Hi,

I have a GP RV-4 that I’d like to put a OS-70FS into – problem being the spinner plate would be about 4 7/8” away from the firewall and the plans call it for being 4 1/2” away. I know this may only pose a balance problem and possibly the addition of weight to the tail, but should I worry and are there other options?

Do they make engine mounts that have a thinner base to be able to move the engine back a little as I have the GP Adjustable mount and it seems rather thick. Or should I not worry about this. I’ve heard of guy’s stuffing 4 stroke 70’s, 72’s and even one that claims a 90! So it can be done, but how?

Thanks!

Does this plane have a cowl? if its a trainer type plane it doesn't matter but assuming you don't want a half inch gap between the spinner & cowl

You may have to look at different mounts going through a catalog and viewing different shapes would probably be best.

G'day Mate,
Can you move the cowl out 1/4", then you will only have 1/8" clearance, 1/4" isn't much, you don't have to follow the rules, if it won't fit adjust as required, anyway, 3/8" isn't a problem, from cowl to spinner.
Don't worry about balancing, that's why batteries are made to be moved.

This is a picture of my RV-4 with a OS 70ll surpass,fits just great, I mounted the engine just like the plans called for and adjusted the cowl to fit. No problems with the CG either.