First Run With the GPz cams in the 810

Hey gang - I finally got the 650/810 out for a squirt with the new Gpz cams tonight.

For those who have read my earlier posts, I had been having a series of nightmares with malfunctioning cam chain adjusters on my bike that have caused me a series of issues.

The first cam chain aduster disaster was my fault when I overtorqued it and snapped the cast aluminum body. Replaced that adjuster with one that didn't extend far enough and even with a new spring and the cam chain jumped a tooth, popped out the tach drive and chewed up the exhaust cam gear drive on the exhaust cam. Luckily it happened less than 100 yards from my house but I left a trail of 10W40 all the way up my driveway.

I got my hands on some GPz cams from Kawaskinman (thanks Steve) and decided to pull the cylinders off to get a close-up look at cam chain spocket on the crank.

Then a buddy who was helping me reassemble the motor busted a ring and cracked the bottome part of the #1 cylinder trying to force the rings into the piston grooves while pushing down on the cylinder. The guy felt like a bag of sh*t trying to stay even with my progress on the other side of the engine.

Located a new Gpz 750 sleeve, had the old one pressed out and the new one bored and installed. Had a little chamfer put on the bottom of the bored 750 sleeve but there isn't a lot of meat to put the chamfer on the overbore, so it is delicate surgery that needs experienced hands. Luckily tom1262 (kzr member) helped me out instead of my other buddy.

Given the drastically different profile on the Gpz 750 vs. the Kz 750 cams I had in, the clearances on the valves had to be changed. On average, I had to go with shims that were about 45-60 thicker. Picked up an APE manual cam chain adjuster from Jeff @ Z1 Enterprises as I wasn't going to take another chance with a factory cam chain adjuster. Pulled the car boots off and resealed them, soaked the carbs and redid the plug wiring on #1 and put the timing light on the bike.

A Kz buddy of mine who is a bike mechanice that drag races a Z1 and also has a Kz650 noticed the bike was running a little rich and backed out the air screws from 1/4 turn to a full turn. This little adjustment made a huge difference on the idle and the look of the plugs.

So, to make a short story long...I finally got everything done after losing 3 weeks of riding and took the bike out for a run tonight. I didn't want to fully wind it out given the new cylinder and rings in #1 so tonight was just a half hour tour to help seat the rings.

With my maiden run with the Gpz cams, the first thing I noticed was the engine sounding different. It has a distinctive ticking on the top end that I didn't notice with the old Kz cams and the idle seems lumpier. The GPz cams have a lot more lift and slightly more duration. Comparing the profiles on the work bench the base circle on the Kz is quite thicker than the GPz which is almost non-existent.

Under acceleration the bottom end doesn't seem as strong as the Kz (I didn't want to hammer it off the line) but above 4-5000 rpm it really wants to pull in the mid-range and above. Previous Kzr posts about these cam differences had indicated this might be the case and it is true.

I had a couple of old Kz veterans listen to to the motor and they said it sounds really strong and that it will just take me a while to get used to the different profile of the GPz cams, but given the run of bad luck I have had over the past few weeks, I am probably a little too sensitive on any changes in engine sound.

There is not much more I can do to make this old 650 run any stronger given the upgrades I have gradually done to the bike. I can't wait to get it out for a good right wrist twist and see what this little middleweight sleeper will do on full song.


Cheers-Colin Firth-Ontario Canada

I'm in the process of doing the same thing.. Did you have Kz750 cams in there? If so why did you remove them? I would like a little more bottom to midrange power, so I would like the Kz cams. Is there a substantial difference in the motor upgrade or can't you tell yet because of not riding it enough yet?
Just curious my man... I want to know what I'm lookin forward to that's all...

I believe the 750 head will flow more
than even a ported 650 one will,in
case one ever pops up.

Hey Guys - I had the Kz750 cams in since I put in the 810 and blew out the tach drive so the exhaust cam was pooched. I had considered the GPz cams at one time and thought this was as good a time as any to swap them in.

I had jst missed out on a set of Andrews Cams with the tach drive that were for sale in the kzr classified section. They were apparently just a little milder than the GPz cams which doesn't have the tach drive, but I rarely use the tach except for setting the idle which I can do by ear anyway.

As far as the 650 vs the 750 head, there are varying opinions on this according to guys I was in touch with who road race these bikes. Trust me when I say that I researched the pros and cons of both sides of the fence and decided to stick with the smaller combustion chambers of the 650, but I did put in the Gpz intake valves which had to be trimmed 15 thou.

With the milled head and the 10.25 to 1 Wiseco pistons I believe that someone recently calculated that the compression ratio on this combo is around the 10.8 to 1 range.

The advantage of the 650 head is apparently a better intake runner design for low-end and mid-range flow. I haven't seen any flow bench numbers on this but am basing my knowledge on the advise of gusy who claim to have tried both heads on the 810.

I milled the head as a drag racing buddy babysit me and look over my should while I did the porting on the intake side where I cleaned up the runners while leaving a rough finish. On the exhaust side I ported and also got them to almost a mirror finish.

With the gearing I am running I feel that this will make up for the reduced power on the bottom end of the rpm range.

As I said earlier, I am looking forward to seeing what this will do after I feel the new rings are given a few miles in their new cylinder but the early indication is that this will be a very strong runner.

Cheers-Colin Firth-Ontario Canada

Before and after dyno runs would be a good way to show the differences throughout the rev range, and also check that you have the fuelling right. You can also pick up other things from a dyno chart that you can't always feel on the road, like clutch slip

When I originally put GPz cams in my 750, like you I noticed a small drop in low end power, but the new top end sure made up the difference. It would just rev like crazy compared to before. I'd suggest you maybe fit a elec tach so you can see whats happening. The old engine peaked at about 9K but with the new cams it was possible to take it to 10.5K quite happily. (I started having valve bounce at 11K so don't go that far.)
The ticking is probably a shim set too loose, I checked mine again after about 500 miles and had to change a couple.

Sounds like a great bike.

Enjoy!

Thanks guys - Lorcan, we dont have a bike dyno in town so I have to go by the seat of the pants feel.

GPzephyr I'm going to give the motor some time to work itself in before I pull the cam cover. All of my clearances were triple checked and they all came in from 10-15 so I should be o.k.

Cheers-Colin Firth-Ontario Canada

So the cams are just drop in??
Did you have to measure/determine the lobe centers when modifying to gpz cams??

I don't know what cams are in my Zn750 (block is marked kz750) but the top end screams. 11-12000 rpm no problem, i don't like or mean to do this but when your coming onto it sometime you forget to shift lol.

Frank wrote:

I don't know what cams are in my Zn750 (block is marked kz750) but the top end screams. 11-12000 rpm no problem, i don't like or mean to do this but when your coming onto it sometime you forget to shift lol.

I know what you mean;). On mine the valves started making strange noises just after 11K so I limited myself to 10.5K thereafter

Glad to hear you got her going Colin. You've put a lot of work into her and with the great weather we are having I'm sure you want to be riding instead of wrenching.
It will be interesting to get your thoughts on the Gpz cams (something I dont have in mine) after you have a few weeks riding under your belt.
Enjoy and ride safe.

Post edited by: JR, at: 2007/06/03 19:18

Good to hear your riding again. Sounds like you'll have a great season.

What type of engine oil you using?
I just switched to Kawasaki Synthetic 10w40 and I swear the engine feels like it revs much smoother.