Since I had the virgin bike pulled apart I decided to check the camshaft cap bolts on a hunch that one being loose was the cause of the noise. Turns out I was correct, the thread's stripped out of the head. What's the best way to fix this? I was thinking helicoils as the tension only needs to be 10nm, however that requires drilling and tapping to an oversize hole, I'm wary of doing that on an alloy head. The other thought I had was dry out the thread hole of oil, fill with JB Weld & let it set, and then drill & tap the original thread size.
When fitting the camshaft, if only a few cap bolts are used to compress the valve springs required to seat the cam then those threads will be taking too much load and may strip. I would use a heli-coil.
Some of the cam cap bolt holes have dowels. 3 on each cap. I imagine the bolts that go through them are the ones that compress the springs? Or they just locate the cam caps? In any case, a member of another forum is going to send me the required timesert and other pieces.
I repaired the head on my CRF450R with a helicoil. It worked perfectly. My advice would be to have a friend make sure you drill vertically. Or use a drill press if you have one. Because if it's at an angle, the 10nm on your wrench will be less at an angle relative to the force needs to hold the cams down. I wouldn't use JB Weld at all. A heli coil will actually be stronger than the original threads too, because the new threads are bigger and the steel is stronger than alloy as well. Or, if you want more of a 'professional' finish, use a timesert.
The dowels are to locate the cam caps accurately because they contain one half of the camshaft bearings. The cam and caps should be fully seated before fitting and tightening the screws. Using a few screws to seat the cam may result in the threads being pulled out or damaged.
Also the thread insert types are usually greater in OD than a heli-coil and that may present a problem in this situation.
