Really need help wtih o-ring comp for engine application

[bob1111]

We are designing a small engine cylinder head that will be seated with a rubber o-ring. There are similar designs already out there that work fine. Problem is deciding what o-ring composition to go with. Most people have no idea. So far, we are looking at Viton but there are several variations of the material.

Most companies spout off specs and crap but we really need a well stocked, common compound to hold the price down for an OEM design. Any ideas here? Who do we need to talk to?

Engine operating temp is max 250F
Compression max is 1500psi
fuel exposure is methanol and ethanol and gasoline as well as some oils.

 

[dgallup]

You will need one of the GFLT compounds for Methanol capability. That is one of the worst fluids for FKM (fluorocarbon). Be sure you really need Methanol compatibility as that will really raise the cost & hurt other properties.

Do not use Viton as a specifier. Viton is a DuPont trademark, using it is meaningless. Learn how to properly specify an o-ring compound using SAE D2000. Buy a copy & spend some time reading it.

I can recommend Precix Inc. They have many compounds with OEM approvals. Something like their F78 would probably meet you requirements. There are many other reputable o-ring manufactures. Stay away from most of the stocking distributors and App!@, they will over charge for material of unknown compounding & origin.

 

[patprimmer]

viper

I feel there is a lot of data missing, like:-

Is this an IC engine.

How is it cooled.

Where is the o ring relative to combustion products and cooling media.

Where is the 250F measured relative to the o ring.

Will the o ring be sealing the combustion chamber or water ways or fuel lines fo all we know from your OP.



Regards
Pat
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[bob1111]

Thanks guys, sorry for the ignorance on o-rings. I should say Fluorocarbon.

Engine, liquid cooled IC 2-stroke

static head seal application.

o-ring separated from combustion gas by .050" Al mating surface.

O-ring also subject to glyco based anti-freeze.

dynamic compression not to exceed 1500psi

Methanol a must but rather limited exposer and in vapor form. All fuels vaporized with 2-cycle oils.

 

[bob1111]

I am looking at a MIL spec M83248/1 Fluorocarbon compound for increased resistance to fuels. Not sure which durometer hardness to use. They have 75 and 90 available.


I agree, I really should talk with an OEM. The suppliers do not know any more than I do about o-rings. I plan to call Parker tomorrow. Any others?

 

[Lou Scannon]

Parker is pretty capable, but a rather large company so I don't know how successful you will be getting through to the right person, or how interested that person will be in helping with a potentially custom application, without a large amount of NRE entering the discussion.
Another very capable company is SIMRIT. I believe they are based in France. I think they tend to cover the niches that Parker finds uninteresting commercially.

 

[hydtools]

For a static seal with metal-to-metal seating with no risk of extrusion, use a 70- durometer. It will seat easily and conform to the gland surfaces.

Ted

 

[bob1111]

Any other OEMs out there? Really having a tough time finding an app engineer for o-ring compounds. Parker has about 30 Fluorocarbon compounds alone.

 

[dgallup]

I mixed my spec numbers. What you want to use is SAE J 200 / ASTM D2000. It is really one spec, started by ASTM but then taken over & kept up to date by the SAE because it is so useful for automotive applications. This single spec can be used for pretty much any o-ring on earth once you figure out how to use it's line call out nomenclature.

I'm not familiar with M83248/1, it has been canceled. I doubt the military has any need for methanol compatibility. One problem with the AMS & MIL specs is the requirement for the QPL, Qualified Product List. In my experience most manufactures don't want to have to bother with it.

Talk to Bob Coleates at Precix, 828-724-1775, he can get you headed in the right direction. I have no connection with the company except they supply some of our fuel system o-rings.

 

[bob1111]

Actually talked to him today. I guess he is the automotive side guru. He recommended their V176 compound. Problem is they will not sell to me and most suppliers buy their stuff from China and do not want to offer specs for their stuff.

It would seem what is already being used in the industry is the standard Fluorocarbon A, Viton 75. I cannot be certain though. We will have to get some samples here for some destructive testing.

Parker has recommended their V0747 or the V1263 for more chemical resistance. At this time, I am thinking we should do testing with the Viton 75 rings and see if we find failures with them.

I am really torn trying to determine if I need a harder compound than 75A. Some say it can make compression set worse, some say it it will resist extrusion failure better. No idea here.....

 

[hydtools]

viper683, the higher durometer will resist extrusion better. However, if you have no extrusion gap you can use the lower durometer material with no worry. You can also use the lower durometer material o-ring and a backup ring to resist extrusion if extrusion will be a problem.
I am assuming your cylinder head seal is a groove with the o-ring in it and will have metal-to-metal closure when bolted down. No extrusion gap on the side of the groove away from the pressure. No? Yes?

Ted

 

[dicer]

I thought there were silicon based rubbers/ synthetics that would work just fine into the 600 degree F range.
I think the better way to go is an integral head, like most all small aircooled 2 cycle engines have saves you the sealing problems and fastening etc.

 

[bob1111]

We don't have the option of an integral head unit.

Hydtools, NO extrusion gap here so I really do not see any concerns with that failure mode. metal to metal contact on the head with an o-ring groove in the cylinder.

 

[pmtoo]

Has 250F been tested/verified as a trustworthy number? I normally work with air cooled two strokes, and .050" from the combustion chamber/cylinder near the head interface I am used to much higher temps. I would expect to see 200F at low load operation with forced air cooling and up to 400F (on air cooled again) at full load and speed if it has a properly functioning cooling system, though I have had some much higher. In my applications I normally use a copper gasket, or sometimes simply a lapped surface, but these are not fit for production. I do have one engine in production using a copper gasket, but it is small volume and hand built.

I find it hard to imagine that a liquid cooled engine would be significantly cooler in an area so close to the heat source, but if that is what you have verified thorough testing or modeling, then it is much more useful than my above statements.

 

[dgallup]

Without looking it up, I believe nearly all FMK compounds are good to 250 C (482 F).

 

[bob1111]

Yes, the liquid cool engines have shown significantly lower operating temps in high heat areas such as the exhaust port side of the combustion chamber. We have not probed the exact surface to be subject to the o-ring but there are similar designs out there that hold up great. Again, the o-ring is a light brown color which is common in the viton 75 compound I guess.

I am sure some testing will be needed here.

 

[dgallup]

Color means nothing.