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YOUR RESEARCH996 Nightmare -Thrust Bearing Failure
Leading reported evidence
Install backward at the factory
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At 30K, this car either had a "clutch rider" for a driver, or the thrust shim was installed backward at the factory.
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These thrust shims (2) are the VERY FIRST part thats installed when reassembling an M96 engine.
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Suggestion
To be fair though, just replacing the crank is quite an abbreviated rebuild, no?
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Just purchased a 2003 4S 3 weeks ago. 30K miles, great shape, clean car fax, clean PPI. Everything I could possibly due to avoid buying a huge problem. I drove it for 3 weeks off and on and then took it in to have the IMS upgrade done and new clutch.
When we pulled the clutch and flywheel we noticed a couple of odd marks on the inside of the flywheel and then looked at the bell housing and it was obvious that the flywheel was rubbing on the bell housing. We dropped the oil pan and a large piece of the thrust bearing was laying in the bottom!! NOT the IMS, but the crank shaft thrust bearing.
That is where it sits today... Now what?? It did not make any noise, smoke, or drop oil, so I have to assume it just happened. No idea how much damage it did yet.
Any suggestions other than drop $20K on a rebuilt motor? I only paid $32 for the car.
Hi there, welcome, sorry to hear your first post is not a very nice story!
Legit sucks
I'm sure more experienced members will chime RE details but usually the options are:
- Rebuild current engine
- Purchase second hand engine
- New short block from Porsche
- Sell as a roller (which seeming you paid a decent price bit wouldn't make sense)
Mode of failure #17... I just finished a build for an RL member (INRANGE) following this exact same scenario.
This one being caught early is a key, before it become a symptomatic.
I see this failure 5-6 times per year, and all too often it leads to collateral damage of a separated IMS shaft, or a broken main timing chain. Why? As the crank dances fore and aft, longitudinally, the chain and IMS drive catch pure hell, as they are now the new longitudinal control surfaces for the thrust loads of the crankshaft.
This one can be saved, but it probably needs a crankshaft. I'm instructing my hands on rebuild class later today, and I have these exact failed components that have failed due to MOF #17 here at the training facility. They came from INRANGE's engine and clearly show what to expect. I'll post some pics.
Why do these fail? The early thrust shims have one less oil groove in their face than the later units. This leads to less lube at the crankshaft/ thrust shim, and that leads to more heat and wear. The shim wears thin, and simply falls out of the carrier and into the sump.
OR the thrust shim was installed at the factory backward... Then it sees greatly reduced oil volumes to the wear face. It overheats, wears, and falls out. Yes I have caught this in process- robots suck.
This one is only a "996 nightmare" if you choose to restart the car before repairing it, or if the wrong person repairs it that is not familiar with the exact fauktbpath of the failure, and how to overcome it.
As it is now you have a best case scenario.
Good luck with it, on the positive side, as Jake points out it looks like you might have had a narrow escape.
I'm in a similar situation and will be rebuilding my engine, more for peace of mind more than anything else. Really don't want to buy a second hand engine and find out I have "issues" again.
BJ, Sorry to hear about your engine trouble. At least you didn't decide to drive into the ground. I hope you're able to reconstruct the motor and get you back on the road asap. What part of the country are you from?
That really sucks having this happen just three weeks down the road. Did the group that carried out the PPI, drop the oil pan or just examine the oil filter?
At 30K miles you don't need a "rebuild"... You need a repair, with updates, as long as collateral damage is limited.
At our level, this can be an easy (very easy) repair to make. Its like a dream come true.
If the car had 90, or 140K miles, the story would be different... At 30K, this car either had a "clutch rider" for a driver, or the thrust shim was installed backward at the factory.
You have more options than you may think.
Sorry to hear that and it really sucks. Since your engine has only 30k miles, it could be worth saving. Definitely discuss with Jake. None of the options will be cheap but if you sell it as-is, it'll probably be $12 if that. So if you can fix it and address the other inherent weaknesses of this engine for $20k you will "break even" given what you have lost already.
