Panhead Head Problem

[RvP]

Panhead Head Problems

Cotton,
I am for moving slowly but my buddy’s patience is getting slim as he has already pulled the tanks in preparation for a tear down (again, #7). I have not gone back over to repeat the pressure test with the timing plug removed. I also want to verify the air coming out the front head follows the compressor fitting in the front head. If the crankcase were being pressurized I would expect to hear air rushing out both heads regardless of which cylinder is being pressurized.

I also got another piece of information, when the bottom end was rebuilt it was rebuilt with 80” flywheels. Don’t know how that affects anything but it is not a stock panhead bottom end (53 or 55, I forget) anymore.

Given the faulty valve guides and valves have already been replaced, checking for cracks in the head from valve guides would be easy to do once the heads are pulled. With regards to the gasket surface I think we can get an idea of the flatness using a flat surface such as a window pane or granite block (thinking out loud here). With the head on the flat surface and a flexible high intensity light through the spark plug hole and rotating it 360 degrees we may be able to see light escaping from the gasket surface if it is warped or uneven.
Thanks again for you help, should have some answers over the holiday.

Ronald V. Papasso
#3129

[Glenn]

just a thought is there a slight crack anywhere that may open up during heating or a porous spot somewhere.

just thinking out loud

moose

[RvP]

PanHead Tests Continued

Went back to do some diagnostics on the Panhead. The test results were different between the front and rear cylinders. First off, we pulled the timing plug and can confirm the crankcase is being pressurized when the cylinder is pressurized. Enough air comes out the timing hole to blow out the typical BIC lighter. This was the same with both cylinders.

What differs is when the front cylinder is pressurized (50 PSI) air is clearly coming out the push rod tube openings in the front head, nothing out the rear head’s pushrod’s openings. When the rear cylinder is pressurized, minimal air is coming out the front or rear head pushrod tube openings, too slight to really tell. The problem seems more severe with the front cylinder and head.

Thinking the rings are leaking, we put oil in the front cylinder and pumped it a few times to get the oil on the cylinder walls. The result was the same, pressurize the front cylinder and air clearly comes out the front head push rod tubes, not the rear. If the leak were from pressurizing the crankcase and that air working up an oil passage, I would expect the same results on the front head when the rear cylinder was pressurized. The problem seems to follow pressurizing the front cylinder.

I am assuming we can rule out bad valve guides and cracks around the valve guides because the push rods are removed hence the valves are shut. Given this is a fresh (less than 200 mile) run in since the valve seats were cut and ground there should be no air leaking past any of the valves to then leak out a guide or crack near a guide.

I don’t know what to conclude from here, possibly damaged rings in the front cylinder letting crankcase pressure through or a crack in the front head. Before tearing it down, anything else we can check to confirm it is not rings? Compression test showed 135 pounds when last run before doing these air compressor diagnostics. Remember that these air compressor tests are with the engine cold and if they are showing up cold, it gets worse when hot.

[Paps]

Before determining a completely faulty head, check the location of the ring gaps. If they are all aligned with each other ??? Problem solved. Paps

[bmh]

Starting to sound alot like a bad headgasket. Air to the oil passages would pressurize both the crankcase and the rocker box. At 200 miles the rings may not be completely seated yet. That may also explain some of the leakage to the crank case.

[rousseau]

I have been following this thread with great interest . A friend had very similar issues with an evo. ( fresh heads but smoking and running poorly). Long story------- finally found the ring gaps were lined up. If I was betting,this is where i'd put my money. Also, If your guides and stems failed after 200 miles, who's to say that your cylinders didn't also suffer some damage. Do yourself a favor. Go ahead and pull those jugs off.
Now I'm going to make a big mistake and tell how I stagger the rings. The gap on the oil expander is lined up with the wrist pin.or at 9:00 o'clock The bottom "scraper" rail is at 7:30, Top rail at 10:30 Top ring at 1:30 second ring at 4:30.
Now,what causes the rings to line themselves up is a complete mystery to me and after 40 years of tinkering with engines of all types ,this Evo was the first time I have actullay seen it. I do however understand that it is common, especially with supercharged racing engines which commonly run 30 plus pounds of boost.

[bmh]

I try to keep the gaps off the thrust faces myself.

[T. Cotten]

Installing the rings spaced is certainly prudent for start up, but if the rings do not rotate in service, then other problems will quickly develop.

(Flatties have the problem of one side of the cylinder distorting more from heat than the other, but still the rings move where they can.)

A line of gaps would allow easier entry for pressure to the crankcase, but it would not explain air out the pushrod holes of only one head.

Ronald!

