Mineral spirits to dissolve carbon deposits?

[ianc]

Hi folks,

I've been having some issues with #2 fouling its plug lately. I've checked the injector and spark, so it seems it must be either a guide or oil control ring, since compression is good. I've read a few reports of this happening to people, and upon disassembly, they found that their oil control rings were just coked up and stuck in the land.

I was discussing this with a mechanic friend yesterday, and he proposed putting that cylinder at TDC, pulling the plug, then putting mineral spirits down the plug hole and letting it sit for a day or two to dissolve the deposits, then changing the oil.

I'm a little leary of that, but it sounds feasible. Any other opinions?

ianc

[BURN-BROS]

Ian, I have used diesel fuel in the engine oil to free up carbon on a wet sump system. I found that it worked to some degree but was a temporary bandaid to a real problem as the rings would continually get gummed up.
The mineral spirits would not get to all of the oil control ring unless the engine was on a stand and tilted where the offending cylinder was straight up and down.
Hope it works out for you..

[Wil Ferch]

Marvel Mystery Oil is essentually this stuff ......


- Wil

[LM3929]

Ianc

One thing you could try and havs worked several times for me is a product called "Purge" or crankcase cleaner.

Purge is sold by GM and Ford dealers and the crankcase cleaner by NAPA or one of the others jobbers .

To use it you would add it to the oil and let it run at a fast idle for 30 to 45 minutes and then change the oil and filter, you can't drive with this stuff in it

[Early_S_Man]

Ian,

Unless you have had an injector sticking in the recent past ... I don't believe it is an issue of 'coking' or sticking oil control rings. The Motronic and CIS engines normally run so lean [ they have to, or you would have a clogged catalytic converter] ... so I can't imagine what your mechanic friend is thinking.

This could be an issue on an old carbed Cadillac engine driven little and getting 10 mpg or less, but not on an '80s 911 engine! Water, diesel, MMO, Bardahl, Techron, or B-12 Chemtool could all be used in the traditional 'pour-through' treatment at 2000 - 2500 rpms to clean out the crud ... but, I think it would be a waste of time!

It is time for an engine pull and teardown, IMHO! The '87 engines were in the 'window' when the orange elastomer valve guide seals were known to cause excessive intake valve guide wear, as I'm sure you are aware.

[Steve@Rennsport]

Warren is right on,....

If the rings are indeed coked (carboned) up, only a good overnight soaking in carb cleaner (engine disassembled) will get the piston's ring lands clean.

A qualified and competant mechanic can check your guides for wear, but I'd venture that its time for a top end overhaul (valve job).

[svandamme]

water injection works extremely well to blow off carbon deposites

[ianc]

Well, the situation is this:

I bought the car about two months ago. The PO had put about 4K miles on it in two years, and very little of that in the last six months or so.

As I said, I'm seeing #2 plug fouled. I took the injectors out and brought them to Rob King at S-Car-Go, who tested them and pronounced them fine. The ignition system is basically new with new cap, rotor, plugs and wires, and I have good spark at that cyl.

That leaves guides or an oil ring. An old 914 I had had bad guides, and that thing used to billow smoke on throttle overrun. I can't see any sign of smoking on overrun with this car, plus, the rest of the plugs seem fine and I would suspect I would be seeing this issue on other plugs if the guides were uniformly worn (bad assumption?).

That leaves me thinking about the oil control ring. I suppose it could be broken, but I'm hoping it's just stuck.

I fixed the last oil leak a week ago, so will be checking oil consumption carefully. I put a bottle of Techron in the tank this AM and filled with Chevron, then took it out for a rip down Lucas Valley Rd. I'll drive it like that for awhile and see what happens. Keeping my fingers crossed of course.

Thanks for the replies guys,

ianc

[CliffBrown]

Ianc

A leak-down test will tell you if it's the ring (or not).

[ianc]

Hi Cliff,

I'm not sure how. I think a leakdown will only reveal bad valves or compression rings. Compression is OK, so if an oil ring is bad, I don't think a leakdown will show anything...

ianc

[CliffBrown]

Ianc

You're right a leak-down won't do a thing to diagnose bad guides, I think I just had a senior moment.

[svandamme]

guess you'll need one of those fiber optics scope thingies
peek throug the spark plug whole, and spin the thing up with the starter
and fuel injectors off...
if the oil ring is not good, it's going to be very , for lack of better word , oily on the cyllinder wall... i mean dripping...

just creative thinking here, someone else may comment on that idea of mine , but other than a tear down , i'm not sure what else could be tried to check that specific part...

[Steve@Rennsport]

Originally posted by CliffBrown
Ianc

A leak-down test will tell you if it's the guide or ring (or not).

Cliff:

Leakdown tests do not always tell you whether the guides are bad. All they tell you are things about valve and ring sealing, and indirectly, cylinder wall condition.

I've performed hundreds of these tests and some motors have displayed good numbers, even though you could move the valve .020-.030 sideways in the guide,...

The only reliable way to assess guide wear (in the car) is for an experienced person to wiggle the valve assemblies and measure lateral movement.

[CliffBrown]

Steve

You're absolutely right and I should have thought first before typing. We're also distracted trying to watch the Steeler's playoff game right now, my wife's from Pitt.

I do leakdowns on all rebuilds (to make sure I got things right and for documentation on the build sheet). Nothing beats the info a leakdown can give you about the upper end of the motor. I do wish we had a similar test for guides.

[ianc]

Steve,

I've heard you talk about checking the valve stem movement laterally for an indication of guide wear.

Is this something you could give a brief description of how to do, and what to look for? I might actually be able to do it.

ianc

[Steve@Rennsport]

Ian:

This is one of those things that requires a judgement call about how much sideplay is normal and what is excessive.

There is no factory procedures here since this has been an aquired skill for people in this business after many years of doing these engines. One learns by measuring guide-to-valve clearances after the engine is disassembled and factoring that against what you see when everything is assembled.

The variables are each engine's guide-to-stem clearances and where Porsche (or a shop/dealer) set them up when everything was new.

Clearly, we now know these setup clearances were different from engine to engine since not all Carrera's required new guides before 100K miles.

In short, this is something where its best to have a pro check those for you and make the call.

[ianc]

Trade secret, I see.

Would you say my assumption about not blowing smoke on decel is a good omen for the guide(s) then? I would expect if one is bad enough to foul a plug, I'd likely see it puffing...

ianc

[Steve@Rennsport]

No secrets on this one,..just plain old fashioned experience makes all the difference is making an ACCURATE assessment,....

If I have an engine thats fouling plugs, the very first thing I do is a leakdown to check ring sealing. Then, I pull the valve covers and check guides. One must diagnose things like this in a systematic manner.

If its not smoking on decel, its more likely to be guides but that all-important leakdown test gives hard information about what is going on and prevents guesswork.

[stlrj]

I too had a problem with #2 fouling all the time. Turned out the #2 ignition cable was rubbing on the fan housing causing enough insulation to wear off and short out.

Cheers,

Joe