Gpz 750 Cylinder Head and Valves

Just had my Gpz 750 ( Kz 750 based engine ) cylinder head overhauled. The valve seats were machined, along with new valves, surfacing, the works.

My question is: The installed valve heights are almost at maximum. I was told that an alternative would be to machine the valve tips, a few thousandths.

Will this technique work ? I know that by shaving off a few thousandths, I will have the clearances I need, and I won't have to use the 2.00 shims.

Suggestions ? comments ?

Yes, the valves can be trimmed or "tipped" in order to shorten them up.
I haven't had it done before, but I believe a member "Bountyhunter" has had it done to his KZ750 (twin) as those shims are hard to find.

A related thread to read:
www.kawasakimotorcycle.org/forum/mechani...ding-valve-shim.html

After doing some math, I figured that machining off between .002" and .004" of the valve tips would be sufficient to get the valve heights back into the usable range. I am also considering having a professional machinist do this for me. The last thing I want, is to do it myself, and end up with lop-sided valve tips.

Specs and procedure should be detailed in FSM.

Good Fortune!

I've never done it on a motorcycle engine but on my dad's 292 y-block I did it on the exhaust valves. Like you said you have to be careful not to take to much. On the Y-block its because of the wear from the rocker arms. The tips are surface hardened and after your done grinding them you have to harden them again to prevent further wear.

Anyway, we didn't machine them. We used a vale grinder that had a setup for it. It worked really and gave me a lot of control on how much I took off. Good luck with it.

So, if I machine .004" from the tips... how badly will this affect wear on the valve tips ? ( Since the hardened material will be removed at the tip ).

I don't plan on riding this bike much. I just want to restore it, and maybe put 500 miles a year on it.

If memory serves, I used to adjust the valves about once every 1500 - 2000 miles on this bike.

I hope that I don't end up doing a valve adjustment every 500 miles !!!

gpzman2000 wrote:

So, if I machine .004" from the tips... how badly will this affect wear on the valve tips ? ( Since the hardened material will be removed at the tip ).

I don't plan on riding this bike much. I just want to restore it, and maybe put 500 miles a year on it.

If memory serves, I used to adjust the valves about once every 1500 - 2000 miles on this bike.

I hope that I don't end up doing a valve adjustment every 500 miles !!!

PAY ATTENTION HERE

.004" is nothing. It's 2 shim sizes. You should't need to touch the valve stems for 2 shim sizes unless you were way down under 220 shims before the valve job was done.


There are some things about the 750 that are worth taking note of.

1 - cams with different base circle sizes were used on some GPz models. Measure your exh and intake cam base circles. You might find the exhaust is smaller.

2 - the OEM manual has incorrect information in it regarding installed height. That's not unusual with service manuals. It was common for Kawasaki to send us corrections to the manuals after they were printed.

IF you decide to tip the valves, they need to be done on a grinder that will grind the tip perfectly flat and perfectly perpendicular to the stem.

If they are cocked, it can cause shim fracture.

Since you only need .004" taken off....if your shim size is 230 or thicker to bring lash into spec....and if you can't grind the stems correctly....LEAVE THEM ALONE.

OTHER S.O.B. SETUP ISSUES THAT CAN HAPPEN

It's possible to run valve tip to retainer top edge problems with SOB motors....if that happens, valves can be dropped.

Put a retainer on the valve with 2 keepers and pull the retainer up tight. Install a 200 shim in the retainer.

If the shim sits below the top of the retainer by more than .004", there are issues that you cannot solve without the proper equipment.

It's not likely you'll run into that last scenario ....just making you aware of what can happen sometimes.

Tipping the valves to put the head in the shim range, as well as the things Larry posted, is part of doing a valve job. That is why you should have your cylinder head work done by people who know how to do motorcycle heads.

You said you checked installed height, but did you put a checker spring in there, bolt the cam down and rotate it to see where you actually are? (with your smallest shim under the bucket)

Since you measured it, you have some sort of spring in place all ready... it's just easier to rotate with light springs.

There are several ways/tools to use to do that measurement and some can be off by a few thou depending on how it's done.

From what I know Kawasaki valves are very hard buggers and I have never heard of having to do any heat treatment after any kind of grinding on them...

This cylinder head has seen x3 valve jobs, over it's lifetime. The shim sizes installed prior to the valve job were 215 - 220.

I matched up the retainers to the valves (outside of the head ), and noticed a very tiny clearance between the tips of the valves, and the top of the retainers.

I did check the original Kawasaki manual for this ( not a Clymer, but the Kawasaki manual ), and cross-referenced the chart + shim size + installed valve height.

I figured that .004" is erring on the side of caution, as I know that it will bump the adjustments only +2 shim sizes. But again, this bike will see VERY FEW miles in the remainder of it's service life. I figure that it will see no more than 100 - 200 miles per year, at very most. Therefore, I want to make sure that 1. the clearances are within spec 2. not to have my machinist remove too much material 3. not to have a clearance issue between valve tips and retainer tops.

The bottom line is: If I have too many problems with these valves, I can easily replace them. ( although I am trying to conduct this project on a modest budget ).

Thanks for the input.

gpzman2000 wrote:

This cylinder head has seen x3 valve jobs, over it's lifetime. The shim sizes installed prior to the valve job were 215 - 220.

I matched up the retainers to the valves (outside of the head ), and noticed a very tiny clearance between the tips of the valves, and the top of the retainers.

I did check the original Kawasaki manual for this ( not a Clymer, but the Kawasaki manual ), and cross-referenced the chart + shim size + installed valve height.

I figured that .004" is erring on the side of caution, as I know that it will bump the adjustments only +2 shim sizes. But again, this bike will see VERY FEW miles in the remainder of it's service life. I figure that it will see no more than 100 - 200 miles per year, at very most. Therefore, I want to make sure that 1. the clearances are within spec 2. not to have my machinist remove too much material 3. not to have a clearance issue between valve tips and retainer tops.

The bottom line is: If I have too many problems with these valves, I can easily replace them. ( although I am trying to conduct this project on a modest budget ).

Thanks for the input.

Based on this latest information, IMO, I would install new valves....but good luck with whatever you ultimately decide to do.

Make sure you're not stepping over dollars to save dimes