Will the 500 pantah rear head fit the 750 paso motor ?
the information I have says yes but just need to check with the experts!
I am aware the valves will need bringng uo to match the paso head,

Hello. The answer is yes and no. The bolt patterns are the same, but the combustion chamber spigot on the 500 is only 95mm across, while it is 100mm for all the 750s. So, a machinist would need to increase that for you. Then, you are left with the small valves and ports for a big cylinder, and might still end up with a lot of compression even with stock Paso pistons---the F1b pistons would likely not fit without more combustion chamber work. You could use newer (or used) 620 pistons and cylinders by having the top of the cylinder turned down to 95mm to fit inside the head, and then check piston-to-head and to -valve and clearances. And then there is the valve-to-piston check depending on the cams. All things will work with time and $$$. MikeV

Hi Thanks for the info, I also have a 650 pantah motor and option on a 750 elephant motor
do you think the elephant motor and some decent cams a better route ?
I do have good access to machineing at reasonable cost old pals network aint it great.
I did intend useind the 650 but realy want to have a 750, too old to race it but use it for classic track days, thanks again Harvey

Hi Harvey, I see the Forum has answered most of your questions. Doesn't your elephant motor have a reversed rear head? I would definitely use the 650 and in the future you can bump it up if need be. They are plenty fast with some head work, cams, and a free flowing exhaust, even with the stock 36mm dellortos. We won an endurance race with just such a motor with a redline of 10,000 RPM for the 3 hour race. Lou

Hello Harvey You have some nice motor choices to pick from and well defined objective “Classic track days”. If your 650 pantah engine is in good condition that would be a fine choice to start. Updates to consider would be fitting the more durable transmission of the Paso to the 650 including that fine spline output for better sprocket choice. Bigger motors do make for more fun on the track especially if not limited to capacity of racing. A cost effective 750 build would be fitting the Paso cylinders to the 650…requiring the already mentioned spigot machining plus the case boring for the bigger sleeves. With a properly ported small valve heads and 89-90 sport flat top pistons (or shave your Paso units) the comperssion ratio would be about 12.5 /1. This combination runs best with lots of cam (900SS or even NCR-7s) and 40mm carbs. Makes for a tractor of a motor that is easy and fun to ride.

Thanks guys, I am on a steep learning curve here, also i have been recomended ST2 cams??
Where will I buy some ncr7s