What's causing this carbon buildup...

700rpm

700rpm

Well-known member
...and what should I do about it? Actually, maybe identifying the cause will also prescribe the cure. But here is what my #3 & #4 pistons and my head look like after only 1260 miles since last having the head off and cleaning it up. I have had some overheating problems since I performed that last cleanup, so I decided to pull the head to see if it was flat and what else might be wrong. (See my thread on overheating: http://fordbarn.com/forum/showthread.php?t=117609 for an update on that problem) Notice there is some moist oil apparent on #3 on the head, but little carbon buildup.

My suspicion is the exhaust valves are leaking on #3 & #4, even though the valves are new and I lapped them min. But the seats were a little questionable, and though the lapping looked good at the time (1260 miles ago) maybe I just need to pull this engine again and have new seats put in.

As I asked on my other thread on overheating, can these two problems (overheating and carbon buildup) be feeding off each other, each one compounding the other?
 

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that clean spot on #3 would lead me to suspect water leakage there, especially if the head was not surfaced prior to installing it. Perhaps your guides are loose and oil is getting sucked in, crating the oil and the carbon. Have you done a leak down test? could be leaking oil rings too.
 
#8 got new guides in March. Not so #7. I could try that. I don't know how to do a leak-down test. Can someone explain?

Truly, I'm about to pull the engine again and just have it rebuilt by a professional. Boy, the thought of that makes me tired. :o
 
basic leak down test. Each cylinder to test should be at TDC

http://www.youtube.com/watch?v=ofSiTGeLXvc.

while you have the head off, check your #3 cyl intake valve for wobble. compare the wobble with the new guide valve in the other cylinder. It does not take much to start sucking oil. Check the intake port to see if there is oil in there. If yes, then its the guide and/or stem. If no, its probably rings. You can verify rings with a leakdown test, as well as a leaky head gasket leaky valves. Since both cylinders are burning oil, I suspect the guide in 3 is feeding cyl 4 as well via the common port.
 
do a compression test before you pulled the head off ???

Do you have the earlier valve cover with the hole for the oil drain tube higher up on the side of the cover?? (thus allowing the oil pool inside the valve chamber to fill higher, thus allowing more oil to be sucked into cyls 3 and 4?)

i am not convinced your 2 problems are related.

BTW there is a Fel-Pro tip posted on their website that states you should remove cyl. head fasteners in the reverse order of how the head gets torqued, else the head can warp. I had never heard that, and I have never seen anyone do this. But Fel-Pro must know something....
 
tbirdtbird said:
do a compression test before you pulled the head off ???

Do you have the earlier valve cover with the hole for the oil drain tube higher up on the side of the cover?? (thus allowing the oil pool inside the valve chamber to fill higher, thus allowing more oil to be sucked into cyls 3 and 4?)

i am not convinced your 2 problems are related.

BTW there is a Fel-Pro tip posted on their website that states you should remove cyl. head fasteners in the reverse order of how the head gets torqued, else the head can warp. I had never heard that, and I have never seen anyone do this. But Fel-Pro must know something....
Click to expand...

Compression is 56-60# on all four.

I have the later style valve cover and oil return tube.

I have always (50+ years working on A's) just loosened the nuts in whatever order was easiest to get to, and I did so today. The head and block are both flat. Not to say anything against Fel-Pro; that's just my experience.
 
ray do you get any blue oil smoke out tailpipe? it may be hard to see while driving but maybe if a friend or club member was following they would see little puffs at times and during up shifts..
 
I would check for a water leak in the clean cylinder. Other wise looks like a engine that is run on a lot of short trips. I would check for a leak, and put it back together., drive it and not worry about unless there is some thing else wrong.
 
I agree with George. A clean side of a piston is usually caused by oil washing past the rings, or a water leak. The gasket looked a little suspect in that area. Use a new copper gasket with Copper Coat on both sides and put it back together after checking for flatness of the head and block.
 
Any wear on the valve stems? I also saw the three holes drilled on the top of one of your pistons. Someone trying to balance? As for removing the head I always follow the pattern middle to out and opposite sides to not warp the head.
 
59mgaguy said:
Any wear on the valve stems? I also saw the three holes drilled on the top of one of your pistons. Someone trying to balance? As for removing the head I always follow the pattern middle to out and opposite sides to not warp the head.
Click to expand...

I suspect the three pin punch marks are marking the piston for number three cylinder.
 
Pat: I'll check for wobble when I get out to garage today.
Mitch: No reports of blue smoke.
George: Most trips around town are 6-8 miles RT. Of the last 1260 miles, 500 were long distance, over 100 miles each.
Tom: The head was installed in March with a new gasket and copper coat as you describe. The head and block are flat as I lay a steel straightedge across them in several directions.
MGA: All valves and tappets were new in March, and just by happenstance I removed the head this time as you describe.
Dave: Right. Those are ID marks.

I also got an email from Bill Barlow suggesting a crack between the intake valve seat and the cylinder, which would explain a lot of things. I'll check that too when I get out today, and report back.
 
