What have you guys found to be the best sealant for the head bolts to block on a 21 stud. I tried thread sealant paste but it didn't work. Thx and Happy New Year
I have used 3m weatherstrip adhesive for longer than I can remember on dozens of not hundreds is engines to include flatheads, small & bb Chevy. Never a leak or issue.
Permatex Thread Sealer part #80632 Available on Amazon in both the 4oz jar and 6ml tube.
This is a Teflon product that I have found seals well and does not harden. . . Chap
I used to use Aviation Permatex and just dip the threaded tips in the can but there are likely better sealers now days. This also keeps the bolt tips from corroding which allows for easier removal during maintenance.
When I install the studs, I do not put water into the engine for at least a day - just to give it some time to seal the threads a bit. Also, I use a thread chaser (not a tap), on the block threads - to get as much rust and old crap out of them as possible.
This method has worked for me on countless flatheads - with both studs and bolts.