TOPIC:

Does anyone know how similar the two engines are? The crank seems to be the same stroke, the biggest difference looks like the bores. Are parts interchangeable, ie. would a 650 crank & rods drop into 750 cases? The cases will have larger bores to accommodate the larger liners, but apart from this, is there a lot of similarity?

It's just that 650 engine p[arts seem to be both commoner and cheaper.

Thanks,
Ian

The basic answer is that the  Aircooled 750/4 is based on the 650/4 with most parts interchangable depending on year as they switched cam chain styles from roller to Hyvo type and also alternator types as the model run progressed.
Later aircooled zr750 zephyr is also a continuation of the 650/750 engine.
You can mix and match parts from different years once you are familiar with the differences.
 

The last model year 650 (1983) used 750 cases because they were phasing out the 650 line. Some 82 model 650 cases were setup to take the lager sleeves, from what I have seen the CSR cases are this way, the cranks also use the larger rod bolts. Earlier 650 cranks have smaller rod bolts by 1mm. The later model where they dropped the kick start also have the better starter motors.
There seems to have been some over lap in the cases from 650 to 750 in 1982-1983.
If you want the 650 to be compatible with 750 components (head) you should stick with the 1982 and later 650 motors.

How much else is interchangeable?  Exhaust....wiring...carbs?  I have access to a free 650 engine if i need it for my 82 750.  Not sure of the year on the 650 but it had CVK carbs, which have been sold.  Don't know if I'll need the engine...I ran out of good weather before i got the 750 totally sorted out....just curious

BobZ post=860862
How much else is interchangeable?  Exhaust....wiring...carbs?  I have access to a free 650 engine if i need it for my 82 750.  Not sure of the year on the 650 but it had CVK carbs, which have been sold.  Don't know if I'll need the engine...I ran out of good weather before i got the 750 totally sorted out....just curious

Since it has CV carburetors, it's probably an 82 or 83 csr. The 650-csr engine is pretty much the same as the 750-4s & have the same charging/ignition systems as the 750e/h. camshafts & timing advancer are different as are the cylinders & pistons of course.  The csr airbox is actually a 750e/h airbox & the 82-83 csr models use the same carb holders & airbox ducts as the 750-4 models.  The csr mufflers are identical to the 750h LTD. Don't know about the wiring harness, but it probably would be useable, but not identical.

Thanks gents, really useful replies!
I hadn't realised that the camchain had changed to be a HyVo; did these work any better - maybe less "stretch" over time?
The carbs on the 650's are I believe 24mm bore; has anyone seen an advantage to going with larger bore carbs? Any preferences for the CV types, which appeared on later engines?
Great point about the rod bolt diameters - I wasn't aware of that one.

Ian

stretch is probably less & a HyVo cam chain is quieter/smoother than a roller chain. Also, the redline on the 81-83 650-csr is higher than the earlier models w rollers.  9500 vs 9000 rpms.  I assume the same goes for the Euro z650 models.

wrote:

The carbs on the 650's are I believe 24mm bore; has anyone seen an advantage to going with larger bore carbs? Any preferences for the CV types, which appeared on later engines?
Ian


 

Yes, standard carbs on the 650's is VM24SS.
Some early model 650's also got VM22ss carbs.

I swapped to CVK32 carbs following Pablo's/z650Spirit tutorial.
Thes carbs came on early ZX600 Ninja's and ZR7's.
ZR7 manifolds (dirrect bolt on) and carb boots (holes in stock air box enlarged) are needed.
Main benifit is smooth operation, no flat spots anywhere in the rev range.
Also has a bit of a power band.
I have one season, 2500 kms, with the CVK32s.