Greasing O-rings

I use disk brake pad lube, just because I keep it on hand for the cars. Works well for me and is a very high temp grease.

I've used ChapStick on carburetor parts, (float bowl gaskets for easy removal and reuse when re-jetting), as well as rocket engine seals.

rstaff3 said:

I used vasoline for years although I have since been told it's a bad idea...

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There is so many "opinions" thrown around on TRF, you really have to make your own decision. There really isn't any right or wrong. It's what works for you.

In my opinion, since Aerotech says to use a petroleum (Vasoline) when you run out of their supplied lube, I don't see how anyone can say Vasoline is a "bad idea".

Handeman said:

There is so many "opinions" thrown around on TRF, you really have to make your own decision. There really isn't any right or wrong. It's what works for you.

In my opinion, since Aerotech says to use a petroleum (Vasoline) when you run out of their supplied lube, I don't see how anyone can say Vasoline is a "bad idea".

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I agree, Vaseline is great stuff being a petroleum product. ChapStick is also petroleum based. Most folks probably never thought of it. I used ChapStick routinely at the strip changing jets or power valves. Keeps the bowl gaskets intact and reusable. Nice when you have three carburetors to deal with.

Handeman said:

There is so many "opinions" thrown around on TRF, you really have to make your own decision. There really isn't any right or wrong. It's what works for you.

In my opinion, since Aerotech says to use a petroleum (Vasoline) when you run out of their supplied lube, I don't see how anyone can say Vasoline is a "bad idea".

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I forget who said that, but I wouldn't hesitate to use vasoline. I changed mainly to use hybrids.

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I stopped using grease after about the 3rd motor build. I disassembled my first phenolic liner motor this past weekend. I believe I will probably start greasing them, and threads again....

When working with little motors that only burn for a fraction of a second to a few seconds, most stuff will probably work. The larger the motor, the longer the burn time, and therefore the more critical the decisions. Think what you are doing would have worked for the Challenger? Hence Dow 111 and probably a host of similar products that we would not encounter.

For Hybrids or Liquids, one has to consider that the environment is now a very hot oxidizer (potentially) and your grease can become a fuel. That would not be good... Plus the grease has to work well over a larger thermal envilope. Hence Krytox.

I use Krytox for some locations on my EX hybrid, but it is expensive. I use Dow 111 for everything else, solids and other parts of my hybrid.

Gerald

G_T said:

When working with little motors that only burn for a fraction of a second to a few seconds, most stuff will probably work. The larger the motor, the longer the burn time, and therefore the more critical the decisions. Think what you are doing would have worked for the Challenger? Hence Dow 111 and probably a host of similar products that we would not encounter.

For Hybrids or Liquids, one has to consider that the environment is now a very hot oxidizer (potentially) and your grease can become a fuel. That would not be good... Plus the grease has to work well over a larger thermal envilope. Hence Krytox.

I use Krytox for some locations on my EX hybrid, but it is expensive. I use Dow 111 for everything else, solids and other parts of my hybrid.

Gerald

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My understanding is that the grease is only to protect the o-rings during assembly so they function correctly during burn. Are you saying that the grease is critical to o-ring seal in larger long burn motors?

If the grease boils off too easily, that bubbling may potentially damage the surface of the O-ring and may even push it aside allowing blow-by.
If the grease solidifies, it may not allow for thermal expansion or pressure based compression of the O-ring without tearing.
If the grease is combustible in an oxidizing environment, we've just coated the O-ring with extra fuel (hybrids).
If the grease is soluble in the oxidizer or the fuel (liquids and hybrids) then we have contaminated things and may have other issues. Ditto the O-rings!
If the grease is chemically reactive at elevated temperatures with any of the items it may contact in the hot motor, that could be an issue.
If the grease is a solvent for the O-ring at elevated temperatures, that could be a big issue!
If the grease (or O-ring for that matter) can absorb oxidizer (hybrids and liquids) it can possibly be sensitized causing big issues!

