Top end rebuild 3k later smmoking, advice.

[ganun]

3k miles after a valvejob the 3.2 smokes like a battleship grade smoke screen generator. Came on rather quickly over several days.

The car had new guides, rockers, shafts. cams, .... 3,000 miles ago.
SO today I pulled the plugs, all looked great except #6.


I think the intake valve seal is shot, Yes?
My " boss", she says the shop should do it for free, I thought that would be great but being a bit of a softie I though negotiate a price.
The engine is sooo clean, I would think a days job. Drop the engine, valve covers, chain cover on that bank, spocket, chain, remove the cam housing, then #6 head and replce the valve seals.
I noticed that they are available at prices ranging from 1 buck to 10 bucks apiece. Humm wonder if they are all failure prone or maybe a poor install?

[Lapkritis]

Not necessarily a valve stem seal. A stem seal is more likely to smoke at idle and on deceleration when vacuum in the manifold is high (also in the intake port sucking against the stem seal). If this is smoking continuously it may be a ring/piston. I would hope for a stem seal.


On a related note, a tool exists for filling the combustion chamber with air from your garage compressor allowing for valve spring/stem seal service without disassembly you describe. Makes the job cake.

[ganun]

Thanks,
I forgot to mention that it starts a few seconds after being at idle, once running there is no smoke visible, so yes at idle there is max vacuum and max smoke.

[Nostril Cheese]

Did you do a compression test on #6?

I'd also suggest using Bosch Supers in your engine rather than NGK.

[ganun]

Oh darn, absolutely should have, Thanks for the reminder!
Those NGKs Iridium even after all that oil never misfired, it amazed me! After seeing that plug I thought it should have been running on 5 cyl.

[Walt Fricke]

If you go with the seal theory (hard to imagine a new one would go bad that fast), the shop absolutely should be able to do the intake pretty quickly (equating to pretty simply). You can just fill the chamber space with compressed air with both valves closed, or you can feed string in through the plug hole with the piston depressed, and then move the piston up to TDC or close to it to compress the string up against the valve head. Either way, this allows use of a readily available in situ valve spring compressor for pulling the springs off, replacing the intake seal, and putting things back together. A shop which does Porsche work should be able to do this. I've done it at the race track to replace broken springs.

But before doing any of this, do the compression test, at least on the oily hole and a neighbor. The numbers should be pretty close if the rings are equally good. And be sure to listen for where air is leaking out. You should hear zero through the intake, zero through the exhaust, and always some through the engine breather (where some always leaks by rings). If a ring issue, you should hear a louder hissing on the leaking cylinder.

This won't test the valve seal, but will help you sort out what is what.

Short term, I'd just clean or replace that plug, put it back in, can check it after some reasonable amount of miles.

Does anyone draw any inferences from the fact that the discoloration on the plug screw threads extends markedly farther down on the sooty plug than the other two?

[ganun]

Thank you Walt.
What should I expect on a simple comp test cold? 150s or 180s

[Walt Fricke]

I've not seen more than 135 or so, but I am a bit above 5,000 feet. And I usually forget to open the throttle all the way when cranking.

It isn't the absolute value which is especially useful, though. It is the comparison. 130, 130, 100, 130,130,130 - hmmm. If you don't have a leakdown tester (they are not expensive), you can determine where the 100 is leaking more than the rest by listening if you can make a fitting to screw into a plug hole, and introduce compressed air while at TDC firing (both valves closed, piston at TDC or else the crank will turn).

[john walker's workshop]

may well be a worn guide, even @ 3000 miles. if the shop glass beaded the valve stems, that can happen. same thing can happen if the steel crankshaft gear is glass beaded. it wears out the aluminum intermediate shaft gear.

[JFairman]

That much oil on the threads and burnt oil everywhere on the business end of the plug sure looks like rings.
A simple compression test check comparison between cylinders while cranking the motor with the throttle is open will tell you, and a more complicated leakdown test with an air compressor and leakdown tester will tell you more.

If you listen in 3 different places, throttle body intake, exhaust, and oil drain hole, breather hose, or the oil tank through a hose to your ear while 100psi compresed air is being fed into the spark plug hole at TDC on the compression stroke a hissing noise should tell you where it's leaking.

Hopefully it's not rings. On some engines when it's an intake valve guide or seal the burnt oil carbon buidup will be greater on the side of the plug closer to the intake valve but maybe not on a 911 notor, I don't now.

[ganun]

Thank you all.
Compression at 160 (WOT) on all cyl after 5 cycles.
Going to the shop with x fingers.

[cgarr]

Isn't there a vacuum line around the #6 cylinder at the intake? I think it goes to the brake booster, just trying to remember.

[Walt Fricke]

I think the vacuum line comes off the throttle body. The drawing I found in a parts catalog of sorts doesn't really show where this is connected, but it has the same Y fitting vacuum extractor that the SC has. Couldn't find anything in Bentley on it.

[ganun]

I went thru all the hoses at the rear of the engine. The hoses attach to the manifold near the throttle except for the case vent hose by the oil switch. All were dry inside btw.
I'll post the results in a few days.
Thanks