76 KZ900 upgrade

j&e pistons are almost too pretty to hide inside a motor.
i always hate to go from a big motor to a smaller motor,but 1200 cc's is nothing to sneeze at.you already have the rest of the stuff to go along with it so it should be nice and nearly bulletproof.what are you using for a block?
keep us posted,you know pics is what fuel's everyone .

leon holmes

i noticed that the distance from the top of the piston to the top of the wrist pin is dif with dif makes. so its a good idea to check your deck hight whenever u make a change.

This is how i check the deck height
. place the piston at tdc with the dial indicator first. then 0 the dial on the piston, then slide it onto the deck . u must do it a couple of times to verify there are no errors. normally your piston will be lower, so u would start on the deck and slide down onto the piston. i had my cases and block milled so they were true to the crank (witch they were not when i got them). therefore i need a thicker base gasket. I have no gasket under the cyl block.
now i can mathematically determine the base and head gaskets thickness after it has been compressed. This is how I will determine my squish clearance . The distance between the pistons outer edge at TDC and the head itself, with gaskets installed and compressed. We do not want the piston to hit the head and we want the piston as close as possible to the head.. On a stock motor u don’t have to worry about this. Kawasaki has figured it out for u. but when u buy used parts (stock or not), or change anything , u should verify that this clearance is correct. People mod parts, such as truing or milling a cyl or head, then latter it gets sold as a stock part. U just never know. Just ask OMR about his cyl.
I do not know how far down in the cyl a stock piston should be from Kawi. Can anyone answer that?
The purpose of the squish area ,witch is the lip around the top of the piston, is to force the fuel air mix toward the spark plug. This speeds up the burn rate and deters detonation . this is beneficial with hi compression and poor gas. The bigger piston the longer the burn takes (farther from the edge to the spark plug).

I do know that last year I ran a squish clearance of .036” without hitting the head with the piston. But I never ran it in very hot conditions either. So don’t go there without accepting the risk fist.
I have been told by a few people that .040” squish is safe for the street. But be aware that big cc base gaskets compress more than stock. This is due to more compression psi caused by a smaller surface area. U need to test before u run. So how do we test, u say. After the motor is assembled u can put 2 pieces of solder (just thicker than your anticipated squish clearance) In through the spark plug hole . place 1 over each wrist pin. Now while holding the solder in place, turn the motor over by hand from just before tdc to just after tdc. squeezing the solder. Now u can measure the thickness of the solder. Remember u have torqued the head, but if u re-torque u should re-measure, if u are running tight clearance. I am going to start at .050” to see if I get detonation.


. you will also notice the o-ring groove is filled with rtv silicone. when you buy a large cc head gasket they come as 1 piece rather than 2 . so u don’t use the o-ring at all but u must fill the groove to prevent leaks.

I tried an APE clutch 2 summers ago. I noticed after a while that the clutch became uncivil. it would grab then release quick. it did not have a smooth realease. after investigation, i discovered that due to the fact that the APE clutches are thinner and have an extra plate, they apply a greater load on the basket with there fingers. this causes premature were on the baskets fingers. so the plate fingers and baskets fingers stop sliding and start jumping as the plates were grooves into the baskets finger. so i have to file down the grooves so the plates can slide smoothly again.

When i took my motor apart i found a small piece of metal in the oil pan. 2 summers ago.It turned out to be a piece of the clutch basket. I ordered a clutch basket spring kit from APE.
U have to drill out the 3 big rivets that hold the front and back halves of the basket together,
As u can see in the pic where the spring is removed, the springs housing gets worn badly over the years. I smoothed this surface so the new springs would slide easier.
Then u replace the springs and reassemble. U will need a press, to press the new rivets and there spacer sleeves back together. Then u just weld the end of the new rivets to the plate . That’s it. I chose to have it ballance just to be sure, at a local shop, for $25. It was only out 2 grams . they said new stock baskets can be out by 8 grams.

hey thanks for the write up mark.i wouldn't be afraid to jump on one now.


leon holmes

What Leon said! Great write-up, Mark! Thanks for sharing!
-KR

Mark, what gearing are you running? Do you have a large front sprocket?

Leon, I'm using a stock 903 block with sleeves that will accept up to 1200cc. this leaves about .100" of sleeve wall left. anything less and u loose reliability. the sleeves can distort and go out of round from heat if they get too thin.

Calhoun, i am using a 16 tooth x 630 5/8" offset sprocket with a 35 tooth rear. With the 17" wheels, this is close to stock gearing. 2.5 teeth at the rear is about the same as a 1 tooth change at the front.

Here u may be able to see the sharp edges around the valve pockets.

i will grind these sharp edges off to reduce any possibility of detonation .Second pic.edges removed.
Detonation can be caused from hot spots around the edge of the cyl starting another burn, that will collide with the initial flame. After a slight grind ,just taking off the edge , I will re-polish the edge.

You can see here that 1 piston is 1 gram light.

In this pic u can see the piston on the right has 2 pin oiler holes and the MTC in the center has none.(they oil from a side hole)
It is normal to have 1 hole for oiling the wrist pin in older pistons. I added the second to remove weight , to get the pistons the same weight. It was an old trick to add a second hole to get more oil to the pins.i will do this to the MTC as well ,to balance them.


Be carefull of grabing a spare pin for a build.here u can see that they come in dif thicknesses,which means dif weights.

Here u can see a MK11 crank on top and a z1 below.
The mk11 has a larger pin through the cam sprocket. this gives it more strength. this is recommended when u got to a big block and head for the stip. The sprocket has 16 teeth rather than the z1, or KZ's 15.So u will need a longer mk11 chain(144 teeth) and new mk11 cam sprockets. also , the stator end has a dif taper than a KZ, so u need the mk11 stator, and rotor, and cover. This will give u more amps for the electrics as well.
The other reason for me changing the crank was the rotors mounting method. the z1 has a small bolt (18ft.lb. torque)and a woodruff key to hold it on. The kz and mk11 cranks have a large bolt (100ft.lbs. torque). this will help keep the rotor from spinning on the end of the crank and sheering the key, while starting with big cc's. I have heard this can be a problem for big cc motors with the z1 cranks.
Both are welded. U can see the pork chop shaped counter weights on the z1. the KZ’s are all round. This makes the KZ crank heavier , so the z1 cranked motor will rev quicker. The MK11 crank is a combo of the 2.
u can see a drill bit coming out of the mk11's con rod. the pin oiler holes have been enlarged by .010" on both cranks. another old racer practice. don’t forget to de bur the inside of the hole on the crank and piston, if u do drill them to increase oiling to them.