odurandina

sorry to hear.

if you put a Goodwrench v8 motor in, Voith will hate you...

but the car will run awesome.

mtnman82

wet sleeves ... drool

dizzyj

It's hard to tell. The pic looks ok. I'm not saying you have the same problem as I have just that it is possible for oil in the combustion chamber to get splashed up into the bottom portion of the intake. I would run a catch can to at least isolate crank case pressure. Smoking oil is coming from somewhere and there are only a few places, although it's hard to isolate.

It's also hard to determine if smoking caused the knock or are different symptoms of the same problem, or different altogether. Unfortunately I find isolating these problems to be very difficult

Dave W.

The piston appears to be damaged from improper clearance between the piston and cylinder, they're too tight. Can you ask your engine builder how much clearance it was set for?
The oil rings look OK.

Humboldtgrin

Do you have a stock manifold? Not extruded honed correct, or custom? EX process is great IF you can remove ALL the meterial used in the process(silica I believe). It will destroy an engine real fast. So I don't recommend it. Poor Ex cleaning will affect every oil surface in the engine. Just had to get that out of the way.

If it's just the Pistons that have the damage then that supposed engine biulder should refund ALL your expenses for both builds, even the fuel it took to drive to his shop. That is unacceptable. You absolutly have to find someone else, you shouldnt be paying for there mistakes. I put together my last turbo engine with all used hard parts, with a full seal kit. Works great. But I did measure the Pistons and ALL the bearings for clearance.

The rings were welded together because that supposed engine biulder probably didn't set the piston ring gap, I'm betting they were way too tight and were touching upon put together, then when the rings wanted to expand they welded themselves together because they have no where else to go.

Also when the rings go out, in this case damaged immediately, at idle or off power conditions where the engine is under vacuum when the intake valve opens and is "pulling" the air in its in a sence "equalizing" the air in the cylinder and the manifold. Beacause of that effect oil will accualy be pulled into the manifold every time the intake valve opens under vacuum. And on hard decel (heavy vacuum) oil will enter the manifold even more. That is why just the inside of your intake is wet up to the backside of the throttle body and not the intake pipes, intercooler or turbo. On boost the GASSES/and a very small amount of oil, from the crank case pressure enters before the turbo but is not strait oil like the piston rings leaking into the cumbustion chamber. The OAS won't make an effect like the direct oil past the rings into the cylinder and then the intake and then under vacuum conditions. Usually when the intake pipes, intercooler and turbo are wet it's the turbo that's in need of help.


10 to 1 he realy didn't have the head rebiult again. But I bet that hackster charged twice. Do I have any takers?

964-C2

In my engine it really looks like the oil in the intake runners in the cylinder head and lower part of the intake is coming FROM the combustion chamber.
But I had a feeling this was not possible (I thought the intake runners could have stream/flow only one way - TO the combustion chamber).
If you believe you have been experiencing the same thing as me (your intake runners were wet with oil FROM the combustion chamber), that could confirm that it is actually possible for oil to come up in the "wrong" direction here.

That theory could explain my failures:
Oil is coming up from the crankcase past the rings into the combustion, causing smoke. Burned oil / carbon build up is causing the rings to get stuck in the pistons. Causing cylinder / piston contact and cylinder- / piston damage. Causing the knocking you hear in the videos i posted (knocking sound from cylinder - piston contact).

Does this theory sound likely to you guys (it does to me)?

Do you have piston squirters in your engine dizzyj? I have that in my engine. I believe that would make everything worse (if the theory above is correct). The piston squirters will leave more oil on the cylinder walls, making it even harder for the rings to clean the cylinder walls from oil.
I tried disconnecting the AOS line from the intake system to see if the smoke got less. It did not. I do not have any traces of oil in my intercooler / intercooler pipes either. To my understanding, the smoke from the exhaust I have, can not be related to crankcase pressure / oil via the AOS system then.

Alan 91 C2

There may be two separate issues going on:
1. Check the oil ring expander, the expander is between the upper and lower oil ring. Turn the piston to see the end of the expander, the two ends should meet, and not be overlapped. I have had a car where the installer overlapped the oil ring expander, and the car burned oil from the first start.
2. As Lart and others have said, the piston to wall clearance is not correct. This can happen for several reasons; the pistons are not uniform diameter, or the bore and hone was not the correct diameter.
3. There could be contamination in your intake runner, grit. But, you should be able to see the grit reside stuck in the piston skirt with a magnifying glass.

