Are aftermarket kohler exhaust and intake valves prone to quick wear and burning? I just rebuilt my k341 with a aftermarket kit that I bought from ebay. Kit came with aftermarket rod, piston and rings, both valves and complete gasket and seal set. This wasn't Stens,I don't recall aftermarket name. Everything went together well, all tolerances were good. After engine was run for 4 or 5 hours I readjusted the valves. intake was good, exhaust was a little tight. Ran for another 4 or 5 hours had rough running issues, backfire through exhaust, poor starting, just ran rough. replaced points, condenser, plug and coil again, Was all new at rebuild. Reset timing and carb, ran better but still not right. Checked valve adjustment again, both intake and exhaust were tight. Set intake at 0.10, and exhaust at 0.19 cold again. Not a big improvement in operation, takes a lot of choke to keep it running until it warms up. Even after it warms up, it lacks power, but otherwise runs pretty smooth. Engine has ACR compression release so I can't check compression, but it seems low on compression when you turn it over on starter. I believe it now has a burnt exhaust valve, but haven't pulled head off yet to look at valves. I don't understand why I'm having such problems with valve adjustment, why they would come tight so quick is beyond me. I haven't ran engine hard, just using tractor for average mowing duties. Running Mobile one 10w30 full synthetic engine oil, have changed oil twice since rebuild. I have already ordered a new kohler o.e.m exhaust valve for it, just haven't taken engine back apart to replace valve. Just wondering if aftermarket valves are this poor of quality, or am I missing something, and new valve will do the same thing in a short amount of time. I should also mention that I had machine shop replace exhaust valve guide and do all machine work to engine before I rebuilt engine. I had crankshaft balanced, removed balance gears, turned crank 0.20, bored block 0.10, planed head. Replaced crank bearings at the same time. I thought that I covered all bases for a long running rebuild, but I must be missing something. Any body else have this problem with valves? Would like to solve this problem, but not sure that a new exhaust valve and regrinding intake valve and seats will solve problem. thanks MH44D.