Panhead Head Problem

[RvP]

I am helping a friend with a Panhaed and we are stumped. Here’s what we have:

The main problem is the front cylinder runs lean, the rear rich. When hot and idling the front cylinder starts puffing smoke (can’t tell for sure black or blue) when it idles. New V-Twin heads were put on that developed scored valve stems and mushroomed valve ends (rocker side) after a few hundred miles. The valves were replaced, valve sets cut and ground, new valve guides installed and new valve seals. The problem still persisted so we ran a air compressor test. With the push rods REMOVED (i.e. both intake and exhaust closed), a compressor fitting for the spark plug and the air compressor set for 50 pounds there are air leaks.

The dilemma is the air is leaking out the heads where the pushrod tubes go. We confirmed this by putting our fingers over the pushrod openings in the head and also with smoke. There is no doubt that air is escaping through those holes with the front worse than the rear. It does not seem to be from the crankcase because it follows the head the compressor/spark plug fitting is in (note: there was always a spark plug installed in the head that was not being pressurized.)

Given the valves, valve guides and seals have all be replaced, what could be the path to allow air to escape from inside the cylinder and come out the push rod openings in the head? Is there another test we can do to narrow this down?

Ronald V. Papasso
#3129

[t-bone]

possibly air pressure going down past the rings filling cases coming up oil passages to rockerarms? the spark plug situation sounds like intake leak.

[bmh]

Was there any air leaking into the ports? Did both heads do the sme thing? Sounds like another bad valve job or defective castings. Air is leaking into the rocker compartment and its only way out is through the pushrod openings. I know this isn't what you want to here but it sounds like you may need to pull the motor so you can do a leakdown test with the rocker covers removed. Or remove th heads, pull the covers, reinstall the heads, then retest. Dealers choice on wich is easier.

[bmh]

One other question, was any air rushing out the crank case vent?

[motorhead1]

You have already answered your question. You pressurized the cylinder with the valves closed. Therefore, the rings are eliminated from the picture since the pushrods are out of the motor. You have a leak between the valve and seat or the seat and head.

[milw.pirates]

You have already answered your question. You pressurized the cylinder with the valves closed. Therefore, the rings are eliminated from the picture since the pushrods are out of the motor. You have a leak between the valve and seat or the seat and head.

remove your heads,Did you lap the valves to the seats to see if you are making a good contact, hand lap the valves to the seat make sure you have a ring of contact between valve face and seat,any defect will show up as a low spot not affected by lapping compound,any low spot on seat,seat would have to be recut or depending on depth,hand lapped with different grades of lapping compound,make sure all compound is cleaned off before reassembly,(brake clean works),check your seats are they loose in head,do they spin,or are they tight,are these v-twin heads? also make sure the intake mounts are not loose in head.

[T. Cotten]

To add to Dan and Ken's scenarios,
It is even possible that there is a breach in the headgasket to allow compression to flow from the chamber up through the drain gallery to come out the pushrod holes.

In other words, the gasket may have "blown" or warped inward without showing on the outside (yet). Removal and inspection of the gasket may be your only means of eliminating the possibility, as well as effecting a repair by re-flatting the gasket/cylinder surfaces. (Eliminating the cause of the warpage, however is a matter of avoiding elevated temperatures in the future.)

With aftermarket heads, anything is possible, so I would suggest testing the removed head on the bench, and corking up the ports to apply strong air pressure to various places while using soapy water to determine if there are any leaks around seats, casting porosities, minute cracks, etc.

I have even found leaks from the chamber and/or intake port penetrating to the headbolt insert in this manner.

....Cotten

[t-bone]

if it is a valve not seating it would take the easy route out exhaust pipe or intake manifold.if ring gaps line up it will leak air pressure to bottom end . try removing timing plug. roll motor over using rear wheel to see anything if changes as breather gear rotates. good luck

[RvP]

Panhead Head Problem

Thanks to everyone who replied, I was hoping for my friend’s Panhead there was a “solution in a can to fix his Pan”. Sounds like it’s another tear down, which makes the 6th one. To answer some of the questions:

To Brian: Yes, both heads did the same thing, the front more noticeable than the rear with regards to audible sound and smoke. Never checked the crankcase vent to see if any air was moving there. Great suggestion and easy to try before we tear it down.

To Ken S.: The valves were done by a local and reputable Harley mechanic who has lots of experience with Panheads. These are also new V-Twin heads that had to be re-worked after 100 miles due to valve stems scored, valves sloppy in the guides and valve stems mushroomed from the rockers.

To Cotton: Never thought of suspecting the head gasket or the head to barrel surface. These barrels worked with the old (and worn) heads and I assumed V-Twin heads would be quality parts. Give the valve problems experienced after 100 miles, you may be correct “With aftermarket heads, anything is possible”.

Removing the heads and making a fixture to seal them on the combustion chamber side and bench test them may be the best way to isolate the head from the other suspect areas (head gasket, blow by, etc.). One thing that does bother me is that regardless of how bad the valve seats may be, wouldn’t the valve seals themselves hold back 50 pounds of air?

[T. Cotten]

Rvp!

I do not think that a plate to block off the combustion chamber will be necessary, as air pressure can be applied from the ports with big (#9) corks or stoppers to inspect the seat's integrity and the valves' seal (although the valves will start to open with 20 psi or more.). A plate covering the headgasket surface would prevent observation anyway, unless you have some thick clear plastic handy.

