Stripped cam bearing threads - shim under buckets

For anyone interested, I've got a KZ "shop" project just started, and thought it might be useful to write it up and post it here. Hopefully it will wrap up in less than two months (I'm away from home a lot these days for medical reasons).....

Typical of many KZ550-750 / late GPz and modified High Performance KZ engines using shim under bucket valve train, a friend has brought his GPz 1100 "bathtub" head to my shop because all of the cam cap bolt threads have stripped out. This seems common for these engines. Mostly it is attributed to using high lift cams, heavy valve springs, and numerous cycles of removing and installing the cams to adjust the valves. The M6 cam cap bolt threads in the aluminum head are obviously not up to the rigors of pulling down the camshafts and being torqued to 11 - 12 ft-lbs repeatedly. Even worse in his case, all the threads in the head have already had Heli- Coils and a few threaded repair inserts (Time-Serts) installed, and now those too are pulling out. So as it stands, his otherwise usable cylinder head would be destined for the scrap pile.....

The goal is to save the head by repairing the damaged threads using some home-made parts, and to re-design the cam cap fastening system to prevent further problems from occurring, on this heavily modified performance engine. We do use machine tools, but they are basic ones, so just about anyone with access to a machine shop, or any local machine shop should be able to do this.

Step one is already done - removing what was left of the old Heli-Coils without further damage to the head. Unfortunately, I didn't foresee to take any actual photos of this being done (last week), But next post I will include a description and photos of the tools and methods used.... I expect to post them 10 days from now..... thereabouts...,.

Well this is a scary thought... Hope it never happens to me.

This thread should be interesting though

if you are tightning them to 11-12 ft lbs that's your problem in the first place when I was running my drag bike I had 500 lift cams and HD springs cams were in and out a lot never had issue stripping the cam cap bolts.

DFIGPZ - Entirely correct - M6 should really only be torqued max. 8-9 ft-lbs. But look at the listed FSM spec for the 1000 / 1100....

I haven't stripped any myself (yet) - but 11-12 ft-lbs would explain why many have come to me that way....

I'll post a photo of the underside of a H cover from a certain Minnesota racer's (drag race) KZ1100 engine w/ 0.480" cams that made about 2/3 of a 1/4 mile pass next post....

Also heard of a racer who has his 300 lbs. "assistant" press down on the cams while he is installing the bolts....

You can use vice grips to seat the cams into the head, against the valve spring pressure, before installing the caps. Doing this removes most of the stress of the threads associated with torquing down the caps.

I've got a photo somewhere. I'll dig it up if anyone cares.

I am no mechanical genius, but over my years of building KZ900/1000 motors, I never had any problems with stripping out cam cap bolt threads. Now the biggest cams I ever used were only .440 lift. With big cams what I would do is use longer length bolts to start to bring the cam caps down onto the head. With the longer bolts you are gripping more of the threads in the head. I bring the caps down close to the head, and then one by one remove the longer bolts and install the stock 6X45 cam cap bolts. Then I would bring the cam caps all the way down to the head. Try it, its worked for me since back in the 70's!!!

I would never use a big C clamp or anything like that on my high dollar cams, or take the chance of scratching the Gun Kote finish on my cylinder head!!!

I think people often use the bolts to seat the cams by force when they bind up. On the 550's, they should go in nice and easy if everything is done correctly. But they do bind up occasionally if a cam isn't lowered evenly. You have to have the discipline to know to stop and start over, or at least back track to where the camshaft is not bound.

Also, the tach gear is a big source of problems, but it wouldn't be if everyone just removed the tach drive spindle like the manual says.

I would never try to tighten the cam cap bolts up to 11 – 12 ft lbs of torque on my KZ650. The KZ650 and KZ1000 Kawasaki Service Manuals call for 95 – 113 in lbs which equals 7.9 - 9.4 ft lbs. Trying to tighten them greater than the specified torque level is almost guaranteed to strip the threads.

The images below are from the KZ650 and KZ1000 Kawasaki Service Manuals. These manuals can be seen at:

www.kzrider.com/modules/ServiceManuals/K...Service%20Manual.pdf

and

www.kzrider.com/modules/ServiceManuals/K...Service%20Manual.pdf

It is my understanding that some manuals have the wrong torque specifications, so perhaps that is where you found the 11 – 12 ft lb spec. I highly recommend you use the torque spec shown below. Ed

Kay-Z,
Are you going to install a stud and nut system in the botched heads?

A ft./lb torque wrench is NOT going to read right at 10 ft/lb. I don't care what brand it is it's just to low of a setting
plus there's no reason to use a 3/8 drive ratchet on a bolt that small..

zukdave wrote: A ft./lb torque wrench is NOT going to read right at 10 ft/lb. I don't care what brand it is it's just to low of a setting
plus there's no reason to use a 3/8 drive ratchet on a bolt that small..

+1

Your best bet is to use a torque wrench calibrated in INCH pounds.

Keep in mind: "All mechanical torque wrenches are calibrated from 20% to 100% of full scale, therefore, they should never be used below or above those limits." That quote is from the CDI torque wrench website (see www.cditorque.com/education.html#Safety ). CDI is a Snap-on company that specializes in making torque wrenches. Ed

Nessism wrote: You can use vice grips to seat the cams into the head, against the valve spring pressure, before installing the caps. Doing this removes most of the stress of the threads associated with torquing down the caps.

I've got a photo somewhere. I'll dig it up if anyone cares.

If you find it, please post it