Manifold clamps, O-rings, and fuel

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Cotten
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Manifold clamps, O-rings, and fuel

#1

Post by Cotten » Sat Jun 16, 2007 12:28 pm

Hey folks,
Look what fuel does to O-rings!

The top is a fresh V-TWIN O-ring. The bottom was immersed in Shell Premium with ethanol for a day. An O-ring immersed in straight gasoline (Casey's General Stores Regular) also enlarged, but to slightly less of a degree.

Just another reason to avoid over-tightening clamps, and to avoid overkill designs of clamps!

I am not certain if there are other varieties of O-rings still available on the market to test, but I invite others to compare.

....Cotten
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#2

Post by Guest » Sun Jun 17, 2007 4:11 am

How tight is too tight...I have noticed here lately that if not TIGHT my clamps tend to slip to the inside toward the throat....I have tried several types/sizes of O rings and still the same...no problem starting...yet...but waiting...Skip

Cotten
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#3

Post by Cotten » Sun Jun 17, 2007 2:35 pm

Skip!

Once a clamp has taken a tweak, it seems like they never want to stay straight. (That's why I keep a half-dozen sets on the wall.)

It would appear that clamps get tighter if enough fumes get to the O-ring.
(Or drool from a leaky petcock while the machine is sitting.)
We cannot assume that the swelling would be even around the ring, either!

Everybody must remember that the Factory never held a carb on a machine with the clamps: There was always a support bracket for that.
The clamps merely compressed the O-rings, allowing the assembly to 'float' with thermal expansions and vibration.

The most distressing thing is that regular gas swoll them up too.

So,
Either they always swelled in fuel, or composition of the rings has changed.

Does anyone know of sources of rings that would likely be different?
(I haven't kept my S&S dealer status up to date.)

....Cotten

FlatHeadSix
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#4

Post by FlatHeadSix » Sun Jun 17, 2007 4:34 pm

I'm going to guess that modern O-rings are synthetic, some variation of Neopreme similar to the Viton tips on the needles. And we all know how those swell up!!!

I would also bet that the composition of the rings has not changed much since they first starting using them, they've always been synthetic. The composition of the fuel is what changed.

As we've discussed in other threads Cotten, it sure would be nice to have some fresh 1967 gasoline to do some comparing. The old leaded regular may have swelled them too. A predictable amount of swelling may have even been engineered into the design to make them seal better.

I'm sure you've seen obviously different seal compositions over the years. Some of them soften and swell where others get hard and brittle.

just some thoughts....

mike

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#5

Post by Fixman » Sun Jun 17, 2007 5:32 pm

Years ago I remember buying special aircraft o rings. This is a current quote about fuel resistant o rings from an aircraft supplier.

These MS29513 series O-rings are resistant to fuel and are ideal for applications such as fuel injection connections and primers. A small amount of fuel proof grease applied to these O-rings helps the installation and operation of primers. Not resistant to automotive fuels.

The last sentence is scary.

Kent

Cotten
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#6

Post by Cotten » Mon Jun 18, 2007 2:58 am

Thank Gawd harleys don't reallly fly.

...Cotten

fourthgear
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#7

Post by fourthgear » Mon Jun 18, 2007 2:12 pm

There is so little of the o-ring that is open to the fuel , That I would not even worry about it . My experience has been with only the o-ring designed manifolds on Pans and Shovels. I have never taken any off that were bloated out of alignment, you do find them installed incorrectly and not sealing ,but that's an installers fault . Sure almost all have shown signs of compression but that's to be expected since you do compress them a little if properly installed , its the way it was designed. They last as long as any other seal if installed correctly ( that includes head / manifold alignment when installing the heads).That o-ring is almost completely encased within the clamp and manifold/head nipple . Some people just don't like o-rings and I don't know why, o-rings are our friends !

john HD
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#8

Post by john HD » Mon Jun 18, 2007 4:00 pm

i always slather mine up with dielectric silicone grease before installing.

i believe it helps them from getting pinched.

john

Skip
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#9

Post by Skip » Mon Jun 18, 2007 4:44 pm

Just ordered a set of these Viton O rings...and a set of the regular black rubber ones...we will see what is what here soon....I will start with the Viton when they arrive......Skip

VT

#10

Post by VT » Mon Jun 18, 2007 4:56 pm

Everybody must remember that the Factory never held a carb on a machine with the clamps: There was always a support bracket for that.
The O-rings are there to seal. That is all. Even with clamps tightened, you can still move the manifold if you don't have the float bowl support installed. I say let the O-rings swell-up. Maybe they'll find a gap to seal.

Cotten
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#11

Post by Cotten » Tue Jun 19, 2007 2:04 am

In normal operation, the O-rings are hopefully not exposed to significant amounts of fuel.
But what happens if you forget to shut your petcock for the weekend (or it leaks all of the time anyway?)
OHVs have their carbs aimed upward when on the kickstand. It is not at all unusual for fuel to make it all the way to the cases!

So consider what happens if only the bottom of the rings swell from total immersion..

Consider also what might happen to the 'rubber' compound after swelling and shrinking repeatedly?

Just something to look forward to....

....Cotten
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