As long as your regulator keeps the pressure constant, any incidental leaks around your fixtureing or valves themselves can be ignored. Bubbles only need a 'differential' of pressure between the inside and the outside to show a breach.

With the pan cover still attached, two (#2) corks can be shoved into the pushrod holes to pressurize the drain gallery for inspecting for other unknown possibilities. Some leakage past modern valve seals should be expected, but not volumes.

I've been there.
It is also a great way to make certain that pan covers won't leak before they are installed; Even pan cover screw holes that have been drilled or crushed through to the intake port show up occasionally.


...Cotten

[Paps]

Cotten...What if the leak only appears after warm up ? Paps

[T. Cotten]

Cotten...What if the leak only appears after warm up ? Paps

Paps!
Good point.
Maybe a hot air gun on the head is in order, if no 'smoking gun' is found upon room-temp testing.

A couple of other questions for Ronald occurred to me in my sleep:

If the air is escaping to the drain gallery as I proposed, why doesn't it also show itself at the timing hole? (Early models should have an open path; later models may have the piston over the cylinder hole, especially if the air pressure has pushed it downward.)

Are these aftermarket heads equipped with properly cast-in bronze seats, or short-fused with steel inserts?
(If inserts, do they have Pan-design intake ports, or Shovel, with the Shovel headbolt pattern?)

...Cotten

[RvP]

Panhead Head Problems

Thanks again, lots of good information and questions. We went back and checked for air escaping out the breather hose. Each cylinder was brought to top dead center, push rods removed, transmission in 1st gear to keep the piston in place and the air compressor attached to the spark plug adapter, 50 pounds of air. There is a slight amount of air coming out the breather, enough to barely move a flame from a lighter, not enough to move smoke as the smoke tended to dissipate faster than we could tell it was moving with an airstream from the breather tube or ambient air currents. The same setup for the front and rear cylinders was used with similar results. There was still air coming out the push rod tube openings in the heads that would visibly move a column of smoke and bend a flame, much stronger than was coming out the breather. Does this mean what we are seeing is normal?

Here’s some more information, both cylinders compression check at 135 pounds. With the test above, when the 50 pounds of air was applied the cylinder, up on a lift (front wheel clamped), the bike lurched forward since it was in 1st gear. I don’t know if the above information indicates that the rings are good and should not be leaking 50 pounds of air.

Answers for Cotton:

1) Never thought of pulling the timing plug to check for air there. Good idea, will try that next.

2) Don’t know what kind of valve sets there are. They look like silver metal if that differentiates them from having a bronze color.

3) Not having worked on a Pan or a Shovel, I will have to defer the question about the Pan-design intake ports, or Shovel, with the Shovel headbolt pattern to the person I am helping since he has worked on both. They are V-Twin heads for a Panhead if that will answer the question if you know what V-Twin sells.

With regards to the bench test we were proposing with blocking off the combustion side of the head and pressuring the head, we thought we could use soapy water to check for air bubbles around the valve stems and the top of the head. For the amount of air coming out the pushrod tube holes the assumption would be one leak, not many small leaks that would each not significantly show bubbles.

As for heating the heads up, they are cold when we are doing these tests. If there is a leak due to valves, seals or a crack, it is already showing up cold.

More to do, more to think about before the tear down. Keep those cards and letters coming!

[bmh]

when you pull the heads take note if any of the head bolts ( especially those on the left) are oily, this will give some indication if the gaskets are sealing good or not. Check the valve seating with a little prussian blue after you take the heads apart. If the seats are in good sealing order I don't see much use in pressure testing the ports as the pressure from the original test would not have gotten past the valves and into the ports. I would be looking real close for cracks or porosity in the heads ( especially since you stated thier origins). A good rough check for this would be to re-assemble the valves in the head, set it on the bench chamber up and fill the chamber with denatured alchohol. then start looking for wet spots were the alchohol seeps through. Don't be afraid to let it sit a while to be sure.Remember during combustion, presures of thousands of PSI are at work to force gases through the smallest porosity or crack. Good luck.

[T. Cotten]

Ronald!

One step at a time, slowly lest disassembly gets ahead of us....

When a head comes off, inspect both sides of the gasket immediately between the drain hole and the combustion chamber. If it is intact, with no discoloration, without even oil passing, then my first theory will seem unfounded. Grinding the headgasket surfaces to flat will display any gross distortions that may also have occurred.

On to pressure testing BEFORE any other disassembly,
Blocking off the combustion chamber will not only be a lot of effort, you cannot see the entire ports or valve seats clearly anyway.
But no doubt IF you see cracks in the intake from the pressing of a hardened seat, then bubbles would be, uh,... anticlimactic, for want of a better word.

On to seat materials, there are very damn good reasons why the Factory didn't put steel seats in Panheads.
The port alignment with a headbolt pattern change allowed them to be used in Shovels, although marginally, as many of have witnessed.
The geometry of evil evo's overcame the problems to an even better degree (every pun of 'degree' intended.)

I have no idea what V-TWIN heads have in them, but STD wasn't stupid when they produced their premiere replacements as Shovel hybrids, even though it didn't do the vintage scene any justice.

Looking forward to your observations,

...Cotten