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Replacement O-rings?
« on: September 03, 2013, 03:55:09 pm »
Where do you guys get replacement O-rings for your cylinder heads? I have my stock head cut for O-rings by MHR and he included the first set when I got it back.  But when I took the head off after about 15 hours of riding, I found that the inner O-ring is already being eaten away where it is exposed to the internal explosions. That doesn't seem like it is normal, or is it? Anyway, I'd like to get some replacement O-rings for it, and I probably want to get something different, but I don't know where to get them or what kind I need. Suggestions? I'm not sure what sizes they are as I haven't measured, yet. Do most builders cut O-rings the same size?

Thanks for the help.
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Re: Replacement O-rings?
« Reply #1 on: September 03, 2013, 04:06:22 pm »
If it was done my MHR its probably not done right that lazy POS. You're probably better off just getting a different head and having it o ringed by a real machinist that actually works.
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Re: Replacement O-rings?
« Reply #2 on: September 03, 2013, 04:39:34 pm »
Get on here and find exactly what you want.  They have everything.

http://www.mcmaster.com/#o-rings/=ocp42s
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Re: Replacement O-rings?
« Reply #3 on: September 03, 2013, 04:58:11 pm »
Thanks for the link. Are the silicone ones typically the ones used for this? They are only rated up to 425 degrees, though, which doesn't seem high enough to stand up to being in direct contact with the burning gasoline.
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Re: Replacement O-rings?
« Reply #4 on: September 03, 2013, 05:12:47 pm »
Use Viton
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Re: Replacement O-rings?
« Reply #5 on: September 03, 2013, 06:53:58 pm »
MCNUKE, what color are the ones you got on right now, orange-brown color ?
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Re: Replacement O-rings?
« Reply #6 on: September 03, 2013, 07:57:52 pm »
Erosion on the inside of the o-ring next to the bore is a sign of detonation or the machine work is exposing the o-ring to the flame in the combustion chamber.  The o-ring should NEVER be able to "see" the flame!

Detonation can be caused  by any one of or a combination of the following:

1. Low octane fuel
2. Incorrect ignition timing
3. Lean fuel mixture
4. A bad cylinder head design
5. A bad exhaust pipe design
6. The LT 250/500 power valve sticking open
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Re: Replacement O-rings?
« Reply #7 on: September 03, 2013, 08:44:26 pm »
Jerry  how often do you recommend replacing  orings if everything is set up right?
Would you say the vitron ones will last longer than silicon ones ?
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Re: Replacement O-rings?
« Reply #8 on: September 04, 2013, 04:18:43 pm »
Quote from: Dirtzilla on September 03, 2013, 08:44:26 pm
Jerry  how often do you recommend replacing  orings if everything is set up right?
Would you say the vitron ones will last longer than silicon ones ?

Replace them when they become eroded or flat on two sided.  Some guys replace them every time they remove the head.  Some guys run them for years.  I only replace them when they are damaged. 

I prefer the viton.  Silicone expands when it comes in contact with gasoline, oil, and antifreeze, making it difficult to reuse the o-ring.  When the o-ring expands you usually cannot get them back in the o-ring groove.  Silicone will with stand a little more heat but I think viton is good for about 400 deg. F.  If your head get up to 400 deg. F., you will have to replace a lot of other parts besides o-rings. 
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Re: Replacement O-rings?
« Reply #9 on: September 04, 2013, 10:52:42 pm »
Good info , thank-you sir
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Re: Replacement O-rings?
« Reply #10 on: September 05, 2013, 06:05:02 am »
Indeed. When Jerry speaks, press C^ to listen.
Cookie for anyone who gets it...
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Re: Replacement O-rings?
« Reply #11 on: September 05, 2013, 10:40:03 am »
Thanks for the info, everyone! My current o-rings are orange, so I guess they are silicone? 

I have a suspicion now as to why it was getting eroded.  When I took the head off, I noticed that when head had been tightened down and the O-ring was compressed, a small portion of the o-ring was squeezed to the edge of the groove and pinched between the head and cylinder surfaces.  So while the metal surfaces were very close, they weren't completely touching. I imagine that this allowed the o-ring to "see" the flame slightly.  I hadn't thought about the metal surfaces not fully touching as being an issue, as long as everything sealed up just fine (checked with leak-down test), and I expected the o-rings to be able to handle the combustion similarly to how a gasket would.  I guess I was wrong about that.

I'll have to order some new ones and make sure none of it is getting pinched between the head and cylinder surfaces outside of the groove. See if that solves it.

Thanks again for the help!
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Re: Replacement O-rings?
« Reply #12 on: September 05, 2013, 07:05:45 pm »
Quote from: MacNuke on September 05, 2013, 10:40:03 am
Thanks for the info, everyone! My current o-rings are orange, so I guess they are silicone? 

I have a suspicion now as to why it was getting eroded.  When I took the head off, I noticed that when head had been tightened down and the O-ring was compressed, a small portion of the o-ring was squeezed to the edge of the groove and pinched between the head and cylinder surfaces.  So while the metal surfaces were very close, they weren't completely touching. I imagine that this allowed the o-ring to "see" the flame slightly.  I hadn't thought about the metal surfaces not fully touching as being an issue, as long as everything sealed up just fine (checked with leak-down test), and I expected the o-rings to be able to handle the combustion similarly to how a gasket would.  I guess I was wrong about that.

I'll have to order some new ones and make sure none of it is getting pinched between the head and cylinder surfaces outside of the groove. See if that solves it.

Thanks again for the help!

I sounds like the grooves were not machined for the o-rings that you are using.  The o-ring cannot "overfill the groove". 

The o-ring has to "live" in a space that will allow it to move the correct amount.  The is why it  is important to never use any type of glue on the o-ring because glue keeps the o-ring from the microscopic movement that is necessary for the o-ring to seal properly and not damage the o-ring. 
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