Andrew, that  is what my engine was like. I ended up with over.004 clearance. My engine was blowing plugs faster than I could install them. I made a big mistake continuing running that engine. I exhausted 3 Merlin plugs, 4 Nelson plugs, 2 of the stock plugs and various used Cox plugs. At that cost I was halfway there to a new cost of a Norvel. I've since had a new bushing installed in the case. This isn't a uncommon problem with that engine. Searches on r/c universe and r/c forum have explained the same problem your mentioning. I know some of the individuals that posted those comments on there. I do have another that runs pretty well. I strongly feel with those kind of clearances, your just blowing fuel out of the nose of the plane and ultimately will suffer performance eventually as more wear takes place. I still haven't resolved my plug blowing issue. I will add more head gaskets until it stops blowing them as I know of no other way to resolve it. I've tried Cox low compression plugs 5% nitro. I still suffer this problem. I think the engine is just hitting a certain harmonic at the rpm's I was running. I see all that have successfully used the engine seem to be using the engine in the 23K range. I was in the 28k and above. I will be going to fly with a speed flyer in the next month or so. He has a tach that works from sound that can tell your engine rpm's in the air. I'm curious to see what I'm getting from the engine. I know I'm exceeding the engines recommended rpm amount. Now this is what doesn't make any sense to me. I use a Stels engine that has so much play in the crank that I don't know why the connecting rod stays on the crank pin. I run that engine 29k all day long. The prop makes a funny noise if you really lean it out as it starts into this funny vibration which kills off speed quickly. I can needle it as to not get into those harmonics. My AP did this as well until the new bushing was installed. Again, I'm not running the engine as most users on here are doing. Ken

I just recieved 2 and one of them is the same way. It has way more play than the other one. I was thinking of sending it back. But now they are out of stock and I do not know if anymore are comming.