I suspect you're trying to torque the head bolts on your 650. I'm basing this upon the code you listed in parentheses in the title. Looks like a Yanmar engine code to me.
If I'm correct, the torque for the head bolts on my 670 is 63 to 67 lb-ft. The 650's should be pretty close to that, but there is also a sequence to follow when torquing.
I strongly suggest you go to the closest Deere dealer and see if they have the maintenance manual for your tractor. If you're torquing the head bolts and do it wrong, you could do some serious damage.