Inlet manifold air leak
Seasoned HDF Member
Joined: Jul 2014
Posts: 8,607
Likes: 3,375
From: Cental, MI
Since the old O-ring or Rubberband days.. I have learned to Not Overtighten anything on the intake.. Worse with the Early Evo Compliance fittings...But..Gorilla Tight is Not necessary, nor desired on the late Evo Manifold either...
HDF Community Team
Joined: Dec 2005
Posts: 5,422
Likes: 2,621
From: NC USA
I stopped using grease, realizing it's such high temp rated it never drys out and can let the (my) manifold wiggle. If it can wiggle up down, it can move forward or rearward and that is a leak if not centered between heads.
S&S flanges are $85. and HD are $35. Any other brand is total junk. You have less that 60/40 chance it will seal.
Seasoned HDF Member
Joined: Dec 2005
Posts: 19,928
Likes: 8,030
From: poway
Muskrat went thru all this last year (?) where he had the large S&S manifold-to-CV adapter and was trying to use James flange gaskets. Took us a while on that one.
I stopped using grease, realizing it's such high temp rated it never drys out and can let the (my) manifold wiggle. If it can wiggle up down, it can move forward or rearward and that is a leak if not centered between heads.
S&S flanges are $85. and HD are $35. Any other brand is total junk. You have less that 60/40 chance it will seal.
I stopped using grease, realizing it's such high temp rated it never drys out and can let the (my) manifold wiggle. If it can wiggle up down, it can move forward or rearward and that is a leak if not centered between heads.
S&S flanges are $85. and HD are $35. Any other brand is total junk. You have less that 60/40 chance it will seal.
The important stuff is making sure that the manifold fits the heads. There can be too much or too little space between the manifold and the heads. Things like bore kits, strokers can change the length of the cylinders. SnS 113 motors use shorter manifolds than stock evos. It's good to install the manifold to the heads without the rubbers and see how much slop there is..
Also one of the worse rubbers is the Jame silicon ones. They'll ooze between the heads and manifold plus squeeze out any crack.
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Tourer
Joined: Jul 2019
Posts: 485
Likes: 445
From: Lithgow NSW Australia
G'day Fellas.
Thanks for the replies.
It's a bog stock 1999 80" EVO. It's getting hard to get genuine HD EVO parts down here and if I can find them $$$$$.
When snugging up the flanges there would only be about 1mm of compression on the rubbers.
I'll pull it apart again this morning and check how much side play the manifold has. I'll try to find some genuine flanges & rubbers (it's a 3 hour ride to the nearest shop).
Cheers
Thanks for the replies.
It's a bog stock 1999 80" EVO. It's getting hard to get genuine HD EVO parts down here and if I can find them $$$$$.
When snugging up the flanges there would only be about 1mm of compression on the rubbers.
I'll pull it apart again this morning and check how much side play the manifold has. I'll try to find some genuine flanges & rubbers (it's a 3 hour ride to the nearest shop).
Cheers
Thread Starter
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Tourer
Joined: Jul 2019
Posts: 485
Likes: 445
From: Lithgow NSW Australia
G'day Fellas.
I think I've got it. Put it together with just the slightest bit of WD on the rubber only. I use a spirit level to get the motor vertical and do the same for the manifold. Manifold bolted on till the rubbers just touched, mounted the carb to the bracket and snugged the manifold bolts. Threw the rest back on (bar the tanks), hooked up the aux tank and tested it. 99.9% fixed. That was the last pair of rubbers I have.
The only other thing I did was look up the jetting for my bike. Mine is 45/185 plus a 0.5mm shim under the needle. So I put one under it's needle. Took it for a test hill run. Sooooo much better and made 140kph at the top.
Mate is coming to take it home today.
Thanks for all your input.