Your installer bears the responsibility to check clearances, and assemble the rings properly.

You can do a simple test in the good bores, by slipping a 0.001-3 feeler along the skirt of the piston into the bore. The damaged piston will not likely give good measurement, but you should try. The measurement is on the piston below the oil ring 90 degrees to the wrist pin. All cylinders should be the same clearance. Check different pistons in different bores to verify uniform sizes. Google piston to cylinder wall measurement for detailed explanation.

You will need a new machinist to check the cylinder clearance. Your guy cannot be trusted.

The oil ring, if installed incorrectly, you can see as you rotate the piston in your hand.

As yes, that much oil would get into the intake from the cylinder.

You can PM me if you want to discuss.
Alan

Dave W.

If the ring gap was set too tight it's most likely the rings would crack and loose their springiness. The pics show good, normal rings, although I can't say if that's the case with the current engine since it's still assembled and running.

It's unlikely that carbon would build up in 40 miles and stick in the rings. It's more likely that the metal that's missing from the damaged piston skirt is caught in the rings.

Which pistons were used in the first and second build? OEM or aftermarket?

964-C2

Wossner in both.

964-C2

Thanks for all inputs!

Getting the piston to wall clearance correct should be basic and very important when you build a engine. My builder is experienced, I would be surprised if he did not do his best get this right, especially for my second rebuild...
But maybe you are right (maybe the clearance is not correct).

What if the piston squirters leaves to much oil on the cylinder walls for the rings to handle, is that a possebility?
I mean: maybe the wall to piston clearance is correct and maybe the oil rings are correct. But if the cylinder walls are "soaked" with oil, it could be to much oil for the rings to handle, and some oil will get into the combustion.
Maybe not very likely?

Alan 91 C2

Did you check the oil rings for proper installation, not over lapped?

Checking the piston to cyl clearance is easy. Need 0.001-0.005 feeler. You need to know these clearance numbers. Put the piston skirt half way into the bore and see what size feeler you can fit, start small and work up.

This will tell you if the installer did his work properly.

Lastly, look at the damaged piston for debris in the skirt wall.

Squirters are not your issue.

Humboldtgrin

Maybe experience at something but not building engines, two engine failures on the same engine in a row tells everyone that. And all 968's have piston squirters, none have failures at 40 miles. In fact most of us would like to have a 968 block to work with. There are two oil scrapers with a mesh between them to collect any the first scraper missed and oil diapers back into the crankcase thru little holes on the piston in the oil scraper grove, below the two compression ring groves, and they do there job well if the engine is built right. The squirters don't spray "that" much oil to make the engine want to smoke, or even damage the Pistons. Oil out the tail pipe would be engine damage or valve stem issues. If you notice all engine have a grimy intake manifold up to the throttle body but not wet with oil. That's because of the effect of equalization of air under vacuum between the cylinder and intake manifold, but other engines don't have that much blow bye past the rings into the cumbustion chamber. The reason your intake is wet is because the rings are improperly installed and/or piston clearance and/or wrong rings for pistons and/or pistons rings not gapped correctly and/or wrong Pistons for sleeves and/or valve stem issues. And as pointed out rings usually do break if to tight but I have seen them weld themselves being to tight. However with that much oil with the piston blow bye I could see carbon building up very fast because the compression rings are failing and then the oil scraper rings become compression rings for a second then fail immediately and burn the oil that they have collected, turning the oil to carbon and seizing the rings to the pistons. The builder is completely responsible for your failed engine. Twice! Third time isn't a charm!!! And if your asking us about why so much oil is in the intake because your biulder can't explain it, it's because they don't know how engines work.

alex_cristocea

Sorry to see this happened. I also think it's a clearance problem. I saw similar piston damage on an S2 engine with installed steel liners also with improper clearance. The piston damage looked like this





944 S2 Piston

The upper part off the piston gets more heat than the skirt and if the bore it's too tight it presses on the cylinder wall ( generating more heat) "cocking" the oil forming carbon deposits on piston rings witch are visible on some of the pictures you posted.



you need to check the piston/cylinderwall clearance at the point were the two pistons touches.

964-C2

You are looking at the pictures from my first engine failure. The engine is back in the car now (rebuilt). I have driven 40 miles on the rebuilt engine and have a knocking sound / engine failure once again. Read my first post again and you will understand. I have not taken the cylinder head off and looked at the new damages yet.
I was thinking if the squirters are installed wrong (this is a S2 block with squirtes installed by my engine builder).

964-C2

Ok, thanks for the input!