Stinson motor mount bolts

[Greg Bockelman]

The Stinson parts catalog specifies AN6-36 bolts and AN310-6 nuts plus cotter pins for the motor mount. What is currently installed is AN6-36A bolts and the all metal lock nuts that I can’t put a number to just yet. Is there a reason why someone would have used something other than the bolts specified in the parts manual?

I need to change motor mounts so I might as well put the proper bolts and nuts on it.

 

[Dan Thomas]

The Stinson parts catalog specifies AN6-36 bolts and AN310-6 nuts plus cotter pins for the motor mount. What is currently installed is AN6-36A bolts and the all metal lock nuts that I can’t put a number to just yet. Is there a reason why someone would have used something other than the bolts specified in the parts manual?

I need to change motor mounts so I might as well put the proper bolts and nuts on it.

What engine? A Franklin? Almost no experience with those, so can't say if the self-locking nut was OK or not.

Some engines used a pair of conical rubbers that fit into conical recesses in ears on the aft end of the engine. Those bolts use castellated nuts and cotter pins, because you could not bottom anything out. (You'd either run out of thread, or badly deform the rubbers and their washers might get pushed up against the mounting ears.) The bolt could move and rotate and a self-locking nut just might work loose.

Others, notably the dynafocal mounts and some bed mounts, use rubber pucks and steel spacers between steel washers molded onto the outside of each puck. The nut gets torqued up pretty tight, and the bolt doesn't move, and the all-steel self-locking nuts work OK there.

The airplane's parts manual will show what should be there. The airplane's maintenance manual will tell you how tight the nuts should be. Now, some old airplane manuals were pretty sketchy on such details, and the mechanic was expected to know what the standard practice might be in such a case.

 

[Bell206]

Is there a reason why someone would have used something other than the bolts specified in the parts manual?

Is this a factory engine install or an STC install?

 

[Greg Bockelman]

It’s a factory 165 Franklin. Dan’s answer was what I was looking for. The Franklin uses the conical rubbers and the manual has a good explanation of how to properly install and tighten the bolts.

I am going to go with the manual.

 

[Otto Pilot]

Greg,

Dan is correct. The rubber mounts for a Franklin powered 108 are very very similar to a Continental part number, functionally identical in fact if you trim off the stub at the top of the cone. You tighten the castellated nut until the distance between the washers is 1 & 11/16ths and the install the cotter pin. The nuts go on top, and the bolt heads go underneath.