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How long to break in rebuilt Jett .46?


Old 10-01-2010, 09:29 PM
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Default How long to break in rebuilt Jett .46?

Bob, how many flights does it take to break in a new piston/sleeve on a .46. It is a 14 year old Jett .46 on a Scat Cat. It finally wore out and lost compression. Sent it to Dub a year ago and he put in a piston,rod, and sleeve. Carb and bearings was updated 5 years ago. I've got about 25 five minute flights with an APC 8.5x9 pylon prop, and K&B 1L plug, 10% Powermaster fuel. I never tached it before so I cannot compare it. It doesn't seem to run nearly as fast as it used to and cannot be started by hand. Used to hand start on the first or second flip. He told me when I sent it in that he had very few parts left for this old of engine. There are no markings on the block to identify the size of it. Could it have been rebuilt to a .40 instead of a .46 and make that much difference? It sure would be nice for it to run like it used to. Thanks, Paul
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Old 10-29-2010, 01:21 PM
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Default RE: How long to break in rebuilt Jett .46?

Sorry for the delay here!! Not like me to miss that many days

It should not take long a all to break in. A few runs on the bench as usual with a 9x6 up at rpm and it should be good to go.

8.5x9 is too much prop. 8.8x9 or 8.75x9W is too much too for the SJ-46. 8.5x7.5, 9x6, 9x7 in that range.

If it is not running properly, check something. Remove the muffler .... look in the exhaust port. Make sure the sleeve is properly aligned in the crankcase.

If it is an original 15 year old SJ-46, then yes, parts are VERY hard to come by. That was the original "rev 1" design. Different crankcase and innerds as todays engines. Usually a new piston can be fit, but depends on what shape the sleeve is in.

My suggestion, first check to make sure everything is lined up. Put it on a test stand, put a 9x6 prop on it (sport 9x6 APC) and run it. Find peak rpm, back off 500 rpm - let me know what sorta RPM you get then.

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