FrankenMotor

I am looking for information into swapping my KZ550 top end over onto a GPZ550 bottom end. Why would you do that one might ask? I got my '82 KZ550 LTD for 4 or 5 years ago as my first motorcycle. Over the years I have done a number of things to the bike and finally had her running tip top shape and not bleeding any oil from anywhere. Well things didn't last for long like that. I still have yet to determine how, but one day taking off from a stop light, my front sproket separated itself from the bike. Upon taking off the side cover, I saw that the splines on the output shaft were all chewed off. Not wanting to even begin the hassel of splitting the case, to replace the shaft, I opted to switch out the motor. I found a GPZ 550 motor (without the carbs) locally and scooped it up. I was told it was an 81, which would accept my freshly rebuild carbs...wrong. Guessing it is a later model GPZ as the intake ports are larger than that of my '82. After loosing my job, I was just trying to put the bike together to try and recoup some of my money, as a non working bike would barely bring in enough money to cover the brand new tires I had recently installed.

So now the business end...I understand that the heads are interchangeable, but how will the different cam sizes between the two affect anything? Will I be looking at clearance issues between the higher compression pistons of the GPZ and the KZ heads? Will there be performance/reliability issues running a higher compression with the smaller lift/duration cams than originally designed? Should I switch out the pistons and jug as well as the head and only use the GPZ's bottom end?

I'm sure the simple solution would be to get the proper carbs for the GPZ, but lack of coin has me searching for alternative solutions. I appreciate any light that could be shed on the situation, and am willing to listen to any advice ya got. Thanks

Motors fall into two main categories... early style and later style. The chain drive Ltd uses the early style. The 82 and later gpz uses the later style.

You can also just put the carbs on the 82 motor by slotting the intake manifold screw holes and using thick washers. That's what I did to use an 82 gpz motor with Tk-22 carbs. The main issue is that you will need an oil cooler if you plan to do that, unless you can truly keep your right hand under control. In that case, you will still need an oil pan gasket to swap oil pans for the non-oil-cooler type. I'm not sure if the early and alter style pans directly swap, but they very well might. If not, then you'll need an oil pan from a later style motor... 83 KZ550A4 is the only chain drive version. The M and F motors are later style, but are shaft drive. Their oil pans may work.

You'll have to check pan and/or gasket part numbers to check all options.

A quality (not cheapo leaky kit) rebuild kit with gaskets etc will cost you as much as a set of carbs.

My signature has links to the cam info for 550's (labeled valve train warning).

It may be faster/easier/way cheaper to simply offer the gpz motor as a swap for a standard motor. Your old motor is the same as any of the KZ550 C model, and the A1-A3 motors. (NOT the ZX550 A, though.)

Do you have any photos of the gpz motor to help identify the year?
Are the ignition pickups in place? That will help identify the motor.
Where are you located?

I appreciate the prompt response, now if only I was just as quick in making time to get back to this project. I like your idea of slotting the intake holes and adding a thick washer. I was lucky in that the motor I picked up came with the oil cooler. While I do not have any photos of the GPZ motor, I do have the serial number... KZ550DF014202. It does have the electronic pickups, but they aren't in place as I had to get to the siezed up ignition advance. And I must say how much I do appreciate all the info you have linked to in your signature. What a valuable resource that has been to me since when I first got the bike and started wrenching on it. Also, I live in the North Eastern part of Maryland.

I guess my next question would be if you remembered the size jets and needle position that you used in making the TK-22's work? I do have a 4-1 header and pods. Thanks again for your insight and assistance.

I can't tell from the serial number what year it is, as all of the GPZ550 motors used the same cases as the first Gpz (the KZ550D). But if the motor originally came with a mechanical advancer, then it would have to be the 82/83 Kz550H1/H1 motors.

The TK22 site shows how to properly shim the needles using washers and guitar strings, and has notes for drilling the pilots.

On my KZ550H motor, running TK22's with Emgo disposable pods and a 4-into-1 with a mid-level Kerker muffler (the K series has several different levels of baffles, racing version is very wide and loud, the street version is relatively quiet and runs a narrow throat), I'm using 103.4 Dynojet mains, 37 pilots, Dynojet needle at 3rdclip shimmed with a 0.78mm shim and the slide lifter is shimmed with 0.034 bronze guitar string. The air screws are 2-3/8 turns out. This is not the best overall setup, though. It's a little lean on cold days. I have it set for more power on hot days (where the same jetting ends up richer due to less oxygen).

The Dynojet parts are expensive. You can use small head Keihin jets and rebuild-kit needles instead. But using the factory-shaped, adjustable needles (found in rebuild kits), your jetting will be different. In that case start with 3rd clip, but you may have to go to one .5mm shim. The main might be somewhere in the 102 to 110 range. I usually drill the pilots to 34 first. Then if I can't get that to work smoothly, I'll go to 37 pilots.