Wavey

Evening all.
While tracking missing horsepower's I discovered a significant loss of compression. Between 125 and 140 psi.
This increased by between 30 & 40psi with a wet test. ( Not all cylinders improved by the same amount).

This leads me to piston rings and a decision as to whether to do it myself or pay a professional.

Can the pistons be removed without removing the engine on an 1983S Euro 3 speed auto?

Thanks,
Robert.

GregBBRD

Absolutely.
The most difficult part of that entire job is getting the cam carriers off, back on, and not have the silly Moly coated gasket between the head and the cam carrier leak.
We have a custom gasket made which works 1000% better than the stock gasket, BTW.

Mrmerlin

smart money says save time,
pull the engine so you can work like a pro.

The Forgotten On

Just pull it.

It is so much easier to work on outside of the car, otherwise you'll be crawling on your back and getting back up to lean over the fender more times than you would think to do this job.

Your back will thank you if you pull the engine and mount it to a engine stand.

FredR

Whereas the need to open up the engine is a very real prospect [sad to say] your test results are not disastrous - clearly they suggest that the problem lies in the ring seal area [not the heads]. The compression pressure you recorded, although of concern, is not a basket case. When one cylinder is down compared to the rest, one has to ask the question why this should be the case. I would think the first thing to do is to get hold of an endoscope of some kind and take a look at the bores. If there are obvious signs of scoring then it would be a motor disassembly job and then you have to decide whether it an "in-situ" approach or a motor out job. Given the quality inputs you have already had I presume that means your model year can get the heads off with the motor still in the chassis. You then have to get the sump pan off and that requires quite some trickery due to cross member interference.

Your current status and the compression pressure you measured begs the question as to whether you have considered some of the methods available to cleanse the piston and ring lands "in-situ"? No one can advise you that such will for sure solve your problem but if I were in your position i think i would want to give such a shot considering such methods involve a few bucks for a can of whatever you choose to try, Products like Liqui Moly Pro line engine flush, Sea Foam, Swepco 502 and/or Rislone are but a few that come to mind- no idea whatis available in your neck of the woods.

Perhaps you might take a step backwards and advise what it was that made you want to check compression pressure in the first place- maybe you can confirm you used the correct procedure [throttle wide open whillst cranking] and what compression pressure you actually measured on the other cylinders.

gbgastowers

Is it using more oil or smoking?

Wavey

@GregBBRD Yes I have heard it is hard to seal up again - how many man hours do you estimate to do with engine in situ? Assume moderate skill level.
Is the work mainly directly above and directly below the cylinders? - any need to remove water pump, power steering pump, timing belt etc?

@Mrmerlin @The Forgotten On Skills and worship space aside, I'de agreed the sensible thing is to remove the engine but I'm worried that if I take out the engine myself there is a chance of huge scope creep and of me not getting it back to where it was.

@FredR
Wide open throttle.
Tests results dry 1-8
120-140-130-130-130125-120-140
Tests results wet 1-8 (slightly cooler engine)
175-175-180-165-160-155-155-165

I have not considered cleaning the cylinders - will give it a shot. Assume the target here would be carbon removal?

Compression test is just one of a few areas I'm working on to improve what I believe is poor acceleration. Also looking at fuel pressures and ignition - but the poor compression results are by far the most obvious smoking gun I have found.

@gbgastowers Does not really smoke and I'm not doing enough miles right now to notice any increase in oil consumption - but there is oil ponding in the air manifold and on the plug threads.

I will continue to look into it before deciding to get it done, do it myself or just leave it.
Would love to see a guide on the process -
The WSM doesn't seem to address this task.

Thanks,
Robert.

GregBBRD

Robert:

You asked if it can be done with the engine in the car. Yes it can.
Should it be done with the engine in the car is a completely different question.
With a bunch of variables.

The job is far easier with the engine on an engine stand.....there's no doubt about that.
However, it takes a bunch more effort and you have to deal with a bunch more pieces, if you pull the engine.
And you will need more room, if the engine is out of the car. Room for the engine hoist and room for the engine stand.

One thing you have to think about is:
What are the odds that the engine will have to come out of the car, regardless?
In your case, it is important to realize that it is extremely rare for rings to be worn out....even with 300,000km's.
Most likely, you have broken rings and broken ring lands.
This is super common on Euro 2 valve engines.
High compression and cast pistons work great....as long a no one ever does anything stupid.
Advance the timing. Run a tank of low octane fuel. Either end up in the same result: Broken ring lands....instantly.

The odds that your engine block will need to come out of the car, for machine work, are very high.
If this car was in my shop, with the same results of your testing, I'd pull the engine....
And start checking if Porsche has inventory on oversize pistons.

karl ruiter

In order to do it with the engine in the car you will have to pull the pan. This means pulling the steering rack and cross brace. Also, you will have to pull the cam carriers and the heads. This is possible with the engine in the car, but hard.

GregBBRD

I don't mind pulling 928 engines. It's the putting them back in part that takes me forever..That's two day affair, minimum. And that's if no one asks me any questions about the 30 other cars which are here. Or if the phone doesn't ring. Or if I don't get distracted by Rennlist.
The whole perfectionist thing just sucks up hours and hours. I can spend 30 minutes trying to get one accessory belt to the perfect tension. And installing a clutch....I'd be embarrassed to tell you how long I spend on that....
Therefore I avoid the whole thing, as much as possible.

I've resealed a leaking lower cradle, in the car, before. (Just the one, BTW.)

Rob Edwards

This was the extent of disassembly we had to do to R&R leaking cam tower gaskets that I didn't get right the first time around, back in 2016.

rexpontius

Just pull the engine, great opportunity to fix other stuff while its out

linderpat

That's exactly why he said he does not want to pull it out.

FredR

Robert,

What concerns me at the moment is that you are not reporting excessive oil consumption or clouds of smoke billowing out of the exhaust that are typically commensurate with degraded compression due to mechanical wear.

I do no know what cranking compression pressures your model year should deliver and presume it should be in the region of 180 psig. The first point of note is that the pressures recorded are reasonably constant. Not sure whether those numbers were attained hot or cold not that it should make a great deal of difference. I would also note that if you had ring or piston issues I wonder if you would still achieve the "wet" numbers you report. Also note that it is more important to have consistent numbers - some test rigs read low. Do you have another engine you can test on to see if they also read "low" on that motor.

One thing that perhaps should be considered at this stage is to ensure that your timing belt has not skipped a tooth on the crank sprocket for whatever reason. If this happens cam timing will be retarded and this will drop the cranking compression pressure. I am not overly optimistic this is the case but for sure well worth ensuring such has not happened.

Carbon deposits can build up in the ring lands and that can also cost some compression loss. Giving the system a clean is not exactly over taxing considering the work involved in a total strip down.

You should also ensure that you are not looking for performance that simply does not exist. Have you checked 0 to 60 times against those specified for your model?

Speedtoys

I'm late to this one..but this doesn't worry me that much.

You said "missing HP" but you dont list what HP is missing.