Bolt/tread size for rocker arm shaft bolts

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Dusterguy

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What is correct bolt size and tread type for rocker arm shaft bolts? I overtorqued them and now I need to replace them all. They stretched so badly I dont even know what tread type they are. I tried google but found no info.
 
5/16th"S in inches,referred to in inches standards,as a "course thread".. I would take a bolt measurement, length wise..& get what's referred to as a"grade 5" ,in tensile strength in bolts..(three stripes ,on the head) new bolts here,make a difference..

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Thanks. Does that "course thread" means same as UNC? So correct size is 5/16 UNC?
 
Yes, UNC is coarse thread; UNF is fine thread. And remember that some FSM's have the wrong torque for these bolts; should be around 15-20 ft-lbs, not 30 as listed in some FSM's.
 
nm9stheham said:
Yes, UNC is coarse thread; UNF is fine thread. And remember that some FSM's have the wrong torque for these bolts; should be around 15-20 ft-lbs, not 30 as listed in some FSM's.
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Right.

Yeah I got book called "How to hotrod smallblock mopar engine" and there was that wrong torque value. There is also wrong torque value for main bearing cap torque on one page. I double cheked that value after torquing them..
 
5/16" UNC = 5/16"-18 threads per inch
5/16" UNF = 5/16"-24 threads per inch

Rocker arms would be the 5/16-18
 
200 inch pounds using a grade 5 bolt. 200/12 = 17 ft lbs

That book has a bunch of incorrect info in it.
 
if you went that tight you might want to check and see if the rockers still slide off the shafts.
 
Not meaning to be a downer here, just covering bases, check the threads in the heads and make sure you didn't strip/pull them out.........having stretched the hold down bolts, you may have damaged the heads.
 
^^ Good suggestion.

The good news is that with the depth of engagement of these bolt threads vs the bolt diameter, the bolt should go well before the rocker stand in this case. (Assumes that the threads were not crossed, or otherwise damaged....)
 
JBurch said:
Not meaning to be a downer here, just covering bases, check the threads in the heads and make sure you didn't strip/pull them out.........having stretched the hold down bolts, you may have damaged the heads.
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If you chase them with a tap, they are usually ok. It's the bolt that usually takes the brunt of the stretching....
 
Just be careful chasing threads on the rocker mount holes where the oil comes up; you don't need metal bits in your rocker shafts.
 
nm9stheham said:
Just be careful chasing threads on the rocker mount holes where the oil comes up; you don't need metal bits in your rocker shafts.
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Put some axle grease on the tap before tapping and it will help catch the chips. Then spray out the hole with a spray can with a straw and then blow it out with compressed air...
 
krazykuda said:
Put some axle grease on the tap before tapping and it will help catch the chips. Then spray out the hole with a spray can with a straw and then blow it out with compressed air...
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You can use a shop vac vacuum to pick up chips.
 
I actually did damage at least on tread in head. But now I have different/new heads that I put on.
 
I replaced the grade 5 bolts with grade 8 bolts on the heads on my 408 stroker motor. But then again, I'm also running a solid lifter cam with some killer springs. To me, it was cheap insurance because I have stretched a few to the point that they were no longer usable.
 
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