Please remind us what year we are dealing with: Early Pans have the head through cylinder drains connected between cylinders in the case gallery, dumping upon the flywheel at the rear. So air to one can easily come out the timing hole as the other.

And,...
Please don't assume you can rule out anything until you have dissected it!

"Never does only one thing go wrong at a time." .... Ridnick Wysdom

....Cotten

[Snakeoil]

I just read thru this entire thread. I have a few observations I like to offer up here. I'm not trying to argue with anyone here. There could be typos in messages that completely change the intended meaning. I just thought it might be useful to have a review at this point and write down a few points that have been made.

Assuming there is a compression leak somewhere...

-The port escape route was mentioned early in the thread by t-bone and everyone seems to have ignored it. Leaks into the ports would vent out to atmosphere. Forget valves, seats or any leaks into the ports. They are the same as venting to atmosphere. Those two big holes called intake and exhaust manifolds would relieve any pressure from a leak.

- Somebody mentioned valve seals. Assume we are talking about a leak from the cylinder into the ports and up the guide and out the seals. Forget it. Even if such a leak existed, even if the valve seals were missing, the air would go out the ports. Forget valve seals. They are not at play here.

-Motorhead said that the rings were eliminated because the pushrods are out and the valves closed. Actually, that tells me that the rings are a primary suspect, NOT ELIMINATED. The pressure should be held within the cylinder, which is between the top of the rings and the closed head. Escape routes which were mentioned were
head gasket leak into oil gallery
ring gap alignment causing leak into crankcase
head cracks into the oil galleries
There is another possibility. First, I have no experience with panheads. If there are oil return lines in the cylinders, and the head gasket suggestion tells me there are, a cracked cylinder wall into one of those returns would pressurize the rocker area as well as the crankcase, and would definitely get worse with temperature increase. It could also allow oil to enter the cylinder and subsequent smoking, more so when hot and the crack is more open.

Whether a cracked jug, or leaking headgasket, when it pressurizes the rocker arm area the path of least resistance is the pushrod tube holes in the head. The reason it does not come out of both sets of pushrod tube holes in both heads is because the pressure is relieved out the cylinder with the problem via the pushrod tube holes. There is not enough flow (volume of air) thru the leak, which acts like an orifice, to pressurize the other cylinder via the oil gallery or the crankcase. Too much volume required to fill the crankcase and then flow up into the oil galleries of the other cylinder.

So, now, after saying motorhead was wrong about the rings, I'm going to backtrack and say I don't think it is the rings. If it were the rings, then the air leak would go down, into the crankcase until it filled and then the air flow would run up the oil galleries of both cylinders and I would expect equal flow out of both heads at the pushrod tube area. But we have flow only out the PR tube holes on one head. That tells me the leak is very near the rocker area for that head and the path in the other direction is long and/or restricted. For that reason, I am leaning toward a head gasket leak since it will spill right into the rocker area and vent out the PR tube holes before preventing it from pressurizing the rest of the engine and hence the rear head. If the head gasket is not leaking, then a cylinder crack or head crack into the oil area and NOT INTO THE PORT AREA.

-There was no mention if pressurized the rear cylinder created a flow of air out the front PR tube holes. I would not expect it on a good rear cylinder since the only leak would be minimal thru the rings and it would only result is a slight breath of air escaping anywhere there was a large opening like PR tube holes. If you do that test and no air comes out either the front or rear PR tube holes, the rear cylinder is not the problem.

- Original post identified two problems. Lean and rich cylinders and smoke. Okay, 3 problems. Before we start telling people to tear apart engines, shouldn't we try to identify if the smoke is black or blue? Are the plugs oil fouled in either cylinder? Is there a white hot plug and a sooty black plug? How do we know one cylinder is running lean and the other is rich? It's a single carb engine. So if one is truly lean and the other is truly rich, isn't it safe to assume that one cylinder is running badly due to carb issues and the other due to another problem? If there are dual exhausts on the bike the rich pipe should be black and the lean pipe should be clean. But assuming it is a two into one, let the plugs tell you what is going on combustion-wise.

And please, before you tear the engine down, make sure you don't have an intake leak on that lean cylinder. Somebody already mentioned this. Tell your buddy to cool his jets and think thru this, instead of diving into the motor. If your car quits on the highway, do you yank the engine or do you check the gas gauge first?

Last comment on smoking. If it is blue smoke and only at idle, does that not point to valve guides and seals being bad. Completely unrelated to the pressure leak issue. But worth looking at. Again, look for oily deposits. If there are none, I would not think you are burning any oil. You are running rich on one or both cylinders. Dry soot on the plug is the telltale for rich.

Good luck. I hope you have a bad head gasket and an intake leak.