Cheers
I think I've got it. Put it together with just the slightest bit of WD on the rubber only. I use a spirit level to get the motor vertical and do the same for the manifold. Manifold bolted on till the rubbers just touched, mounted the carb to the bracket and snugged the manifold bolts. Threw the rest back on (bar the tanks), hooked up the aux tank and tested it. 99.9% fixed. That was the last pair of rubbers I have.
The only other thing I did was look up the jetting for my bike. Mine is 45/185 plus a 0.5mm shim under the needle. So I put one under it's needle. Took it for a test hill run. Sooooo much better and made 140kph at the top.
Mate is coming to take it home today.
Thanks for all your input.
Cheers
Seasoned HDF Member
Joined: Mar 2010
Posts: 21,116
Likes: 7,640
From: Poolville
I always use a silicon grease as in caliper slider bolts silicon.. It can take the heat pretty good and when the cylinders expand the gap at the Intake will increase.. If your flanges are bent from torquing on over sized seals you can always pound them out again, I have without issue.. Not necessary to purchase new flanges.. OEM seals are the go to if possible...
Stage III
Joined: Nov 2025
Posts: 3
Likes: 1
G'day Fellas.
I'm helping a mate with his 1999 EVO Fatboy with only 18,000Km on it. I found it had an air leak. Many years ago a "shop" had installed a set of pipes and K&N air filter and jetted the carb with 48/200 jets. I suspect to mask the air leak. I thought I'd tackle the air leak before doing the jets.
Well haven't I had "fun". Had the manifold on & off at least 10 times! After the first few times (with new rubbers) I had a good look at the flanges and found them to be slightly bent. I ordered new flanges and more rubbers. I've watched all the youtube videos and tried everything putting it together (dry, with oil, grease, hylomar, even silastic) to no avail. The leak is definitely at the flanges, not the carb or voes or vac line to fuel tap.
Question: with the flanges bolted up hard should I still be able to twist the manifold?
Any suggestions.
Cheers
I'm helping a mate with his 1999 EVO Fatboy with only 18,000Km on it. I found it had an air leak. Many years ago a "shop" had installed a set of pipes and K&N air filter and jetted the carb with 48/200 jets. I suspect to mask the air leak. I thought I'd tackle the air leak before doing the jets.
Well haven't I had "fun". Had the manifold on & off at least 10 times! After the first few times (with new rubbers) I had a good look at the flanges and found them to be slightly bent. I ordered new flanges and more rubbers. I've watched all the youtube videos and tried everything putting it together (dry, with oil, grease, hylomar, even silastic) to no avail. The leak is definitely at the flanges, not the carb or voes or vac line to fuel tap.
Question: with the flanges bolted up hard should I still be able to twist the manifold?
Any suggestions.
Cheers
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Seasoned HDF Member
Joined: Dec 2005
Posts: 19,928
Likes: 8,030
From: poway
The flanges are bolted up properly, you definitely shouldnt be able to twist the manifold any movement means the sealing surfaces arent seating. Double check the manifold alignment by dry fitting it without rubbers, make sure the spigots arent out of round, and use good-quality (preferably OEM) rubbers. A light smear of silicone grease is fine, but if you need sealant to stop a leak, something isnt flat or aligned. With fresh, flat flanges and proper fitment, the manifold should lock solid with zero twist. Cheers.
You can twist them if they are greased. Done it a number of times I've messed with different length manifolds a bunch. Last one was cutting down a manifold from a SnS 116 ci motor to make a standard length all bore 107.
https://www.hdforums.com/forum/engin...l#post20483984
Seasoned HDF Member
Joined: Mar 2010
Posts: 21,116
Likes: 7,640
From: Poolville
You can twist them if they are greased. Done it a number of times I've messed with different length manifolds a bunch. Last one was cutting down a manifold from a SnS 116 ci motor to make a standard length all bore 107.
https://www.hdforums.com/forum/engin...l#post20483984
https://www.hdforums.com/forum/engin...l#post20483984
Necessity is the mother of invention...
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