Drilling th efirewall?

[Steve Sampson]

Can someone tell me the correct way to drill the engine frame to the firewall. Is it OK to just put a 3/8 drill through the frame using it as a drill guide and drill through that way. Alternatively, should I be using a centre drill?

My concern is can one damage the engine mount with the side of the drill?

Thanks

[frankh]

Pretty hard to damage the engine mount.

You may find the lower holes are out of line (I drilled without the engine mount and this was a 4 hour repair of my mistake).

Anyway In my RV7a the perfect way would have been to drill the top left hole to full size without the mount....Then bolt the engine mount in place.

Then drill the top right hole...and bolt up

Then drill the bottom holes with a full size drill, maybe grease the side of the drill bit for the lower holes as they were pre drilled a ways off.

You might want to consider drilling the two center lower holes before drilling the outer (pilot drilled) holes as this will keep the mount from flexing towards the incorrectly placed lower pilot holes.


Frank

7a

[dan]

If you're concerned about damaging the engine mount, you could use a drill bushing in the mount "eyes" to drill centered starter holes. Then you could use a reamer, after the mount is removed from the firewall, to enlarge the holes to full size.

I didn't do this...I just used a drill bit. But I think the undersize-then-ream is possibly the cleanest way to do it. Just my 2 cents.