SonexBuilders.net

Hey All
I’m getting ready to put the Pistons into the crank case. Directions call for using a silicone sealant. Which types of people use? It looks like the perma Tex red RTV has a max temperature rating of 650°F. Is there another one that’s better suited for the high temperatures associated with the piston?

Thanks very much!

Whatever you do, be *extremely* careful using any silicone sealant/RTV on engine parts. Any that squeezes out into the interior of the engine is liable to crumble or break off over time and wind up clogging an oil port or filter.

This is why Aviation form-a-gasket #3 (aka anaerobic sealant) is recommended for most of these situations - it only cures when it’s in contact with stuff, and any “squeeze out” gets washed away by oil in a still-liquid state so it won’t cause problems elsewhere in the engine.

Note that if you look on the Sonex website under “Manuals”, the latest version of the AeroVee assembly instructions specify using Form-a-gasket #3 under the piston barrel and shims.

—Noel

Thanks very much for the info! I’ll use the #3 gasket instead. I’m going to also compare my aerovee instructions to the most recent to see if there’s other updates.the previous guidance I got was to stick to the assembly manual that was for my aerovee. This wouldn’t allow me to take advantage of any lessons learned incorporated in subsequent editions

Hi All,
I listened to the wing rigging sonex podcast and there was a mention of an alternate sealant used. Can't remember the name but it may be of help to others who used the #3 gasket material and are looking for something different.

I used Permatex #3 twice. I hate it and could not get a good seal. It stinks, it's messy, it runs like water, and it gets everywhere. I used Hylomar Blue the last time. If it wasn't for that $6 valve adjuster, I would still be flying it and it still wouldn't be leaking!

Lou - Was that the aviation form-a-gasket #3?

It is stinky, but it should *not* run like water… sounds like maybe you got a bad bottle!

—Noel

Yes, Permatex Aviation Form-A-Gasket #3. OK, maybe it didn't run quite like water, but it drips off the cylinder bases and shims and down the engine cases. It was most noticeable after the engine ran a few times. I started to see nasty brown, heat-set, drip stains on the cases. There was no way to get them off without sanding and repainting.

Don't use Hi-temp red silicone or clones. Use an anaerobic flange sealant that is less runny than Permatex #3. Others have had success with #3, I am just not one of them.