Crank thrust bearing issues
08-26-2005, 04:07 PM
#62
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I guess the point has been clouded a bit.
The spec taken on the motor as the bearings sit are in spec, accrding to Porsche. When we assemable them they are still in spec yet that spec is large. So, the motors coming out of the factory have play in them.
The spec taken on the motor as the bearings sit are in spec, accrding to Porsche. When we assemable them they are still in spec yet that spec is large. So, the motors coming out of the factory have play in them.
08-26-2005, 05:07 PM
#63
I spoke to someone who has built quite a few Cup and R engines for Japan, and showed him the photo's of the bearings. This is what he told me.
He has seen this type of wear on all 4 Cam engines, even the ones with the straight cut drive gears, as well as the chain driven types. He also told me that he has built a very samll number of street engines, where the exact same condition was present. On these street engines, the engine case and Crank where both bad. He thought the problem was the same as the Boxster engines. When the problem was seen, it was repaired in a typical fashion, same as any engine with excessive thrust wear. I asked what backlash they ran, and he told me very normal amounts for any engine, nothing special for this engine. I was told that typically, these engines which have the earlier style case are always having this problem, as the loads are very high at the thrust end, and the case is very flexible, due to the limited number of fastners. Any case that is split across like these are where the number of fastners is small will have movement. Its how much you can tolerate, before failure occurs.
I was told no oil will help this, but he did agree with whoever suggested the GM additive. He did tell me what this stuff was, and that all modern oil does not have this stuff in it anymore, and this stuff is great on parts that run against one another.
He also told me that typically Porsche cranks all need to be straightened, as in manufacturing, these style of cranks are the hardest to make. Holding tolerance is very hard, and in street production the tolerances will be higher.
Stephen, I was asked to ask you what the Crank you measured, measured. From Front Main to Center Main, from Rear Main to Center Main and from Rear Main to Front Main. Any amount will load up the Thrust, as the one in your photo shows. He also asked how do you measure the Main bore, referenced to the rear Flange machined face. I was told often the Main Housing bore is measured for concentricity, and for straightness, but this just means the crank run true to itself, not the case. I was told the wear patterns on the bearings you posted showed some misalignment. How much backlash are you measuring?
I was told that any wear or mis alignment will show up and typically become worse expotentially as the engines performance is increased.
If you have too much backlash when new, then your stuck if you want Porsche to fix this under warranty, until they consider this to be a problem. The only course of action left is to have it lowered and pay. While this is been done, have the crank checked and the main housing bore checked too.
He has seen this type of wear on all 4 Cam engines, even the ones with the straight cut drive gears, as well as the chain driven types. He also told me that he has built a very samll number of street engines, where the exact same condition was present. On these street engines, the engine case and Crank where both bad. He thought the problem was the same as the Boxster engines. When the problem was seen, it was repaired in a typical fashion, same as any engine with excessive thrust wear. I asked what backlash they ran, and he told me very normal amounts for any engine, nothing special for this engine. I was told that typically, these engines which have the earlier style case are always having this problem, as the loads are very high at the thrust end, and the case is very flexible, due to the limited number of fastners. Any case that is split across like these are where the number of fastners is small will have movement. Its how much you can tolerate, before failure occurs.
I was told no oil will help this, but he did agree with whoever suggested the GM additive. He did tell me what this stuff was, and that all modern oil does not have this stuff in it anymore, and this stuff is great on parts that run against one another.
He also told me that typically Porsche cranks all need to be straightened, as in manufacturing, these style of cranks are the hardest to make. Holding tolerance is very hard, and in street production the tolerances will be higher.
Stephen, I was asked to ask you what the Crank you measured, measured. From Front Main to Center Main, from Rear Main to Center Main and from Rear Main to Front Main. Any amount will load up the Thrust, as the one in your photo shows. He also asked how do you measure the Main bore, referenced to the rear Flange machined face. I was told often the Main Housing bore is measured for concentricity, and for straightness, but this just means the crank run true to itself, not the case. I was told the wear patterns on the bearings you posted showed some misalignment. How much backlash are you measuring?
I was told that any wear or mis alignment will show up and typically become worse expotentially as the engines performance is increased.
If you have too much backlash when new, then your stuck if you want Porsche to fix this under warranty, until they consider this to be a problem. The only course of action left is to have it lowered and pay. While this is been done, have the crank checked and the main housing bore checked too.
08-26-2005, 05:40 PM
#64
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Bottom line for poor folks like me who have to buy used and then mod the cars, becasue we can't afford new... is that this is big time scary if the car is out of warranty... and if the problem is exacerbated by big HP, even if the car is in warranty, Porsche will make warrranty claims tough...
