manifold problems

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manifold problems


Post by 49er » Wed Dec 24, 2008 2:30 am

Hey! I made a plate and tested my intake.with a hand pump I was able to produce bubbles as big as a pecan. so I pulled everthing off. the manifold was crome and it peeled right where the brass hits. i wire brushed the rest of the crome off, it was easy. now the surface is rought. not pitted. just a million little dots on there. I dont see how it could seal like that. I heated my 30 year old brass rings in the oven at 500 for 15 minutes then 350 then 100 for all night. then turned the oven off and let it cool down. do you think this will help? the dots on there must have come from the factory, there are still grooves from the cutter used to machine the manifold. the crome side is smooth except a line around that is a break in the crome. I have held 600 grit paper in my hand and spun the mani around to smooth it. can ya put JB Weld on it and sand it back smooth? they are tiny.

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Re: manifold problems


Post by FlatHeadSix » Wed Dec 24, 2008 7:29 am

The "EVIL" chrome strikes again. I have always considered any old OEM part that was sent to a chrome plater and has seen years of service and weather, etc., to be nothing more than scrap iron. Once the chrome goes bad it is usually not worth the effort to try to save the part.

A plumber type manifold is at the top of the list, you can try all the tricks you mentioned above but there is still no guarantee that it will seal properly. The best solution for a worry free repair is to put it in a lathe and turn it true again, but you would need new seals of the correct size to complete the job. Mr. Cotten can provide this service, the seals that he provides are custom fit to the manifold and much better than brass.

You have nothing to lose by assembling your old manifold after sanding it smooth and installing your freshly annealed brass rings, if it doesn't leak you should be OK for a while. If it still leaks, send it to Cotten.


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Re: manifold problems


Post by john HD » Wed Dec 24, 2008 2:03 pm


you may try getting your rings hotter than the oven, heating with a propane torch might work better.

as mike suggested it may be a last resort, cotten has the fix for it if it still leaks.


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Re: manifold problems


Post by Cotten » Wed Dec 24, 2008 3:09 pm


When pressure-testing, it is important to have a constant, regulated source of air. The smallest fissures will take a minute to produce 'blisters' of foam.

(1948 and) "Early" '49 Big Twin manifolds were steel tubing seamed together with silver solder. Their flanges are particularly malleable, and should be ground flat arbitrarily. The black arrow in the photo shows where the flange distortion "mirrors" the carb's flange, which is held back in that region by its idle gallery casting.

The white arrow points to one of the dimples from a staking tool used to hold the flange to the tubing for soldering. This one has sealer upon it, as they occasionally leak.

The replacement ferrule shown is of the material called PEEK. There are now several sources for this solution for the un-forgiving brass.
The spigots must be blemish-free, however, and "straight and round".
Constricted Big Twin manifolds can be swaged with a proper press puck to stretch them back out in the range of the original dimension, and then easily lathe-dressed.

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Re: manifold problems


Post by 49er » Wed Dec 24, 2008 8:56 pm

Thanks for the info. I think Cottons method is the way to go. I have to save up some money after Christmas.

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