O.S. 61 SF vs. SF long stroke
 

I just got a mint O.S. 61 SF. It is an ABC engine. Can any of you tell me how to tell if it is the regular 61 SF or the long-stroke SF? Mine measures 2-15/16 inches from the top of the mounting lug to the top of the head. Are there any distinguishing features between the two engines?

Thanks.

RE: O.S. 61 SF vs. SF long stroke
 

I thought SF-61 is long stroke only.

RE: O.S. 61 SF vs. SF long stroke
 

All of the 61SF and RF engines had the long 24mm stroke. The SFN helicopter version had the short 22mm stroke parts in it because the long stroke made too much vibration for helis. The SF crankcase will accept both short and long stroke internal parts.

RE: O.S. 61 SF vs. SF long stroke
 

17702 - 61 SF
17710 - 61 SF-P Ring
17712 - 61 SF-P
17801 - 61 RF
17802 - 61 RFP
All these engines use the same crankshaft OSMG 4561

The 61 RF Hanno in both ringed and ABC used the same crank which was the OSMG 4634

The RFN uses the OSMG 4630 crank

Enjoy,

Jim

RE: O.S. 61 SF vs. SF long stroke
 

Anyway, all these were and are very good and reliable engines! :)