Thread sealant for cylinder studs

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Apr 15, 2004
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Hi folks,

Once again I seek advice :)

I'm starting the reassembly of my 850 engine (look for a project report soon) and am wondering what to use for sealing those problem cylinder studs. There's the one at the base that sits directly over the cam, and those two studs near the pushrod tunnel at the top. The drilling for the base stud goes all the way through, and the drilling for one of the upper studs breaks through into the pushrod tunnel. So they have to be sealed.

I have a variety of fine Permatex products at my disposal, including:

red, blue, and green "loctite"
"high temperature automotive grade thread sealant"
copper high-temp RTV
good old #2 gasket dressing

I also have a tube of Threebond 1104 (like Yamabond). I have some Hylomar too, but I don't think it would be up to the job.

I was thinking of using the red loctite. It's rated to 300 degrees F. Is that good enough? I'm not sure how hot these areas get. And would the red loctite cause trouble if I ever have to remove the studs? The crankcase threads are all helicoiled at the factory.

thanks again,
Red Loctite (Permatex) is what I think you should use (that is what I'd use) as red compound is generally meant for studs (in the UK at least) as it holds tighter than the blue which is for normal fasteners, and green is for holding bushes or spindles that have become a loose fit in their bores. I would not use a gasket sealant. There should not be any problem removing the studs later on with the red compound.
Red loctite it shall be. And after a discussion with my machinist, the crankcase joint will get getting the Threebond. It's the local favorite.

I've heard of some stuff called Wellseal being popular in the UK, but I don't think it's available over here.


Be careful with the 1104. It is not an anaerobic sealant, so any squeezed out inside the crankcase could circulate through the engine as little rubber balls.

I prefer to carefully mate both sides of the crankcase with valve grinding compound on a sheet of glass. When I am satisfied they are as flat a possible and trial mating seems to provide a seamless joint, I will use an anaerobic sealant (Loctite 518). These do not do as well on uneven joints as 1104, but when done properly give an oiltight surface.

Used sparingly, 1104 will do an excellent job.

My $.02.
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