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OS 300 twin upgrades available?


Old 01-17-2006, 03:40 PM
Bill Fleming
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Default OS 300 twin upgrades available?

I have a OS 300 twin that was purchased new approximately 15 years ago. They hadn't been out long and I suspect mine was one of the first. I am finally getting ready to put it in service. My question is: Are there any upgrades/improvements available that I should consider? Better bearings, stronger rods, etc.

What RPM at WOT should I expect with a 20x10?

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Old 01-17-2006, 04:22 PM
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Default RE: OS 300 twin upgrades available?

Between the earliest of the O.S. FT-300 engines and the current ones, only the connecting rod has changed. They went through a few iterations in the early few years because the rods were seizing to the crankshaft. The main problem was oil and breakin, but they decided to change the alloy in the rods.

The engine should be broken-in with fuel that has about 18% oil content. Fuel with some castor oil in it is good. You want to run the engine as rich as possible and still run at full throttle. Run the engine this way for 20-40 minutes before you start to lean the engine. Lean gradually. You should be able to have the engine running at full throttle and leaned to just rich of peak RPM by about an hour's total running time. Then adjust the idle.

At this point, it's a good idea to replace the glowplugs and then go fly.

With an APC 18 x 12 prop, we normally see an idle of about 1,700 RPM, and full throttle running of about 7,300 RPM. If you add an on-board glow plug battery, idle can be reduced quite a bit lower.
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