I have installed several propane kits they are much cleaner burning that gasoline.Oil don't have tobe changed as often. Propane has about 80% of the BTU's as gasoline but because it mixes with the incomeing air as a gas rather than small drops of liquied as gasoline Millage is only a little less. The valves will wear quicker on older moters that were set up to run on leaded gasoline which was a lubercant between valves and seats.A rebuilder can put in harden valves and seats. The same as a motor that uses unleaded gasoline.