Resurrecting this thread.
Has anyone tried regrinding the crank say .010 over on the thrust and making a custom thrust bearing out of silicon bronze?
And why not double thrust the bearings?
Looks to me like you would just have to cut in the tangs on the other crank box half, the recess is already there.
Facing the same issue.
The heat treat only protrudes into these crankshafts .003"
Any regrinding of these cranks is very difficult, as a custom heat treat profile has to be applied for any longevity at all. So far I have only found one company in the world that can do this effectively, and they are located in France.
My crank guy (40+ years, cranks only, biggest in Canada) has already reground the thrust, he didn't believe there was a heat treat issue in this area. Passed magnaflux and all other specs.
He has an alfa builder that does this and it's common on big equipment.
If the car is a tiptronic it may live.. The clutch load is too much longitudinally. Thats what kills the shims anyway.... As long as the factory doesn't install the shims backward. Thats usually what causes this issue with OE engines.
The clutch with is easily bypassed... I don't do it from a liability perspective, but it most certainly is a great idea from a thrust wear perspective.
Very easily done, I did mine, do not like dry starting any vehicle with clutch in, under the dash are two switches at the brake pedal and one at the clutch pedal, take the clutch switch wires and got a spade connector and connected the two wires together for the clutch switch and heat shrink a cover and tie strapped it up so not hanging. can be connected again if wanted to.
I'm not sure I'm understanding how disengaging the clutch is creating a thrust load on the crankshaft??? Wouldn't engaging the clutch release the load on the flywheel/crank?
The pressure plate in the clutch system is over 3,000 pounds of force. When the clutch pedal is depressed the release bearing contacts the pressure plate to release the clutch. To do this, it must fight the load of the pressure plate.
So, since the pressure plate is attached to the flywheel, and the flywheel is attached to the crankshaft, this force is placed longitudinally on the crankshaft. Its the job of the crankshaft thrust shims to carry this load.
But at start up there's little lubrication on these shims, so the forward facing shim is solely responsible for carrying these forces made by the pressure plate. If the clutch is depressed to start the car, then this makes for the worst possible scenario for the crankshaft thrust shims, as they start dry, and with all that load.
This makes them wear thin, and fall out of the crankshaft carrier... Then the crankshaft starts banging around, and when you pull off the oil sump to help diagnose the issue you are faced with whats left of the shim laying on the sump plate.
I documented this as mode of failure #17.
Hell NO!
These thrust shims (2) are the VERY FIRST part thats installed when reassembling an M96 engine. Once the crank carrier is assembled, it holds the shims captive, and they can't even be seen.
This one is a 100% teardown to remedy.
That clutch switch is a really stupid addition to these cars, mechanically speaking. Any car I won has any switch like this bypassed, and I start the engine with my foot off the clutch, transmission in neutral.
Of course, I am the type that rips every safety switch off every piece of equipment, or car that I own. If I hurt myself, its my own damn fault, but I'll be damed if some safety switch is going to fail and leave me on the side of the road, or in the middle of a field!
I would think that the cruise will not work with the switch "jumpered" - under normal operation the cruise drops if the clutch is depressed... perhaps a way around this is to wire a switch (one of the open dash positions?) that will jump the switch without pushing the clutch pedal. Once the car has started, you can turn the pedal switch back "on" which will allow the cruise control to operate as it normally would - i.e. Drop off if/when clutch is depressed.
Mine starts without the clutch and cruise operates normally. I do need to look underneath to see if it was jumpered by the last owner or if it has a RoW ECU flash. I've heard that the flash disables the clutch requirement for start as well.
It's not an issue, the cruise uses a different switch. I bypassed this switch this weekend after reading Jake Raby's post. Took less than a minute and my cruise operates exactly the same as it did before.
My '04 is a RoW Australian delivered and have always wondered if the previous owner bypassed the clutch switch or if it came like that from the factory.
RoW FTW!!
