Need 9A engine mount hole info.

[airguy]

I am nearing the point (very soon) of rolling my canoe, and I have a rotisserie arrangement I purchased from another builder in Austin. The rotisserie attachs to the firewall at the engine mount bolt hole locations. I don't have my finishing kit yet, so without the engine mount itself I don't know the location or size of the mount bolt holes. In the firewall there are 4 pre-punched holes in the corners, I'm assuming these are for the engine mount holes as I can't see any other reason for punching holes in a firewall. The rotisserie was set up for a 6, so the holes will not be the same and I'll need to make the rotisserie stand match my firewall.

What I need to know from others is this - are these prepunched holes actually the location for the engine mount bolts, and what size are the engine mount bolts that will actually go there? I need to put a couple bolts through the firewall to attach the nose section of the rotisserie, and I don't want to screw up and overdrill those holes or punch holes in the wrong place. Small bolts will hold the weight of the fuse on the rotisserie, I just need to know what final size those holes will be so I can make sure and stay UNDER that size, so as to still be able to matchdrill to final size once I get the engine mount.

For what it's worth - I sent an email to Vans Tech support asking this question 10 days ago, and got ignored. No response at all.

 

[RV9A Bill]

9A bolt holes

My engine mount did not line up perfectly centered over those holes. I could see the holes, but drilled using the mount as a guide.
Rv9A Bill

 

[N941WR]

Greg,

I'm with Bill on this one. Do not drill your mount holes until you have the mount in hand.

I drilled out one hole, bolted the mount in place and then get it as close as I could to the other holes and used the mount as my drilling jig.

 

[rjcthree]

Same here, along with total misuse of a tool . . .

The four corners fit well for me, but the two center lowers weren't quite perfect. I had read about bushings, etc. I went the 'abuse a tool' route, and bought a cheap centercut end mill, swiped a taper chuck and big honkin' drill from work (used to drill truck framerails, about 500 rpm max) and with a lot of PBlaster, went to town. Worked well, I had to clear chips a few times each side, no biggie. Make sure to grease/lube the tool first, or the alum of the angles may get sticky on you.

Moral of the story: always more than one way to get it done, stop and think about it.

Rick 90432

 

[Jeff R]

I think they are AN5 holes, but don't drill them out now as they don't perfectly align with the holes in the firewall (the one set of holes that aren't perfectly match drilled). Figure out something else for the rotisserie. For that matter, put off mounting the firewall for a long as you can. It is a lot easier to work on the fuel vent plumbing and the fuel lines/fuel selector with the firewall out of the way.

 

[Rupester]

Funny you should ask ...

I just drilled my engine mount holes in the firewall. The two bottom corner 1/4" pilot holes were dead-on perfect for the engine mount. I drilled those out, and with the 3/8" final bolts in those holes, the top right (starboard) hole also lined perfectly. I drilled that one to 3/8" and bolted it, to see the top left (port side) 1/4" pilot hole was off by 1/16"+. I used the engine mount as a drill guide there like others said. The two inner bottom holes are straightforward drilling after the other four.

 

[airguy]

Thanks for the feedback guys, that's what I needed (and suspected). I'll find a way to mount the rotisserie with the existing holes (without drilling them out) or cobble something else together to serve the same purpose without punching new holes in the firewall.

One thought that comes to mind is to make a dummy firewall out of scrap angle to connect up to all the mount points, and use that to support and spin the fuse until I'm ready to work on the FWF.