Need to drop engine after rebuild

polizei · 10-15-2008, 05:14 AM

Hey guys,

I recently completed a top end rebuild and turbo conversion on my '87 Carrera. Once I got to driving the car, I found that it was going through 10 quarts of oil over 2,500 miles.

I ruled out the turbo as there is no trace of oil in the charge pipe going to the TB. There is a leak between the cam towers and the heads, but it only leaves a very small amount of oil on the garage floor after sitting overnight. I believe the leak is caused by a poor sealant, so that will be resolved when we drop the engine. My friend who is doing most of the engine work believes either the rings have not seated or there's a problem with the valve stems.

It smokes slightly to moderately at times on idle. It smokes VERY heavily through the first three gears after it sits overnight. My friend drove behind me on his motorcycle and said at speed it smokes slightly while cruising, and he said he could definitely smell it. It smokes moderately on engine deceleration.

A couple things come to mind as to what the problem may be. We didn't measure the thickness of the cylinder walls, so perhaps one or more cylinders are out of spec. We used a ball hone as opposed to a diamond hone on the Mahle cylinders. What are the measurements I should be seeing for an in-spec 97mm Mahle cylinder? Is it advisable to send the cylinders out to be measured and re-honed? Does anyone know of any shops near Eastern Pennsylvania that are reputable?

What should I be looking for as we tear the engine down?

As usual, thanks for your help guys.

lucittm · lucittm's Garage

I don't know much about the various metals that make up the Mahle cylinders that Porsche used but I didn't think we were supposed to hone them. I heard that 2-3 seconds with a Scotch-Brite pad was enough to give the rings something to grab onto and seat themselves. Some folks don't even do that.

Thanks,
Mark

dtw · 10-15-2008, 06:20 AM

Quote:

Originally Posted by polizei

We used a ball hone as opposed to a diamond hone on the Mahle cylinders.

I think that's it right there. Definitely damaged the jugs. Many don't even Scotch-brite these. If they're in-spec, a little soap and water and that is it.

Take measurements and see if they're salvageable - Troy @ EBS can discuss re-plating options w/you.

mb911 · mb911's Garage

As I stated on your other thread odds are there is a broken oil control ring and you did not know this when you installed them in the cylinders. I find it very hard to believe that it would go through 10 qts in 2500 miles unless that was the case. In my former life I rebuilt aircraft engines for a living so fairly versed with what can go wrong.

as to cylinders I would look to EBS for replating or go the QSC route with JE pistons on a tighter budget.

les_garten · 10-15-2008, 07:06 AM

The Nikasil is neat stuff. I took my motor down around 80K. It still had all the original cross hatches despite every compression ring having been broken for who knows how long.

Ball hone--- Sounds like a bad idea... And most likely a MAJOR contributing factor here.

polizei · 10-15-2008, 08:43 AM

Thank you all for your replies. I called Troy at EBS, and he indicated that it would be $150 per cylinder to get them re-plated ($900 in total). I believe it may be cheaper to just find another set of jugs that are already measured and honed properly. Ben, I'll keep an eye out for a broken oil ring. Do you know what would have caused that?

Should I replace all of the top end gaskets again?

dtw · 10-15-2008, 08:46 AM

If you've got CE head gaskets, I'd replace those - though you might hear others that say 'nein'. Return tube o-rings should be fine, and you can probably salvage the thrust plate o-rings and gaskets if you are careful. New intake and exhaust gaskets, though, sorry

polizei · 10-15-2008, 08:48 AM

Quote:

Originally Posted by dtw

If you've got CE head gaskets, I'd replace those - though you might hear others that say 'nein'. Return tube o-rings should be fine, and you can probably salvage the thrust plate o-rings and gaskets if you are careful. New intake and exhaust gaskets, though, sorry

Not what I wanted to hear, but I want to do it right.

polizei · 10-15-2008, 12:29 PM

Could you guys elaborate some more on how a ball hone would damage the cylinder walls? Is it that Nikasil is a softer metal than what most cylinders are made of?

304065 · 10-15-2008, 02:39 PM

There's a huge thread in the archives on why you should not dinglehone Nikasils.

mb911 · mb911's Garage

Quote:

Originally Posted by polizei

Thank you all for your replies. I called Troy at EBS, and he indicated that it would be $150 per cylinder to get them re-plated ($900 in total). I believe it may be cheaper to just find another set of jugs that are already measured and honed properly. Ben, I'll keep an eye out for a broken oil ring. Do you know what would have caused that?