[rousseau]

I re read the original post to be sure. He says both heads are leaking from the push rod holes. The front is worse than the rear.

[flthead]

Panhead In Question Is A 1955

[koanes]

I think Brian has the right idea. Just something I ran into once. The counterbore on the head was not deep enough for the cylinder spigot clearance, wouldn't alow for full copression of the gasket. Easily solved by removing material from cylinder.

[RvP]

Panhead Head Problem

Rob,
A lot of questions and places to revisit. I will address these and see if it helps clear up some of the work we have already done and fill in some gaps in what I may have left out.

We did pressure test the intake manifold by removing the carb and plugging the carb hole with a rubber plug and adding 25psi. With our rudimentary equipment the intake manifold and intake valves seem to hold pressure. Note to anyone trying this: Make sure you bleed the pressure from the intake manifold before prying out the rubber plug. With 25 PSI it comes out with so much force if you don’t duck quickly it will knock you unconscious!

The exhaust was a little harder to diagnose and with the cylinder pressurized and using the flame/smoke test, there does not seem to be any air moving out the exhaust on either cylinder.

With the pushrods removed, both intake and exhaust valves closed and good valve to seat seals, the ports, valve guides and valve seals should be blocked from any air. We agree, valve guides and seals are ruled out.

Rings are high on the suspect list and right now we have no way to know if the gaps moved from where they were set until the cylinder is removed carefully to not disturb them. The cylinders do have an oil return passage from the head to the base of the cylinder with a small hole in the cylinder. This is also a suspect area if the front rings are leaking pressurizing the crankcase and allowing air to come up the return passage in the cylinder back into the head.

Relative to the air coming out the timing plug, the air coming out the pushrod tube holes in the front head is much weaker than that at the timing plug. The air coming out the timing plug blows out a flame, the air coming out the front push rod tube holes merely bends it.

A head gasket leak was dismissed until someone posted that the counterbore in the head may not be cut deep enough. Given the front cylinder has been re-sleeved, this is highly suspect now. Had never considered this and this has moved high on the list! This engine has had the heads pulled at least 6 times and even though the gasket has impressions on it, they may not be deep enough to seal. Great idea and a place that was never looked at or considered!

It appears that only the front head has this problem when the front cylinder is pressurized. The rear head when pressurized does not seem to move air out the rear or front pushrod tube holes in either head. It flows only out the front head pushrod tube holes when the front cylinder is pressurized.

The cylinders do not run the same when the plugs are looked at. There are dual exhausts on the bike and the front exhaust builds up smoke at idle and then blows it out when the RPM is increased and then clears. The rear cylinder does not do this but the best idle is obtained when the front cylinder hits evenly and the rear gets a miss every 3rd stroke. The hotter it gets the worse the smoke problem is at idle from the front cylinder even though it is hitting evenly. Can’t tell for sure if the smoke is blue or black, it has been observed by many people and it’s not clearly black or blue. I’m close to color blind with poor color perception so I can only tell you its some dark color and have to rely on the other observers for the color, which no one agrees on.

When the heads were pulled there is carbon on the rear piston and the front piston was clean enough to eat off of, looked cleaner than when it was first installed. This made us suspect the front cylinder was running rich and washing out the carbon. The intake manifold was suspect and was not real tight so it was lengthened, new O-rings and clamps installed. Now the front piston is starting to build carbon but the smoke problem still persists. Given the intake manifold to the intake valves is holding pressure we think it is sealed.

It was the smoke trail and uneven plug burning that lead to the following work:

1) This was a fresh rebuild including cylinder boring, new pistons and rings, valves reground with the original heads.
2) The original heads starting getting noisy and it was found the valve guides were starting to split. This was attributed to many things such as the valve seats being cut too deep causing the valves to go up father than they should, valve guides not pressed in as far as they should or valve guides too long. Since the heads were old and starting to get loose rockers, new heads were installed.
3) With the new heads everything was good until a few hundred miles, the spark plugs went from burning even to the front one being oil fouled. Another tear down found the front piston was 0.020” loose in the bore when measured with a flat feeler gauge on the front face, it was that bad. The front cylinder was re-sleeved and bored to match the rear. New piston, rings, etc. were installed in the front cylinder.
4) This is when smoke from the front cylinder started to appear so the heads were pulled again. This is when the new heads with 200 miles on them had scored valve stems, valves wobbling in the guides and mushroomed valve stems. New valves, valve guides, and seals were installed and regrinding was performed on both heads. This did not change the symptom and the front cylinder still would smoke at idle and clear when the RPM went up.

