924Board.org

[wdb]

pull your spark plugs, if your burning oil in the cylinder they will be black. if they are clean ,its your turbo

[TroyDest]

Hey Dad. That canister you mention on the driver's side is the oil separator. It acts as a breather and lets any oil drain back to the pan. They do get plugged up and it could be your problem. You can temporarily eliminate that possibility by removing the hose that goes to the air cleaner and letting the vapors vent to the atmosphere. Cap off the hole in the air cleaner so you don't suck anything into it. Also, if you have the aluminum canister, look for a later black plastic unit. They have a better drain. You can clean out the canister just by filling it with your favorite solvent (gasoline) and shaking it. There isn't any filter material inside to worry about.

Check your rings by doing a compression check. First dry, then wet with a couple tablespoons of oil put in the sparkplug hole. If the pressure comes up considerably, your rings aren't sealing very well.

Good Luck, Troy.

[clhughart]

I'll have to get back to you on the color of the oil. The last time we changed it (approx. 2500 miles after the rebuild) the oil looked pretty good. I'm not exactly sure what you are saying about particulate since I assume the oil filter would get anything very big. The oil was discolored but didn't appear to be unusual.

As far as the rings, we got them from Total Seal, but they are not the gapless rings. I assumed this is what you are talking about. We did buy crome rings but they were typical rings with gaps, and the oil ring type was the two small rings with the spacer between. They didn't look like what came out of it but they looked like rings I have used in other engines.

Disclaimer: As stated before, I need to qualify my statement about being a mechanic. I am not a mechanic, but I usually do my own mechanic work most of the time, usually due to necessity and because I don't trust a lot of shops. Don't claim to be good at anything; just satisifactory most of the time, except maybe this time. But after all, how hard is it to put together an engine after you have the head work done by a qualified machine shop? The hard part is getting all the "Stuff" back on the engine.

Does anyone know if an engine hasn't broken in by 6,000 miles, will it possibly still break in?

[clhughart]

This message is to Zufflen. The color of the smoke is blue. My question to you is, where is the deceleration valve on an 82 924 turbo? I looked in the Haynes manual and saw reference to one but I really don't know what I'm looking for. I assume this engine does have one? (It is a 5 speed.) With all the things on these engines, it is possible we hooked it up wrong, but I don't know where to look. The manual didn't show a picture.

[numbers]

Hey cl, if you had valve guides replaced as part of the rebuild, and that is when the problem started, Bingo! The head guy probably left a little too much clearance in the new valve guides. Not likely that the turbo seals were working before the rebuild, and then just happened to fail during the rebuild.

[wdb]

I havent removed my valves so I dont know if this info applies to the 924. If you take an old chevy head apart the top of the valve stems will be mushroomed . If you dont grind down the deformed metal it will score the valve guides when you pull the valves out of the head . you mentioned the mechanic said a few of your guides were OK and didnt replace them. I bet they werent as OK as he thought. what did the plugs look like .

[Rick MacLaren]

So have ya found out anything new yet? No tragedies?

[clhughart]

OK, here's the latest. We ran a compression check and all the cylinders had 120# - exept number 2 cylinder which only has 40# (uh oh). That spark plug had oil/carbon on it. We checked the valve clearance and it was OK so my guess we broke a ring or something. We added some oil inside the cylider which raised it to about 75#. My question now is, is it possible that this cylinder just hasn't seated? Would it be that low if not seated, or is it more likely a broken ring? If it was a broken ring, it doesn't look like oil would have raised the compression that much.

Also, even if it was a broken compression ring, would that cause it to use oil? It looks like the oil ring would still swipe the oil away and keep the oil out of the cylinder.

My son (crazyme) is going back to college this weekend and I guess he'll keep driving it until Christmas break. (Uses about a quart of oil per 400 miles.) When we rebuilt the engine, we bought the head gasket set from Porsch (around $200 I think) but this time we'll only need the head gasket. NAPA or other stores don't show a listing for a head gasket for the turbo model. I have always liked felpro head gaskets but couldn't find anybody with one for the turbo. Any suggestions out there on other acceptable brands, or where we can get one?

OH, one other question. We bought the rings from Total Seal (but were convention rings, not the gapless rings). We originally had problems with them in that you could see past the rings between the rings and the cylinders. We sent them back and they made them over and we checked all the new ones and they looked good, but if they weren't perfect, this could also be our problem. Anybody else out there had experience with the Total Seal brand? Can you buy rings for just one cylinder?

