Someone talk me out of this: kz200 engine-Kz250 crank-bayou 300 cylinder

Currently running a kz200 bottom end (minus the crank, which is a kz250), with a kz250 top end. I was working on a friends 2000s bayou 300 and noticed that the cylinder bolt pattern is exactly the same, the alignment pins match up, and the oil passages are the same. The only difference being the bore size. The stroke on a bayou matches a kz250 (64mm). Im already running an aftermarket carb (mikuni vm24) and I have a mikuni vm26 if I need to step up a carb size for the larger bore. My question is, because I know almost nothing about how the engine actually works, am I going to run into timing issues, or is that mitigated since the stroke is the same length so presumably the same travel time? I can get a new production top end kit for the bayou for ~$250, which would be nice since Im currently running used parts and I worry about how long its going to hold up. 

It's an interesting idea, but there are a lot more considerations than just the jug size, bore, and oil passages. The stroke is an important aspect but the piston height also needs to be the same, and it needs to be the same weight too (or very close). You'll need to find a larger piston that matches both wrist pin, and the bore. The cam chain will need to line up, have the same size sprocket, and be the same height (otherwise the cam chain will be too long or too small).

Now having said all this - looking up the cam chain numbers both the kz200 and bayou 300 use the same chain (from a quick search - don't quote me on that). The sprockets have different numbers, but they may be compatible (the ratio between bottom and top just needs to be the same). The bayou pistons may just happen be the same size and connect straight-up to the wrist pins so a bayou piston could maybe work. A lot of kawasaki parts are just longer/wider models of other parts which can make them easy to exchange.

Ultimately, unless someone on this forum has done it, the answer is that it will be a lot of time and effort and may not work - but it also might work. It may literally just mean bolting the bigger engine on with a bigger piston. But you'll never know until you have the parts in front of you to measure and compare.

It's an interesting idea, but there are a lot more considerations than just the jug size, bore, and oil passages. The stroke is an important aspect but the piston height also needs to be the same, and it needs to be the same weight too (or very close). You'll need to find a larger piston that matches both wrist pin, and the bore. The cam chain will need to line up, have the same size sprocket, and be the same height (otherwise the cam chain will be too long or too small).

Now having said all this - looking up the cam chain numbers both the kz200 and bayou 300 use the same chain (from a quick search - don't quote me on that). The sprockets have different numbers, but they may be compatible (the ratio between bottom and top just needs to be the same). The bayou pistons may just happen be the same size and connect straight-up to the wrist pins so a bayou piston could maybe work. A lot of kawasaki parts are just longer/wider models of other parts which can make them easy to exchange.

Ultimately, unless someone on this forum has done it, the answer is that it will be a lot of time and effort and may not work - but it also might work. It may literally just mean bolting the bigger engine on with a bigger piston. But you'll never know until you have the parts in front of you to measure and compare.

Thanks for your response. I figured it wasnt going to be quite as simple as I hoped, which is why I asked. Know what you dont know and all. I may try finding a cheap used wrist pin/piston for measuring purposes, since I cant find any parts lists that have measurements. The cam sprocket out of the bayou I was working on actually has markings for a kz200/250 on it (which spurred the idea more or less), so that might actually work. I also saw that the cam chains used are the same. We're about to enter into our long non-riding season here so I'll have a few months to work it out and make it happen if its possible. 

Decided just to go for it. All the stuff I could research without the products in hand checked out. Was pretty inexpensive to get the cylinder/piston/gasket set. If its a total fail, I'll just return it if I cant figure out a way to make it work. If it all checks out, I'll probably make a short project thread about it. If it doesnt work, for future searchers who might be as crazy as I am, I will try to remember to update this thread. 

Other things to consider are compression height, deck height, bore and if the cases need to be bored for the larger sleeve.


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