KZ650 > KZ400 Engine Swap?

Hello everyone! I'm new here, with a recently 76 KZ400 acquired, I have some ideas...

Number one on the list is finding out if an 82 KZ650 engine will fit in the frame of my KZ400. The transmission is slipping and instead of just replacing that, I was thinking I could get some extra power and just dump in a new engine.

Does anyone have any info on this? Every tried it? Any issues you run into if it is possible?

Thanks everyone!

Easiest way is to trash the 400 and buy a 650. Anything else leads to tons of cash and massive decline in your mental health.

Really not a good idea, by the time you're done there will be no KZ400 in the bike.

Buy a 650 if you want something bigger, or even better, put a KZ440 motor in the 400.


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steell wrote: Easiest way is to trash the 400 and buy a 650. Anything else leads to tons of cash and massive decline in your mental health.

Really not a good idea, by the time you're done there will be no KZ400 in the bike.

Buy a 650 if you want something bigger, or even better, put a KZ440 motor in the 400.


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So the KZ440 motor would be easier? Wouldn't be apposed to that upgrade as an alternative. The bike already has a bunch of work put into it. A lot of custom work. Rather not start from scratch. I've attached a picture.

Putting the 650 engine into a small frame will require MUCH modification. I don't understand the problem that leads you to believe "the transmission is slipping." Transmissions don't slip. Is it possible the clutch simply needs to be adjusted? Please describe the problem as there very likely is a simple fix that will save you tons of time & $$$. Ed

650ed wrote: Putting the 650 engine into a small frame will require MUCH modification. I don't understand the problem that leads you to believe "the transmission is slipping." Transmissions don't slip. Is it possible the clutch simply needs to be adjusted? Please describe the problem as there very likely is a simple fix that will save you tons of time & $$$. Ed

Hi Ed, Thanks for the reply. I've been told that the 76 frames are the same for the 400 to 650. I came on here to clarify that and find out if it was true. If it's not, than it's not something I will do. I will work on the engine and the trans. By slip, I'm referring to what is actually happening. The bike will slip out of gear and into neutral. It used to just be 2nd, but now it will slip out of any gear into the magical place between gears. I've heard multiple explanations for this. Some people believe it's the clutch, some the trans. I've been dealing with it for a while now, but it's getting to the point where I've had some scares around a bend. Looking up parts and whatnot, it seems it's a similar price, on ebay, to get a full motor or the parts for the trans. I figured I would get a whole motor, put that in, then I'd have a second for spare parts and be able to play around with it, see what was wrong. Any and all help you can supply would be greatly appreciated. If you know the easiest way to fix my problem, I'll be happy to hear it. Thanks again Ed.

Whoever told you that ANY KZ400 frame is the same as any KZ650 frame was wrong. The frames are very different. If your tranny is popping out of gear when riding along it most likely is not clutch related. It may be that the dogs in the tranny are worn or something could be wrong in the gear change mechanism, you will need to take a peek inside to pinpoint the problem, but it may be an inexpensive repair. If you can find a good KZ400 engine or maybe a KZ440 engine at a decent price you might want to make the swap; but keep in mind that the charging systems are different on different model engines, so unless the engine you buy has the same dynamo type as your 1976 KZ400 (field coil type) you will need to make changes to the charging system (rectifier / regulator). There may be other differences too, such as airbox, etc., so do some research before buying just an engine or you could end up needing $$$ to make the swap successful. Ed

KZ400 Frame




KZ650 Frame

Hey Ed,

That's why I came on here to ask. I wasn't sure if they knew what they were talking about. Always ask multiple sources when you don't know the solution to your problem. I didn't believe it was clutch related though, but wasn't certain. My biggest issue is living in NYC, you can't take a bike apart without being able to put it back together the same day.
I'm trying to gather info on engines. That's something I'm trying to do on here because you guys are much more knowledgable than I, when it comes to KZs. Thanks again for the input.

This may help - Take a look at Kawasaki.com. On left side put cursor over "Owner Information" then on drop down menu click on "Parts Diagrams." The click "Continue" next to "Motorcycles" and click on model/year/etc. on drop down. Once you get the list of parts for your bike you can click on the category of parts - such as "Air Cleaner" and you will see a diagram of all the parts for that category. Then when you click on an actual part number on the list under the diagram it will say if the Item Status is "Active." If it is “Active” Kawasaki still sells the part through dealers. Also, at that little page you can click on the yellow highlighted question mark for a cross reference of which bikes share that part or click on the red highlighted S to see earlier part numbers for the same part. By looking at the various parts diagrams for the engines you are considering, you can see what kind of dynamos, etc. they use and determine if they're a match. That's where those frame diagrams I posted are from. Ed

Thanks again Ed! I'm going to look into this when I get a minute. It's going to take some studying and deduction!