Bigger point IMHO is that the spec is much larger than the other engines... soo ... WTF... how can you even get it fixed in warranty?? WHat is the obvious driver to get it fixed if TECNically it's in spec???? Not to be an alarmist, but left unchecked (and maybe still within spec).. what probable longterm issues are there?? That's part of the reason I asked if anyone has seen any other (next in sequence) bearing wear... The case and crank issues really are worrisome though... Being a junkie, I also struggle with the extra garbage in the oil, though I know it tends to be soft.. it's still garbage...
e
Bigger point IMHO is that the spec is much larger than the other engines... soo ... WTF... how can you even get it fixed in warranty?? WHat is the obvious driver to get it fixed if TECNically it's in spec???? Not to be an alarmist, but left unchecked (and maybe still within spec).. what probable longterm issues are there?? That's part of the reason I asked if anyone has seen any other (next in sequence) bearing wear... The case and crank issues really are worrisome though... Being a junkie, I also struggle with the extra garbage in the oil, though I know it tends to be soft.. it's still garbage...
e
08-27-2005, 01:32 PM
#65
There must be hundreds of engines running fine at the present, that if disassembled would require repair, but still run OK now, if you follow what I mean. You repair what you see in front of you at the time. Unless a more seroius issue arises, I would not sweat it. It may not be right, but is it creating a problem.
08-27-2005, 11:46 PM
#66
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I believe I read earlier in this thread that the issue was more prevalent in earlier cars? Did I read that correctly? If so, after what build date is the issue not (less of) a problem?
08-28-2005, 11:48 AM
#67
Do I understand that a rattling noise on start up is indicative of this problem? Would that be a cold start - 1st time of the day or after sitting a few hours? What has Porsche or the dealers done to address a rattling noise on start , or have they been claiming that "they all do that" ?
08-28-2005, 11:53 AM
#68
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No Mike, that was the 996, not the TT.
Simon, I will get to your questions. Sorry for the delays. We had a couple of events that has consumed the last couple of days. I need to pull the files for one of the motors. I will then post the numbers.
Simon, I will get to your questions. Sorry for the delays. We had a couple of events that has consumed the last couple of days. I need to pull the files for one of the motors. I will then post the numbers.
09-08-2005, 12:21 PM
#71
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Although I have no involvement with Porsche motor building , this situation reminds me of a problem when I was building race Audi motors.
Factory bearings moved over to the combined main and thrust set up seen in the pictures in this thread. With a race clutch the thrusts lasted no time and chewed the crank face so we moved back to the older seperate thrust bearing setup.
These thrusts were wider and so spread the load better - the thrust problem went away .
Sorry no pics , too long ago !!I dont think Porsche has used seperate thrusts so this isnt on option but it may be useful to know this has been seen before on another motor.
Geoff
Factory bearings moved over to the combined main and thrust set up seen in the pictures in this thread. With a race clutch the thrusts lasted no time and chewed the crank face so we moved back to the older seperate thrust bearing setup.
These thrusts were wider and so spread the load better - the thrust problem went away .
Sorry no pics , too long ago !!I dont think Porsche has used seperate thrusts so this isnt on option but it may be useful to know this has been seen before on another motor.
Geoff
09-09-2005, 06:05 PM
#74
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Do a search on the 928 boards and you will see we have had similar problems in our cars, all automatics though and after much higher mileage. Our cure is to routinely go under and release the clamping pressure on the front pinch bolt that secures the drives shaft to the front flexplate. When this is done it is not uncommon to see the flexplate pop back 2-4mm to its normal postion. This would be stress constantly placed on the thrust bearing of the motor if not periodically released.
Nasty stuff either way. Symptoms show them selves when the car starts to idle roughly then eventually quits when warm....caused by the crank grinding into the block when the temps come up.
Nasty stuff either way. Symptoms show them selves when the car starts to idle roughly then eventually quits when warm....caused by the crank grinding into the block when the temps come up.
09-10-2005, 03:26 AM
#75
Put your hand in hot water and its going to get hot.
Same can be said when you put the thrust at the Rear Main. Every Porsche engine shows this same problem. Some worse than others. My posts earlier were somewhat vague, but Red rooster got it. He has experience and from that, saw the same problem. Well done. I take my hat off to you, Sir.
There is a quote that seems to apply here.
"There are only 2 types of people in this business. Those that see it wrong and fix it, and those that don't see it at all".
Same can be said when you put the thrust at the Rear Main. Every Porsche engine shows this same problem. Some worse than others. My posts earlier were somewhat vague, but Red rooster got it. He has experience and from that, saw the same problem. Well done. I take my hat off to you, Sir.
There is a quote that seems to apply here.
"There are only 2 types of people in this business. Those that see it wrong and fix it, and those that don't see it at all".