Intake tract sealing issues

[Eddie G]

Having a hard time getting the intake manifold to seal. I made a pressure test per Cottons tech article & put 15psi on it. Air bubbles coming from both flange nuts at the washers. If i really tighten them hard & i mean hard, i can stop the leak. Any tips as to what i might be doing wrong. I have a new manifold,sealing washers & nuts. I've been chasing the problem for a long time now. Found a bad intake valve & guide so i did a fresh topend rebuild with new valves & guides.

[kval]

Having a hard time getting the intake manifold to seal. I made a pressure test per Cottons tech article & put 15psi on it. Air bubbles coming from both flange nuts at the washers. If i really tighten them hard & i mean hard, i can stop the leak. Any tips as to what i might be doing wrong. I have a new manifold,sealing washers & nuts. I've been chasing the problem for a long time now. Found a bad intake valve & guide so i did a fresh topend rebuild with new valves & guides.

Eddie
what I was taught by an old timer long ago, when doing a top end, coat the base gaskets with grease, leave the base nuts loose. put the intake manifold on and tighten, this allows the manifold to align with the cylinders. then tighten up the base nuts. I have done this every time and have not had a problem YET!!

[Sargehere]

Get a good end seal by burnishing the mating ends of the manifold with emery cloth over a good flat backing, like a piece of glass. Nicks in the manifold or cylinder can leak.

[T. Cotten]

Eddie!

Sorry for this late reply, but this site's format makes my uploads sit and spin without end.

First, there is no reason to polish the ends of the manifold, as the ends touch nothing.
The seals contact the nipples' faces, and the outside of the manifold's spigots.
Polishing the spigots themselves will make common brass seals far too loose.
The faces of the nipples may need dressing as noted in my VirtualIndian bubbletesting article.

It is not common with Chiefs, but leakage is possible between the nipples and the cylinders themselves.
The manifolds nuts obscure this seam, so each nipple should be tested separately, using a #8 rubber stopper instead of a testplate.

Brass seals must be pristine and annealed.
Modern compliant seals are available from many sources.

.....Cotten

[Eddie G]

Thanks everyone, a little history, bike has been a strong runner & very dependable. Joe Gimpel did a complete rebuild 3 or 4 years ago. Ran strong for 1,000-1,500 miles (due to circumstances was not able to ride it very much) then a starting issue began. Cleaned carb, Rebuilt carb, changed to 12volt, electronic ignition, new intake manifold, new seals, new peek seals new gland nuts ect. The more i worked on it the worse it got. Another pressure test and found bad valve & guide. Tear down and installed new valves, guides and rings. After starting it up the carb adjustments were very vague and could not find a setting where it would run well. Another pressure test revealed leaks on the manifold which is where i am now. I do remember reading about installing manifold before tightening the base nuts but didn't do it. I always use grease on paper gaskets and my next question was should the seals be annealed? I will try this and see what happens.

Thanks Eddie

[T. Cotten]

Eddie!

Brass seals need all the annealing they can get ,

No information about annealing molded PEEK has come my way.

Machined extruded PEEK,
as I pioneered for vintage machines a decade past,
actually is spec'd for annealing.

If this site wasn't so contrary, I would post a scan...

The bottom line is that machined PEEK seals have not presented any problems from lack of annealing after machining, and they are in use worldwide, from many sources.

It may very well be that the heat of the motor does it quite well.

Let us know how the nipple test goes:
Your chances are good that they are intact with a Chief,
as the Wigwam used a sealer.
(I have no evidence that Milwaukee did,... yet.)

....Cotten

[Eddie G]

Annealed the sealing washers and it seemed to work better. No leaks for now. I will road test tomorrow.

[Eddie G]

Pressure test was good. Started easily and runs strong but has a wicked flat spot at the low to high speed transition. Any ideas?

[T. Cotten]

Pressure test was good. Started easily and runs strong but has a wicked flat spot at the low to high speed transition. Any ideas?

Eddie!

Spots that cannot be bubbletested are the seam between the carb and manifold,
and the throttleshaft bushings. The un-lit propane torch trick may display an airleak at those regions.

Within the carburetor, a gap around the outside of the venturi, or a poor fit of the nozzle spigot within the venturi will interfere with the transition.
And excessive borewear from the throttledisc will also confound tuning, as it reduces the air directed over the idle bleeds dramatically.

Another condition commonly overlooked is the lowspeed needles lift-lever spring collar seat upon the body. The spring collar hole is a metering orifice for air.
If the seat upon the body is not flat, it will allow leakage beneath the collar, as well as prevent the collar from sliding properly, causing wear upon the needle and orifice.

And please remember that bowl itself is a third circuit.
The float must be of proper buoyancy for the 1/4" spec to give the proper fuel level.

Good luck!

....Cotten

[Eddie G]

Cotton, do you rebuild carbs?

[T. Cotten]

Eddie!

Liberty specializes in servicing American motorcycle carburetors and their manifolds from the teens through '65;

Please post me direct at liberty@npoint.net,

Thanks!

....Cotten
Liberty Motorcycle Specialties, Inc.
118 N. Washington Street
Lacon, IL 61540 USA