650 bottom end, 750 jug, Head???

I hope your not sick of all the questions yet. I understand that i can fit a 750 cylinder block on my 650 crankcase (i will have to do minimal removal to get sleeves to fit). so what about a head? will the 650 head fit or am i stupid for doing so even if it does fit? do i just need the 750 cams and my 650 sprockets? I feel like if im going to bore a jug out and pay for new pistons i mind as well end up with an 810 not a 700.

also, are my stock 650 carbs not going to do the trick w/810 kit?

im trying to figure out how much more it will cost to go 810 rather than 700.

thank you for all the help.

You can fit 750 jugs/pistons with minimal work IF you get the correct year 750 parts. The only year that I know of that SHOULD always work is 1980. After 80 some of the 750 motors were hyvo cam chains and don't have the machining for the 650 cam chain rollers and tensioners. The 750 head will flow better for you so would be worthwhile as well. The 750 cams with 650 cam sprockets will do the trick.
Your stock 650 carbs will come up way short for larger displacement. I'm running vm26 carbs on a stock motor (stock are vm24) and it made a world of difference in every aspect of performance. If you tried to run a 700, 750, or 810 motor on the stock carbs you'd be missing out on a lot of the bikes potential. Hell, running the stock vm24 carbs on a stock motor you're missing out on a lot of the motor's potential!

Thanks, great info. I guess i should have got the vm26s b-4 i dove into the engine hahaha. well I just bought a 81 750 cylinder block on ebay, it looks like it has the fittings for my cam equipment. now i need 750 cams i guess. are all the years the same? and my sprockets will fit? sorry to beat this dead horse some more, but i cant find someone who has kept the 650 head w/ this swap.

i can tell you that i am fairly sure you will be splitting your cases very soon.
i wrote somewhere here before that the 750 cylinders would not fit my 77 lower half.
but they slid right into the 80 csr 650 motor i had.
i see case boring in your near future.
don't get me wrong, the improvements will be worth it.
just a pita.
i don't want to discourage you either. it's really not that hard to do.
so you can tackle this one of three ways.

1. build a 750 instead
2. split the cases and have the upper case bored to accept 750 sleeves.
3. have your 650 block bored to accept 750 sleeves, but i would shy away from that option. it just makes them too thin for proper cooling.

or, one more option, find a 80 motor and swap the crank from your 78 into it.

you can use a 650 head on a 810 motor but why?
unless you port it, a 750 just flows better.
but you need to find one with the upper chain idler.
here are two pictures for you.
first is a 650 head with the provisions for the idler.



( and for all you eagle eyed viewers, i know those are hyvo sprockets. i didn't change them yet. )

and here is a gpz head without.




see the 4 holes where the idler goes in the cam chain valley in the first picture?

wow, great help. good to see pics too. I guess im off to the bone yard to find a 750 head. thanks for all the help, this place is great.

I'm currently assembling something very similar. I have the 1979 650 cases and 1980 750 cylinders (that will use my 650's rollers and chain etc) and I'm going with the 650 head since I have one and it's cheaper. I am however swapping out ot 750 cams and KZ1000 26mm carbs.

As far as boring the cases to fit the 750 juggs I just dremeled it till it slid in. The cylinders are pinned on each end to the cases at the oil passages so alignment should be dead on. So far I'm fully assembled except for the head. I'm going to disassemble it and clean up/reseat the valves.

Good luck on your project.

any way you can post a pic of the work you had to do to the case to get the jug to fit?( or anyone for that matter) how did you keep the metal out of the bottom end? im going to the bone-yard this Sat. to look for a 750 head that is compatable w/ my chain.

Are your 26mm carbs going to work w/ head? Do they make bigger boots that just fit the same bolt pattern?

keep me posted too!
best of luck.

oh also...will my exhaust (V&H) fit the 750 head??

thank you

Well in my case I had the engine apart. I'll have to use the kz900/1000 rubber intakes and elongate the holes a wee bit to get them to mount to the 650 head. Eferything I've heard is that yes the pipes will fit the 750 head. It's the same mounting points.

WELL I'm afraid it's going to next to imposable to keep the shavings out of your bottom end. You may as well just split your cases. I did when I put the 750 jugs in my motor. I also use a ported 650 head.
Mark

excellent, thanks for the pics too. any way to clean the cases/cyl/head so they look like they did new, or at least a bit brighter. have tried engine degreaser, Zep cleaner/ degreaser, and a whole slew of other stuff thats not good for your health.
thanks always

So i went to the bone yard Sat. looking for a 750 head for the conversion. the only thing i could find was an 84 GPZ750. I didnt take the valve cover off, but this engine wont have the 4 holes for my chain roller will it?

also, did I read somewhere that this (GPZ)motor will bolt right into a 650 frame? if so any details would help.

thanks always