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Discussion Starter · #1 ·
I broke an exhaust rocker stud on my 565" bbc yesterday. I t was cruising about 3000 Rpm and made a quick metallic pinging type sound and just quit running. tried to turn it over and it made a couple revolutions then stopped ( bent the starter bolts ) Pulled the valve covers and found the #2 exh stud snapped off at the bottom of the poly lock. Valve train geometry is good, lash was correct no binding or any spring contact with rocker. the motor can be turned over by hand until the exh stroke on #2 then it gets hard to turn, let it sit a while then you can continue to turn it over until you get back to #2 exh stroke.

What are the chances that there is any damage to the rod or piston from having the exh valve not open and the engine stop running abruptly?

It looks like the studs are too short as the set screw is threaded down into lock body. They were the ones that were shipped with the heads ( BMF 350's) So I am going to get some longer ARP pro studs and probably a girdle.
 

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I would look for more something besides it not having enough threads in the lock nut broke it, I dont think it would bend the starter bolts on comp not getting out, it should pop back in the intake when the intake valve opens
 

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I don't think you should hurt a rod on an average motor cause air still compresses unlike a liquid which will bend a rod no problem. Some hugh high compression monster with a light rod could do it. You sort of suggest by your limited comments this is a pump gas street motor so I'd think you got a decent chance it could be OK. I'd run a girdle on the thing to reduce the strain on the studs myself if you can't afford shaft rockers. You already proved they are seeing excessive stress. RM
 

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If you go to page 46 on here http://www.arp-bolts.com/catalog/catalog.html there is a big selection of rocker studs for BBC. Check to see which stud length "B" & thread length "D" best suit your application. Pick the stud that will give you the most non-threaded area inside the rocker pivot and still give you at least 7/16 thread engagement in the nut. Support girdles are a plus, just make sure the adjuster nuts you have will work with them.
 

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Discussion Starter · #5 ·
it's a 12:1 engine ,eagle 4340 rods no light weight rods or pistons. checked to combustion chambers with a bore scope and didnt find any damage, probably going to pull the motor and at least take off the pan just to make sure the rod looks ok. Thats what I'm most worried about.
I noticed when assembling the rockers that the set screw went much further into the lock than on my previous engines but kind of forgot about it. There appears to be maybe a 1/4 inch of thread engagement in the locks. The wear pattern on the valve stems is centered pretty well front to back and side to side, the pushrods dont hit the heads or have any contact marks on them, nor do the rocker arms. definately will go with a stud girdle as well as longer studs this time.
 

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I would put my money into a shaft assembly, overall not that much difference in cost.
 
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