Bertrand Daoust

I know that Porsche changed the lenght of the rack sometime in the 1990's I think. They went from 795 mm to 810 mm I think. I read that last night in my WSM. Could it be possible that at the same time it changed the pipe location???

ROG100

Bertrand,
I think you and Stan maybe on to something here - worth persuing further.
Easiest solution from my end is to cut down the bottom stud by "X" amount.
X yet to be determined. That would cover all eventuallities.

Bill Ball

Oh, I didn't think that mount was Roger's. The small locator pin looks much longer than the one on mine.

I just installed the mounts on a 90S4. Here's a picture of the passenger (right side). It clears but is close. The racks do move up and down on stock mounts. There is too much crap in the way to get a good shot of the driver side, but a slight glimpse I can get of it looks REAL close. Too close for comfort. I will pull the rack down and Dremel cut off some of the studs on each side.

Passenger side:

Mrmerlin

Bill if you can a self locking nut you can thewn install it then cut the stud off flush with the nut , thats what i did, I was also wondering if the later years have a slightly different rack design, as it seems others have not had any fitment problems, my rebuilt rack had a date stamp of 91

Bertrand Daoust

Well I did grind the MM bolts and it did not changed nothing in my vibration problem. After that, I checked my flex plate and released about 4 mm. Now I know that:

1) Releasing 4 mm. did make my engine run more "freely". After we released the flex plate pressure, the motor was more easy to turn "manually" (by hand at the front of the engine). Before the release, we tried to move the crank to get the allen key alligned and it was quite hard to move. After the release it was A LOT MORE EASY TO MOVE.

We changed the oil pan gasket last week and nothing was wrong there (no metal residue at all). So I guess that there is nothing wrong with the thrust bearing. I hope so. The car runs very well too.

2) Releasing the flex plate DID REDUCE THE VIBRATION.

It's not perfect but it's better. A lot better. Now, maybe that a MM liquid filled from Porsche would be perfect for me. But at 1/10 of the price of the Porsche MM, the ones that I have does a good job.

Now thanks to (in no particular order):
1) Andrew Olson for his thread on how to support the motor from the engine bay. Very easy to built and very effective.

2) Roger from 928areUS for the good product and very good service.

3) François and his son Charles who, without there generosity and knowledge, this job would not have been possible for me. Also there lift and air tools were more than a good help...

4) All the Rennlisters who, by there comments, gave me the will to go ahead. Without you all, It would not be possible for me to take good care of my 928.

THANK YOU VERY MUTCH.

dr bob

Bertrand--

Sounds like you might be in the midst of a thrust bearing problem. I would immediately take the time to measure the end play on the crankshaft in the block. That's the amount the crank will slide in the beaerings forward and back in the car, indicates the amount of clearance in the bearings. If you have excess clearance now but the bloack is not yet damaged, it may be possible to replace the main bearings now and not have the block destroyed. This would save you from needing a whole engine, at the immediate expense of pulling the current engine and replacing the main bearings and a bunch of other stuff only.

Don't delay on this end play check on the crankshaft!!

ROG100

Betrand,
I'm with Bob 110% - you must check the crank end play ASAP.
Roger

Bertrand Daoust

Thank you guys. I will for sure.

the flyin' scotsman

If indeed the thrust brg is going would that result in a more frequent need to release the flex plate tension?

I ask as every year I undo the clamp the plate springs back similar amount..............~3mm.

Bertrand Daoust

Maybe. But do not know for sure.
I did mine last spring and again last week. Both time I released about 3.5 mm. Now, correct me if I'm wrong but I think that as soon as the flex plate is bent, there is a pressure applied to the thrust brg. If this is the case, then:

1) That means that it would be "normal" that the motor would be harder to "turn by hand" from the front of the engine before releasing the pressure on the flex plate and easier after.

2) It is realy important to release the pressure as often as possible or to stop it for good (using Constantine's part or the "Locktite fix").

I would like to know if anybody had ever try this (moving the motor by hand before and after the release)?

Thank you.

the flyin' scotsman

Bertrand............its been quite a few months and many Kms since I released the pressure so my car should be a suitable candidate to answer the 'hard to turn over by hand' question.

Give me to this weekend and I'll let you know.

Mrmerlin

if your checking the flex plate dont forget to also check the rear pinch bolt, this has to be done atleast once to verify that the rear clamp is tight, I am in the midst of a T tube replacement and even though its a stick the rear pinch bolt was loose IE only torqued to about half of the recommended torque, and this isnt the only time I have seen this, a few cars seem to have rear pinch bolts that are not as tight as the fronts, i remove the bolt and replace it with a new one add some blue loctite to the bolt and torque to 66 ft/lbs. To check/remove the rear bolt you also need to remove the exhaust system and the center heat shield

the flyin' scotsman

Excellent info.............I'll inspect the rear bolt this winter.

thx............MrM.

piccardo

I remember that my 90 model was turning over slowly and started to make a strange whiring noise. To me it sounded like a bad accesory, like a smog pump. Released the pressure of the flex plate and presto noise was gone, and the engine turned over a bit faster too. So it stands to reason that releasing flex plate tension reduces cranck shaft friction..... Last week I noticed a vibration during acceleration at about 3k RPM. I took her out again today and it seems to have gotten worse. It is almost exactly at 3k under load and fades gradualy above this RPM. I will release tension on the flex plate (again) this weekend to see what if anything changes.

the flyin' scotsman

I'm very curoius to your results.

If they correspond with mine perhaps we have a seperate topic....................ie we all shall eventually suffer the issue.