Engine basics > Four strokes only

OS 40 Surpass assemble

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Dennis Toth:
OK after scrambling around the shop I had some 2.5mm for the carb and cam cap. Then found the 3mm for the backplate. One thing that is tricky and a little strange is there is one bolt that adds support to the intake manifold to the case that is a slotted bolt not socket head. I think it is a shoulder type that is a little larger on the shank that goes through the case into the manifold. All good but I think it will get a bit more compressions after it runs a bit.

Best,    DennisT

Russell Graves:
Hi Dennis, I would be interested to know how it runs on the test stand and also in the air. I recently got an OS FS-40 Surpass in bad shape. I took it all apart by watching probably the same video on YouTube that you watched. I replace all the bearings. It took me over 25 hours over the course of 1.5 weeks to do that. It took a really long time to get the wrist pin out to remove the piston and liner. Then it was extremely difficult to get the cam bearings out. No problem because I got really good experience working on this motor. When I finally got it all back together and put it on the test stand, it ran perfect. I can't wait to get it on a plane and get it in the air. I need to build a plane first.

Dennis Toth:
Russ,
Sounds great. What fuel are you using? When I last had this engine in a plane it was my YAK YAK biplane (two Sterling Yak 9 wings, lots of wing area. The setup was 10%N, prop 11x5 BBYO, worked well. Might go with a 6 pitch to allow little lower rpm.

Best,    DennisT

Russell Graves:
Hey Dennis,
On the test stand I was using 10% nitro, 5% castor oil, and 15% synthetic oil. I also tried 20% nitro with 20% synthetic oil and no castor. It ran fast but not as smooth. I think this motor likes a little castor. OS recommends some castor and synthetic, but Saito recommends all synthetic. I will try some different props and fuel to see what is the best combination. I will not try to run this motor fast like a tuned pipe with a 4 pitch prop. I will run it down low at maybe 8000 - 8500 rpm with an 11x6 or 11x7 prop. I will also try 12" props, and higher nitro with some castor just for fun. Running them at low rpm with a high-pitch prop is the way to go.
Russell

Brett Buck:

--- Quote from: Russell Graves on December 05, 2023, 08:19:36 PM --- Running them at low rpm with a high-pitch prop is the way to go.

--- End quote ---

   That's something to try, Igor Panchenko was the first guy to explore that. But I am curious how you came to that conclusion, since the only real success with 4-strokes has been with ~4"or so of pitch and 10,000 rpm, going all the way back to the mid 80's and Ted Fancher.

     Brett

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