What caused this engine failure?

[JohanR]

The mower itself is a swediah quality all aluminum self proppeled chassis, they last forever. In this spec they cost 7-800$ new so its a real shame it wasnt serviced enough.

Im throwing 20$ Of parts in it and then be on the lookout for a replacement engine to swap during winter.

From my web investigation(lol) ive found out the chrome rings is hard to get and that the kartracing-guys hone the kool bores and pay extra attention on cleaning the bore afterwords. They use 400-600 grit stones, all i have is 280 though, they want the walls to glaze quickly for performance gains. All i need is a few runninghours of a bit less smoke

 

[JohanR]

I honed the bore with 280 grit stones. It came out pretty nice, the big scoring is still visible but i could barely feel them with my nail.

New iron cast rings arrived and the gaps were measured to 0.0157" for the two top rings and 0.0137" for the oil ring, not within the desired 0.003"-0.010" but still well under the max 0.030", probably due to my aggressive hone. A set of oversize rings would perhaps have been better.

Anyway, lapped the valves and set the clearences, hammered out a new gasket and put the engine back together. Mounted it on the mower and filled it up with oil, turned it around a few times by hand before adding fuel. Then gave it a good pull and it fired right up. Started to smoke a little after a minute but after a few more minutes it stopped.

I mowed the lawn and it went really well, besides the lack of bluesmoke and nasty smell it was strong like an ox.

Great success

 

[ML-TOYS]

Glad it worked out