Rocker Arm Thread Damage
This comes up so frequently that I would like to explain 2 easy fixes that exist for this situation. We have encountered so many people who try to fix these stripped bolt holes themselves and wind up not solving the problem. It is our experience that this usually is inexperience or bad advice on the best way to fix it.
First thing is there are 2 different bolt sizes, 8MM (usually on passenger cars) and 10MM (usually on trucks and SUV’s). The 8MM torque is specification: 89 in/lbs plus 30 degrees. The 10MM specification is 24 ft/lbs. Since the 8MM and the 10MM are interchangable same year, you could get either one.
Below is a picture of a cylinder head a customer brought to our shop after he had tried to install over the weekend. In his haste to get the cylinder head installed he wound stripping 2 threads. After unsuccessfully trying to repairing one of them, he didn’t even attempt to repair the other head. This image below is the one he attempted to repair. The hole was drilled too big for a Time-Sert (or Heli-coil).
The most common method of thread repair is a Heli-Coil (coiled insert). In most instances a Heli-Coli does a satisfactory job. However, we have seen too many fail later. For this application we prefer a solid insert such as these shown below:
The Pioneer insert on the left, the Time-Sert on the right.
As you can see, these are solid inserts versus “coiled” like Heli-Coil. The one on the left is for the oversized repair, one on the right for standard pulled threads. Either of them will work well and the first is probably easier for an individual to get the materials (and cheaper too).
The first repair is using a Time-Sert kit part# 1812 with part# 18129 insert. The reason we like the Time-Sert repair is the method used to lock the insert in place (we’ve never had a failure). The bad news, the kit is around $70 (as of this writing). We buy ours from:
The only “trick” to using this method is to run the counter bore tool deep enough so the shoulder of the insert will be just below the slot for the rocker stand as it is in the previous repair.
Now for the instructions: I’m going to cheat; here is a link Time-Sert‘s website. Scroll down and find the videos: (1) Standard Bolt Repair Demonstration and (2) Standard Bolt Repair Close Up. We also recommend Loctite 263 (red) with this repair.
How to install the larger (Pioneer) inserts
- The Pioneer Inc., Automotive Products insert part# is EL-41. Unfortunately they are normally sold in boxes of 10. If you can’t find a single insert, call us.
- 27/64″ (.4219″) drill bit
- 1/2″X13 tap.
Using the 27/64″ drill, drill the rocker bolt tower 7/8” deep from the tip of the drill bit. To be sure to get the right depth, put a piece of tape on the drill at 7/8″ from the tip as shown below.
Tap and thread the hole using a tapping lubricant or equivalent. Clean the threaded hole with Brake Kleen or equivalent. The EL-41 insert has some kind of thread lock compound on it from the factory. I suggest you remove that, clean the insert and apply a small amount Loctite 263 (Red) or equivalent to the insert as well as the top threads of the hole. Screw the insert until it is just below the bottom of the slot the rocker arm pivot fits in the slot pictured below. View from the top is the second picture.
Below is the picture of the second failure, the threads were simply stripped out and no one had attempted any repair.
Hopefully I have helped someone out with this article, call if we can help in any way.
12.25.14. Just did a rocker arm thread repair with a coworker, on his daughters Chevy Impala 3.4L. The TimeSert repair insert is the biz! He’s a machinist & he really liked them!
Repaired one by drilling the rocker hole and stand out to 27/64. Then tapped the head for a 3/8-16 thread. Used a 3/8 nut drilled out to 27/64 as a spacer above the rocker arm. (3/8-16 socket size just fits between the rocker arm flats. Used 3/8 bolt long enough for included spacer nut. Worked perfectly.