Scotty1

Hi folks , I acquired a 1987 s4 auto recently that was dried stored for a few years and not driven at all.it would not start due to a failed ignition ECU and bad fuel pump and filter.As part of my recomissioning so far I have replaced the radiator and thermostat fuel filter and pump ,distributors and spark plugs tested Maf and engine ECU which were fine.i eventually got it running and it idled nicely ,temp was spot on and good oil pressure. I decided to go for a quick drive to test on the road and it drove good with plenty of power no smoke and not overheating .When I drove back however it stalled and took a number of attempts to start eventually got home turned it off and tried to start again which was very difficult it was like the engine seized and would barely turn .after charging the battery and checking that the TB had not snapped it eventually started and there seemed to be a knocking sound coming from the front of the engine ? Is this a bearing failure bent valves is the engine toast ? what are my options at this point ?could it have slipped timing ?

C531XHO

Did you check the flex plate/crank endfloat?

FredR

Sounds as though you need to eliminate the possibility that thrust bearing failure may have occurred- the info you have posted is a bit "ominous" to say the least but it is not conclusive either.

Suggest you do a Rennlist search regarding this terrible affliction that potentially can affect automatic transmission models built after approximately 1984 and then feel free to ask any questions about it.

You may also find it better to search via Google- just type in "Rennlist Porsche 928 thrust bearing failure" - you may get better results than simply searching within the Rennlist search engine.

In the mean time keep an open mind and avoid doom and gloom scenarios at this point in time unless and until something untoward is uncovered- there are a number of other issues that could be in play given the background you advised.

GregBBRD

So many possibilities.
TBF mentioned above is one.
Water in combustion chamber from blown head gasket is also possible.
Fuel injector stuck wide open filling combustion chamber also possible.

Severe engine damage can occur from cranking over an engine that is resistant to rotating, from "hydraulic lock".

I'd suggest that you shoud not have done this/do not continue to do this.

If an engine is ever resistant to turning over, remove the spark plugs and them try it. If fluid sprays out of one or more cylinders, you need to isolate that issue, before proceeding.

SwayBar

Let's keep this simple for starters - check your engine oil to see if there is any debris in it.

If it's clean, you've dodged a bullet.

Scotty1

Thanks for all of the advice so far .I will definitely look at removing the plugs to see if any fluid sprays out .I checked the oil from the dipstick and it looks good with no metal shavings also the coolant is clear and levelsok if it was a head gasket would the temp gauge be high and either water in the oil or oil in coolant ?

Mrmerlin

NOTE to check the oil condition,
drip the oil onto a black piece of cardboard ,
look at the oil in the sun ,
if it has metallic specs in it then the engine is making metal.
checking of the flex plate should be next on your list

Kevin in Atlanta

TBF BTHT - All the symptoms plus being stored for years. There's a lot of good and mostly bad reasons these cars are stored and not driven for years.

Do not drop the oil yet.

Start with crankshaft end play.

GregBBRD

TBF is all about who owned it and how it was driven.

The "harder" the car was driven (driven using peak torque often) the worse the flexplate preload will be.

Kyle took out an '84 engine, today.
These virtually never have any flexplate preload, due to the lower torque of the US 2 valve engines.
This one had the flexplate crushed into the flywheel.
The only way to do this is to drive the car like you stole it!

SwayBar

The next step I would do is to remove and cut-open the oil filter - it will tell you for sure if the engine is dying.

If you find lots of debris in the filter, the engine is dying, and there's nothing else to do except remove the engine.

Pete in DC

So the catchphrase has been wrong the whole time.

Constantine

The suggestions received to check for TBF are the most relevant to your symptoms and should be done as the very first steps. If there are signs of TBF in the engine oil and crankshaft end play measurements, the engine must come out since it is done, as SwayBar said.

Actually, anyone who purchases an automatic 928, regardless of the year, should do TBF checks before doing anything else to it and is a must during a PPI.

I have talked to my share of such new owners, and looking at an engine rebuild is sobering after putting money into other areas of the 928 right after purchase.

Good luck with the diagnosis.

SwayBar

From the little I know about TBF, it is my understanding that:

If the transmission and torque tube have never been removed, there is little chance of a TBF.

However, if the transmission and/or torque-tube were removed/reinstalled, all bets are off due to the possibility of not installing correctly.

Is that an accurate assessment?

76FJ55

No, I don't think that is an accurate statement. It may be when referring to early cars (pre 84, IIRC) with 25mm shafts that came from the factory with the shims and clip installed that limit flex plate clamp movement, but I don't think that would apply to anything that didn't come with the shims and clip or with the later 28mm shaft (doesn't accept the shims and clip).

FredR

Simple answer is no.

TBF happens on examples that have not been touched since they left the factory we have to assume they were assembled correctly in the factory and TBF typically [but not exclusively] seems to happen in the range of 50k to 100k miles. TBF happens on examples that have been removed and installed correctly. A slipping clamp is most likely a pre-cursor to either TBF or shaft failure

Needless to say anything that is not installed correctly can also fail. I believe there is a good possibility that examples that have been driven hard may be more prone to this problem and there could also be other factors such as ambient temperature the car is driven in and my "favoured". theory - production tolerances of the splines and flexplate coupling .

About the only thing one can say with absolute certainty is if the clamps do not slip the problem does not happen and neither does shaft failure on the 28mm item.