810 option

I have just got myself a 750 block to build an 810, I have several engines for candidates 78SR650, 81650CSR,or 84700(this one runs and is on a bike at present) the 78 is a good engine but the case needs modifying I think and has a kick start, the 81 is good too and the case doesen't need mods to fit(as far as I know), the 700 runs like a bear and I would hate to tear it down, I also have three other 650 engines one apart(78) and one locked(77) and another running(81) kinda on a bike, but this bike may get the 810 when done, which engine would be best to use

Hey agawam - What year are the 750 jugs? This makes a difference as the 1980 750/4 cylinders will work with your early 650's roller chain. After that year you will need to modify the jugs or go with the latter model's Hy-Vo cam chain assembly.

Modifying the case are not a big deal as all you need to do is have a variable speed cordless drill with a couple of aluminum cutting/grinding bits. Just take your time and do test fittings as you go along. It think this took me a couple of hours with a beer break or two thrown in.

If you have any questions on the 810 project send me a U2U and I will do my best to lend you my experience. Let the 700 live to ride another day and rebuild the 650 engine that looks the best.

Cheers-Colin Firth-Ontario Canada
1977 Kz650 Custom-810 big-bore with lottsa go-fast goodies tucked away inside.

the block has not arrived yet, and I don't know what year it is,the 700 engine runs unbelievably strong so I will leave it alone,I will need some advice on the 810 when I get all the stuff together

As far as we have been able to determine, only the 1980 KZ750 block has provision for the roller cam chain idler/slider/whatever

So unless it's a 1980 block, your choices are going to be limited to 650's with the HyVo cam chain (or some modifications).

assuming the block is not an 80, what mods would be needed, is the hyvo set up less desireable, if so why ? I was looking at the megacycle site they have several cams I may be interested in a 354 lift a 380 lift or a 410 lift and springs of course, any cam recomedations? I usually get all parts together before I start

To switch from roller cam chain to HyVo cam chain you have to swap the crank and cam sprockets, and the guides, that's the disadvantage. I suppose you could also machine a recess into the later blocks to use the roller cam chain guide, but I have not heard of anyone doing it.

As far as cam choice, it really depends on what you are planning to do with the bike.

Post edited by: steell, at: 2006/10/29 00:09

agawam wrote:

..is the hyvo set up less desireable, if so why ?

Actually if you´re rebuilding the entire cam chain setup the Hy-vo setup is more desirable - this setup uses a front and rear plastic slider guide and a rubbing block in the valve cover, these can all be replaced for app. $100 or less. The single roller setup uses a center rubber guide wheel at the cylinder base and 3 idler sprockets - while the rubber wheel is not too costly ($15-20), the guide sprockets are, they´re $110+ a piece for OEM (I´ve seen them as high as $177). You can get pattern idler sprockets for slightly less ($65-80 a piece), but they don´t have the dampening rubber coating that the OEM ones have.

Btw, if you´re going to replace the idler sprockets, the ones used on the 650s and the ones used on the 900/1000s are the same even if they have different part numbers.

Post edited by: OnkelB, at: 2006/10/29 06:55

this is the block I got

Post edited by: agawam, at: 2006/10/29 20:08

another shot maybe this will tell which engine to use

Post edited by: agawam, at: 2006/10/29 20:10

Post edited by: steell, at: 2006/10/29 20:22

1980 KZ750 block, it will work on any of the 650's.

Look at the difference in the photo posted by Mark Wing in another thread.



Here's the original thread

Post edited by: steell, at: 2006/10/29 20:37

OK then,because the bottom ends are, so to speak "bulletproof" as many people say, I plan on droping the oil pans on a couple of these engines to see which is cleanest and do the top end on the best,what are the chances I get away with it

Hey Agawam. Those 1980 Kz750 jugs are the same as the ones I had bored for my 810 project. From what I remember, for 1980 they were and evolution from the 650 castings but with bigger sleeves pressed in.

I stuck with the roller cam chain set up that came stock in my 1977Kz650 Custom. The research and advice I received from other Kz enthusiasts was to stick with the roller as it spun the revs up quicker than the Hy-Vo. There was no data to back this up, just a gut feeling from the gang.

You will need to split the engine cases to do the enlarging work to have the bottom of the 750 cylinders fit into the top of the 650's cases.

Set your top case in a vise and pick up a couple of aluminum cutting bits for your variable speed drill. I had one bit that was cylindrical with a flat and as well as one that was more egg shaped with a rounded end. Take your time and keep a Sharpie marker handy to mark the areas that need to be trimmed after each test fitting. Go slow with the metal removal as it is impossible to put any back on:)

What type of cams and carbs are you planning on going with? I used my 650 head with Kz750 cams, valves and Gpz springs.

You will have fun with the 810.

If you have any questions fire away.
Cheers-Colin Firth-Ontario Canada
1977 Kz650 Custom - 810 big-bore, WG Mikuni 28's and lottsa go-fast goodies tucked away inside.