[wdb]

if the rings have broken there will be pieces of the rings in the oil pan ,maybe you could get one of those telescopic magnets from a parts store and fish it through the oil drain plug and see if there are any pieces of rings in there . its possible for the new rings or rebuilt head to have failed but I would think there still good . one possible cause for low compression and burning oil is a leaking head gasket . pressure is lost and gases and oil mist are drawn into the cylinder . you might try adding 5-10 pounds of torque to the whatever toque setting you used to torque the head bolts and try tightening your head bolts in the proper sequence . try NOT to exceed the torque spec window .I forget what the specs are. then do a compression chech to see if that fixed it .

[Rick MacLaren]

Not meaning to be nozy, or intrusive, but I would personally advise that the son not drive the car.

(Heavy German accent: "Sir, zis iss a newly rebuilt Porsch-ah engine, and you do not fuking viss it!")

From your description you've obviously spent a lot of money on new parts, so why risk your investment? Make him take a bus until the engine is running properly. Make up some lie like "It builds character" or something. Tell him he needs to walk more and get into shape.

I hope WDB is right! But compression tests do not tell the whole story. And if a compression test is done, and the head isn't torqued down, won't you see or hear air (at very high pressure) escaping from the breach or gap between the head and the short box? I dunno. I think also if the head had problems, you'd be burning white smoke, not oil, but I'm no expert.

A leak-down test will give more data. Popping the head and having a look is good. You can also drop the oil pan, filter the oil through a tissue, and have a look.

Here's a worst-case scenario ONLY from the depths of my imagination. It's hard to diagnose with such scant information...

Earlier, I thought there was something wrong with this motor when the smoking problem first appeared. Especially after a rebuild! There is NO reason why a newly rebuilt motor should have smoked in that fashion. I can see a 'puff' of smoke when the turbo kicks in, but not this crap. You should find a new rebuild burns cleaner than normal after about 3000 KMS.

My paranoid intuition is that the rebuild procedure had two vital steps reversed. So here's the most important question: Did you (or your machine shop) try to fit the cylinder rings to the measured diameters of the pre-existing (i.e., worn) cylinder walls? (I suspect 'Yes'). If so, was the factory cross hatching still visible? (I suspect 'No'). Or did you bore the cylinder walls (complete with nice cross-hatching) to fit a set of matched, new piston rings? Put in a less wordy manner: Was there a rebore?

Cylinder walls can be rebored perfectly to each overbore spec. The tactic in most competent machine shops, when a rebuild happens, is to BUILD THE CYLINDER WALLS TO SUIT THE RINGS AND PISTONS, not the reverse! Were these the same pistons that were originally in the car? Or new pistons? I can see this with old pistons, cause they can warp in an oblong fashion over time, along with the cylinder. I'll explain later...

First, I don't know how many miles you have on the rebuild, but if you broke in the engine properly, and are now at the 3000 KM mark, there's no reason for the seating process to be incomplete. But I suppose anything is possible. Still, compression variances like this are bad, really bad. The variance in compression across the driveshaft causes uneven forces to be acting lengthwise along its rotational axis. Not exactly to spec. It also increases the chance of a ring shaving off small portions of your cylinder wall, equally 'not good'.

Second, yes, you COULD buy rings for just one cylinder. But why? It's simply not worth it, or wise cause you're in there anyway.

So why the screw up?

The problem with the rings should have been the first indication. I can't see any competent parts person providing undersized rings, but again, it's possible. So the onus of responsibility comes back to the rebuild partners or engine building shop.

As I said earlier, I suspect you or your machine shop measured the cylinder walls and then bought rings to fit. This is a reverse of the more safe option of reboring the cylinder walls to fit a matched set of rings. That said, what is done is done.

Who measured the ring chambers? From where were the measures taken? If it was a digital instrument, was it RECALIBRATED between EACH measure? Even if it wasn't digital, was it CLEANED of debris between all measures? Were the measures taken along multiple axes? Or just one axis?

