KZ650 to 810cc

Ok so my 1981 KZ650 CSR H1 has some engine noise that I can only attribute to worn chain guides for the cam chain.

I replaced all the springs in my automatic chain tensioner had some reduction in noise but I still get that rattle in the engine.

So I was thinking I would really like to have some more power and was considering going up to a 810cc and while I was at it I could replace the worn chain guides (if they are worn) and of course replace all the gaskets to stop any leaks, etc.

My question is what do I need?

From what I have been reading I gather to go up to 810cc I would need to get a cylinder block from a 1980 kz750. Would I just need the cylinder block or do you need the cylinder head as well?

I plan on getting the kit from APE which includes the cylinder boring and the pistons.

Thanks for your help.

There is a possibility that you can simply bore your cylinder block for the 810 kit. I believe your motor uses the same HyVo cam chain as the 750's, and it's basically a KZ750 motor with a smaller bore.

This is assuming your bike doesn't have a kickstarter.


A good first step would be to do some research in the kawasaki.com parts diagrams for the 81 KZ650 CSR, see what parts interchange with the 750 motor. Next step would be taking some actual measurements after the motor is disassembled.

The cam chain is the same and I don’t have a kick start.

I am going to get my shed setup to work on the engine this winter.

I don’t have a lot of experience doing engine work but I am good at following directions and I consider my self very patient.

I have the original service manual, although I don’t know how much that will help with re-assembly if I get the APE kit.

What engine parts should I be looking at for interchangeability?

If I can bore my cylinder block then would I just be able to keep my top end?

Would it be better to get a different top end?

I want to keep the cost down so I am not looking to go crazy with performance mods, however I would like a little more bite.

you can bore your 650 cylinders but i have heard that it is not advised and that the sleeves will be too thin after the bore. The 750 sleeves can be pressed into the 650 block, but most often the easiest option is finding a cylinder block from a 80 750. This is only because they still use the same cam chain/idler assembly. You will be able to use your 650 head, but they do have a smaller combustion chamber. I dont know how big of a difference a 1980 kz750 head will be over your 650 head though. Also, if it is at all possible, find a set of 1983-1985 gpz cams. You will have to use the cam sprockets from your 650 if you choose to go with them. Also, web makes aftermarket cams if you want to spend the money. Other than the gaskets you may want to rebuild your head. Valve seals, cleaned up, maybe portwork, and resurface valve seats/faces.

Jordan, the 1981 KZ650 CSR is quite a bit different than the earlier KZ650's, like I said above it's basically a KZ750 motor with smaller bores. Same cam chain, same cam gears, same bottom end, the entire 83-85 GPz750 top end will bolt right on, which it won't do on the earlier ones.

Think I'll take a look at the parts diagrams again to see what parts are the same, I did it before but it's been awhile.

The following models all use the same crankshaft.

KZ650-H1 (CSR) (1981)
KZ650-H2 (CSR) (1982)
KZ650-H3 (CSR) (1983)
KZ750-E1 (1980)
KZ750-E2 (1981)
KZ750-E3 (1982)
KZ750-F1 (LTD Shaft) (1983)
KZ750-H1 (LTD) (1980)
KZ750-H2 (LTD) (1981)
KZ750-H3 (LTD) (1982)
KZ750-H4 (LTD) (1983)
KZ750-L3 (1983)
KZ750-N1 (Spectre) (1982)
KZ750-N2 (Spectre) (1983)
KZ750-R1 (GPz) (1982)

1981 KZ650 CSR uses the same valves as the earlier 650's, and the same cam chain as the 750's. Cylinder head and block are listed as 81-82 only.

I've wondered if the 81 KZ650 CSR used thicker liners than the earlier 650's, and if they could be bored to 810 size. I'd really appreciate it if you would check into that and let me know.


Just so there's no confusion, the 1980 KZ750 uses the same HyVo style cam chain as the later 750's, it just has provisions for the earlier style roller chain (as does the 81 and possibly 82 KZ750).

oh, i guess i didnt even look at the year, i just saw 650 and started typing. I knew the later ones were a little different, but have never actually researched it. I am also interested in finding out if the later 650 sleeves are different, it would be nice to know.

I will see what I can find out after I take the engine apart. It will be a few months until I have to get my shed setup and get some things done around the house to get started.

I am really excited to get the engine running better it has put me off riding this year as much as I normally do.

Based off what I am gathering I may just need the APE kit and some cam chain guides and some gaskets.

I will let you know when I get started and take a lot of pictures so I can figure out if I can use my block and have it bored to the 810cc kit.

and a cam chain that is mostly streched out by your description of what is wrong with the bike and why your tearing it down in the first place.

It may just need a new cam chain . . .but I think that its the chain guides and tensioner I could be wrong but I think I am just ready to have a bike with a little more bite. And I would rather put some money into this engine then to start over again with a new bike.

I'm still building.....78 650SR, with 84 KZ700 engine GPZcams,81 650 head cut to 45degree seat, dyno jetted mikunis,.... 81 650CSR engine, 80 750 block bored for 810 kit set of V&H cams, 84 750 head cut to 45degree mark BS34s from suzuki jetted, got interupted when my H1 500 needed a new engine, now 020 ported and very quick, now I can get back to the KZs