Sealing manifold 61"

[Pan6161]

Changing carbs to S&S Oring lips on the heads are in bad shape pieces chipped off etc. Decided to use adapters and shovelhead style bands. Things went back together good. Have read about soap test for leaks how much pressure should you use (old lady has good set of pipes)?

[Cotten]

Twelve to fifteen psi is fine, but is has to be constant.
(Absolute vacuum at sealevel is ~14.7psi).
More details at http://virtualindian.org/11techleaktest.html
Today I found a manifold that leaked through porosities in the casting nowhere near the seals: Sure enough, someone thought it was a better idea to hog out the insides.

[Pan6161]

Thanks Cotten! 1st time on the site. My hats off to the hosts of this site it is awesome. Good info on link as well Thanks Again

[57stroker]

So, how do you fix an intake manifold leak? Yesterday I serviced my bike and finally used my manifold adapter. The back o-ring was leaking like crazy! I bought new split clamps last summer to replace the worn out aircraft hose clamps. When I took the split clamps apart, they had "sawed" the o-ring in half where the clamps bolt together. What is the best clamp to use? Is there a better o ring, maybe viton or silicone? I used a small rat tailed file and rounded the ends of the groove in the split clamps take the sharp edge off them. I tried putting the manifold back together with new o-rings, but I never could get the back o-ring to seal. I worked on it for about 4 hrs. I took the intake manifold on and off 4 or 5 times. The intake manifold has about 1/16" gap between it and the heads. (1/32" per side) It looks like everything is sitting square and in line. I did notice that the back o-ring groove was narrower at the top and back than in the bottom/front. I filed the intake manifold until the groove was uniform all around. I have old 61" EL heads that had o ring spigots welded to them years ago. I'm using an S & S E with the intake manifold that came with the carb. With the adapter bolted to the manifold thru the S & S carb bracket and the split clamps off, the o rings are sitting pretty in their grooves and everything looks in line, but when I put the clamps on, drawing everything down evenly a little at a time, the back one still leaks. Please Cotton, I need your wisdom. I finally have a digital camera and could post pics if that would help. You sure are right about the intake manifold leak, the bike starts like shit and idles even worse. It sure was a long 3 mile ride home last night from the shop to my house. I embarrassed to ride it when it runs this bad.

[Cotten]

Obviously, you must discard the split clamps.
The best clamp seems to be the lightweight aircraft-style clamps with a #10 screw instead of a 1/4" stud to tighten them. (Just as the Factory used!)
Assemble completely clean and dry: no goobers, sticky stuff or tape. (They may appear to seal at first, but vibration and cyclic expansion and contraction will eventually eat through,...if the nasty gasolines don't first.)
Do not over tighten. Cinch them up to where the bubbles stop, and no more. The purpose of the clamps is to expand the o-rings, not to secure the carburetor! (Band-style seals wrinkle.)
Make your carb support bracket fit in a manner so that there is no tweak or bind upon the manifold.
The rest is careful observation and attention to detail. Often pesky leaks are not the o-ring's fault, such as the over-ported casting I found, or micro cracks on the o-ring lip from over-tightening. Please make certain that conversion nipples are airtight by themselves: test them with a cork without the manifold installed. (And I always test the pancover screw directly over the port as well. )
Quite frankly, original plumber-style manifolds are easier to seal, now that there is a modern alternative to brass seals. Converted heads are severely depreciated in value.

Good luck!

[panfreak]

Now that I've got my manifold holding air nicely, I have halted installation of carb. It turns out that the mounting surface is not as flat as I would like. I'm probably not the only person who's Linkert has slightly bent corners. I was worried that doubling up on gaskets might make it worse, and I don't think sanding it down until flat is a good idea. A mechanic friend said that high temp silicone would help (I just went and got some) but now Cotten's got me worried. I can see dry and clean being ideal, but my conditions are less than ideal, so what does everyone else suggest I do?

[Cotten]

Yes, sillycone goes to hell real quick in P4gas.
Why are you afraid to sand it?
I ritually grind every 4-bolt flange to flat on a large disc sander, affectionately dubbed 'The Mexican Mill'.
(If anyone is offended by that,....just post me direct, okay?
I'll tell you not only about my Swedish Mills, but amuse you with my precious Polish Mills, where the stone stays put, and the operator runs around it with the workpiece. )
Note that carbs with three-bolt manifold flanges must be set up in a lathe because of their spigot.
With both varieties, the last spot to 'clean up' to flat is nearly always right at the idle gallery plug: the gallery ridge on the side of the casting stiffens the flange at that point, whereas the rest of the malleable flange pulls to fastener torque.
Occasionally this transfers to distortions upon the manifold's flange as well.

[dereborn]

Hey Cotten, you got any pic or number for the lightweight, aircraft-style clamps? I'm dumping my splits...

[Cotten]

OEM 27063-57

Your local V-TWIN dealer can get you a stainless version: #35-9177

[dereborn]

OK - Thanx!

...but.... V-twin isn't the "standard" supplier here in sweden, their URL?