Sorry I can't be more optimistic. But you've got a GREAT opportunity here to do a simple rebore and match up pistons AND rings to the cylinder and have a great engine. Alternatively, if there's a bright guy out there who knows of a good reason why the compression on this cylinder is off, it'd be great for you to have a nice inexpensive solution. I don't trust putting in new rings on one cylinder, but maybe you can get 50,000 KMS out of such an arrangement and not drive it hard, but I dunno. For the price, and considering you have a nice new crank, I'd write this off to experience and save the good parts for a nice new rebuild. Save the head, save the crank, save all the other work, and drop $1000 on the bottom end. Good luck.

I've got a Mahle parts catalog. Don't screw with off brands. Get Mahle. That's what Porsch-ah used.

[ This Message was edited by: Rick MacLaren on 2002-08-25 00:32 ]

[wdb]

did a little reading and learned that uneven compression can cause your engine to burn oil , book did not detail the exact mechanism .so its possible that the burning oil is a side effect of the uneven compression.
there are 4 possible causes for the uneven compression .
1 cylinder bore wear. - you said the machine shop honed the cylinders , they would have checked the wear and reported excessive wear .
2 problems with the rings - broken rings worn or broken ring lands ( the grove the ring sits in ) the rings were installed wrong ( upside down depends on type of rings used ) I think you would have noticed if the rings groves were damaged when you installed the rings
3 the valves on the # 2 cylinder are not sealing the cylider - burned, or not adjusted right , or BENT the 931 is an interference engine isnt it . was there a reason for the rebuild . loosen the adjustment for the valves on the #2 cylinder so your certain that the valves are not being held open because the adjustment screw is in too far .
4 the head gasket is leaking - its possible there was dirt in the threads of the head bolts and that gave you a false torque reading, try retorque the head bolts .

I would think the most likely cause for the low compression would be 3 or 4 the valves or the head gasket . if the head gasket is the problem you oil has been diluted with gasoline and should be change so your new bearings dont fail. hope this helps

[Rick MacLaren]

I agree with WDB on the first three counts. Still can't see how you'd burn dark smoke without white from coolant. But I guess anything is possible.

Elimination of WDB's option #3 is possible with a leak-down test. If a leak-down test showed excessive leak on #2, then you've got ring problems. If not, you can look to WDB's option #3 as a good candidate, and the same with #1 and #2.

WDB: The reason I'm not looking to the head as a cause is that I understand there was a rebuild done to the head, and the short block seems to be the less-overhauled component with the most used parts. And re: #1, you said "you said the machine shop honed the cylinders, they would have checked the wear and reported excessive wear." That's a solid assumption in a perfect world, but I can't assume the world is so perfect.

I checked with a buddy of mine and he said under very cost limited circumstances, you could replace rings on one cylinder. But, he noted, they'll typically, on the 944 Turbo anyway, rehone and recoat the cylinder walls anyway. So if you do it for one, why not the others? Again, only cost can really hold you back, and it's not that much. You've still got the engine out of the car by then, and you still have transported it to be machined, so what the hell difference can a few hundred make? Anyways, to each his own.

Haynes, if my buddy is not mistaken, from 944 Turbo experience, says you gently bring the car up to boost a few times, then up to full operating temperature, stop the engine. Check for leaks and other mishaps, and the rings will seat within break in, if not before. It's very unlikely that the rings aren't seated after fully working through the Haynes procedure. Besides, if they aren't, why not? It's still trouble.

Just for curiosity sake, did anyone, by chance, tear-ass drive the car during the break in period?

$0.42 CDN: If it were me, and I didn't have a shop and a lot of time on my hands, I'd just take it to Porsche, save the engine, pay the Piper, and make the best of a bad situation.

Instructions for Porsche:

1. Leakdown test
2. If leakdown inconclusive, diagnose.
3. Substantiate diagnosis.
4. Make recommendations.

Leakdown
Diagnosis (If necessary)
Back up for diagnosis (Extra labour to prove their hunch)

If WDB is right, you're looking at an added, what, $500 parts and labour on top of $550 for a solid diagnosis? If not, you're looking at, what, the cost of 1 year of Junior's tuition?

Don't drive it.

