OS 10

[Garf]

I have picked up an engine identified only as an OS 10. It is a schnurle ported engine, most likely steel P&C. It looks more like an SF than an FP type. It is also plain bearing. It needs a P&C assy, so I need to positively ID it before buying parts. Anyone recognize it?

[Clancy Arnold]

Garf
I posted this originally on the Ringmaster forum.

If you show more of the engine I could tell you for sure but it appears to be an OS 10 FSR that was introduced in 1976. It is the only FSR that is plane bearing. The other schnurle ported, plane bearing engine is the OS 10 FP.

The OS 10 FSR came with a two needle carb, had a distinctive rectangular hump on the left side and the marking on the left side were:
OS
M
A
X

and on the right side was a 10 in a circle.
The OS 10 FP came with a single needle and an air bleed carb. The bypass was smoothed in like an OS 25 or 40 size FP engine and the marking on the left side were:
OS
MAX
10

Clancy

[Garf]

Replied to on BOTR w. pics.

[Garf]

I took it apart and torched the piston to cherry red, then let it cool. It now has just enough compression to start easily both cold and hot.

[Clancy Arnold]

Garf
I posted this information on the "Ringmaster Forum" but thought others here may not be aware of this information.
Clancy

OS Engine Manufacturing Timeline Gallery, 1936 to Present.

[Garf]

I bench ran this thing with high castor fuel and it sounds good, but has low power. I have a 10S venturi on it with a ST 35C NVA. This doesn't leave much room for airflow. I need to know what the proper venturi bore is.