All too common. Cambridge Motorsports has some improved rocker shaft bits
for non-roller rockers that look like they'd help. Probably a bit pricey
though. I think part of the problem is that the shaft flexes a lot and puts
a shear load on the studs.
Did you recently upgrade your pushrods? I broke two rocker studs a year or
so ago when I upgraded the pushrods to large diameter titanium ones--they
don't flex at all. I fixed the problem with aircraft bolts. I saw a video at
an auto parts show where someone put a strobe light on pushrods while the
engine was under load on a dyno--they were flexing like soda straws (of
course it was at a booth selling better pushrods). The flexing probably
reduces the load on the bolts, but it's not something you'd want to do
intentionally.
I would try even better bolts--there's a lot of stuff marked grade 8 that's
just junk. You might also try grade 5 -- they're tougher. Or check the back
pages of Grassroots Motorsports for the guy selling really good
aircraft-style bolts and try them.
|