Small Engines (Lawn Mowers, etc.): Tecumseh HM80, ariens snowblower, spring retainer

Question
Hello,
I have an Ariens snowblower with a model HM80 8 horse horizontal shaft engine. It quit running and when I took it apart the exhaust valve was broken as well as the retaining clip on the valve spring. I put in a new valve with .020 clearance and started the engine, it ran for a couple of minutes and then stopped. This time the valve spring retainer was not broken but it was damaged to where it would not hold onto the valve. I replaced the retaining clip and the same thing happened again. Any idea what may be causing this?
Thanks, Tony

Answer
got me on this one??????   but back track,  is it the right retainer?  is it the correct retainers?
is it the correct valve spring?  and all the above had been mounted correctly??  if the clearance is correct> which is checked while exhaust should be closed, then i,d say you need to go deeper into cam shaft.