I checked the price on these replacement studs that go into the cylinder heads and through the intake manifold. 5 bucks each from Courtesy. Need 4. These studs are strange, they are narrow in the middle body portion and wider at the ends where the threads are.

Anyone know why they are designed this way?

 

IIRC, it's because the narrow section is rolled too increase it's tensional strenght!

 

So they break off easiliy

 

 

 

Rolling them increases the tensile strength of the steel, but due to the smaller diameter, it weakens it overall.

Generally the reason bolts like that are undercut is to provide a good range for the bolt to stretch when installed just under its yield strength and it will maintain that torque value over time because it's under constant stretch.

go take a look at some of the higher quality rod and head bolts/studs out there and you'll see the same thing.

I would suspect this may also have something to do with the high change in temperature on those parts because of the difference in engine temp vs. intake temp. there's likely to be some funky temperature gradients in the manifold right there so you want some give in the system somewhere to keep from warping and ruining gaskets.

Just my $0.02.

 

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