Should I replace all of the top end gaskets again?

it happens in the ring compressing and then the installation of the piston in the cylinder. it happens more often then you think

930gt-40r · 930gt-40r's Garage

Im no expert, but I've been bringing my parts to Verdan tool for a long time and they have earned my trust through many good years of service to other engine builders- they honed my cylinders with the "dingle-berry hone." But from working with dirt-bikes and Go-karts back in the day I do remember that were diffrent types of hones for diffrent types of cyls. They offered silicon-oxide, aluminum-oxide, etc... Long story short we used to hone the dirt-bike nikisil stuff if that is of any help. I just believe that when you hone these you are just to give them a slight "scratching", not go nuts with it.

930gt-40r · 930gt-40r's Garage

do I need to hone this?
This is the thread that Henry went above and beyond the call of duty to make sure that everyone was turned against honing. I can agree and not agree with it. If someone doesn't hone very much then the chances are they shouldn't try it on Porsche cyls. If you are a machine shop that knows to be verrrry light with it then maybe ok. This is a great thread though and I definitely recommend it.

polizei · 05:29 AM

Quote:

Originally Posted by mb911

it happens in the ring compressing and then the installation of the piston in the cylinder. it happens more often then you think

Is there anyway to test whether they're broken before reassembling the engine?

Thanks for the link, Kris. From reading the thread, it sounds like honing a nicasil cylinder with a flex, ball, or grape hone results in premature ring wear, but I didn't read anything about it preventing the rings from seating or otherwise causing oil to leak into the combustion chamber. If the rings just haven't seated, that's a different story. Can someone explain how using such a hone causes oil to leak through?

les_garten · 10-16-2008, 05:35 AM

Quote:

Originally Posted by polizei

Is there anyway to test whether they're broken before reassembling the engine?

Thanks for the link, Kris. From reading the thread, it sounds like honing a nicasil cylinder with a flex, ball, or grape hone results in premature ring wear, but I didn't read anything about it preventing the rings from seating or otherwise causing oil to leak into the combustion chamber. If the rings just haven't seated, that's a different story. Can someone explain how using such a hone causes oil to leak through?

The other issue with Nikasil is that re-ringing has a significant instance of rings not seating. BMW motorcycles were notorious for this.

polizei · 10-16-2008, 06:26 PM

Henry at supertec was kind enough to take the time and give me some direction over the phone. He said that given the quantity of oil being burned, if the rings were the problem the spark plugs should be wet with oil, but we didn't find any oil residue on them. He suspected the turbo as others have indicated, but the compressor outlet and the charge pipe had no traces of oil. Could it be that oil is being leaked out of the turbo into the exhaust outlet and being burned by the turbo? Any other thoughts/ideas?

930gt-40r · 930gt-40r's Garage

If your rings are not bad and your plugs look fine, you need this part and plumb it back into the breather cap at the top of the motor since your oil tank has no provision for a turbo oil return.

les_garten · 10-17-2008, 01:15 AM

Quote:

Originally Posted by polizei

Henry at supertec was kind enough to take the time and give me some direction over the phone. He said that given the quantity of oil being burned, if the rings were the problem the spark plugs should be wet with oil, but we didn't find any oil residue on them. He suspected the turbo as others have indicated, but the compressor outlet and the charge pipe had no traces of oil. Could it be that oil is being leaked out of the turbo into the exhaust outlet and being burned by the turbo? Any other thoughts/ideas?

When mine was blowing past the seals it leaked across both sides of the Turbo. It is possible it may only leak into the hot side as you mentioned.

930gt-40r · 930gt-40r's Garage

Les- So did mine on both sides- but it would make sense that the hot side would be the weaker link. Also- if it is not blackening the plugs, it indicats that wherever the oil is burning, it is bypassing the motor completely. I bet if he cut his muffler open he would have a few quarts stuck in there.

mb911 · mb911's Garage

yeah tend to agree. Mine almost could use a scavange pump as the oil sump can't keep up at idle. What do you guys think though are the turbo seals now shot or can he get by with just the pump?