rocker arm bolt broke in the head
10-28-2013, 02:56 PM
#1
rocker arm bolt broke in the head After doing a 1/8 mile pass in my carbed ls3 i had a noise in the motor and pulled the valve cover off and found a broken rocker arm bolt.......is there a better then stock GM bolt that i should be useing ??? ARP ??? or just replace it with a new GM bolt ? Also should i just leave the rocker arm spacers bolted on as a guide for when i drill and tap the hole ??? Any one know the thread size that would be great....also if you know the torque setting that would also be great...........or a link with info will work....thanks for your time.
10-28-2013, 04:27 PM
#2
After doing a 1/8 mile pass in my carbed ls3 i had a noise in the motor and pulled the valve cover off and found a broken rocker arm bolt.......is there a better then stock GM bolt that i should be useing ??? ARP ??? or just replace it with a new GM bolt ? Also should i just leave the rocker arm spacers bolted on as a guide for when i drill and tap the hole ??? Any one know the thread size that would be great....also if you know the torque setting that would also be great...........or a link with info will work....thanks for your time.
1) Even stock bolts shouldn't break. IIRC, they are a M8 x 1.25 but taking one to a hardware store and matching up the threads wouldn't be a bad idea.
2) If you do want to upgrade, try something like a 12.9 grade bolt. I believe the GM rocker arm bolts are similar to a 10.9. Be careful of the footprint of the head of the bolt and make sure it fits in the recess of the rocker fulcrum.
3) Take the head to a machinist to repair. The angle of the rocker arm bolts is pretty important and must be correct in respect to the valve centerline. Its not something I would repair with a cordless drill and eyeballing it. A machinist would be able to drill it out and tap it for a helicoil on an end mill and get the angles correct. If you can drill a small hole down the middle of the bolt to relieve tension and work it out without damaging the threads, that would probably be your best move.
4) If you're asking the torque spec now, I'm suspecting that you didn't torque the bolt to spec, which may be the cause of the failure. The torque spec is only 22ft-lbs, which isn't a lot.
11-10-2013, 03:19 PM
#5
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id take a punch and slightly tap it to get a dimple in the center of the bolt so you drill in the center cause broken bolts don't usually break even and last thing you need is to screw up the threads fairly easy fix for the intermediate mechanic though...just don't drill the bolt with the same size bit as the bolt!!! id use like an 1\8 in bit