I'm probably missing some etceteras in there somewhere.

Gerald

I've used Tommy's chicken grease before. Worked great!

I was wondering if it was "Slick Honey." Sort of a sticky-slippery snot sold as a lube for mountain bike suspension components--probably a repackaged or slightly reformulated version of other industrial lubricants, with a little bit of marketing thrown in for extra performance.

Super Lube is recommended for a good reason. It works and it will last you a very long time. No reason to skimp on something that is already cheap and can save you $100s by keeping your casings intact

RocketryBen said:

I ruined a 24/40 case once when I used olive oil..

Ben

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This IS news! Olive oil didn't work; why? Was the failure of the case an o-ring issue?

Best -- Terry

Handeman said:

My understanding is that the grease is only to protect the o-rings during assembly so they function correctly during burn. Are you saying that the grease is critical to o-ring seal in larger long burn motors?

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There's one other thing that heavy grease does in large motors; it minimizes the o-rings from being cut by the snap ring grooves when you fill that groove with grease. I think it was Pat G told me that.

Best -- Terry

Dow 55 provides a superior seal over all others IMO. It causes o-rings to swell after assembly. The longer the motor is built before flying, the better the seal. Harder to disassemble though. Not hybrid safe.

I have a large can of super lube if anyone wants it. Yes it's open and about 80% left. You pick up the shipping and its yours

Binder Design said:

Dow 55 provides a superior seal over all others IMO. It causes o-rings to swell after assembly. The longer the motor is built before flying, the better the seal. Harder to disassemble though. Not hybrid safe.

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Well holy carp, I just learned a thing.

Molykote[emoji768] 55 O-Ring Grease
should not be used with the following
materials unless thoroughly tested for
your specific application:
• Silicone rubber (SR)
• Polycarbonate (PC)
• Acrylonitrile-butadiene-styrene
(ABS)
• Liquid oxygen (or other strong
oxidizers)

I forget which of the many Krytox variants is the correct one, but fortunately I don't need it just now.

Binder Design said:

Dow 55 provides a superior seal over all others IMO. It causes o-rings to swell after assembly. The longer the motor is built before flying, the better the seal. Harder to disassemble though. Not hybrid safe.

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I would be very leery of anything that caused the o-rings to swell. That means it is chemically affecting the o-ring and their mechanical design properties. This could be contributing to a failure. I haven't heard of any o-ring manufacturer or equipment manufacture using o-rings that recommends a lubricant that chemically affects the properties of the o-rings. Engineers select o-rings base to the physical properties they have for the application. If the lubricant changes those physical properties, the whole reason for selection of that o-ring goes out the window and now you're just flying on a hope and a prayer.

Are you sure the 55 causes swelling? If it does, personally I won't be using it.

Handeman said:

I would be very leery of anything that caused the o-rings to swell. That means it is chemically affecting the o-ring and their mechanical design properties. This could be contributing to a failure. I haven't heard of any o-ring manufacturer or equipment manufacture using o-rings that recommends a lubricant that chemically affects the properties of the o-rings. Engineers select o-rings base to the physical properties they have for the application. If the lubricant changes those physical properties, the whole reason for selection of that o-ring goes out the window and now you're just flying on a hope and a prayer.

Are you sure the 55 causes swelling? If it does, personally I won't be using it.

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It's all I've ever used but I use buna-n rings too. It is specifically designed to swell o-rings, but they do not recommend it be used with silicone rings. I've used it with silicone rings and it swells them too much if you leave the grease on. Which means it also softens them up over time. Although I have fired motors that were assembled up to ten years prior without incident. For most motors that are assembled and fired shortly thereafter, the whole point is moot. It takes some time. Most lubricants will swell silicone rings unless they are specifically designed not to , like Dow 111. Pretty much any silicone based grease on a silicone ring will swell it given enough time. But I'd avoid hydrocarbon based grease on silicone rings altogether. Those two don't play well together and the rubber can break down over time.