dcdrechsel

There is a real need for the book .I would like to buy it-soon .
Dave

nick49

On a conventional motor, I'd say ring seal is OK and your compression is as well. I'd question your gauge and method of taking the readings. Your maximum differential is 4% or less and that is in the range of a very good performing motor. Generally ring seal will not deteriorate uniformly like this.

If things are getting oiled up on a couple of cylinders, I'd suspect vg seals first on a conventional motor.

I've never been inside an M96, so as pointed out in earlier posts, things are different with them. If power is good and drivability is fine, I'd keep going and play things out a week at a time. A hotter plug might work on the cylinders that are oiling. The motor most likely won't get better, but it may not get worse either.

After rereading your post, I'm questioning your leakdown numbers. Average 25% leakdown on all cylinders, and the car runs really well? Low compression too, and it blows oil only on one bank?

Any possibility the AO seperator is askew, or it's an external problem pusing oil in the intake?

Does the car seem to pull has hard as before? I'd think the large leakdown and low compression numbers would make the car feel pretty underpowered.

No expert with the M96, but some things to think about. GL!

logray

dcdrechesel. Regarding bore/taper measurement:

"As there aren't any published specs for the lokasil bore that I am aware of, I'd say anything over .002" ovality is too much. Most of the blocks we get here for re-working have at least that much and upwards of .005-.006".

The bores are finished straight and that's how we do them. We did tests years ago and found that trying to use torque plates and simulate actual engine parameters was a crap shoot. You get the best results with a bore as round as possible within .0005". "

- Charles Navarro

From https://rennlist.com/forums/996-foru...000-miles.html

I'm pretty sure after 75k miles, fitting new rings without re-boring is going to be a band aid (if the rings will even seal). And then after what I've read and understand about the 3.4L cylinders it is only a matter of time before they oval.

Although If I do end up pulling them and the bores are still within tolerance, I will do a backflip and marry my dog. Only then perhaps might the topic come up of replacing just rings and perhaps a piston or two. Of course, who has the specs for pistons?

Porsche does but isn't telling us - your guess is as good as mine what tolerance range x is:

"99610305118 piston tolerance range X"

Damn you Ferdinand!

edit:

actually they do give us weights in grams...

996 103 051 18 piston tolerance range X -01 6
number plate - 544 -547 G

996 103 051 19 piston tolerance range X -01 6
number plate + 547 -550 G

logray

I am going to redo the numbers in a couple weeks as I also suspect something is strange considering the symptoms. I would have expected different results based on what the visual keys are giving me. My compression gauge is old and my leak down tester is cheap. I am going to invest in some better tools in a couple weeks and repeat the test. I'd rather have reliable results to base my decision on, if I'm going to drop another $5 grand or more on the engine.

Well seeing as how the car is on it's third AOS, this latest one was brand new from Porsche, fitted while the engine was removed, and all of the hoses and tubes replaced. Also the problem with the soot was present before the valve job. When I pulled the heads both intakes had the same amount of oil residue on them. And recently I tested crank case vacuum with a slack tube manometer and it was steady at 5 inches of water drawn indicating normal vacuum.

It pulls much harder than before the valve job, but not nearly as hard as it once did.

nick49

Wondering about the quality of the valve job. I've seen shops use a Serdi cutter improperly and actually make a worn valve to seat seal worse after their job. Seen machine shops do poor work as well. Has nothing to do with the overall reputation either. One tech that doesn't understand fully what he's doing and the job quality will suffer.

Some valve jobs I've done with Nuway cutters on 24 valve Superbike motors would take days to get right where I was happy with the seal, the contact relationship of valve and seat.

Was valve to guide clearance checked before and seal at valve to seat interface after the job?

logray

The valve to guide clearance was checked on all guides before the work. I have the numbers somewhere written down. 5 of the guides in the bank 1 head were so far out of tolerance they were replaced.

I'm not aware of the valve to seat being checked... they were pressure / vacuum tested after the job and were found to be good from what I was told.

If I do pull the heads again, perhaps I'll take them back to the shop.

speed rII

logray, just do what I did, stop worrying so much

My car stil makes (sometimes) that od starting noise, but who cares.

Just drive it, and when/if the time comes, build new engine for it. Or trade it to 997

logray

Thanks speed rII. Trust me I'm enjoying the car and driving it just as hard as I used to. I've invested a lot of time and money into it recently and I don't want to see all that good hard work and money go to waste. Certainly I've got some time to think about this and keep driving the car, because the oil and soot is not going to cause an immediate problem.

