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OS Surpass 52 Four Stroke
BY: Mark Fuess

          Bore: 23.0mm (.906") Stroke: 20.6mm (.811") 
         Weight with muffler: 15.2oz (431g)
          Power Output: .90 BHP at 12,000 RPM
          Practical RPM Range: 2,300 - 13,000 RPM
          Crankshaft Thread Size: 1/4-28
          Construction: Aluminum and Aluminum alloys
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The Surpass series is the 2nd series of 4-stroke engines. The 1st FS series was replaced by the Surpass series around 1987. "Surpass" refers to this series gaining 30% more power than the previous FS series engines. The Surpass is the most copied engine on the market, by mfg's around the world. One thing you won't get with a knock-off is the quality, fit and finish of a genuine OS Surpass engine. To illustrate this point I will completely dis-assemble a Surpass 52. Then re-assemble it in detail so you can see for your self why OS Engines are superior. This isn't a new engine. In fact, it has likely had over 200 flights on it. In essence, I'm overhaulung this engine.

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The first thing to observe in this illustration is the quality of the casting. This is investment-casting at its finest. You can also see the inner cam bearing which is a stainless steel shielded ball bearing. There's two of these supporting the camshaft. You can also see the vent nipple just below the camshaft support. I haven't quite figured out why it's located here, but I have no doubt it was well planned for this application.

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This is the back view of the crankcase. The photo depicts the wristpin access port for removing the wristpin, piston, and rod. In order to gain access to the wristpin, the sleeve must be removed. The wristpin can be difficult to remove because of build-up from oil & fuel residue.I extract the nylon button from the wristpin then tap a tapered brass rod into the center of the wristpin. The brass rod tightens up on the wristpin for easy removal. I'm sure there's a tool available for this, but I like my tapered rod method.

I might note at this time, that the engine was thoroughly cleaned in Berryman ChemDip then the parts were tumbled in Wallnut media for a final polishing.

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This is the TOP VIEW of the Head Assembly.

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And the Bottom View

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This doesn't look like a crankshaft that's had several hundred flights on it! That's because of the HIGH QUALITY Plating that OS uses and there's not a speck of corrosion to be found.

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The camshaft is the same way! The plating completely eliminates the possibility of corroding.

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But then there's the bearings... the OEM bearings are steel and eventually corroded. This is the only weakness of the 52 Surpass. A set of Stainless Steel bearings would have prevented this. My replacement bearings are CERAMIC. Not only will they NOT corrode, the Ceramics are LIGHTER, STRONGER, and SMOOTHER. They also have 1/3 less rolling friction.

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The Connecting Rod is excellent, and has Bronze Phosfur bushings at both ends.

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Here is the sleeve & piston ring. The sleeve is HARD STEEL and likely has a plating, probably  Nickel. The piston ring is cast iron for fast seating and good compression seal.

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The Rockers are plated just like the crankshaft and cam. Again, eliminating corrosion.

You have now seen a simple overview of the OS 52 Surpass. It's time to BUILD an engine...    

CLICK here to  BEGIN


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