nipple vacuum leak

[108]

The last month or so I started having erratic hot idle speeds and sudden intake backfires, even durring a steady idle on my '48 FL. It used to idle fine earlier in the summer so I suspected a vacuum leak. A pressue test blew nickle sized bubbles from where the nipple screws into the rear head. Cut, collapsed and removed the nipple and it has no O ring. I've owned it since '76 and its never been out. Did it originaly it have one? I have a new nipple with an O ring but looks like if the nipple is screwed in real tight it will smash the O ring because there is really no room for it. Any advise ?

[Panacea]

I had Headhog weld up and re-thread my pan intakes, he also installed a set of new "o"ring nipples which came with a thin gasket that gets sandwhiched beetween the nipple and the head. When I put the heads into service I found they both leaked badly. I had to build a special wrench to remove the nipples (spanner). The new gaskets were "munched". I cut some new ones from gasket material and also used steam pipe dope on the threads. So far no leaks....Mike

[FlatHeadSix]

Mike,

I thought headhog was supposed to be the "Cadillac" of head rebuilders. You had to rebuild his rebuild because his new nipple inserts leaked fresh from his shop???? Did you call him on it? Did his shop not test them before they shipped them back?

A previous owner converted my '49 heads to "O" ring long before I got the bike and I've been thinking of sending my heads in to have them converted back to the original plumber nipples, but now I'm not sure I want to do that, right now its a one-kick bike.

mike

[Cotten]

108!

There was no O-ring or seal on the original nipple.
It was one of Colony's innovations, along with their disastrously over-sized rivets made of mud.

You are right, it is obvious that there is no room for an O-ring, and it just splits if you attempt to tighten the nipple firmly. Any success at all would be temporary anyway, as heat and fuel take their toll on gummyworms.

Please inspect the surface of the counterbore where the new nipple will seat. It's width makes it difficult enough to seal (Knucks had a wonderful thin lip), so any blemishes or distortions are a real concern.

I can supply a thin wafer of PEEK for a repair gasket, but it still won't be an easy task to achieve a perfect seal..

Beware also of some of Colony's nipples that have an excessive chamfer where the manifold ferrule would seat. Quality replacements are available from http://www.carlscyclesupply.com/

Panacea Mike!

After welding up the damaged threads, the counterbore surface would have had to have been re-machined square to the new threads, while the head was still fixtured, giving a pristine surface for the nipple to butt against.
Although a proper sealer would still be prudent, I'm sincerely disappointed to hear that a repair gasket was necessary.

FlatHeadSix Mike!

If the threads in the head casting are not torn out by previous botched nipple extractions, installing new nipples is certainly something you can handle yourself!


....Cotten

[Panacea]

Cotton, thanks for the insight, my "home made gasket" was made to replace the failed install from Headhog. I'm sure the steam pipe dope is responsible for sealing up the leaks....for now. I have great respect for Don and his head service, I may be partially to blame for pressuring him to "hurry"...Mike

[108]

Thanks guys for the info ! Cotton, I think the nipple I have is a Colony part (no name but I recognize the package design) the threads fit perfect on both sides, and the counter bore and ferrule surfaces are plenty wide so it should be OK. I'll remove the O ring and use my favorite sealer (GMS) . I never intended to use their rivet. The old nipple was locked in by a very nice 1/4" fine thread stud with a screwdriver slot and a 1/2" size nut with multiple cotter pin holes and a copper seal washer. I've never seen this type on another Pan before--do you know who made them ?

[Cotten]

108!

The reason for the rivet is to insure that the nipple doesn't back out the next time you wish to loosen and remove the manifold.
Especially if heat or corrosion makes a 'marriage' or the threads, it would lead to a situation where you are forced to remove both heads for any disassembly at all, and any seal you have worked so hard to achieve would be sacrificed.

"Plenty wide" is NOT actually a good thing, although there is no other choice with a Pan.
Just like a narrow seat seals best on a motor valve, the wide mating surface of the nipple to casting interface is what makes it so difficult to seal.

I'm not familiar with GMS, but if it resists P4gas and heat, I'm very very anxious to test it. And so is the rest of the modern world.
(If "S" stands for silicone, uh oh.)
Although it is not perfect, I still endorse Seal-Lock "Fluid-weld", after blasting the parkerizing off the internal threads.

The nutted screw assembly you describe is OEM Factory, for '52 Pans, although that vintage quote is trusting to a poor memory without Palmer's handy.
If your heads do not have the large drain gallery welch plugs of a '48-'49 issue, you have later models.

The nutted 'rivet' was another vain attempt to elude the evil vacuum leak, and they soon returned to the pressed rivet.
If you can get it to seal (zero bubbles), perhaps with a fresh replacement for the copper washer, then by all means stick with it.
(One of my '49 projects was "updated" to the design, and I shall cut the modern thermoplastic PEEK to go under the visible copper seal, as if I shall ever get around to my own projects....)

....Cotten

[fourthgear]

Ya , one leak out of what ,maybe thousands , ya, all his good work over the years, is now in question .

Hay, I gotta stick up for a fellow Buckeye !

And he did fine work on my heads !

[108]

Cotten, My heads are the original '48's so I guess the threaded rivets were installed years later and have never leaked. A contact test of the nipple shoulder with yellow gearset-up dye showed good contact. "GMS" is what I keep calling it but its a GM "engine assembly adhesive" I get at the Chevy dealer where I work. Yes, it's a type of silicone sealer but not the wet, shiney stretchy stuff your thinking of. Its flat aluminum colored and much thicker when wet and firmer when curred. It's rated to 600 degrees with amazing adhesion ability to CLEAN metal and you can use it (sparingly) for many things. For example, I have it as a sealer/ insulator/vibration absorber between my exhaust pipes and (original)spigets. I have it all back together now and no leaks at 20psi. and the idle is perfect again . I just hope the seal holds after a few months of expansion cycles.