Small Engines (Lawn Mowers, etc.): 12 Hp B+S engine, vertical shaft, hand thread

Question
I am trying to swap engines from two vertical shaft lawnmowers and everything is straightforward except removing the clutch/pulley assembly from the shaft. There is a bolt on the end and the shaft is keyed. I'm guessing that the bolt has to come off but is it left or right threaded. I don't really want to shear it and it is very tight. Also I am doing this because this is the third time this engine has just suddenly quit due to no compression. Loose valve seats last time. Is this a common problem and is there another way to fix.  

Answer
It is right hand thread.  Loose valve seats is not that common but it does happen.  The best thing you can do to fix this is by applying the correct high-temp retaining Loctite and, using a centre punch, peen the surrounding aluminum (about 8 - 10 equally spaced peens about 1/32" deep) around the seat to secure it.  It shouldn't be an issue after that.  Hope this helps.