Charles Hubbard wrote:
>
> Has anyone ever replaced the intake and manifold bolts and studs with
> hardened allen head bolts. I'm wondering if this would be worth a try.
If you do this you will want to install dowel pins to hold the manifold and
gasket in place. The studs serve this function and without them the installation
is harder. You can glue the gasket to the manifold and then hold the manifold in
place while you get two bolts started, and then ditto the exhaust manifold, but
doing it that way is a pain. Besides, using dowels to index the gasket and
manifold to the head is a good idea anyway. It ensures the ports line up
correctly and the gasket isn't protruding into the airflow. Its mostly a racer
trick, but it's a good idea for any engine.
One thing to remember is that studs do less damage to the threads in the head,
than bolts will, because you are not rotating the stud in the head when you
tighten things down. Use a bolt and you are, and that increases the chances of
damage to the threads in the head, especially with aluminum heads.
Another thing to consider is how the bolts you end up using will expand when
heated. You have uneven heat loads in the various bolts/studs that hold the
manifolds in place, and some of the bolts/studs do double duty, holding both
intake and exhaust. If the bolts you use expand too much when heated, they may
cause uneven clamping during operation and lead to leaks. You must also consider
the bolt's ability to stretch when heated and not take a set. Remember the
intake and exhaust manifolds are made of different materials and subjected to
different heat loads and will expand differently, putting uneven and varying
tension loads on the bolts/studs. They must be able to withstand this and do so
while heat cycling repeatedly and without losing their elasticity. Most grade 5
or equivalent bolts/studs will be okay, but some exotics or alloys will not work
well. Besides, there is no need for a hardened bolt and you will gain no
advantage using one.
--
Marc Sayer
82 280ZXT
71 FJ510
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