912 overheating after maintenance

The mechanic got the #3 head off.

The exhaust valve is moving but apparently it’s leaking because that cylinder is 60/87.

could this really have been the cause of the overheating?

Carb needle clip was in the factory recommended position (#3 I think he said). Remember the gph was way down, 30% less fuel burn than before maintenance.

I checked the new muffler with an inspection camera and it looks the same as the old one inside. It appears all the baffling and pipes are correct from what I can tell but obviously you can’t check the entire assembly without cutting into the muffler.

This is very strange coincidence that as soon as we get the plane back it’s overheating and we have a leaking exhaust valve. Ofcourse they might not be related but it would be one heck of a coincidence.

I find mechanical coincidences to be very rare…

It’s hard to see how a leaking exhaust valve could cause the engine temperature increase you are seeing. I guess that you could argue that (with a leaking valve) some of the heat energy normally being to converted to mechanical energy is instead expelled into into the exhaust as heat, but overheating is not on the symptom list for a burned or stuck valve. But then we would have to allow for the VERY unlikely coincidence that your exhaust valve just happen to fail right after the maintenance.  I can’t go there. 

Yes its possible the exhaust valve has been leaking for a while and has nothing to do with the engine temp increase, but that requires another coincidence, albeit more feasible.  

Take all the coincidences out and it seems more likely the cause of the excess engine heat could have damaged an exhaust valve.  In the automotive world, a burned exhaust valve because of a clogged catalytic converter is not that uncommon.  I know I seem stuck on the muffler, and I’m ready and willing to be wrong, but if it were me the muffler would not go back on the aircraft until a flow test was done on it.  I bet that if you called the manufacture and explained the situation they would gladly test or swap it with a new one - even if just to rule it out.