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Monday, October 10, 2011

OS 48 4 C Surpass Model Airplane Engine

In Stock at the Trading Post


Circa 1987







Design History :-
Designed and manufactured in Japan in1987's by the OS Engine Manufacturing Company.


Design Features:-
Rear induction;
Front valve train;
Ringed aluminium piston;
Steel cylinder liner;
Aluminium crank case.
;



Specifications:-
Displacement 0.48 ci 7.89 cc;
Bore 0.906 in. 23 mm;
Stroke 0.748 in. 19 mm;
Weight 14.5 oz. 412 g;
Max Power 0.8 BHP @ 12,000 rpm;
Practical Speed 2,200 to 12,000 rpm.





Observations:-
This is the only engine that I have owned that I can say, failed  suddenly and catastrophically in service
Shortly after acquiring the engine used from a friend I was looking forward to testing it in a 72 inch span Unionville Beaver . The plane had barley become airborne when suddenly the engine sound ended with a bang I was extremely surprised to say the least when I witnessed the airplane's nose drop and glide in to a landing with the propeller still turning As I approached the Beaver I tried to imagine what would cause the engine to stop so suddenly but, the only thought that came to mind was, the prop-nut had backing off which is a common fault associated with 4 cycle engines. When I reached the plane I was surprised to find the propeller still firmly fastened to the shaft which was still spinning like a top.
Closer examination revealed that the complete bottom of the crankcase  was broken out front to rear. Apparently the connecting rod broke through the case when the crank pin sheared off from the crankshaft. Later after disassembling the engine it was discovered that the pin had failed in a classic high cycle fatigue fracture surface; with it's typical minute crack initiating flaw, it's large smooth striated area and  it's much smaller rough overload failure zone.
The engine was not worth replacing all the broken parts so a decision was made to only replace the broken crank shaft with a new one and attempt to repair the ruptured crank case by pressing the erupted material back into the void and welding the area shut with JIB Weld a fibre filled cement. 


Click the play button below to view a short video featuring the starting and running of this older 4 stroke engine and witness how she performs after the the unusual repair.

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