I wouldn't be so quick to assume the head is flat based on a straight edge. I recently checked a V8 head that I knew was warped from gases in the radiator. It checked out flat. In the first place, unless you are using a machinists straight edge, a small gap will not be detectable. .004 is enough to cause a leak, and odds are you will not see it. In the second place, with this V8 head, I took it to the machinist, and he found it was twisted from corner to corner, so a simple straight edge showed it was flat in that thin plane it measures, but it would not show a twist. A slight skimming with the proper machine will show even the smallest warps and dips. I think its worth the cost to find out the facts with the proper tools rather than suffer the further expense of gasket and time to re install the head, only to continue to have trouble. I really hate having to do things over. Something is causing that clean piston in #3. I cannot tell from a photo whether its coolant or oil from a bad ring below, but it is not typical of a good combustion chamber and should be investigated.

That being said, a leaking head is probably not the source of your carbon issue, but will contribute to over heating, coolant loss and poor running.
 
Pat: I agree about the head. I'm going to have it resurfaced as a matter of course. Regarding wobble on valve #5, it also has new guides, and there is a very, and I mean very, slight wobble, less than 1/64" I'd say.

Bill: I just cleaned and wire-brushed the head correction: block around all valve-to-cylinder areas and there are no apparent cracks. I'll give all those another closer look later with a magnifying glass, but right now I'm encouraged.
 
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is there any sign of oil in the intake port? Sometimes new guides fail quickly, especially if lapping compound got on the valve stem or in the guide. With modern guides, new ones should not show any detectable wobble. Unfortunately, the repro split guides can. I prefer modern guides, reamed to fit the valve stem.

A new valve job can draw oil up through old rings, when it did not prior to the valve job . The new valves and guides increase the vacuum and suck the oil up past worn rings. A leakdown test will produce a hissing in the crank case when pressurized at TDC and faster rate of pressure loss in any bad cylinders than the good cylinders if that is the case.



700rpm said:
Pat: I agree about the head. I'm going to have it resurfaced as a matter of course. Regarding wobble on valve #5, it also has new guides, and there is a very, and I mean very, slight wobble, less than 1/64" I'd say.

Bill: I just cleaned and wire-brushed the head correction: block around all valve-to-cylinder areas and there are no apparent cracks. I'll give all those another closer look later with a magnifying glass, but right now I'm encouraged.
Click to expand...
 
I don't have the manifolds off. I think I'll resurface the head and put it back together and have the leak down test done. Then I'll pull the manifolds and see what I see.
 
FWIW: The exhaust valves on 3 & 4 (and 2)look about right. They do not look burned, from the pics anyway. Maybe get one of those little flexible mirrors from NAPA to look at the faces and seats to see if there is any gross leakage (you need to remove them for fine inspection) but I doubt you have any problems there.

Does #2 look similar to #3, and #1 similar to #4? IE, #1 should be more "oily" than #2, and I would guess 1 & 2 are a little cleaner than 3 & 4.

How many miles on the rings? The compression check seems to be within normal limits. A leak down test is more accurate, but my guess is there will not be much difference.

Are the plugs fouling? If not, there is not a serious oil problem. I suspect your plugs might be a bit greasy, but not fouling. Or are they the proper color? If so, oil is not a problem. If just dark, lean the mixture.

This looks within normal limits to me. I had similiar conditions on my head and pistons, had a panic attack, ran a thread on it here some time back, worried about valve guide clearances, pulled the engine down and checked them and other things, to find all within specs, and have run the engine since with no probs.

Just asking because I would like to know, not trying to be a Smart A**, I would like to see pics of what the "ideal" combustion residue should look like on a Model A, how common that is, and what the driving and engine conditions were that produced it.

Your residue is about the same as my recent rebuild was, and about the same as my pal Jerry's was in his beat out coupe 55 years ago. If this condition is a concern to you, I would just run it a quarter turn leaner and burn it off. If anyone supplies pics per the above request, please let us know the mixture and timing settings if possible. (I know I am being facitious, you need an air/fuel ratio gauge at least to be accurate about that. The point is that it is a Model A, and there are so many variables that the range of "normal" is quite broad. Unlike a modern car, 10K A's will have 10K different timing and mixture settings. )

The cooling problem is unrelated.

Good luck, and please keep us advised of your efforts, because I suspect there are many with your symptoms.
 
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PC/SR: Good questions. THe plugs are a nice light gray-brown, and clean. No idea on the age of the rings. #s 1&2 look very similar without the carbon buildup, just kind black, as I have seem most engines I open up. The whole reason I took the head off was to determine if it was the cause of my overheating. I'm thinking I got distracted by the carbon and the heating problem was caused by rust and junk in the water jackets. I will just proceed to deck the head and use Evapo-rust to clean the engine when it's reassembled and see if that takes care of things.
 
I personally never like re-using rings once they've been seated to the cylinder. It's cheap to get a new set and lightly crosshatch your cylinders. Even if its not smoking, your old rings are no longer sealing well and are blowing by enough to carbon things up.
 
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