Josh B

First I would like to say that Rennlist is practically useless now as it takes forever for things to load if they do at all. Is it just on my side?

The topic of this thread is a study of my 1987 944 turbo engine that wouldn't start anymore. This happened during a DE at Road Atlanta - came in off the track for a tire pressure issue - turned the car off and she wouldn't start again.

After getting towed home and examining the engine I had 80% leakdown and 50 PSI of compression on 1, 2 and 4 and 85 PSI on 3. I also had slightly bent intake valves. Even after getting the head fixed the compression and leakdown numbers did not change. The leakdown showed the air was getting past the rings.

I gave up on this block and sourced another one. The old one is torn down now and figured I would post up pics. It looks like the rings are all frozen in the in position. Any thought or comments would be welcome. I think some of the scratches on the pistons/cylinder walls are from me not knowing the best way to pull out the pistons and taking them out from the top. I tried lubing the cylinder walls up but it seems like I still got scratches.

Is this block still good? What would be recommend to get it back in working order - looks like it is a tolerance 1.

333pg333

Just from what I can see the walls look ok enough to get them honed but the pistons seem to show fairly decent scratches though? Did the pistons show valve kiss marks on the top?

rlm328

You may want to get a bore gauge to see how much wear you have in the cylinder bores. The highest wear is perpendicular to the crankshaft. There is a certain amount of wear difference between perpendicular and parallel that is tolerable, I don't remember what it is just use search as it is on this site some where.

Josh B

No valve kiss on the top.

Is it best to pull the pistons out the bottom when taking the engine apart or should it not matter?

lart951

I always taken them from the top.

fortysixandtwo

They can't be removed any other way.

Chris White

The critical wear issue is bore taper (other than scores and scratches!)
The cylinders will wear more at the top of the piston travel than the bottom – this creates a tapered shape that is not good. The rings have to compress / expand to follow the taper and doing this at 200 times per second (at 6k rpm) is asking a lot!

It looks like a typical high mileage used engine. OK for street use but I would consider freshening it up for track / hi performance use.

Josh B

Hi Chris - any thoughts as to why the rings would lose their spring and be stuck in like that? Is that typical when taking apart an engine or do the rings normally pop out?

Chris White

Several things will do that –
Just being gunked up and sitting for a while (can be common on a ‘parts’ engine that has sit for a while)
Overheating (not coolant but localized overheating at the rings – very high EGTs)
Damage to the ring lands – detonation

But most likely #1 – it sat around for quite a while. Be careful removing the rings if you are thinking about reusing the pisotns – any nicks or damage to the ring lands is a real problem

Willard Bridgham 3

If the scratches in the block bother you, you can have the bores honed and re-alusiled.