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Panhead air inlet adjustment

Post Mon Oct 05, 2009 4:38 pm

Posts: 5
I ride my 50 Panhead that I've owned for over 30 years daily. If it ain't raining I'm riding.
This past July I rode her from Southern California to Sturgis and back. She ran, and runs, like a finely tuned watch, BUT... here lately I've noticed that she's wanting to idle higher than what I consider normal and adjusting the idle doesn't seem to have the desired effect.
I also have noticed a slight "whistle" that goes away as soon as I crack the throttle even the slightest. I've done the WD-40 trick by spraying a very light spray through the little red tube that comes with the WD-40 onto the intake manifold and have proven to myself that I have a very minor intake leak where the forward intake adjustment fitting meets the head.
It's NOT the O-ring(s) on the manifold tube. It's definitely where the adjuster threads into the head.
The threads aren't messed up on either the head OR the adjuster and there are NO cracks that are evident and I've looked really closely with a lot of light.
I've tried high temp silicone gasket sealer...
I've tried teflon tape...
I've tried High Tack-High Temp sealer and I still seem to have the same intake leak.
Can anyone tell me what these were originally sealed with, or what to use to get it to seal?

Post Tue Oct 06, 2009 12:52 am

Posts: 1654
I would suspect that you may need to do some kind of NDT test to find a possible crack.

I do this at work sometiomes, there is one test in particular using a spray containing very fine steel particles and a magnet which will reveal blemishes not visible to the naked eye.

or, it may be that after so many years of use some part of the assembly has warped slightly and no longer seals, although no defect is visible.

I know these are both a bit speculative, but it sounds as though you have covered all the obvious ones and still have the problem
Shoot, a man could have a good weekend in Dallas with all that stuff...

Post Tue Oct 06, 2009 4:11 am

Posts: 377
Location: madison wisconsin usa

just for clarification what do you mean by "adjuster"?

have your bikes heads been modified to accept the newer oring style manifold? are you describing the threaded steel insert that goes into each head?

if so, what is the condition of the threaded portion in the head itself?


Post Tue Oct 06, 2009 7:03 am

Posts: 3158
Location: Central Illinois, USA

A simple bubble test will show even the tiniest of leaks:

You will find some notes on nipple replacement as well, which is NOT an easy chore.

PS: I'd pull them both and go back to original design, myself.

Post Thu Oct 08, 2009 9:34 am

Posts: 5
Thanks for the feedback.
I have inspected pretty closely the inlets where the nipples screw into the heads and can't see any cracks. I know that some cracks are small enough that seeing them is impossible, but judging from the "whistle" noise I'm getting I'd say that the leak is most likely either my O-ring seals, OR where the nipples thread into the head. Actually I believe it to be just the front head based on my spraying minute amounts of MAF cleaner around. The only place that there was any evidence of a leak, as indicated by the motor's idle slowing down noticeably when I spray the MAF cleaner around, is where the front nipple screws into the head.
All of the threads look good. When I restored her I had the heads completely redone, including intake and exhaust inlets & outlets. My heads have always been the "O-ring" type for the intake manifold. At least they've always been that way as long as I've owned her.
I will fabricate myself a plate to cover the carb inlet and pressurize the intake manifold system and see where the bubbles show up. Looks like probably the easiest, and most positive method. I assume 15 lbs psi is sufficient.
Now for my original question... What, if any, sealant can or should, I use to seal off the leak once I verify it's where the nipple threads into the head.
Another question... What is the proper adjustment of the nipples in relationship to the intake manifold? Should they be adjusted so that there is minimal clearance between the intake manifold and the nipples, OR should I have the nipples adjusted so that the "O-ring" takes up whatever space there is between the nipples and the manifold?
I appreciate your input and info. I've owned this bike for over 30 years and am constantly learning things about it. Your experience(s) are invaluable.


Post Thu Oct 08, 2009 7:17 pm

Posts: 3158
Location: Central Illinois, USA

The sealing surface between the nipple and the head casting is, unfortunately, where they butt up against each other. Since it is broad, without a thin biting lip like Knuckles, not only must it be torqued as tight as possible, introducing a sealer after assembly is impossible, especially if contaminated with carbon and volatiles.

So not only is there no room for adjustment, the nipple must nearly always be removed and a fresh one installed for a sealer to be effective. (Please refer back to the leaktesting article for a preferred sealer.)
O-Ring manifolds are very limited in available widths.

And more Pans have been ruined by twisting out a boogered nipple than anything else (but perhaps hard seat installation). That's why they must be cut and crushed.

Like I said, it is NOT an easy chore;
I don't even know anyone brave enough to offer the service.


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