What is this Goop?


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Well-known member
Feb 24, 2023
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Cedar Lake, IN
Getting ready to replace broken thrust plate/upper motor mount in my 1975 'Rude 9.9. The parts are hard to find and pricey. There is a guy on ebay selling reconditioned assemblies that have some type of goop substituted for the original rubber bushings. If I knew what kind of goop to use I could just fix the ones I have. Looks a bit like urethane to me, but will urethane hold up to the high temps in the exhaust tube?


  • Thrust Mount Rebuilt.jpg
    Thrust Mount Rebuilt.jpg
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It's someone common to fill worn out automotive motor mounts with window weld (urethane). It works okay.

Window weld is black so that's certainly not it, kinda looks to me like it might just be a type of polyurethane sealant/adhesive. The melting point is probably not high enough, however if it's pumping enough water nothing in there should really get that hot, and it may surpass whatever rubber OMC put in there.

I'd send a message to the seller and see if he's willing to give up what he uses.
Not sure what he has on his but I used Locktite brand marine threw hull adhesive sealant and it has held up for 2 years now. Have o be careful to get the metal sleeves back in the right spot. Clean both parts well first. I let mine set for about 6 days before installing them to give them a chance to cure
Many companies like Sika, but even companies other than those selling boat products, make both 1-part and 2-part polysulfide-based (think 3M 5200) in gray or grey color.

To me it looks like they used something like this …

Very cool. Thanks for the ideas gentlemen. Never ceases to amaze me the wealth of info on this web site! Now I just need to get off my butt and start tearing into it.
Silicone is very high-temp. If you doubt this, take some regular GE kitchen and bath silicone, and let a glob of it dry. Take a blow torch to it and see what happens. Surprised?

Silicone definitely has it's place, but it needs a very clean area if you want it to stick.
Not surprised. I've read the side of the tube before, what is the max temp for pure sili, 450 or something isn't it? Think they also make a high temp sili, but like you say, it may not stick very well. I am considering it though.

The other thing I'm thinking about is, is it really necessary to have some sort of rubber in there? Seems to me it should be just fine with a solid metal mount. It's not like a 2 stroke is a smooth quiet running motor anyway. Whatcha guys think?