Per the Porsche guide, I am pushing on the flywheel small teeth with a big flat blade screwdriver at an angle attempting to rotate the FW 15mm.
Is this the correct technique?
Mine doesn't move at all without my efforts starting to rotate the entire engine.
Has my dual mass FW been replaced by a previous owner with a solid FW?

 

Given that band of rust around the flywheel next to the starter drive teeth it strikes me as a standard factory dual mass flywheel as the solid ones tend to be aluminum. That flow chart from the WSM is interesting, perhaps there are a few more details like pull the spark plugs so whilst trying to turn the flywheel your also not pushing against the compression of the motor. Perhaps it is meaning to turn the middle mass and not the outer mass ?? The middle mass is the only way I could see a movement and then a return without having to turn the motor too?? If thats the case then grab the clutch pressure plate and try to turn the middle mass against the outer flywheel mass bolted to the crank. My sense now after typing all this....that is what they must mean.

 

Thanks John,
That makes allot of sense. I'll test it that way Friday.
I'm hunting down a very strong vibration. I've changed motor mounts and double checked the belts (I've done two 968 timing belt jobs before so I feel good that its right).
The vibration is independent of clutch engagement. It gets a little less at higher rpm.
So, wondering if the DMF FW is bad.
Previous owners Corvette mechanic replaced the clutch - is it possible to reinstall the clutch or flywheel off from rotational centerline?
Mark

 

If my memory serves me correct you should be able to simply put a 12 point on a PP bolt, turn it clockwise, and see the clutch assembly move slightly without the ring gear moving. Don't over torque these. I can't see a clutch a clutch assembly being off rotational center.
If the car is new to you and the vibration was there when you received the car I'd be looking for proper clocking of the balance shaft belt sprockets. A lot of people mess this up.....

From Clark's garage:Checking Balance Shaft Alignment

One of the most important parts of ensuring proper balance shaft alignment is ensuring the balance shaft sprockets are properly installed. Since we've already discussed proper installation, you should have no trouble installing them correctly. However, if everything is assembled, how do can you tell if the sprockets are correctly installed ?

1. With the balance shaft sprocket covers installed, it is impossible to actually see the woodruff key to determine proper alignment.
2. Each balance sprocket cover has a number of round openings and one rectangular opening. At the rectangular opening, there is a tab on the back of the cover which gets inserted into the groove that does not have the woodruff key.
3. If the sprocket is properly installed on the upper balance shaft, the "O" stamped on the sprocket will be visible in one of the round openings on the cover.
4. If the sprocket is properly installed on the lower balance shaft, the "O" stamped on the sprocket will be visible in the rectangular opening on the cover.

 

Thanks Shinrai,
I appreciate thoughts on Center Line and method for rotating Pressure Plate.
I am familiar with the reversed sprocket "N" / "O" issue.
In fact I checked this some time ago and it was indeed incorrect (the top sprocket was reversed). I fixed it and some of the vibration went away. Seeing the "O" through the holes strikes me as a trick I didn't know before. I'll triple check it this weekend - I'm always willing to admit I could have made a mistake.

 

Mark, Even when everything is correct on the balance shafts that clearance at the bottom is critical to not having it jump a tooth or more. Cliff posted some really good info to add to the Clarks Garage info on this forum. That little gauge you can buy from Porsche for this process is priceless...understand typical feeler gauge can work but it just helps that you can push it in and have your hands free the way it will just sit there while you look and work on the tension. Depending on how many miles you have on the torque tube there have been some reports of vibration coming from bad torque tube bearings.

 

So it appears the DMF is fine. The technique is to rotate the silver non-rusted part in the pictures.
Mine moves to the left and the right approximately 3 teeth (15mm). It has consistent resistance both ways and returns.

I took the belt covers off, re-read Clarks and everything checks out fine.
Yes the idler should be closer to the bottom pulley, but its partly the angle of the photo and note I did not make any adjustments - the belt had not jumped since I last checked it.






SO, I'm back to square one.

The vibration was there when I got the car.
The vibration is strong enough that when your hand is resting on the gear shifter you can see and feel it shaking vigorously.
This happens at idle through high revs - not RPM dependent. If it changes with RPM , I can't detect it.
This happens when in neutral so it shouldn't be the Tourque Tube bearings - right?
I've change the motor mounts.
I have another 968 for comparison and its smooth with no vibrations.

Any fresh ideas greatly appreciated.

Note: the engine runs strong but ...
Is it possible for the cams to be off enough to explain this?
Is ti possible to have a "bad cylinder" that would cause this?

 

Mark when you say this happens in neutral....the torque tube drive shaft is always spinning Unless the clutch is pushed in ....even in neutral. Do things change when the clutch is pushed in while in neutral ?

 

Good question. I should have been more clear.
Yes, this vibration occurs all the time - regardless of clutch pedal engagement.

 

Follow-on thoughts:
Could I be dealing with an engine performance issue?
Bad injector?
Poor compression in one cylinder?

How advanced is the computer engine diagnostic software in our cars?
In a car today, virtually any rough engine issue would throw a check engine light - but in 1992, what all was covered by the software?

 

I broke down and pulled the clutch components.
I had been dreading this. But, it only took 2 1/2 hours beginning to end. Of course, I do have the luxury of a lift and I pre-read all of the guidance on this forum first.
It was a bad throwout bearing. Obvious very rough to rotate by hand.
In retrospect, telling sign was the pulsation that could be felt in the clutch pedal.
Also, of note, I did pull the DMF to check it in a horizontal position because some info on the web says that a vertical position won't give a true indication. For me, it responded exactly the same way whether vertical or horizontal.
Thanks again to everyone for their help and suggestions.

 

It appears the tensioner has been tightened in the counterclockwise direction, which raises the upper belt run and does not allow proper position of idler.
The tensioner pulley must be tightened clockwise which will also increase belt wrap on the lower balance shaft pulley.