Mounting O.S. 91 Surpass
 

Trying to figure out how to mount an O.S. 91 Surpass in my Sig Skybolt. If I build per the plans, the engine will stic out if the cowl about an inch or so too far. Do I try to move the firewall back, or try to lengthen the cowl some or do I run down to the LHS and get a different engine? Any help would be great!

Regards,

Jeff

Mounting O.S. 91 Surpass
 

I have used the OS .91 Surpass for several years. On all the planes that show a two stroke engine I move the firewall back an inch to inch and a half. The plans of my Bingo show two different nose sections one for a four stroke ( the plans are in FL so I can't tell you the measurement).

Moving the engine back also helps with the balance as four strokes are a bit heavier.

Mounting O.S. 91 Surpass
 

Ditto, Move the firewall back. Check both views (top and side) on the plans. Often they will show a 2-stroke in one view, and a 4-stroke in the other. Otherwise, just lay the engine on the plans to figure out how far back to move it. And remember, it is better to go back 1/8" too much than to come up 1/8" to short. You can always slap some scrap plywood behind the engine mount to bring the engine forward a bit if need be.