[ This Message was edited by: Rick MacLaren on 2002-08-25 09:14 ]

[wdb]

about the head gasket leaking oil and not water . if the mating surfaces of the block or head are damaged by either using a drill or grinder with a wire brush to remove the old head gasket. a channel can be worn from the cylinder to the oil drain ports that is barely noticable, smooth and rounded where the deepest part is only a couple thousanths of an inch. or ( done this personally ) using a putty knife to scrape the old gasket off,accidently digging into the aluminum head of an old chevy. that was a bad day it seemed everything went wrong . had socket wrenches sticking out of holes in the sheetrock of my garage . anyway ,since the oil drain ports on the 924 engine are at the back of the engine and not near the #2 cynlinder this is not likely in this case. so retorqueing the head bolts is prolly not neccesary . 1 posible cause eliminated - next.

[clhughart]

OK, here goes my response again. To those interested, I can't tell my son not to drive the car. He bought the car, he is paying the insurance and he paid for the rebuild. He's my son but in his 20's, he's in the national guard, and knows how to take care of things. As far as running too hard during breakin, I really don't think so. He knows what it cost and if anything, I'd have probably got on it before he did. From reading some of these e-mails, I have a feeling I'm outclassed when talking about what's another $1000, or $500 or whatever. To me, that is a lot of money.

Here's the story of the rebuild. Like I said before, I'm no mechanic but I've rebuilt a few engines. This engine was torn down originally because of a blown headgasket, and my son decided to rebuild the whole thing since we didn't know the history (or mileage since, as apparently many others, the odometer doesn't work). The head was warped and had already been shaved to the limit, so we took one off of another car and had it rebuilt. The block itself showed no wear at all at the top; I took the block to the machine shop and they checked the block for roundness and wear (I watched them do this in all cylinders, at probably 90 degree axis checks, but no it wasn't cleaned and calibrated after each cylinder.) I couldn't see having it bored; I've never had to do this before if everything looked this good. They did the normal hone like I've seen done many times. We put new bearings, rings, etc. I mean, come on how hard is it to put together an engine as long as you have the right parts, watch the torque spects, etc.? The hardest part is getting this thing in and out of the car with all the stuff hooked up, right?

I suppose it is possible we broke a ring putting it together. I know I did this years ago when the ring compressor lifted off the deck and the ring popped out about the time I knocked the piston down, but this motor seemed to go to together good.

Regarding rings, no there was no original cross hatch. The shop honed the block (not rebored), I bought rings from another source, I put each one in the block to check the end gap. Pistons are expensive (in my book) and I avoid boring and new pistons when I can. (Maybe this was mistake #1.) Anyway, it's always worked for me before. The reason I would only replace rings in one cylinder is because the others are already seated, they are new, and why mess with them? I might fix cylinder #2 and have one of the others screw up. From all of you out there, do you honestly think this block should have been rebored under the conditions noted above? I mean the block looked like new (except for the cross hatches.)

Pistons. They all looked good. No broken lands, and I'm sure (99.99% anyway) that we didn't put in rings on upside down.

valves. We had checked the valve clearances before my last posing, and the clearances were OK. Didn't back it off anymore since we had the proper clearance. I really don't think this is it.

I doubt the valves bent, but I guess anything is possible.

We oiled the head bolts slightly and ran them into the block before we put the head on to make sure nothing was blocked, corroded, etc. We retorqed head after a short while (probably 1000 miles), and have retorqued since. They did get tighter on the first time but have not had any movement since.

The machine shop checked the deck surface.

One last comment. Not loosing any water. No steam in exhaust. No visible water in oil or oil in water.

I guess, we're into having to tear this beast down again. I kind of think something happened to the rings; come to think of it, I think we did loose a screwdriver somewhere. Thanks for the information, and we're still open to suggestions.

Oh, and anybody have any comments on where to buy a head gasket?

[Rick MacLaren]

I have a head gasket in the package, still shrink wrapped with the original part number and label, from my 931 rebuild. Write me and we can work out a deal.

Ok. I read your message.

Good on him for paying for the rebuild!

Anyway, if the factory cross hatching was not visible at the time of rebuild, I think that is pretty telling stuff. True, it MIGHT only be a thousanth of an inch, or it could have been MORE! And you did say you had trouble with the rings not fitting right originally, yes? I think it means the cylinder 'might' have needed more than just a re-honing, personally, and I think it might have needed to be re-bored.

Now, if your rings were the same size across all cylinders, then this means the diameters (taken at 90 degree intervals, which is the right way to do it), of the troubled cylinder should be only a fraction greater (like 1/10,000) on that cylinder than the other three. This is easily verifiable now...with the engine apart. But it should have been obvious to the engine builder if it were troublesome.

