A Little tip for those putting 650 head on 750 jugs

Hey Gang - I spent the last few nights getting my parts in order to do the assembly of my 650/810 motor next week. Everything is here or on its way.

Instead of going to the machine shop to have my '77 engine case enlarged to handle the 750 jugs I did the job myself with an aluminum die cutter and an electric drill. As with any metal work it comes down to patience and taking a little bit off...trial fitting and a little more trimming with the cutting bit.

All in all the job took about 2.5 hours which is far better than paying a machine shop $40+ per bore hole. I cranked up some classic Bob Seger and Skynyrd and the time flew by.

I discovered that when fitting the head and jugs onto the enlarged cases, the two center, inner bolts (under the camshafts- there to secure the front and back of the head to the jugs) are a different size. For the '77 650 head the bolts were 6X43 but for the 750 jugs the bolt size is 8X43.

I carefully enlarged the head's two bolt holes with an 8 mm drill bit and picked up and 8 mm bolt. Works fine.

If anyone is looking on doing this swapping of parts keep in mind the enlarging of the holes for the 650 head/bolts to properly mate to the 750 jugs. In all of my research on this project I cannot recall anyone ever mentioning this requirement before.

Cheers-Colin Firth

'77 Kz 650 Custom - (Miss July on 2006 Kzr Calendar,) Newest rebuild includes Wiseco 810 kit, Kz750 cams, Kz750 intake valves, 750 GPz springs, Ported head, WG Mikuni 28's, Velocity Stacks, Dyna Ignition and coils, MAC pipe, 14 tooth sprocket, going back to original '77 Moon Dust Silver. Goal is to have a stock-looking bike that will tighten up any loose dental fillings off the light.

I noticed that too, just hadnt got around to changing it/mentioning it.
Scott

Just if there are any out there that still dont believe us that the 750 jugs can be made to fit the 650 case, here you go, a pic of my setup so far;)

(the 650 jugs are on the white box)

Post edited by: 77KZ650, at: 2006/04/20 21:00

Post edited by: 77KZ650, at: 2006/04/20 20:58

Post edited by: 77KZ650, at: 2006/04/20 21:01

Great to hear guys, that it is coming together.

Have you seen the new 650 info site? Check it out and add your mods etc there. The link is in my signature.

Ok, I've decided to go ahead and do the 810 mod. I won the cylinder and a complete head off an 81 750 just this weekend;) By the way thanks to all who may have let me win this:P

My question is : can this case modification be done IN FRAME. I was thinking of using my shop vac and following my die grinder around to pick up all the chips:whistle:

this has now become my project bike as I just bought a ZRX:evil: :evil:

MadMac74 wrote:

My question is : can this case modification be done IN FRAME. I was thinking of using my shop vac and following my die grinder around to pick up all the chips:whistle:

I wouldnt trust the vac to get all the metal, you should split the cases because it also helps to be able to see/work from the other side

I just did this little job 2 weeks ago and I can say with confidence that it can be done in the frame if you are a contortionist, and don't mind cursing every five seconds, but it would be foolish to try:)
Here are the reasons why I wouldn't try it.

1. You would have to remove the crankcase studs (a tough job while the bottom end is in the frame) to be able to get in close with your eyeballs to take a look on exactly where to remove metal.

2. The connecting rods will get in the way and you stand the chance of nicking the rod and journal.

3. A shop vac will not catch all of the shavings and they will just coat the crank and gears with ground aluminum. This has the potential to cause problems down the road. Having owned a commercial air duct cleaning company (65 HP. vacuum truck with an 8" hose) I would say that even the strongest shop vac wouldn't be able to create enough of a closed suction area to pull in any fast flying shavings.

4. The job will take longer by a factor of five.

5. You will not be able to view the inside cylinder walls to properly trim the casings. Remember that you are not just opening up the top lip of the crankcase opeings, you have to get inside, down about 3-4 inches to the sides where the crankcase has structural reinforcing.

In short, trying to save the effort of pulling the motor and splitting the cases is not a smart way to go. Do it right, and the job will be considerably easier. Trust me...I know of what I speak:)

Cheers-Colin Firth-Ontario Canada

I discovered that when fitting the head and jugs onto the enlarged cases, the two center, inner bolts (under the camshafts- there to secure the front and back of the head to the jugs) are a different size. For the '77 650 head the bolts were 6X43 but for the 750 jugs the bolt size is 8X43.


So every one dont get the wrong impression the later year 650 cylinder block also uses the larger 8mmx43mm bolts.I found this out a few weeks ago when I had to switch the orginal cylinder block after a rush job to get the bike out of garage after wife kicked me out.
:pinch:

Thanks for the info guys, wasn't sure now to go about it exactly. I do agree with the "do it right or don't do it at all " thoery however. Winter project:)

The REX will have to do this summer;) :evil: :woohoo:

Post edited by: MadMac74, at: 2006/05/20 14:56

77KZ650 wrote:

MadMac74 wrote:

My question is : can this case modification be done IN FRAME. I was thinking of using my shop vac and following my die grinder around to pick up all the chips:whistle:

I wouldnt trust the vac to get all the metal, you should split the cases because it also helps to be able to see/work from the other side

Take the cases out of the frame for sure. I would split thr cases firsr so the major cleaning is on the top half. You have to clean the cases VERY good, ons little chip of metal could cost you big time.