Rocker arm bolt stripped:::...options

while I was driving the power cut and there was a loud tapping noise. The MIL
came on , scanned at home P0304 , Took the valve cover off, cylinder 4 rocker arm 8mm bolt was stripped. What are my options ? the bolt pulled out the threads in the head

http://i53.photobucket.com/albums/g80/viking_03/P03042014-11-22111650_zps7899c02a.jpg

http://i53.photobucket.com/albums/g80/viking_03/rocker2014-11-22130341_zpsc5fa1433.jpg


http://i53.photobucket.com/albums/g80/viking_03/NO32014-11-22130539_zps0c2f9e27.jpg

This is not uncommon. I've had several, and with my luck it is usually one of the rear bank, making as much "fun" as possible.

The hole can be re-tapped for a thread insert. They are a permanent repair. The bolts are M8 x 1.25. You'll need a thread insert of that size, the appropriate tap, and the insertion tool. I've found entire repair kits for less than $30. That's cheaper than a head gasket.

Here is a brief overview:

http://www.wwdsltd.com/files/1-3-5ValveTrain.jpg

I've had good success with several of these by installing ChrisLynn (http://chrislynninserts.com/cr_product/82160/) or Heli-Coil (http://www.summitracing.com/parts/hll-5546-8) stainless thread inserts in the head and bolting it back together. P/N 82160 should be the correct 8mm insert for that application.

Incidentally, when installing these rockers it is very important to torque the bolts to the spec. You can see what happens when they are over-torqued, or under-torqued and allowed to flex. Removing the other, non-damaged rockers might be prudent just for inspection. When threading into the aluminum a drop of mild thread locker seems to help.

Another item concerning these rockers and their failure is the tendency for this to happen with a cold engine. It's not uncommon on the 60º Chevy V-6 engines when they are over-revved when cold. While no engine should ever be subjected to that kind of intentional abuse, these engines are particularly susceptible to thick oil pumping up the lifters and popping the rocker bolts.

when you drill out the hole to be tapped what is the best way to get a straight hole? especially on the back bank. I would think that high rev's under a certain temp with no load would fall under the "abuse mode" and the PCM would not allow. I know you cant do stuff like rev high and slam into a gear . I think even over rev is abuse mode. its already cold here not sure how thread lock and gasket cement will cure before it might freeze. they should have used
coarser thread bolts. these bolts they use now are probably same bolts they use for cast iron heads. your pic looks like a 3.4L I recognize the MAP and mounting hardware for the coil packs

The drill for the insert tap is not much larger than the major diameter of the threads in the original hole. If you align as best you can by eye and allow the hole to guide the drill as you very slowly feed the bit, you should be able to detect whether the drill is following straight or at an angle to the original hole. There is a wee bit of latitude, but the hole should be drilled as straight as is practical.

Gasket cement may be affected by the temperature. Thread locker, such as LocTite 242 will not be adversely affected, but the cure time will likely be longer at lower temperature.

It will be important to clean out any chips from the drilling and tapping steps. Packing paper towels or other aids around the hole and into the oil drainbacks to prevent anything from getting into the sump would be a good idea.

It just so happens I have an M8 X 1.25 Heli coil set left over from my motorcycle days. Its around 30 years old still should be ok. that's definite about the metal chips from drilling along with the area being covered with paper towels and duct tape going to try and use the shop vac close to the area while drilling. I saw at Rock Auto they have heads that take a 10mm bolt. I assume that the shank of the bolt is bigger , so that would mean different rocker arms etc. oh well I will just do the heli coil for now, going to check the other rocker bolts to see if they are over torqued.

http://i53.photobucket.com/albums/g80/viking_03/HELICOIL_zps152fd179.jpg