Dwindling RPM

[Brambo]

Lyc IO-360 M1B with MT CS prop.

About 3 months ago as part of my pre-first flight engine checkout, I did a full power static run and was pleased to see the full power RPM stop at precisely 2700. On my first flight some weeks later I noted full power RPM on takeoff at 2680 (good enough for me). Well as the 40 hour fly off continued I started to notice on each subsequent takeoff the full power RPM contained to drop. By the 25hr mark I was getting between 2600 and 2640 RPM on takeoff. After 40 hrs the takeoff RPM has stabilized around 2600 to 2630 RPM.

My question is what has caused this RPM drop? I live just outside Las Vegas and although I always fly in the relatively cooler mornings, it's still significantly hotter now than it was when I did the first static test. Could the increase in pressure altitude explain the drop?

[pierre smith]

Does your governor have a low pitch/high RPM stop screw/locknut. I wouldn't be surprised if it just broke in along with the engine and is now settled. I'm not sure how many turns or fraction of a turn on the stop screw produces how many RPM's but I'd turn it 1/2 a turn, allowing the prop cable to move toward fine pitch a little and go fly. Adjust a little, go fly, or just do a full power runup. Is there a little space between your prop control knob and the dash?

Regards,

[Fredrik]

Bill,

I had problem with the rpm on my MT. It was more of a fluctuating max rpm, than gradually decreasing rpm.

My sugestion is to contact MT. They upgraded my governor to a never revision, free of charge. Now it's steady as a rock.

Good luck,
Fredrik

[Brambo]

I guess it could be the governor just breaking in. I'll try and adjust the set screw and see what happens. If that doesn't fix it then I'll call MT.

[nucleus]

Mine has done a similar thing, but only down to 2660. flew it like that for three weeks before I adjusted it back up. One of those break-in adjustment things, like the idle.

Hans