaft to lengthen slightly against the flex-plate and push the crank shaft against the internal thrust bearing. If caught before there is any damage, there are several easy solutions that will fix the problem including a newer design for the pinch coupler.

1984 was the last year that used spacers and a circlip on the end of the TT to prevent Thrust Bearing migration. I don't believe that I've ever heard of Thrust bearing failure on a 1984 engine with the spacers and circlip intact. After 1984, the spacers, the circlip and the groove in the TT that held the circlip were discontinued and Thrust bearing failure began showing up. I often wondered why the circlip/spacer combination couldn't be retrofitted to the later cars.

[JK McDonald]

Hey Stepson, I agree with you in the torque tube/drive shaft design and thrust bearing issues. I have also noticed that MOST cars didn't began seeing any serious thrust bearing problems until the later models (928 S4) with their horse power around the 300+ hp range. Like you mentioned - this is when the deadly combination of HP/Torque/Pinch Coupler/Drive Shaft Design = Thrust Bearing Failure - changes came together.

Luckily I bought both my 928's from mild mannered, milk toast, drive it only on warm sunny days at a safe and sane 55 mph owners......

Michael

[harborman]

I own a 86' 928S but never checked the thrust bearing on it. The car has 68K original miles. It had 37K when I bought it 5 years ago. I am rather conservative driving it, no burn outs! I wonder if it is necessary to do the thrust check.

[Mrmerlin]

Harborman yes check the thrust bearing clearance,
and also re torque the rear , then the front pinch bolts,
after you recenter the driveshaft.

tighten the bolts to 66 ft/lbs with a some blue loctite on the bolt threads

[stepson]

Originally Posted by JK McDonald

I have also noticed that MOST cars didn't began seeing any serious thrust bearing problems until the later models (928 S4) with their horse power around the 300+ hp range. Like you mentioned - this is when the deadly combination of HP/Torque/Pinch Coupler/Drive Shaft Design = Thrust Bearing Failure - changes came together.

Luckily I bought both my 928's from mild mannered, milk toast, drive it only on warm sunny days at a safe and sane 55 mph owners......

Michael

Michael,
Don't forget that the EuroS 928s also generated 300 HP all the way back to 1980. Since the circlip/spacer design was abandoned after 1984, any 928 from 1985 on, or any 928 that has had the circlip/spacer disturbed should be checked for crankshaft endplay. Better to be safe than sorry in my book.