Only when timing gears were wore out and that was back in the 190 days before hardened gears and the designation for that engine was 2900 back then. Other then some broken rings from to much ether or operator overheating they have been great. Of course they need coolant changed ect. from time to time also.
Thanks for the comments- bought an M2 in Iowa in Dec, really good shape. Bought another with broken cam in Mn in Mar- either for parts or fixup and resale. Heard a couple comments about the cam weakness- never heard of it before.