Hi. I've been poking around here a while but never really had a reason to post anything, until now...
I've got a '87 928 S4 auto that I purchased over the winter (first Porsche). I've read a lot of the hoopla regarding TBF and, although I'm not a skilled mechanic by any means, I thought I'd give it a try myself and measure any play in my car.

After I removed the cover exposing the flex plate and fly wheel, i used a straight-edge ruler to see if the flex plate was bowed... and it was. i didn't measure how much it was bowed...probably about 2 mm in the center.

After that, I loosened the 8mm allen bolt on the coupler and the flex plate went flat. with that bolt still loose, i used a 12" pry bar and moved the entire fly wheel assembly back and forth on the driveshaft. With the flywheel in the aft most position, i measured from the flywheel to a spot i picked out towards the rear of the car. then i moved the flywheel as far forward as it could go and measured again. i measured dozens of times and the movement i'm getting is about 1.5mm. WAY above spec. Am I doing something wrong? Clearly it is moving about 1/16th of an inch.

Now, I'm using a plain caliper and I know I should be using a more precise tool (and i will do that next), but in the end, I know I'm moving this thing quite a bit. Even if I'm being very generous, I'd say it's moving 1mm at a minimum.

So getting to my question... the car runs and drives fine. no issues at all. would it be possible to have 1.5mm of end play and have the car still run and drive fine? or am i doing something wrong with my measurements?

 

Get a dial indicator at HF for $20 and get an exact measurement. If you play is really 1.5mm, you engine is on it's way out and should not drive it anymore.

 

What he said.

 

Although I use a dial indicator, you can do it with a caliper just as well, if done like Tony shows here.

http://members.rennlist.com/v1uhoh/cranksha.htm

2mm bow is pretty common and usually would not overly alarm me. However, 1.5mm endplay would be likely fatal.

 

yeah, it really is that much. granted, it may be 1.25mm, but does it really matter what the exact number is at this point? i know it's over 1mm of play. maybe as much as 1.5mm. i'll get the dial indicator regardless just so i know the exact #.
so is there anything i can do at this point to save the engine? or, if the engine is past the point of no return, should i just drive it and enjoy it until it stops on it's own? i certainly don't have the mechanical ability to pull, replace or rebuild an engine. i was kinda hoping i was measuring the wrong thing and someone would tell me that there's no way the engine would run and drive fine with 1.25-1.5mm of play. this is depressing.

 

Make sure you are measuring when the flywheel is in a resting position. You can flex the flywheel with a pry bar and get a false reading. If the play is really that bad, you won't enjoy the car for much longer. It's a matter of hours, probably less than half a dozen. before it locks up for good. If you take it apart, it might be savable. Or sell it right away. It's up to you if you want to tell the buyer of the end play issue.

 

What about getting another motor? I'm sure 928 International can sell you one if it fits within your budget.

 

1+ on what Imo000 said. You can flex the flywheel if you pry at the edge. However, you may need to hold it in position front and rear. If you do so with a prybar lightly applied toward the center rather than the periphery of flywheel, your measurements should be accurate. Anything over the 0.4mm (0.016") limit is a signal to take the engine apart. A healthy engine usually runs less than 0.2mm (0.008")

 

what does that mean and how do i make sure it's in a resting position?
i'm not prying on the flywheel and measuring at the same time, if that's what you mean.

Does it matter what gear the car is in? I just have it in Park with the e-brake on since i have the front end up in the air on jacks.

 

You are kidding, right?

 

.016" is a dead one too....

 

no, i definitely don't have to hold the flywheel in position. it moves pretty easily back and forth (front and aft) and it stays there. i can also hear a clank each time i move it either forward or back, so i know it's moved all the way it can.

 

Hi bobbin88,

Best way to measure the end play is to first take off the six bolts holding the flex pate/clamp to the flywheel and move the whole assembly off the flywheel and onto the splines of the drive shaft.

Then move the flywheel all the way forward and then back to get the end play measurement. This takes the flex plates out of the equation from possibly skewing this very important measurement.

HTH,

 

OK, so if you aren't prying while measuring and you get more than 0.4mm you have a serious problem.

 

I'm curious what made you go check it? Were you just trying to be a good 928 steward? Or was there something "not right" about the car?

I don't think your method is very accurate. I also recommend you go to Harbor Freight (or your other favorite tool shop) and get a dial indicator and a magnetic base. This will allow you to zero out the dial and then move the flywheel (crank) to see what the true endplay is.

If it's less than 0.4mm then continue to drive it. If it's more than 0.4mm then you have two choices:

1. Get a known good motor for it. I'm guessing you can get a good one for $1,500 ~ $2,000. You might need another $500~$1,000 of bits and piece on top of that for knock sensors, powdercoating, etc.

2. Pull the motor do a complete teardown and see if the block/crank are salvageable. Then realize they are not and go back to option 1.

Did you get a PPI on the car before you bought it?