Inlet manifold bushing clearance issue

[49WL]

I just bought a reproduction inlet manifold with nuts and brass bushings for my WL. I see what might be a problem with the spigot O.D. on one side. It is .005" smaller then the other side which makes the bushing loose on this particular side. Spigot sizes are:1.435" & 1.430" O.D. . Bushing sizes are both 1.435" I.D.. Now,with this much clearance on this one side, is the risk for making a proper air seal too great? I've read in Palmer's book that the fit should be more of a .001" press fit. Is any clearance ok, or should I send this back as being defective? Thanks for any advise.

[Chris Haynes]

should I send this back as being defective? Thanks for any advise.

Definitely.

[c.o.]

Here we go again with less than desireable re-pop junk. I know some is good and it's better than nothing but a manifold has to be right or your gonna have big problems. I'd be searching for the real deal and if it needs work I'd fire it off to Cotten for a refurbish. There's no better fitment than real parts.

[exeric]

You should also be using PEEK intake manifold seals. I got a set from ENFIELD RACING.COM for my '51FL and they work much better than the brass seal. They will squish down more than brass but like Cory said, you should have a good manifold to begin with. You can't go wrong with genuine H-D and they should be commonly available on ebay.

[gary.h]

just curious as to where you obtained your intake from?? thanks in advance.

[c.o.]

You should also be using PEEK intake manifold seals. I got a set from ENFIELD RACING.COM for my '51FL and they work much better than the brass seal. They will squish down more than brass but like Cory said, you should have a good manifold to begin with. You can't go wrong with genuine H-D and they should be commonly available on ebay.

Eric!!! I wholeheartedly agree that PEEK seals are the way to go!!! I hate finding bubbles on the air test...

[c.o.]

just curious as to where you obtained your intake from?? thanks in advance.

Gary, are you in need of a manifold???

[gary.h]

Gary, are you in need of a manifold???

not at the moment,amigo but im gonna be needing one to rplace the one on the 45" coz it had a flat spot on the one side i built up and filed down.....no panic for one yet though..

[49WL]

Thanks for all your advice and support.The manifold came from the Depot. Good group,never had any problems before. It just looks like a manufacturing mistake that got out the door.Somebody,somewhere, in some mfg. shop, screwed up and it got shipped.Hope to get this resolved soon. Charlie

[T. Cotten]

Gary!

Worn manifolds can be reconditioned of course!
But you will have to custom-cut your PEEK, as Moldthread/Enfield Racing's fine seals only fit perfect manifolds.

If there are any blemishes on the spigots, or if the seal must be crushed upon the spigot because it is too loose, the re-useability of the expensive material is greatly compromised.

Otherwise, PEEK can last "forever".

....Cotten

[KDR]

Okay......the question was.....will the brass bushing seal when the nut is tightened correctly with a .005 clearance.... not if PEEK seals are the best way to go? The way the two parts are made the nut has a crushing effect on the brass seal as it's tightened. I think it will tighten up just fine and not leak as the brass is soft enough to conform to the .005" difference. I'll replace that one just the same.

[gary.h]

thanks cotten!when the time comes for it and your not too busy it would be nice to send it out to you,ive seen your craftsmanship first hand...NICE STUFF!...take care and all the best in the new year.

[T. Cotten]

Okay......the question was.....will the brass bushing seal when the nut is tightened correctly with a .005 clearance.... not if PEEK seals are the best way to go? The way the two parts are made the nut has a crushing effect on the brass seal as it's tightened. I think it will tighten up just fine and not leak as the brass is soft enough to conform to the .005" difference. I'll replace that one just the same.

Kurt!

The nut presses upon the seal in two directions.
Unfortunately, it presses harder straight against the nipple than it does downward at an angle upon the spigot of the manifold.
So after it has bottomed out upon the nipple, extra force must be applied to crimp the bevel downward, hopeing that the seal will somehow arch itself.

The more gap between the seal and the spigot, the more overkill torque must be applied.

For this reason, whether a brass seal or one of a compliant material, the fit to the spigot must be as tight as possible to begin with, with some interference preferred.

If an extreme torque is applied to conform a loose seal, there becomes an immediate risk of loosening the nipple within the head, and egging an airleak at the rivet.

That can be a minor disaster in itself.

....Cotten

[KDR]

Thanks Tom, but this doesn't make any sense: If an extreme torque is applied to conform a loose seal, there becomes an immediate risk of loosening the nipple within the head, and egging an airleak at the rivet.

How can it loosen the nipple in the cylinder if they are both being turned in the tightening direction? The nipples are not reverse thread last I checked.......and if the nipples are installed correctly in the first place, there would be no way they would rotate tighter.....especially with the rivet installed.....because the nipple should be butted up against a machined surface inside the cylinder. If you can turn a nipple in the tightening direction enough to damage or sheer the rivet.....it's not installed correctly.

I do agree with: The nut presses upon the seal in two directions.......but only to the point it touches the face of the nipple where it creates the seal and can go no further, but then due to the beveled part of the nut and the taper on the seal....it starts to create a clamping force on the inlet......all the way around....and if installed and tightened correctly will create a wide contact area with the inlet creating the seal.

I would bet .10 that if this inlet were installed correctly, there would be no leakage at the seal. Hell....I might even try it when I get it back on a bike I'm building now just to see.

Kurt

[Chris Haynes]

My money is on Cotten.