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From the department of “for whatever it’s worth,” I have a heads-up for folks running a Lycoming angle valve engine with exhaust valves/guides with 1000 or more hours of operation. The following may also be relevant to other engine models.
The engine for my 4-place plans built came from a Mooney M20J (200 hp angle valve 4 cylinder) with 1200 hrs on it since factory remanufacture (zero time logbook). I have put an additional 360 hours on it. Not long ago I got a faulty reading on a borescope inspection and thought I had a burned exhaust valve. I pulled the cylinder and handed it over to a repair shop for IRAN. Good news was that the valve was not burned. Bad news was that both the valve stem and guide were worn way past allowable limits. Valve and guide were replaced and cylinder reinstalled; all good...except. I began to research Lycoming exhaust valve/guide wear and discovered that Lycoming recommends a valve wobble test every 1000 hours for my engine model, which was built in 2000 with newly designed hardened exhaust valve guides. There is a service bulletin and a service instruction on how to do the test; however, it seems that doing it properly requires a fixture that costs about $1500. I could find no evidence in the engine’s logbook that any such test had ever been done prior to my purchase.
Anyway, with all that in mind, I’m not too surprised that with over 1500 hours since new, the valve and guide were worn. It also seem logical that if the valve & guide in one cylinder were badly worn, then the others were probably in the same condition. So, I pulled the other three cylinders and delivered them to the same shop for IRAN. Sure enough, all three needed exhaust valves and guides and had to be replaced.
The engine for my 4-place plans built came from a Mooney M20J (200 hp angle valve 4 cylinder) with 1200 hrs on it since factory remanufacture (zero time logbook). I have put an additional 360 hours on it. Not long ago I got a faulty reading on a borescope inspection and thought I had a burned exhaust valve. I pulled the cylinder and handed it over to a repair shop for IRAN. Good news was that the valve was not burned. Bad news was that both the valve stem and guide were worn way past allowable limits. Valve and guide were replaced and cylinder reinstalled; all good...except. I began to research Lycoming exhaust valve/guide wear and discovered that Lycoming recommends a valve wobble test every 1000 hours for my engine model, which was built in 2000 with newly designed hardened exhaust valve guides. There is a service bulletin and a service instruction on how to do the test; however, it seems that doing it properly requires a fixture that costs about $1500. I could find no evidence in the engine’s logbook that any such test had ever been done prior to my purchase.
Anyway, with all that in mind, I’m not too surprised that with over 1500 hours since new, the valve and guide were worn. It also seem logical that if the valve & guide in one cylinder were badly worn, then the others were probably in the same condition. So, I pulled the other three cylinders and delivered them to the same shop for IRAN. Sure enough, all three needed exhaust valves and guides and had to be replaced.
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