The following is a copy of a question (and his answer) that I asked
George Aldrich about the ST51 breakin. (This was back in 2000, I think on the CL forum on the RC oriented site (long gone now!)
A question for Nobler,
I have seen you mention the ring gap several times with respect to the ST51. What is the correct gap? I
have a ST51 CL which I plan to use on a Sig Magnum at some future date. I have personally witnessed
the long breakin (and frustration) a fellow club member is having with his ST51. I would like to avoid
some of the long breakin by setting the ring right in the first place.
Every one I have talked to loves their ST51, but they always preface their praise with "..but it sure took
a long time to break in" . Thanks, Alan
added later
Nobler, Thanks for the reply. Alan
[This message has been edited by Alan Hahn (edited 09-30-2000).]
George Aldrich's reply
Everyone of the current ST's I've seen, clear up to the .91, have come with NEGATIVE ring end gap ! The
piston rises to the very top of the cyl. on all of these designs, and if you remove the ring from a new
engine, it will not fit in the cyl. at the top where it get hottest ! The ring ends will actually over-lap !
The end gap should be increased to about .003", and then a more normal run-in will have the engine
purring in about 30 min's. to an hour of slightly rich flying runs.
Above all, at least 20% lube, with 5% min. of castor for fuel.