When my 931 was torn down, and remember, my engine looked like a granade was dropped inside Piston #2, the cross hatching was still evident - same with #1, #3 and #4. If yours was gone, man, that engine had real problems prior to the rebuild effort. Lack of oil? Who knows. But honest, that's not so good, IMHO. It also might suggest, especially if it was significantly more on one piston than the rest, a clogged oil line.

That said, and I don't have a lot of experience with rebuilds, I wonder if the wear on that particular cylinder was just too much? I honestly don't know. But that's my suspicion.

I'll comment where apt:

You said: "This engine was torn down originally because of a blown headgasket, and my son decided to rebuild the whole thing since we didn't know the history (or mileage since, as apparently many others, the odometer doesn't work). The head was warped and had already been shaved to the limit, so we took one off of another car and had it rebuilt."

Ok, so if the head gasket blew it withstood some heat. Heat can cause an engine cylinder to become oblong. And other crap too...

You said: "The block itself showed no wear at all at the top; I took the block to the machine shop and they checked the block for roundness and wear (I watched them do this in all cylinders, at probably 90 degree axis checks, but no it wasn't cleaned and calibrated after each cylinder.)"

It should be cleaned and recalibrated after each cylinder. Why? Dirt can be as much as 10 thou in size. With digital calipers this isn't a problem. But it should be cleaned nonetheless. Varsol.

You said: "I couldn't see having it bored; I've never had to do this before if everything looked this good."

Yeah, but the small question I have is "Just how 'good' can it look when the cross hatching is worn away?" It's certainly not optimal. I thought one of the criterion for whether or not to perform a re-bore of the cylinders was to examine the cross hatching? If the cross hatching is gone that's a first necessary prerequisite. But it's not the whole story - you 'can' rehone the cylinders and not worry about the miniscule difference. But I think it just depends on how much you think you can tolerate.

You said: "They did the normal hone like I've seen done many times. We put new bearings, rings, etc. I mean, come on how hard is it to put together an engine as long as you have the right parts, watch the torque spects, etc.?"

lol! Well, it's easy stuff when you consider each individual task in isolation, but it's when you put them all together that an engine rebuild becomes a complex administrative task.

You said: "The hardest part is getting this thing in and out of the car with all the stuff hooked up, right?"

Yes - Can't get it out without 2 guys, a hoist and muscle.

You said: "I suppose it is possible we broke a ring putting it together. I know I did this years ago when the ring compressor lifted off the deck and the ring popped out about the time I knocked the piston down, but this motor seemed to go to together good."

Or the ring wasn't seated in the piston properly at installation time. This happens with 944's.

You said: "Regarding rings, no there was no original cross hatch. The shop honed the block (not rebored), I bought rings from another source, I put each one in the block to check the end gap. Pistons are expensive (in my book) and I avoid boring and new pistons when I can. (Maybe this was mistake #1.) Anyway, it's always worked for me before. The reason I would only replace rings in one cylinder is because the others are already seated, they are new, and why mess with them? I might fix cylinder #2 and have one of the others screw up. From all of you out there, do you honestly think this block should have been rebored under the conditions noted above? I mean the block looked like new (except for the cross hatches.)"

I guess that's where I would have put new pistons and done the rebore. But lots of guys use your tactic and have no trouble. Again, my builder guy advised the rebore to match the rings I purchased. It changed the whole method by which my engine got rebuilt.

You said: "We had checked the valve clearances before my last posing, and the clearances were OK. Didn't back it off anymore since we had the proper clearance. I really don't think this is it."

Me either. But until the diagnosis is done anything is possible.

You oiled the head bolts? No. Do not oil head bolts. Porsche recommends they be put in without oil, as I understand. This strengthens WDB's head hypothesis temporarily. But I don't think it's conclusive.

Best Guess

If the cylinders turn out to be the problem, the troubled cylinder needs:

(a) To be rebored to the next size up of rebore;
(b) New rings and one (1) piston;

The next size up of Mahle piston is precisely the same weight as the stock sized Mahle piston, so you don't need to worry about weight. But again, if you've got it out of the car, might as well go the nine yards.


[ This Message was edited by: Rick MacLaren on 2002-08-27 04:17 ]