SB rocker shaft bolts (Grade 8 ??)

[3406pk]

I'm rebuilding my 340 from 72 Challenger after the machine work. Bought a used set of 273 rockers which look good, but most of the 5/16 bolts Gr5 were stretched. I know about the torque specs being wrong at 30 lb-ft. Put in adjustable pushrod checker and ordered the new custom pushrods. I put in new Gr5 bolts and torqued to 15 lb-ft for the test, but that tension seems loose for higher pressure springs. Question Is there reason not to use Gr8 bolts at proper torque of 18 lb-ft? Has someone used Gr8?. Thanks for response.

 

[Coronet 500]

I always change them to 8 on any engine I have had, better to use new bolts anyway.

 

[krazykuda]

Question Is there reason not to use Gr8 bolts at proper torque of 18 lb-ft? Has someone used Gr8?. Thanks for response.

There should be no problem using the grade 8 bolts with the proper torque.

They use grand 5 from the factory to save $$$. They only buy what they need to do the job, nothing more.

 

[3406pk]

Thanks Krazycuda and Coronet500. I would think the threads in head should stand that torque too.

 

[crackedback]

I never use grade 8 bolts for the rocker shafts. You are clamping a tube which can be distorted. Grade 8 bolts require more TQ to get the required stretch.

 

[moper]

^^ what he said.
Get some grade fives, but make sure they engage as many threads as possible. I get longer ones to make sure they do that, and then tighten evenly & don't over-torque.