Schocki

Hi guys,

quick question from Germany I was asked when it is absolutely necessary to replace the thrust bearing before the block is history? I have no experience with a TBF engine, so I thought to ask you guys

The max. factory tolerance is 0.4 mm, I know. The person asking measured the tolerance @ 0.55 mm. Any experiences when the crank starts to damage the block???

AO

Took me a bit to understand which TBF your were talking about.

Good question. What part of the block get dammaged first with Thrust bearing failure? Are the bores the first to go?

Schocki

Edited the headline, hope this makes more sense know, sorry.

dcrasta

Looks like you answered the question you asked. I wouldn't run the car with the tolerance over the factory limit. Probably just adding more $$ to the repair, and eventually will make the block unusable.

Is repair / servicing the bearings an option ? If not I would park the car until it can be repaired correctly.

blown 87

the problem is that he is all ready past the "Babbit" part of the bearing and into the copper.
The "Babbit" is what gives the thrust bearing the Anti_Galling" properties.
From what I understand is that the crank grabs the thrust bearing and spins it in the block and that is where the trouble starts.

He needs to get the motor out while he still has a block left to work with.

I have only done a couple of TBF engines, mine at .012" was almost through the "Babbit" and the other one at .020" was into the copper, yours is at .0173".

The only way to tell if the bearing has spun is to look at the bearing, which means a motor pull.

Black Sea RD

Greg is on point.

At your friends measurements, good likelihood he has already done some block damage.

blown 87

I was shocked that Paul's block was still good with .020" end play, but the bearing had not spun.

We had a 928 in the shop today and it had .081" of bow in the flex plate, i would have bet money that the thrust bearing was going to be toast, it had less than .010" of end play.

He is coming to the shop tomorrow to look at some things, I may ask him to buy me a lottery ticket with luck like that.

It will be getting a Superclamp and your bearings for the TT.

SeanR

I had one come in that had 8mm of movement on the flex plate, I was worried just looking at it, showed it to him and explained the potential issues. He then showed me a receipt from the local Porsche dealership where it states they had checked the flex plate.......farking idiots.

The crank end play was under .4mm

The same idiots diagnosed loose rear flex plate bolts as a bad transmission. This is the same dealership one of our DFW want to be's touts as the best place to take your car. Can't wait until it blows up.

blown 87

I can pretty much promise any one that a dealership is not the place to take any car out of warranty.

We both know that they did not check the end play and MAY or may not have know what was going on with the rear flex plate, but were going to charge this guy 5-6 grand for some bolts, loctite and cleaning the trans.
There is a TSB on them, I think that is what you are talking about, the rivits?

I had a new MB customer a couple of years ago, and the car looked like it had never had any service, i worked up a list and called her, a fuel filter was on the list, still had the undercoating on it from the factory.

She came down to look at the car and told me that she did not believe me, but all it took was one look and she knew it had never been changed, she had receipts from the dealer where she had been charged TWICE for changing this filter at $156 each plus a hour labor each time.

She was furious, and rightfully so, she also was a lawyer, you could hear her yelling at the dealership guy from far away, no idea how it ended but we still work on her cars.

SeanR

No, these are the bolts that hold the rear flex plate to the torque converter, same as the fronts. 2 were hanging out in the bell housing, rattling around, 2 were loose, 2 were tight.

It was on a 91. They wanted to charge a buttload to replace the transmission.

And I agree, stealerships are not the best choice.

Schocki

Thank you for all the answers, I will forward them to him...

Hayk928

Thank you Schocki for your quick help! (yep, its my car... )

These are bad news - it seems, the devil's kicking my a** in different ways...

Its shocking me that I've had released the flexplate only 1k mls before and now it had already a 2mm movement

Sharky is my only daily driver and that engine is - compared with the past ones - simply too good (122k mls) to drive it into the ground... Very good responding, strong pulling and especially after flex-release with clean mechanical noise (yeah, I can listen that...)

Question now - how difficult is the swap of the TB? I've had an Audi 5000 where you could swap the crank bearings with installed machine... I assume, that's not really working here...

Cheers

Marc

FredR

Marc,

The not so good news is that thrust bearings [when working correctly loaded] more or less do not wear unless mega miles are covered. This almost certainly means that you have been running with a superimposed load on your crank causing premature failure.

Once this problem manifests itself it does not take long distance wise for the problem to return if the correct measures [Loctite or Constantine's clamp] are not taken.

I dare say it is possible for a thrust bearing lateral face to wipe without spinning the bearing but having seen several examples of TBF sad to say I have not seen one where the crankcase survived. Of course I hope your engine will be more fortunate and that you have caught this before it becomes total engine failure

It is possible to remove the thrust bearing without removing the crank but once such a bearing failure has occurred the manual recommends changing the cam buckets to ensure no metal contaminated oil has made its way in there [along with other measures such as flushing the crank].

I purchased my current GTS with a TBF'd engine and re-built it with my late 91' S4 motor. The full extent of the damage could not be fully evaluated until the engine was completely stripped and only then could one see the cracking in the casing that had been induced by the bearing spinning. The gouging on the crank thrust face and the web face was obvious but then the engine crank end float was about 0.8mm and end float was controlled by crank to crankcase contact.

Bottom line is do not assume the worst but be prepared for it and laugh stupid for a day or two if you get away with it. At .55mm end float I doubt there will have been any metal to metal contact casing to crank webs- but that may vary model to model. As stated earlier, almost certainly the white metal will have been wiped- if it melts it then welds itself to the crank which in turn spins the bearing and when the engine stops it then seizes the engine. I presume from the description you have not experienced this and that leaves hope for optimism.

Good luck and best wishes

Fred R

F18Rep

Just a related data point... I have an 83 engine opened up (from a 5 spd car with 135k miles) and the endplay was only .007". Bruce

Lizard928

I have recently experienced a car with TBF too.

It had .014-.016" end play, and was very obviously cooked. (metal on mag drain plug, and metal in the filter). It was very difficult to turn over when hot, and was slow to crank. Engine had 79K miles

The motor I put in was from another auto, and had 174k or so miles on it. Its end play was .007"