Stripped cam bearing threads - shim under buckets

VTEC wrote: I've been thinking, next time I have the cam cover off, drilling the cam cap holes a bit deeper, running through with a tap, and using a set of the next size longer bolts.

This should eliminate any future problems, as opposed to helicoil every hole.

A few extra threads can make a major difference in strength.

I must be getting old. Just thinking about it makes me nervous.

:whistle:

VTEC wrote: I've been thinking, next time I have the cam cover off, drilling the cam cap holes a bit deeper, running through with a tap, and using a set of the next size longer bolts.

This should eliminate any future problems, as opposed to helicoil every hole.

A few extra threads can make a major difference in strength.

On the inlet manifold side and exhaust manifold side there is not enough scope to go deeper, hence why i use a stepped stud system.

Ok. Pay attention. I just measured my J head. The cam cap bolts are 6x43. The cap height is 22mm. That means the bolt goes 21mm into the hole. The hole depth is 30mm, leaving 9mm to spare. I'm sure you can use a 6×45 bolt without doing anything, there's always a few extra threads in the hole. Very possibly a 6×50 by just running a tap deeper. And looking at the casting below the bolt hole, drilling a couple of mm won't hurt anything if needed to make the 6×50 work. You got more than 10mm deeper before drilling out the bottom of the casting.

www.boltdepot.com/Product-Details.aspx?product=17740

VTEC wrote: Ok. Pay attention. I just measured my J head. The cam cap bolts are 6x43. The cap height is 22mm. That means the bolt goes 21mm into the hole. The hole depth is 30mm, leaving 9mm to spare. I'm sure you can use a 6×45 bolt without doing anything, there's always a few extra threads in the hole. Very possibly a 6×50 by just running a tap deeper. And looking at the casting below the bolt hole, drilling a couple of mm won't hurt anything if needed to make the 6×50 work. You got more than 10mm deeper before drilling out the bottom of the casting.

www.boltdepot.com/Product-Details.aspx?product=17740

Good luck.

+1

Just be careful not to monkey up the threads. :whistle:

Well, after a tooooo long hiatus away from this project we are back at it. The owner went down a different trail, literally! He devoted most of his project time and effort to his new dirt play-bike built from a nicely warmed up 78 XL350 motor and frame mated with CRF250R wheels, brakes, suspension, etc.. Plus we put a few other bikes in some shows back in the late spring, but I digress...

As for the project - All of our machined thread inserts are now Red Loctite glued into the head, the cam caps have been faced to the same height above the head, the cam cover is drilled, the specialty studs have been carefully trial fit, remaining fasteners are ordered, and I'm machining the spacers that will go between the cam cap nuts and the underside of the cover to keep the cover from bowing in or cracking. I've used this method on other shim - under engines before, BTW, and it does work - really well, in fact.

Here is a link to the owner's post on Instagram....


More photos and description to follow....

I done this in 2004 and the bike is still racking up the miles, had to mill out a little in the cam cover to allow for the nuts, the studs are 8mm stepped down to 6mm with the 6mm parts of the studs in two different lengths to allow the continued use of locating dowels, not sure i am keen on your solution as it appears you have deleted the locating dowels thus allowing the possible movement of the caps when under load and the added potential of 16 extra oil leaks through the cam cover, there are many out there who will not grasp what you are doing, but all said and done this is thinking outside of the box and to be commended, i wish you every success and will keep watchin this threadd.

Kevski,

Still using the 8 mm knock pins / dowels, 2 pins per cap - same as stock on the intake cam, but the exhaust caps were tricky on this head as the previous heli-coil repairs destroyed the index of one 8 mm locating holes on each of the exhaust cam caps. Our solution was to use one of the other holes as the new location for the 2nd knock pin, after carefully checking the bearing alignment. Particularly the end play thrust caps (no.s 1 and 3, if memory serves) need a secure index point, as all bearing caps tend to wander around a bit when engine is running, if not located with more than just bolt clamping force alone.

Plus this "GPz1400" will get 410 cams now, with potential for a set of 465/435's in the future. I'm putting these studs in my twin plug J head also, but not for "repair" as my original 6 mm threads are undamaged / intact. I'm running up to 485 lift and heavy springs, and the cams will be in and out routinely, so the studs should help the threads last and prevent them from ever pulling out and ruining the engine....I hope.

Reviving this thread as i have run into a similar issue. This head I have had an old heli-coil repair that failed. I was able to remove that heli-coil and install a time sert deeper.... which failed, the entire hole is now stripped. I cannot install a big-sert as this is one of the holes with a dowel. I like the stud idea, but because of the completely stripped hole I cannot install a 8mm stud, I could go to 9mm but this would remove the 8mm dowel. How bad would it be to run only one locating dowel?

The caps are self aligning once bolted down on the cam and the dowels were primarily there for their location during the line boring process at the factory.
Caps 1 and 3 are slightly more crucial to their lateral position as they control cam float to prevent the cam sprocket nuts drifting into the head casting.
Running just the 1 dowel in either of the caps won't affect anything.

thanks for the info Zed, what would be your choice of repair for my situation?

If you haven't a lathe.
You can drill and tap to M10 max ( decent pillar drill needed )
Then fit a solid steel M10 slug flush with the head. ( use M10 x 1.25 or 1.5mm threaded bar, studs or bolts as slug material )
Bolt on the cap and use the hole as a guide to get the center for drilling and tapping back to 6mm.
Once done you can then drill 8mm to take the dowel.
The success of this obviously relies on your skill, accuracy and mechanical competence etc
If you have a lathe you can make the whole slug and location dowel in one piece as in the attached pic.

I'm just about to do a head that needs all 16 doing.