Also as to nick's question, here is what the shop gave me. These are all after measurements:

intake all between: .0012 and .0020
exhaust all between: .0015 and .0025
stem height: 1.695 to 1.702
valve stem diameter: "negligible wear"
new valve seat angle: 30 - 60 - 45
vacuum/pressure test: good
new customer provided valve seals installed

I also personally watched them take some of the measurements. One of the exhaust guides below #2 cylinder was so bad, we put a valve in and could wiggle it around quite a bit.

nick49

Your specs look ok. A good fail safe way to check the valve face to seat seal is to fill the port with solvent above the valve level, then direct a stream of compressed air around the valve perimeters on the combustion chamber side. Any small bubbles on the port side will indicate leakage. Sometimes (rarely) any very minute leakage may improve as the valves peen the seat surface. This could depend on the hardness of the seats and valve face material and the method of cutting or grinding the seats. Personally, I like zero leakage and will work at it until I get a 100% seal.

logray

Thanks nick49 and everyone for the input and suggestions !!!

logray

Had time to do another leakdown and compression test after some new tools arrived. Just as a tip for anyone considering buying a Harbor Freight leak down tester. DON'T DO IT.

Engine up to operating temp, all spark plugs removed, fuel pump disabled, oil filler cap removed, throttle flap all the way open. Engine rotated to TDC for each cylinder being tested. Survey says!!!

leak down (air through filler cap) 1 - 7.5%, 2 - 7.3%, 3 - 7.6%, 4 - 7.4%, 5 - 7.4%, 6 - 7.4%
compression 1 - 150, 2 - 150, 3 - 149, 4 - 149, 5 - 150, 6 - 149

I'm pretty confident in the leak down numbers at this point, performed at 100psi and with a $100 tool.

As for the compression, I suspected my old gauge was bad so I also sourced another one. UNfortunatley I got exactly the same numbers with the new gauge. Since I didn't have a baseline on a rebuild engine with either gauge I tested the 8 year old Dodge and saw numbers in the 180's.

I didn't bother oiling the cylinders to see if the numbers went up. Yes the piston rings are worn, yes they are sucking oil into the combustion chamber, and yes it is rapidly coating the spark plugs with oil as well as the entire exhaust system below it including the O2 sensors.

I suppose it is even possible the professional valve job did not attain 100% valve seal despite their post-job pressure/vacuum testing, which I will most certainly test if I do pull the heads again (thanks nick's tip which I also recall seeing on wheeler dealers using gasoline). But I doubt it, considering the leakdown test did not detect any leakage past the valves.

With such even wear I am considering gambling again even after reading ad-nausea about the shortcomings of lokasil, the thin walls, and ovality on high mileage engines. The gamble would be not touching the cylinders and just replacing the rings, and of course bearings, and other case/bearing carrier cracking while you're in there items. I guess I would have a good idea if this might work if I measure the cylinders wear. Then of course since they will probably be out of tolerance, I would have an engine all in pieces knowing I don't want to spend $10,000 on a car that's not worth even twice that.

This sucks. Really really sucks.

I ran the numbers and an LNE 3.4->3.6 rebuild done the right way including crankshaft balancing, magnaflux, JE pistons, Nickies, and all new gaskets and ARP hardware will run me $7000. That's assuming I don't find any major problems on tear down (rods/shafts ok). That's on top of the $3500 I've already spent on the heads and other ancillaries ($1500 of which was recouped). So the total spend would be about $10,000. On a car that might be worth $18-20k ????? Ludicrous !!!!!! Of course, possibly the car would be worth less given those low compression numbers.

I could just do rings for about another $2000.

I could ignore it for free.

I could buy a used engine for around $5000 and gamble even more.

It's a shame the car is running so well. It is hard to ignore the soot spewing out of the right tail pipe from bank 1.

Does anyone have a used 1999-2001 3.4L engine for sale? LOL.

Anyone have a good short block for sale?

jrgordonsenior

3.4 complete or short block motors in rebuildable condition are far & few these days and getting quite expensive. My advise would be to yank it apart and do the bottom end before it implodes leaving you with a un-rebuildable core. You're halfway there already, finish it....

dcdrechsel

Not so sure reringing without some cylinder treatment is an option .Something has caused the rings to degredate.It would seem logical that if Hartech can bore these blocks someone in the states should be able to do it .Of course that leaves the pistons and rings sourcing issue to be sorted out .Hartech might be a option there .

Ubermensch

I don't think replacing the rings makes much sense. If they cylinder is out of round and the rings are worn it's probably where the diameter of the cylinder has been reduced. That means your blowby is occurring where the gap between the cylinder and the ring has expanded. Putting new rings that still don't mate with the enlarged diameter wouldn't seem like a meaningful solution.

-Shawn

fpb111

spend the 7k and enjoy the car for another 10 years.