O/H Breakin Help Needed (X Post)

[Lance F]

A couple of hours ago I did the first breakin flight after a complete overhaul of my Mooney's IO360A3B6D Lycoming. The cylinders are brand new Lycomings and the cam is also new. I ran it exactly as the O/H shop specified: short ground time; full power, full cowl flaps, shallow climb; level at 2200'; 75% power (2500/26.0"); very ROP (about 1225dF EGTs). Everything seemed great for the first 20 minutes. CHTs were all in the 350 dF range, oil temp was only 175 dF (OAT was about 82dF). At 20 minutes I felt a vibration, not huge but certainly noticeable. A glance at the JPI showed that the CHT on #4 had just hit my alarm point of 400dF and seemed to be rising. I pushed in the mixture, although it wasn't out very far to start with, started reducing power at a slow but consistant rate and landed uneventfully.

Observations on the ground were all OK. Both top and bottom plugs on #4 were dry but sooty as I would expect from running so rich. CR was 78/80. There were no oil leaks and no discernable oil in the crankcase vent tube. Started the engine and did both a regular and lean mag check. On the regular check the L mag drop was about 60 rpm and the right mag 100 rpm. On the lean check EGTs rose as expected on all cylinders on either mag.

The overhaul shop had closed for the day, so I can't ask them. I was told to land and find out what's wrong if a cylinder goes over 400. Well, this happed; I can't see anything wrong; and I don't know anything else to check. Any ideas? Should I try another flight?

 

[mikea]

I dunno about Mooneys but I haven't been too concerned with the CH temp temporarily hitting 400. I idled for while post maintenance and after the later run-up I got the CHT alarm abd saw a couple of cylinders had gone past 400. They got to as high as like 408 degrees on a couple as I took off. I kept the nose a little lower and the temps came right down thanks to the air flow over the cylinders.

No, I don't usually idle that long. I do lean it on the ground to purge lead.

I didn't have that high CHT problem when I flew the break-in after my top overhaul. I had repeated cold cylinders due to the persistent oil fouling. The engine shop pulled the plugs a couple of times and cleaned them. Once the rings seated, which takes a while with chrome cylinders, I hadn't had the problem since.

 

[gismo]

I'm under the impression that it's common for CHTs to spike during breakin as the rings seat. As long as there's no obvious baffling problem and the EGTs were "normal" I'd try it again but stay close to the airport for a while.

 

[Lance F]

The smoking gun was found. (I sure hope so anyway.) Had a good test flight last night, and the breakin should be more than finished by Gaston's. Thanks everybody for your comments!

 

[gismo]

The smoking gun was found. (I sure hope so anyway.) Had a good test flight last night, and the breakin should be more than finished by Gaston's. Thanks everybody for your comments!

Given the brand new look of that plug, I'll bet it was dropped.