650/750 head interchangeability?

A friend of mine has an extra 650 bottom end I think I could get fairly cheap. I would like to use my spare engine parts from my 810 build to finish this motor. The stock 750 pistons should fit the 650 rods right? My biggest concern is with the head. I have a 750 head I plan to use. Will it fit over the studs? Is any modification required? Would I have to get different cam sprockets to work with the older style cam chain? and lastly, 650 heads have a chain idler wheel thing correct? This wont fit a 750 head will it? Just unsure if this swap is doable.

Since there are several 650/810's here on KZR, I think you can take "doable" as a given

You can use the 650 cam sprockets on the 750 cams, the 750 head bolts right on, as does the block (clean up the top case opening with a dremel to fit the 750 cylinder liners).

IIRC, the KZ750 heads have the holes already drilled for the roller mounting bracket.

Oh yeah, if you are going to use a 650 bottom end with the roller chain set-up (any prior to 81) you have to use the 1980 KZ750 block, as it has provisions for the roller cam chain.

Since your 750 was a 81 I don't believe it will work, take a look at the front of the cam chain tunnel and see if it has a place for the roller cam chain guide. There was a recent thread that had pics of an 80 and a later head so you can compare. I think it was in the engine forum and said something about 810.


Forget looking for the pic, since the change in board software none of them are showing up.

The 750 blocks have sort of an oval at the front of the cam chain tunnel, the ones that will work with a roller chain have a notch on each side directly behind that oval shape. If you don't have those two notches, it won't work.

The thread was the bad rod bearing thread just a little ways down on the main page of this forum.

Yeah, the head is from an 81. It does not have the mounting spot for a cam chain roller. Is there any other way to take up the slack? Would I just be better off using the 650 head?

Oh yeah, almost forgot. 750 cams will work in the 650 head correct? Are the 750 cams better than the 650 cams or are they the same?

[img size=150][/img]

this is the earlier roller chain style head with the center roller idler. look in the cam chain area and notice the 4 bolt holes for the idler

this one is a 750 gpz head without the provision for an upper idler.
i have yet to find a way to make the one available from ape fit right.

750 cams will bolt right in if you have the right cam sprockets.
they are a little better then the 650 cams but the hot set up is the gpz 750 cams.
but with the good comes the bad.
no mechanical tach with gpz cams.

you can still get new aftermarket cams for the middleweights for around $300 to 350.

yeah, got gpz cams for my 810 motor, but this is going to be a cheap build. Just so I can have a backup motor in case one of my 3 kz's has problems. I will check out the ape idler, thanks!

jordan wrote:

but this is going to be a cheap build.

isn't this an onxymoron? :laugh:

there is not nothing cheap on a kz motor.
being cheap cost you a lot in the long run.

do it right the first time saves you future Aggravation and future posts here.


it's only money.

Jordan. the 1980 KZ750 head is identical to the head in the top picture, does your 81 750 head have the place to bolt the cam chain roller like the head in the top pic does?


kawsakiman, The head in the top pic has HyVo cam sprockets on the cams, is that a 750 head, and if it is, is it a 1980 KZ750 head?

I'm just trying to determine if the 81 KZ750 head has the provision for the cam roller or not.


I know that the 80 KZ750 cylinder block is the only 750 block with provision for the roller cam chain guide, I just don't know if the same is true of the head.

oopppps
i just didn't change the sprockets yet.
those are andrews cams that were in a gpz 750 when i got it.
that is a 650 head though.
that picture was after i got done bench shimming it.
i'm trying to locate some adjustable sprockets for a roller chain before i take the dremel to the other ones.

Ok, thanks.

The 80 KZ750 head is identical to that one, including the drilled and tapped holes for the cam chain roller, and the 80 KZ750 cylinder block is the only one that has provision for the roller cam chain guide. I "think" the 80 KZ750 head is the only one that the roller sprocket will bolt on because it changed for 81, but I haven't been able to confirm that yet.

I have an 80 KZ750 motor disassembled, and 83-85 GPz750 motors disassembled, but I don't have any 81-83 KZ750 motors disassembled. I do have a 81 KZ750 motor, but I don't plan to take it apart as it's a low mileage motor and is my test and development mule for the EFI conversion.

kawsakiman wrote:

jordan wrote:

but this is going to be a cheap build.

isn't this an onxymoron? :laugh:

there is not nothing cheap on a kz motor.
being cheap cost you a lot in the long run.

do it right the first time saves you future Aggravation and future posts here.


it's only money.

Sorry, I believe we both have different ideas of cheap. I know this is going to take probably a little over $300 to finish. When I said cheap, I was referring to not buying lots of aftermarket parts that would rack up a bill over $1000. I just plan on building a nice stock reliable motor. Gasket set, bore and hone with 750 pistons. Then top it off with my 750 head with resurfaced valve faces. Nothing too unordinary. and BTW, I went out to the shop today to get another look at the old 750 head. It does have the mounting location for a cam chain roller. Must not be an 81, thats just what the seller said. One more question, can the 650 cylinders be bored over to fit in 750 pistons? If not I'me sure I could find some 750 cylinders

That's a good question, but you are going to have to pull the 650 cylinder block off and measure the thickness of the liner at the bottom of the cylinder block.

If you can bore the 650 cylinder to stock 750 size and the lower part of the liner ends up at the same thickness as the 750 cylinder liner measured at the same place, then yes. If the liner will end up thinner than the stock 750 liner, then no.

You can push out the 750 liners and bore the 650 block to fit the 750 liners, then install the 750 liners in the 650 block.

Since the holes 650 case have to be enlarged so the 750 liners fit in there, I'd say the 650 liners are probably to small to be bored to 750 size.