Garth S

Here's an approach on lopping off bolt heads ... but not with a real sawzall: anything is possible I suppose ....

AO

Bill-
Wonderful writeup. It's so good, I think I'll give it a try one of these days!

Bill Ball

Ooops! That's written backwards. I didn't do that at all. Let me fix that!

F451

Excellent write up Bill. This will be very useful for so many people.

I just checked the flex plate tension on my '85 and did the exact same thing you did with a ruler. Measured it from a few different spots and could find not any bowing of the plate. I did release the clamp just for the hell of it, and detected no movement at all, as I expected.

I did not do the crank endplay check as I wasn't sure what to do, now I can get back under there and check it out.

And for the lower bellhousing cover, I managed to get all of the bolts out on my '85. It was a real bear and took some time, but I did get them out.

Bill Ball

I'll 'splain it by saying it's wrong and I didn't do that. I actually pulled it to the rear. No preload, just moved to the rear, but definitely not the front. Let me fix that.


....FIXED! Thanks to you and dr. bob for picking up my mental lapse during the write-up.

Mrmerlin

I have been prying the crank to the rearmost travel then tigtening the bolt to 66ft/lb , since the driveshaft likes to grow in distance it seems logical to give the system the most travel, we are not talking much travel but any little bit helps.
Bill, Nice pictures and writeup, it would also be interesting to see what the readings would be if you took them on the flywheel instead of the flexplate, as the flexplate can move or not move on the driveshaft possibly due to locktite.
Also if there is found to to be a lot of preload on the flexplate, this should require that the rear pinchbolt be checked and refitted and torqued to 66ft/lb, this requires that the exhaust system be removed to gain access to the rear driveshaft. I know there is a relief cut into the rear driveshaft where the bolt passes but this wasnt made to hold the bolt/clamp in a certain position, Stan

Bill Ball

Stan:

I have no loctite on the shaft. There isn't supposed to be any, and it's pretty clear that anything short of red Loctite doesn't stop the shaft from moving, so I don't use it.

Certainly, you could measure at the periphery. I should have done it both ways because it is probably easier to position the gauge at the periphery anyway. It's just that that is where I pry on the flywheel. I don't think I'm flexing the flywheel, but it seemed the center would be more relavent, obviously providing the flexplate is perfectly free to move, as mine was.

Another afterthought - I should have checked the endplay WITHOUT releasing the TT clamp, and checked it at the crank pulley or the crank bolt, as well. We like to release the TT clamp anyway, but it would be worth doing this other way to see if that could work for the Red Loctite crowd, as well as serve as a quicker external check. Oh, I recall now that Garth has already done this, although w/o a direct comparision.

wds928

Bill, great writeup and pictures. The underside of your car is way too clean!! Printing this out now and will do this weekend, as I haven't done it yet.

Bill Ball

Yeah, that's what I was refering to. Sorry to have accused you of using something so crude as a Sawzall.

Jim R.

Bill,

Great writeup!
If I buy another 928 with an automatic, this has got to be part of the PPI and yearly maintenance program.

This definitely needs to be put up in the 928 DIY section. Very slim pickings there, and this is perfect material.

Jim

docmirror

No prob, I've made far worse. Dr Bob felt it needed further questioning.

Tails

Bill,

Excellent write up, enhanced tremendoulsy by the photographs. How did we ever write such clear reports without digital cameras?

As my car is not fitted with cats, it is easy to remove bell housing, so all bolts are refitted. During inspections I have removed the bell housing, released flexplate clamp, renewed set screw, reclamped up to torque setting plus 10% and painted clamp and torque transmission shaft splines.

Initial inspections done via drain hole with a small light on fixed extension piece to view migration via gap in paint.

Initial migration measured at 3.08 mm with crankshaft end play at 0.008 inches. Every year detected migration to a lesser degree, but seeing still getting movement resorted to loctite 290 in 2006 as Garth has done.

Each time when I reclamped I would move the crankshaft forward against the thrust bearing and then clamp, as this gave me 0.008 inches movement during windup of torque transmission shaft (shortening due to twist up) and its drawing out of clamp in a aft direction. As previously stated every little bit of clearance before draw out begins is helpful.

In February this year at the yearly service (12 months since loctite applied) no movement of flexplate clamp detectable via paint. This was doubly checked by measurement from bell housing to flexplate flange via inside calipers and measurement remained the same, no migration.

I tried to measure crankshaft end play, but got no movement as probably not enough force applied. I was a little reluctant to apply too much force. Maybe next time I will give it a bit more to see if I can detect thrust bearing clearance as stated by Garth.

With write ups like yours my 928 technical library is growing.

Keep up the excellent work.

Tails 1990 928 S4 Auto

IcemanG17

Bill
Great write up......you got the exact same result I did a little over a year ago

https://rennlist.com/forums/showthre...ight=flexplate

Bill Ball

This is the opposite of what I did. It's a good question as to which side of the thrust bearing sees the most load, and if there is any measurable wind-up shortening of the TT. Since I always have found the crank pressed forward by the TT, I've thought to not only relieve the pressure but move the crank back, so, in theory, it would take longer before it accumulates preload. I need to rethink this.

Even if you are pushng against the flexplate, it shouldn't take that much force to move the crank the tiny distance involved. I'm going to try doing an external endplay check at the front crank bolt myself tomorrow.

Black Sea RD

I wasn't going to post since I do not want to seem as a party pooper or nay sayer, but...

We did a pretty extensive research into this whole affair and it's relation to TBF. We studied the Porsche workshop manuals and they describe a procedure on how to set up the flexplate and flywheel currently. I would use this new procedure and not deviate from it.

The 66 ft lbs. of torque currently being used by many at the front pinch bolt actually came from a post long ago from a gentleman who was chasing around the whole driveshaft pullout in his car. His mechanic shop placed a call to Porsche AG who advised to use this new torque rating *and* change the the front flexplate with a new one. Over the years the new front flexplate seemed to be forgotten as the other part of the equation since it's expensive and not easy to do. We found using the higher torque rating had minimal to no effect even with a new pinch bolt. The reason being the front flexplate clamp is not designed to be re-used much and after a time stretches out and cannot hold as well.

As always we do not recommend using loctite to fix the driveshaft pullout since it can cause problems for the owner later.

This posting in no way is meant to diminish the excellent write up by Mr. Ball on checking the front flexplate and thrust bearing for this problem. The Porsche workshop manuals also describe how to check thrust bearing wear for any who are intersted to do so.

Constantine