Hello All:

     I am currently attempting to break in an older O.S. .40S that is new.  I searched the web but I did not get a definitive answer.

     I have run it with a cut down prop that is now a 9X6 at about 9000 rpms.  This is a very slow rich but steady 4 cycle.  I have run one quart of fuel through it this way. 

    What do I do next? Perhaps about 30 minutes with a 10X6 prop at the same rpms? I want to put it into a stunter when it is broken in where I may fly it without it overheating.

     The instructions for the O.S. .35 Stunt calls for a 20-30 minute run with a 9X6 or a 10X6 prop and an additional time of 20 minutes in a two cycle mode.  The .35 is a lapped engine with a bushed crankshaft so we are not talking aples=aples.

       What are your suggestions?

                                                                                                                Tia,

                                                                                                                Frank     

     

Pretty much as Randy said in the above link although I'd suggest a fuel with at least 20% oil with a fair bit of castor. Personally I use 75/25 all castor for all types of engines (iron through to ABx). With the old H-40S using a bushed front end I'd continue using a fuel with a fair bit of castor after it's run in. Some day I'll have to give mine a run too .