For small block Chevy's they make stamped steel things that go under the
header bolts and provide tabs you can bend into the flats on the bolt to
keep them from backing out. Many people complain about this problem,
some say the star type lock washers work but I never tried them.
There used to be some allen head header bolts on the market that were
drilled for stainless steel safety wire. I used them years ago on a 1969
Olds 442 that I had. They worked great, I believe they were made by Mr.
I took a mini-grinder and split the flange, making two with 2 ports
each per hedder. This stopped the problem in my case. The hedder
heats up quickly because of the thin - steel - hot exhaust and the
engine head heats up more slowly given the thick - cast iron - coolant
passages. Effect is to make the flange move and the bolts loosen
because of all the moving around.
I have heard of all sorts of other tricks but that is what worked with
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