Given the above and all the great responses from everyone, the best suspect area is the counterbore in the head or the re-sleeved front barrel is not correct causing a poor head to cylinder fit. This is an area we had not pursued at length other than a casual observation.

Having gone though many top end tear downs and finding something it appears we have overlooked the head counterbore to cylinder fit, especially since the re-sleeving. What is the best way to check the fit of the cylinder to head counterbore? If somone can attach some numbers to it or observations then we can check that more accurately.

There have been many problems we have sorted through and many red herrings along the way and this may be the “smoking gun”, how apropos.

Ronald V. Papasso
#3129

[Snakeoil]

Couple of comments on your feedback.

I would not expect a rich cylinder to look clean unless it was not firing at all. Rich means incomplete combustion and that means carbon. The only way a piston would get "washed down" is if the plug was not firing at all. You are not going to have some gas burn and the rest just splash around in there. If you had so much gas that it washed down the cylinder, the cylinder would miss a lot and probably not fire at all and just flood.

If the air flow is more pronounced out the timing hole, then I lean towards ring gap or maybe a broken ring.

You might have more than one thing going on here. The counterbore/spigot issue should be checked as well.

Regarding the smoke, I have to go back to plugs and deposits. If you are burning oil, it will show up as an oily sooty deposit on the plugs, head and piston dome. If you are running rich it will be dry soot. I also find it hard to believe you cannot tell the difference between blue and black smoke, unless this engine is running rich and burning oil. Blue smoke is very obvious to see. And if you stick your finger into the tailpipe, it should have some oily residue if you are burning oil. Even if you are totally color blind (I'm red/green) the smoke would appear to be gray if oil and black if gas.

I mean no offense here, but from some of the "theories" you and your buddy have had, I get the feeling you are not experienced engine mechanics. There could be something very obvious here that you are not seeing and hence reporting. You might have several things wrong with this engine and the combined symptoms are taking you all over the place.

I'm inclined to recommend you take this to someone who does this for a living. It will cost you a little and that might be a problem. But it could also save you a bundle if there is something else wrong with this engine that will do even more damage.

[RvP]

Panhead

Rob,
Not offended by your comments, we are amateur mechanics (especially me) and I am often referred to as having “office hands”. I am new to this and if the parts fit and everything works properly, I am a great mechanic. If they don’t, then I am lost and have to seek help from those more experienced. The amount of help I have received from this forum alone during those times has been exceptional. Debugging from long distance is an art form and part physic of which I have greatly benefitted from both.

The owner of the Panhead has been in this hobby for over 30 years and has lots of experience but not enough to debug this. As for the local mechanics, they have made mistakes on this engine and they have corrected their mistakes and provided lots of guidance. We may have stepped outside their comfort zone since the stock ’55 engine was rebuilt with 80” flywheels, high lift cam and non-stock heads. This may be something that they do not want to get intimately involved with other than the piece work they have done.

As you can tell we have had many things going on here and have tackled them one at a time. To say we are lost and traveling around in circles would be an understatement. These posts came about because we needed to put the wrenches down, sort things out systematically and seek help outside of our pool of knowledge.

The question of black and blue smoke is still a debate. I have put a clean white cloth over the front exhaust and the residue appears black and dry. Inside the pipe, about 1” in, you can pull out on your finger tip an oily black substance, even after the pipe was cleaned with lacquer thinner and run for a few miles. To me this is oil, to others this is unburnt gas mixing with the carbon. I do not have the experience to enter that debate but have always questioned how you can have carbon build up in the pipe but not on the piston.

What is not debatable is on the last tear down after running the engine for 200 miles. Prior to removing the heads there was no doubt the engine was idling without a miss on the front cylinder and a miss, every 3rd stroke on the rear. Great top end, just an uneven idle. No matter how we tweaked the low speed needle we could not get the miss out of the rear cylinder. At both extremes, lean and rich needles settings, the mixture was off so much the engine would not idle at all. This was repeatable all the time. The best idle was with the front cylinder hitting every time, the rear missing every 3rd.

When the heads were pulled, the rear piston had carbon on it and the front piston was 100% shiny, no signs of carbon on the piston at all. This may be a sign that has nothing to do with the problem at all but another red herring.

The front and rear spark plugs are not showing signs of oil which is why we are suspecting it is not oil. The plugs are not burning the same and I forget which is rich and which is lean. This is how we got to this point, visible smoke from the front cylinder, no signs of oil on the spark plugs but one cylinder rich and one lean plus an uneven idle.

Your advice on seeking help from a professional is well advised and is up to the owner of the Panhead how far outside of our local area he wants to go. Thanks again for your input and no offense taken, appreciate the help, opinions and anything else you can muster.

Ronald V. Papasso
#3129