Os 25F vs. OS 25FSR

[Steven Kientz]

Was the FSR an upgrade of the 25F? What are the differences?

Steve

[Paul Taylor]

I am not the expert, but I think the 25F is what Clancy had us use for our JYW plane. It was a real work horse!

[Wynn Robins]

the 25F is ABC - the 25FSR is steel liner iron piston........

[Bill Little]

the 25F is ABC - the 25FSR is steel liner iron piston........

Didn't know that!  Thanks, Wynn.

Mongo

[Wayne J. Buran]

The FP is plain bearing. The FSR is dual ball bearing. I am not familiar nor do I remember an F.
Wayne

[Wayne J. Buran]

Oh BTW the FSR was available in ring and ABC versions in several sizes although I am not familiar with a 25 ringed.
Wayne

[Bill Little]

The FP is plain bearing. The FSR is dual ball bearing. I am not familiar nor do I remember an F.
Wayne

I have a .25 F?? with BB and ABC(N??).  I have a new OS 10, on the box it has ".10F"  and I *think* it has SR below it.  Would have to dig it out and look at it to be sure.  But, it doesn't have the "SR" beside the "F".  Never had a "Box" to any of the other F-S-R engines so I don't know how they were designated.  My 2 OS .32s only have an F on them.

Good engines, though!

Big Bear

[Steven Kientz]

Thanks guys
The OS timeline shows several years between these engines, I just wasn't sure of the differences.

Steve

[Clancy Arnold]

Steve
In June 1977 OS introduced their new 25 Schnuerle ported engine.  This engine can only be identified by the case having ball bearings and a 25 in a circle under the exhaust.  In July & August 1977 OS advertisements called it a FSR.  That designation is only on the box.  It is rated at 0.8 HP.

In 1982 OS introduced the 25 F ABC engine.  It differs From the 25 FSR by the ABC construction and a F below the 25 in the circle below the exhaust.  It is rated at 0.8 HP.

In 1984 OS introduced the 25 FP which is a sport timed engine with Plain sleeve bearing.  It is rated at 0/6 HP.

I own samples of all three engines and did a comparison run on the different engines using the same 10 x 4 Top Flight Power Point wood propeller and 10% fuel.  Three 25 FP engines ran 9,800 to 10,100, the 25 FSR ran 10,800 and the 25 F ABC ran 11,000.  These tests were ran using the original RC Carbs and factory mufflers.

As a side note I measured the diameter of the hole through the carb throttle barrels on several OS engines.

The OS 25 FP comes with a 2A carb that has a .180 dia. hole.  This carb is an Air Bleed type carb and the spray bar goes all the way across the hole.

The OS 25 FSR and 25 F ABC comes with a 2B carb that has a .216 dia. hole.  This carb is a dual needle type carb and the spray bar only goes half way across the opening.

For comparison the OS 40 FP comes with a 3A carb that has a .205 dia. hole.   This carb is an Air Bleed type carb and the spray bar goes all the way across  the hole.

In 1989 OS introduced the 25 SF ABC Ball Bearing engine that replaced the 25 FSR and F engines and can be identified by the SF on the left side on the engine.

Clancy

[Steven Kientz]

Thanks Clancy

Steve