Cam holder bolt stripped - Need advice

Good day fellow KZ riders and lovers,

Hope all is well.

I started a 1980 KZ750-E as a long term project some time ago, but a very rude thing happened to me.

I borrowed a torque wrench from a workshop to torque the head and cam holders after valve clearance adjustment, but I never tested the wrench before use. I adjusted it to the required torque value, but 1 bolt stripped the thread on the top end. I asked another guy to try and fix it, and he rammed a bigger bolt into the whole without much result.

Now, the problem: The amount of metal left is not enough to do an inset, as a mm more would touch the cam, and the bolt that is currently in there can only be torqued to about 7-8nm... The bolt is long enough that it would not run around the top end if it comes loose, but it does not torque well.

How big of a problem do you guys think I'm looking at? Should I get the top end welded and rethreaded or should I leave it be?

The bike started fine but I dont want to run it like this knowing something might go horribly wrong

Any advice or opinion would be highly valued.

Kindest regards,
H

Pictures

This is a seriously good system.

The cam cap bolts are 6mm and thread pitch is 1.0 with its length at 38mm. It looks like the threaded portion of bolt is about 50% of the bolt, so a 20mm timesert looks to be correct.

www.timesert.com/html/mtrcsert.html

www.cmsnl.com/kawasaki-1980-kz750-e1_mod...head-6x38_920011105/

While I'm a believer in Timeserts, this might call for a heilcoil instead.

The timeserts I've used have a shoulder that binds the insert into the hole to keep it from backing out when you wrench on it later. This shoulder can sit proud of the hole and cause the cam cap to not seat correctly. A 15 or 20 mm helicoil will sit completely inside the cam cover base and (if inserted correctly) will never sit proud.

For spark plugs and other places where the shoulder height isn't critical, Timeserts are definitely the way to go. In this one case, I prefer HeliCoils.

Cynjut wrote: While I'm a believer in Timeserts, this might call for a heilcoil instead.

The timeserts I've used have a shoulder that binds the insert into the hole to keep it from backing out when you wrench on it later. This shoulder can sit proud of the hole and cause the cam cap to not seat correctly. A 15 or 20 mm helicoil will sit completely inside the cam cover base and (if inserted correctly) will never sit proud.

For spark plugs and other places where the shoulder height isn't critical, Timeserts are definitely the way to go. In this one case, I prefer HeliCoils.

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yep, your right. could use a full thread bolt with no shoulder....could drill out poor threads and re-tap for a 1/4 sae bolt....this is a common idea.

I don't think 1/4" would work very well - 6mm is 1/4mm smaller than 1/4", so the new threads would only gain an almost imperceptible additional bite, If you could find a 1/4" bolt the right length and pitch, you could probably just use one of them without tapping anything,

Instead of that, I've heard of people replacing the 6mm bolts by tapping the holes out to 7mm, which is what the tap for the helicoil is. The trick with the 7mm tap is that you don't have a second 'bite at the apple' if you over-tighten your cam cap bolts again. You can't go to 8mm (IIRC) because the inside diameter of the alignment collars are 7mm, and going to 8mm doesn't give the collars enough shoulder to work reliably.

By The Way! The reason these so commonly strip out is because the books all have the torque for this bolt wrong - they all list 144 in pounds (12 ft pounds). These 6mm bolts should never be torqued more than 90 in pounds. The "right" torque is something like 84 in pounds. I stripped out about half the bolts in my KZ1000 trying to use 12 foot pounds. That was also when I figured out the TimeSert versus Helicoil difference.