Thrust bearing wear on 3.2 and 3.3 crankshaft

[vinyl_tien]

last week my tech man had open my 2 porsche 911 engine for repair(87 3.2 and 87 3.3 turbo).
After my tech man open these engines, he said there is some wear in thrust bearing. Rest bearing is fine
In the spec book it say thrust bearing width A (28.000~28.06mm)
Here is the measure result
911 3.2 crankshaft measure is 27.90mm(should be around 28.16mm)
911 3.3crankshaft measure is 27.80mm(should be around 28.26mm)

What should I do in the next? machine it to undersize and buy a -0.25 undersize thrust bearing?

PS.I also have 2 crankshaft from friend(964 and 3.2), it also show same wear in thrust bearing. Is that normal wear for porsche engine?

Need you guys input~~
Thanks!

[fred cook]

Unless I am badly mistaken, the thrust bearing presses against the side of the crank to prevent the crankshaft from moving longitudinally when the clutch is depressed. So, is the wear on the bearing itself or on the crankshaft? If the bearing is worn, then simply replace it. If the crank is worn (less likely) then some machining and an oversize thrust bearing might be needed.

[vinyl_tien]

Hi Fred
Thanks for your replay, right now the crank is worn.
I just want to know is that a common problem? because I have 4 cranks with this symptom.
Does the undersize bearing did help?(my tech man told me some undersize thrust bearing only have -0.25 in bearing side not in against side)
Really appreciate your input!!

[vinyl_tien]

My tech man use old bearing to measure the gap.

[vinyl_tien]

What is the worn out limited for this place?

[fred cook]

What is the gap measuring with a new bearing shell? I'd be willing to bet that most of the wear is from the bearing, not the crankshaft. After all, that is what the bearing is for, to be the sacrificial part that wears while protecting the crank surface.

[AlfonsoR]

I am not sure how you arrived at 27.80 & 27.90. Please explain in more detail.

The A dimension is for the width of the crankshaft. Remove the #1 bearing and measure the width of the crankshaft, not the bearing. It should be measured with an inside micrometer in at least three places, then average. That width should be between 28 and 28.06mm, as you stated.

Axial play or end play is simply how much axial movement the crankshaft has. That measurement should be 0.110 - 0.195mm. There are different ways to do this, I guess. The Bently book says:
"Axial play should be measured at the center main bearing journal with the crankshaft supported on roller on the outer main bearing journals."

I don't know exactly what that means, but from working on other machines, I believe that the best way to measure is to install the crank in the case, all bolted up and then install a dial indicator on either end. Push the crank from one end to the other. Zero your dial indicator, then push to the other side. Cycle through three measurements. Each time you should got to zero on one end and on the other and you should repeat the same value as well. If it is not repeating, then most likely there is some debris on the crank or bearings that needs to be cleaned, and you will have to repeat the measurement. This is the most accurate way because when you bolt your case together to the specified torque, the bearings will deform ever so slightly. These small changes in the bearing shape can also possibly have an effect on the axial play.

Clear as mud?

[vinyl_tien]

Thanks fred and AlfonsoR.
it did clear my thought , I think I made miss take on measure, they should be like 28.26mm or 28.16 mm, I will ask my tech man to do the half case test.

[Mark Henry]

Those are some knarly finger nails...how many cranks per day does he drop on those piggies?