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Should I Drill The Reference Engine Bracket Holes?

PhatRV

Well Known Member
Each of the engine mount brackets has a large #12 hole that corresponds to the hole on the stainless steel firewall. Should I drill these out while assemble the firewall or leave them alone until I install the engine mount. Van's manual doesn't mention anything about these holes in the instructions at this stage of the build.

Here is a picture of the hole

 
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I suggest you wait until you get your engine mount.
Nothing like trying to fit a mount to unmatched holes. :(
Once your mount arrives, you have 3 choices; drill to the plans, drill to the mount, or send it back.
Otherwise, you may end up with some '8' shaped holes.
I just rebuilt my wife's RV-4 engine mount....Actually Russ McCutcheon Metal Fabrication rebuilt it on his fixed tooling, and it fit back on the airframe perfectly.
So the original builder maybe drilled to the plans and everything fit, plus after Russ rebuilt it, it fit again! Who could be so lucky?
 
Wait. My engine mount only came close to the pre-punched undersize holes with a lot of "encouragement". Use the mount for the drill guide.
 
Thanks everyone for your advice. It seems prudent for me to wait until I decide on the engine and engine mount before attempting to drill these holes. I am planning to purchase a new engine from Vans but that time is in the future, or depending on my financial state at that time, buying a used engine from somewhere else.
 
My Rule

When it comes to drilling holes in a Vans kit I have a rule, " always wait as long as possible to screw up a part"
 
Clamp!

When you drill to the mount, clamp that mother down. Clamp, clamp, clamp. Also bolt down each successive hole. The holes in the brackets will not be exactly centered on the mount holes. Th drill will walk trying to center on the prepunched hole and carry the mount with it.

It's also a whole lot easier to profusely clamp if the firewall is not riveted to the fuse. I also withhold riveting it until all fuse prep and riveting is complete. Being able to remove the firewall for forward access during the build is really nice.

Consider ordering the mount now if the firewall is still loose.

John Siebold
 
This is one of the easiest parts of the build.

Set the mount asdide then drill and ream one hole to final size, it doesn't matter which one. Bolt the mount to that hole.

Get a brass bushing that fits in the mount's bolt holes. Drill the second hole under sized using the bushing. Remove the mount and drill & ream that hole to final size.

Reinstall the mount, bolting it down with two bolts.

Repeat for the remaining holes.

Get the mount as close to the prepunched holes as possible but don't worry if they are not exact. It won't matter if your engine is slightly cocked to one side because you aren't going to see it under the cowl, or with the cowl removed.
 
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When you drill to the mount, clamp that mother down. Clamp, clamp, clamp. Also bolt down each successive hole. The holes in the brackets will not be exactly centered on the mount holes. Th drill will walk trying to center on the prepunched hole and carry the mount with it.

It's also a whole lot easier to profusely clamp if the firewall is not riveted to the fuse. I also withhold riveting it until all fuse prep and riveting is complete. Being able to remove the firewall for forward access during the build is really nice.

Consider ordering the mount now if the firewall is still loose.

John Siebold

Thanks for the tip. I was wondering about the same thing about how to access the firewall from inside while drilling the engine mount if the firewall is firmly enclosed by the fuselage. I will keep this in mind when building out the rest of the fuselage.
 
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