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Aft Gear Leg Holes in Engine Mount...Undersized?

SilverEagle2

SilverEagle2

Well Known Member
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I've searched here, and maybe I've lost my search mojo...read a number of good and trusted build blogs to no mention...so maybe y'all can help.

My aft gear leg socket holes on my engine mount appear "undersized" while the forward holes are "right-sized" for the AN5 bolts that should go in them.

The build manual is SILENT in my docs about this condition.

Instructions simply say "Installation could scarcely be easer: a round rod is inserted into a round tube and secured with one bolt."

Trouble is...can't get the bolt all the way through.

Is this normal? I see builders who say, slid right in, inserted bolt. Saw some older threads of "had to ream out with a .3110 reamer."

I was able to run a 5/16" reamer through the forward (turning ONLY by hand) clearing the powder coating...but it's not right-sized on the backside.

Can someone give me a lowdown on this?

Thanks!
 
Measure the inside diameter of each bolt hole and the hole through the gear leg. You may have a slight burr on the inside of the tube or the gear leg. It's ok to "clean up" the hole(s) by drawing ( key verb here ) a 5/16 (.312500") reamer through each one individually.
 
Thanks Brian,

I checked that first...it's a clean, but undersized hole. I can certainly measure it when I get to the shop later today.
 
Can you slide the AN5 bolt through the hole in the gear leg until it hits the backside hole? If so, I would install the gear leg into the socket, then carefully push a 5/16" drill bit into the hole on the front of the socket and through the gear leg hole until the bit bottoms out on the backside hole. Then drill out the back side hole - stop drilling once through the backside hole

Proceed with caution - you do not want to "wallow out" the front hole and the gear leg hole in the process.
 
Use a mirror, borescope or camera to look. I know several builders used a .311 reamer but it's a good to look first.
 
I checked the gear legs today and the bolt and my .3125 reamer both fit nice and snug as expected.

IMG_0163.jpeg

The aft holes are definitely undersized. The tail of my .3125” reamer will not pass through the aft holes at all.

IMG_0162.jpeg

IMG_0164.jpeg

You can see the bolt here won’t make it through.

This being so critical makes me nervous.
 
ColoradoSolar said:
Don't know if that is standard on the 7 but on my 10 it was undersized and called out in the plans. You run a drill/reamer through to bring it to size.
Click to expand...
It's NOT called out in the plans or manual...quite the opposite. It's supposed to be as easy as inserting leg, run bolt done.

That said...the undersize is JUST small enough that my reamer's beveled/pilot end also does not center...start...

I do appreciate the advice and assurances.

This should be obvious, but be sure to have the gear leg in place when you do this.
Click to expand...
Yup...that IS obvious.
 
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Powder coating can make that bolt hole a little snug as well. I would recommend using a reamer instead of a drill bit to clean up that hole. Reamers make a much more circular hole than a drill bit will. Drill bits actually make the hole somewhat irregular, kind of like the outline of a Wankel engine rotor (exaggerated, but that's the shape). A little lube on the bolt may help as well, but make sure the bolt threads are clean before you put the nut on.

If that exit hole is really small, you may have to run a drill bit through initially that's one size smaller than the final size of the reamer.
 
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