Hi,

I'm putting a CRRC GF26i in a Yak 54 Seagull. It has holes drilled for a 90 glow. This is the first model I build where I didn't have a template to mount the engine. I know the it has to be off set, how can I find out what that is.

Hi Timber99, Establish the center line of the firewall. Measure the horizontal distance of the existing mounting holes from the center line. Are they offset? If not, just locate the new engine centered on the firewall. If they are not the same, you will have to get out your geometry book to locate the rear of the prop at the same point that the original engine put it. Hopefully, the engines are the same length from the firewall. If the new engine is shorter and the prop does not clear the cowl, you will have to epoxy a spacer to the firewall. You can live with the new engine being longer. Dan.

Thanks Dan, The holes drilled in there are off-set. But I thought going from glow to gas that the off-set would be different. But I'll gave that a try. Thanks again.

The holes might be offset but is the firewall offset? If the firewall is straight, you can shim the mounts to get the offset. You can measure the distance from the back of the mounts to the thrust washer. Use that as the radius of a circle and calculate about 3deg. of offset. That 3deg distance is the offset to the right from the centerline(as you look at the firewall). It should put the thrust washer back on the center. Other folks put the engine on the centerline and use the rudder to correct the left pull.