Z750 cams in a Z650

I believe aI saw a comparative photo showing Z650 & Z750 cams; the 750 cam lobes appeared to be wider, so longer valve opening times.

Can 750 cams be dropped straight into a 650 engine, and will it give any advantages?

Thanks,

ian

Depending on model and valve lift , duration etc the later cams such as the GPZ750 are comparable to a mild sports cam and will perk up the 650 motor.
Just as fitting GPZ1100 Unitrack cams in the earlier Z900/1000 motors ( all other 900/1000 models run pretty much the same spec cams) you may need to clearance the head fore and aft of the cam bucket to clear the higher cam lobe and also depending on model the later cams may not have the worm gear provision for a cable operated tach if needed so that would need to be addressed by fitting an electronic tacho.
 

Thanks Zed, that's useful to know. I wasn't aware that GPZ750 cams would also fit, I'd been thinking about the Z750 cams. Looking at them, they seem to have switched from a centre chain drive to an end chain drive later in life; obviously only the centre drive will fit. Sounds like a nice upgrade!

Some 750 cams don't have a mechanical tach like the 650.

wrote:

Thanks Zed, that's useful to know. I wasn't aware that GPZ750 cams would also fit, I'd been thinking about the Z750 cams. Looking at them, they seem to have switched from a centre chain drive to an end chain drive later in life; obviously only the centre drive will fit. Sounds like a nice upgrade!

All of the 650/750 air cooled motors are based on the same design with center camchain.
The end camchains are on the water cooled stuff and bear no relation.
750 aircooled four engines are found right up the the more recent ZR750 Zephyr models.

also note base circle different on 750 cams vs 650 cams.

wrote:

also note base circle different on 750 cams vs 650 cams.

Yes, good point, you need ca. 0,20 - 0,30 mm thinner shims!

wrote:

wrote:

also note base circle different on 750 cams vs 650 cams.

Yes, good point, you need ca. 0,20 - 0,30 mm thinner shims!

I thought the base circle was smaller?  Wouldn't that mean thicker shims?

Oh, and this only applies for the later GPz750 cams.  Not all 750 cams.

One other consideration is that the older 650 used a roller cam chain, switching to HyVo sometime near 1980 or so.  So, I think, the 650 cam sprockets would have to be transplanted onto the newer cams.

I can only verify that GPZ 1100 UT cams have a 0,20 - 0,30 mm larger diameter base circle than KZ cams, so other GPZ engine cams could be made the same BC. If your need a shim thickness  less than 2,00 mm, it would be an option to adjust then correct valve clearance.

wrote:

also note base circle different on 750 cams vs 650 cams.

Yes ! but only fractional which does not prevent any of the 650/750 cams being interchanged and well within the scope of shim sizes.
The installed valve stem heights are all the same throughout and in the case of the GPZ cams you will that find the corresponding lifter thickness has been adjusted to compensate and unless you are on the limit of valve adjustment the base circle difference is inconsequential.
 
 

Maybe punch up the article "KZ650 76 historic race bike". Has some good info on this. The 1980 KZ750 has the cam chain, tack drive and .342/.335 lift vs .304 and 10 degree's more duration.

Helped but not quite as much as I hoped. Would probably do the 83-85 GPZ cams if I had it to do again.