possible causes for cylinder head leks and fouled plugs

[COL 911]

I appreciate any theories for the causes of these symptoms - 1987 Carrera, 117,000 mi, stock engine. Three weeks ago I noticed a 'new' leak around the exhaust outlet on #6 cylinder. It is confirmed that it is NOT leaking from the crankcase breather hose or gasket, the oil cooler thermostat, or the oil pressure switch. Inspection of topside shows all to be dry. Weekend driver, always try to run her enough to get temps up, never tracked, by me - yet...additional info from receipts: valves adjusted at 113,000 mi, ignition wires replaced 90K mi

She doesn't leak alot of oil, but now, the engine sounds louder and initial triage by well respected local tech confirmed she was missing, and # 6 plug was fouled (brown black, oil and ash). I cleaned the engine thoroughly today a ran it abit - maybe it was my imagination, but I swear I heard 'tick-ticking' from 4-5-6. No new oil apparent on the front side #6/backside of oil cooler, so that may rule out oil cooler seals. Placing my hand near the exhaust when running I felt and heard a pop intermittently- I suppose that confirms it's missing on a least one cylinder.

Can anyone suggest probable causes, could it be injector/fuel/spark related or is this a symptom that it's just my time for valve guides, etc.?

Is a leakdown test recommnded as part of the estimates so I know the possbile extent of repairs? Thanks!

[willtel]

I am in a very similar situation with my 930.

From what I understand we should pull the valve covers and verify that the head studs are torqued to specs and hope that none of the studs are broken. My car has about 68000 on it, last time I pulled my plugs all were black and filthy and I now have a sound like an exhaust leak under load. I think it just may be time to pull it apart. Let me know what you discover with yours.

[E Sully]

Good chance it is worn valve guides. My '86 engine needed the guides replaced @ 65,000.
The 3.2's are known to wear, and with your mileage if it has never been apart it may be time. Oil leaking past the guides would foul the plugs, gum up the valves, etc. Does it smoke when you take your foot off the gas? How is your oil consumption? If it is using quite a bit between changes it is time for a top end job. If the guides are worn enough you could drop a valve, and that would cause a lot of damage.

[COL 911]

Thanks, Wiltel, I'll let you know. i just found post from Vancouver 86 in JAN 2010 with good photos, much better than mine. He hasn't updated in awhile...and I'll keep searching the old posts.

[COL 911]

E Sully. Thanks, worn valve guides are hopefully my worst case scenario. She ran great up until this mis-firing started, and while the valves were last adjusted by previous owner, it was only 5,000 miles ago, but also more than a few years ago, too. If that's the case, and the engine comes out, I've started th list of things to do so often recommended on the forum. Tanks.

WS

[willtel]

Originally Posted by E Sully

Good chance it is worn valve guides. My '86 engine needed the guides replaced @ 65,000.
The 3.2's are known to wear, and with your mileage if it has never been apart it may be time.

Ed, if it were just valve guides wouldn't the oil stay inside the engine and be burned off by the combustion process?

It seems that in my case there has to be some separation between the head and the cylinder as there seems to be oil leaking from that area. I think it is pretty common on Turbo cars that run higher than factory boost (1 bar in my car) for the heads to lift if there are issues with the studs.

[COL 911]

I had the same thought Will - guess that's why my best worst case scenario could be valve guides, as opposed to broken head stud. I have slight smoke on start up, but none at idle or under throttle/decelleration. I suppose oil getting past valve guides, under pressure could find it's way out through the cylinder head gaskets, and also foul the plug in that cylinder.

Would a leak down test determine if problem is worn valve guides vs. a broken head stud, or would results be similar?

[Steve@Rennsport]

Sounds like worn guides to me. At your mileage, I'd be shocked if it didn't need new ones, based on some long-term experience with these things.

Guide wear doesn't show up with leakdown or compression testing. One must pull the lower valve covers and measure the side-play in each valve/spring assembly, however this takes some experience to assess condition.

[COL 911]

Steve, so worn valve guides could manifest by allowing oil past the stem, fouling the plug and causing a misfire AND causing a leak in the vicinity of the cylinder head? I'm worried the leak at #6 is indicative of broken head stud, in addition to probable valve guide replacement. Thanks for your opinion.

Wayne

[Steve@Rennsport]

Wayne,

Yessir, thats correct. Worn guides, in addition to compromising proper valve cooling, permit excess oil past the guide and into the combustion chamber. This can cause plug fouling, increased propensity for detonation, and reduced power.

Its easy to check for broken studs, just check each one gently for proper torque. If you have the original Dilavars, I would replace all of them when the engine is disassembled for the valve job.

[Dixie]

While it could be valves, you need to do some investigating to determine the actual cause. For example broken head studs or a loose rocker shaft. I'd pull the valve covers and check the heads and rockers. Then I'd do a compression check and a leak down test if needed.

If it provides any solace, you can rationalize it this way. If you need to replace either the studs or guides, replace both. You'll already be in far enough to replace both. And when you put the rockers back in, install the RSR seals on the rockers.

[COL 911]

I'm settling into the right searches and with the advice here, beginning to mentally organize what's needed. Valve and rocker inspections certainly - if there is a broken headstud issue, is it possible to replace them (assuming none broken off in the case) withut pulling all the P/C?

[Flat6pac]

The pistons and cylinders have to be pulled so the debris can be removed and chase the threads and broken studs removed.
Bruce

[COL 911]

Bruce, that makes sense. I'm resigned to the extent of the repairs now, after a few days and lots of reading. It's time to research the choices for materials used; Divilar vs steel head studs, types of seal materials, etc. I'm sure I'll find lots of opinions on the forum to consider and discuss with the re-builder when I pull the trigger. Thanks again to all for your advice.
Wayne

[COL 911]

I'm currently 'under the knife', the car is at the local shop with top end disassembled. 1987 Carerra, stock, 118K miles or so. Existing service records show no major services performed by previous owners. 20-50 dino oil only. Oil consumption was 1 qt every 600-800 miles, some blue/white smoke on start up and no unusual leaks until recently when # six began to show seepage at cylinder head/case junction. Power seemed ok, with exception of miss on #6, where inspection of spark plug showed alot of sooty deposit. No track, no missed shifts, although it did 'sound' louder toward the end - hard to quantify.

I'll try to get pix of components posted soon showing wear patterns . All studs OK-none broken. Heads not disassembled yet, intakes look really clean, exhaust is black and built up with soot. Trusted technician suspects valve guide wear is going to be present, as per original diagnosis.

Upon disassembly and measurement, what surprised us is the amount of wear evident on the cylinders (Mahle Nik) at this mileage. All 6 reported outside reuse tolerances, no signs of scuffing (or cross hatching, for that matter) beyond spec. Only very light scuffing on the piston skirts, rings all seem OK. Rocker arm shafts showed unusual wear pattern and rocker arm wrist pins may be out of round - meaning we need to open the bottom end, as well.

Theories are that at some time it ran hot or low on oil , but confident that didn't happen since I've owned her. Wouldn't P/C wear severe enough to exceed tolerance specs have produced secondary symptoms, like excessive smoke, etc. earlier? Aside from the financial pain, I really just want to understand more - P/C wear doesn't seem to be a common issue with engine symptoms like I experienced with the mis-fire occurring rather suddenly. Thanks in advance, and will post pix ASAP.
Wayne