difference between 631 and 641

[bobbari123]

what is different between 631 and 641? i own 641 and i was able to get manual for 631, i always thougt that those two are quite same 641 with longer wheelbase but when i check the wheelbase is same

 

[OldMachinist]

Looking at the specs the only physical differences I see are the 641 has a little more ground clearance and it holds 13 gals. of fuel vs. 10 gals. for the 631. You'd have to compare the parts manuals to see other differences. I know the 641 had several changes to the drive motors(spline vs. tapered shaft) depending on the serial number.