Adam Geist

Mike Frye and I had the gold '86.5 on the lift this morning to clean the crankshaft bolt threads and retorque to spec (I inadvertently used anti-seize on the crankshaft bolt threads). Before we knew it, one thing lead to another and we had the lower bellhousing cover off.

We found the flexplate to be under tension so I loosened the pinch bolt and the hub slid back on the splines. I didn't take before and after measurements, but Mike had the video camera on so we'll be able to tell from that.

Next we attempt to check the crankshaft endplay and this is were it got interesting. The flywheel did not move fore and aft using a prybar. We manually rotated the engine several times and tried to move the flywheel. Again, no noticeable fore and aft movement. Mike checked the clearance of the start gear to the flywheel and the flywheel to starter mounting bracket and both were fine.

When we did the endplay check on my other '86.5 last Fall, you could feel the flywheel/crankshaft move ever so slightly even though it was .008".

According to the previous owner, the engine was replaced less than two years ago with one that had 51,000 miles on it. I'm going to put the dial indicator on the flywheel next but I am expecting to see zero movement.

Does it sound right that I could have zero crankshaft endplay?

Thanks,
Adam

ROG100

I have never seen less than .006" IIRC

Mike Frye

Yeah, we're trying to remember how much force was required on the prybar, but we're sure it wasn't much.

We were surprised and a little nervous when we saw how much bow was in the flexplate. Then when Adam released the pinch bolt, we expected at least some movement.

The pinch collar is clearly loose and not holding things in place, and we also made sure the starter gear isn't binding with the ring gear. There doesn't appear to be anything keeping it from sliding back and forth, but no dice.

My inclination is that maybe we're just not applying enough force (18" prybar, pulling enough for the toothed gear to flex a bit, but not really leaning on it).

Any ideas would be greatly appreciated.

Bill Ball

The factory tolerance range is 0.1mm to 0.4mm (0.004" to 0.016'"). So far, I've only seen 0.007" to 0.008", and that provides a noticeable "clunk". If per chance you had 0.004" of endplay, that might be hard to detect with ears and eyes.

It should not require much force to overcome any resistance. If you pry hard enough you flex the flywheel.

Adam Geist

Just returned from the garage. I noticed the flex plate was slightly bowed so I loosened the flex bolts and rotated the engine several times by hand. The flex plate is nearly flat now and when I pry against the crankshaft I now can feel the "clunk."

Heading back the garage with the dial indicator. I'll keep you posted.
Adam

Bill Ball

I trust you are leaving the flexplate clamp loose when you check endplay.

Adam Geist

Bill, yes I did and I made sure the clamp moved easily on the splined shaft. I also left the flex plate bolts backed out a few turns as well.

I checked the endplay several times after manually rotating the engine. I had readings in the range of .009" and .010". This is a little too high for my liking so I'll keep a close eye on this engine.

Thanks for your help!
Adam

Mike Frye

Hey Adam,

I'm glad you got it figured out, and that the flex plate returned to it's original shape. But I'm mostly glad that the amount of play is within the acceptable tolerance. I'll finish up that video and post it tonight or tomorrow. Everyone is going to be really amazed at how much that thing was flexed. I think you got it just in time though.

Adam Geist

Thanks Mike!

BTW - I should have mentioned this earlier. The pinch bolt had a 13mm hex head and not the allen head type. I believe the bolt grade was 8.8 (I would check now but the car is off the lift).

I would like to install the Constantine clamp in the future, but not right now as I need to get this car ready for motor vehicle inspection.

Has anyone encountered a hex head pinch bolt for the torque tube clamp?

Should I replace it with the Porsche replacement bolt?

Adam

ROG100

No and yes

Mrmerlin

porsche bolt spec is 12.8, so dont try to tighten the bolt to 58 ft/lb or 61 or 66 yikes

ROG100

I am watching the Spanish GP so not in a good place to check this info, however IIRC Porsche increased the torque from 56 Ft Lbs to 66 Ft Lbs.

Mike Frye

Yeah,

Wait until you see how much flex was on that plate and how much it sprung back. I've only ever seen one other, but this one had a LOT of movement. Fortunately it doesn't seem to have affected the end play that much since it's still within spec. I think Adam got it just in time.

Tails

Could you please define a lot of movement in engineering terms, actual measurement of distance moved or an approximation?

Some flexplate clamps have been reported as having over 3mm of migration movement by what ever reason causes the flexplate clamp to move forward towards the flywheel.

However, in my opinion the migration of the flexplate clamp will reach a a maximum movement when the counter force applied by the flexplate, due to its distortion, overcomes the friction resistance between the splines on the flex plate clamp and the drive shaft. Once this stage is reached I believe the clamp will oscillate axially on the drive shaft, but will maintain its relative migrated position. This oscillation will actually cause wear between the splines resulting in less friction and easier migration of the flexplate clamp once reset to the zero position.

Any migration will of course apply a forward axial force on the collar of the crankshaft thrust bearing. In some instances it will cause failure of the thrust bearing and in others cases, even with a movement of over 3 mm, the thrust bearing bump clearance have remained within specification tolerances after may years of operation. If you require an indepth knowledge regarding why the bearing can fail you will need to study the art of "Tribology".

As stated above, in this thread, Porsche recommended an increase of the collar clamp Allen headed set bolt by 10%, to try and prevent migration, but this did not solve the migration problem.

As a precaution it has been recommended that at each yearly service or at more frequent intervals the flexplate clamp be inspected for forward migration and if discovered then the clamp bolt should be released, flexplate checked for 'no load position' and reclamped to 10% in excess of specified torque.

There are two main current methods used to prevent flexplate clamp migration:
Constantine's Clamp; and
Locktite.

The choice is up to each individual.

I personally applied locktite and the flexplate clamp on my car has maintained its position for over two year with a crankshaft axial clearance of 0.008", however, I do like Constantine's Clamp, a great piece of engineering design and it is very effective, in my opinion.

If I ever have to remove the clamp I will apply heat to the clamp to release the locktite.

If the end play is within Porsche's specification figures then the crankshaft thrust bearing is satisfactory for further use (usually manufactures apply a safety margin to tolerances).

The thrust bearing should only be change when the clearance is outside the specified range. In my experience more damage is done pulling satisfactory operating equipment to pieces to carry out preventative maintenance than leaving well enought alone. "If it ain't broke why fix it"

Tails 1990 928 S4 Auto

Landseer

This thread is helpful, as was another that Mike had started recently.

For the record, I too, just measured end play.
86 Auto, 75,000 mi.

Flex plate moved roughly 3mm.

End play was 8 thousandths, 9 thousandths, 8 thousands on three replicates.

Good to go! Am just inside the lower 50% of the factory range, according to spec #s mentioned above.