Some months ago I acquired a NIB, Lew Woolard prepared, OS Max 35 FP-S.  Last evening I finally started to break it in following Randy's recommendations for such rituals.  I put a total of twenty minutes on the motor, so it still has a way to go before I will put it in a plane.  The motor was swinging a 10 x 4 Zinger prop and was being fed with Power Master GMA 5-22 fuel with castor added to bring total oil to 24%.

When doing the periodic short two-cycle bursts the motor tached at 10,800.  On that prop and fuel, what peak rpm should be expected when the motor has, say, an hour's run-in time on it?  I would like to know this as just one indicator of when the motor might be ready to put in a plane and not because it will ever be flown at that setting (at least not intentionally).

Thanks in advance for your input.

Hi, Lee.  Thank you for your suggestions.  I, too, have read that, during break-in, one should use a prop that is one inch less in diameter than that on which you will fly.  Some say that one should also use one inch less pitch.  I started out using the 10 X 4 thinking that two inches less pitch would adequately reduce the load on the motor during break-in.  I suppose that prudence dictates that I resume break-in with a 9 X 5.  It certainly can't hurt, so long as I keep track of rpm, and, if it might help, then that is the way to go.  Thanks, again.

Thank you all for your comments and suggestions.  And, Randy, you relieved me of the nagging feeling that perhaps I had overloaded the motor in the critical break-in phase.  I did, however, try a 9X5 APC for a couple of short runs and with just my tach, my ear, and a heat sensitive finger tip I could detect no significant difference in how the motor ran with the 9X5 as compared with the 10X4.

Lee: I have a total of about 45 minutes on the motor.  The pinch the fuel tubing test for readiness that you mentioned says the motor is not quite ready for prime time.  While the motor does come back to the needle valve setting after pinching the tubing there is a delay that is longer than what I experience with motors that are well run in.  A few more cycles and I think it will be there (where ever "there" is).