cooling fin interferes with mount bolt?

[Wheels]

Im switching out my old engine with a new one. The old engine (pictured) had the cooling fins on the #4 cylinder ground down to make installing the rear adapter for the mount easier.
I can't get the mounting bolts into the adapter without hitting the fins and I don't want to grind them off, Nor do I want a shorter bolt. Do I really have to grind off the fins? Shorter bolt seems like a bad Idea too. I'm open.

[efwd]

If your old one had ground down fins, what's the aversion to doing that same thing? The way you describe it, it seems geometry is geometry. Square peg won't go in a round hole. I would not want to use a short bolt myself.
Eddie

[Slyfox]

I also had that bolt break. so when I replaced it I went to a harder bolt. now the new one had a round head with allen wrench type. no need for grinding that area down. my old bolt was that type also. now ask me where I got that bolt, can't remember. I'm sure I got it local. sorry.

I think I went to Fastenal in Spokane.

[jmodguy]

McMaster Carr has a huge selection of hardware. www.mcmaster.com

[Wheels]

I actually have both styles of bolt, (hex and standard) The hex doesn't fit either.
I'm pretty sure its a grade 8 bolt that I am putting into that aluminum case. I don't think it will break, but, it looks like I will actually have to grind on the cooling fin to make it work or decrease the thread engagement with a shorter bolt. (Not) I"m going to make sure I don't have some wierd bolt that isn't stock to the IV. I"ll call Kitfox Monday and order all new hardware and compare the ones I removed from the previous builder's install. I just can't imagine the original 912 requiring the fins to be ground down. I"ll do it, but I won't like it.

[Slyfox]

my advice is to do everything exactly like on the other motor. But I would put the round head bolts in that location, it is very tight and you won't be able to put a good socket on it to torque it down if you use those big bolts. Just do things like before and get this unit done so you can fly it again.