Engine Mount Bolt Torque

A few days ago I mounted my engine. The instructions say to torque the bolts to 160 - 190 inch/pounds. When I torque the bolts to 160 most of the cotter pin holes don't line up so they can be used. Re-torquing to 190 doesn't move the bolt enough to open up the holes. In order to line up the holes one has to exceed the 190 setting by a considerable amount. I researched the issue and discovered that the advice is to insert an extra thin or thick washer and try again. Problem is there doesn't seem to be any extra washers furnished in the kit to use for this.

So, do you over-torque and live with that, or obtain some extra washers on your own and try to get the final torque in the 160 - 190 range?

What have others done?

I had to pull my engine this last winter for overhaul and when I reinstalled it I used locking nuts instead of putting those castle nuts back on and trying to get the torque and cotter pins lined up.

You'll need extra washers throughout the project. Buy plenty of them of all sizes and the "L" flats as well. The kit does not come with everything necessary necessarily. A great washer selection on hand is very handy if not mandatory.

This tidbit may be of some help...

My call out for the bolts was AN6-24 which translates to a 3/8 - 24 thread. That is 24 threads per inch. It takes roughly 24 full turns of a nut to travel 1 inch.

That means each complete turn of a nut moves the nut 0.0416 inches along the bolt.

Since the nut has 6 flats, each 1/6th turn of the nut moves the nut about 0.007 inches.

The AN 960-616 washer is 0.063 thick, and the xx-616L is 0.032 thick.

Sometimes you can grind down one of the standard washers less than the 0.007 inches to get a cotter pin to fit. If you try this, keep the washer flat, and maybe use sandpaper on a flat surface and move the washer across the surface with your finger. Prime part when finished.

The tolerance on AN960...

noelf said:

My call out for the bolts was AN6-24 which translates to a 3/8 - 24 thread. That is 24 threads per inch. It takes roughly 24 full turns of a nut to travel 1 inch.

That means each complete turn of a nut moves the nut 0.0416 inches along the bolt.

Since the nut has 6 flats, each 1/6th turn of the nut moves the nut about 0.007 inches.

The AN 960-616 washer is 0.063 thick, and the xx-616L is 0.032 thick.

Sometimes you can grind down one of the standard washers less than the 0.007 inches to get a cotter pin to fit. If you try this, keep the washer flat, and maybe use sandpaper on a flat surface and move the washer across the surface with your finger. Prime part when finished.

Click to expand...

...steel washer thickness is +/- 0.010 inches -- so just using a micrometer on your pile of washers might help you select a better one, since 0.0035 inch equals half a flat by the above numers.

or,

The following from the Wicks Aircraft site:

Torquing
Excep as a last resort, do not torque a bolt by turning it. Tighten or torque castellated nuts as you would any
other standard nut. If the slots and cotter pin hole in the bolt will not line up for safetying, tighten the nut to
next slot even though the recommended torque values will be exceeded. This over torquing leeway applies
only to castle nuts and not others. Cotter pins when used should fit snugly but not so tight you have to
hammer them into the bolt hole. Bend the ends so that one end is over the end of the bolt reaching to its
center or slightly beyond. The other leg is bent snugly against the nut. Coarse threads require slightly less
torque and so do shear nuts. Actually, about 1/2 the amount of torque is sufficient for them. And, finally,
even if you don't use a torque wrench - no self-respecting homebuilder will ever allow himself to be caught
using a pair of pliers to tighten a nut.

Comments? I assume the reasoning is since proper torque has a range, tightening to make the slot "line up" is acceptable - but presumably with the proviso that one stay in (or close to) the range, using washers as necessary.

Bill Brooks
Ottawa Canada
RV-6A finishing

Engine Mount Bolt Tourque

John,
What has been previouly stated is quite true. AC-65-9A, A&P Mechanics General Handbook, states on Pg. 135 under Cotter Pin Hole Line-up, " When tightening castellated nuts on bolts, the cotter pin holes may not line up with the slots in the nuts for the range of recomended values. Except in cases of highly stressed engine parts, the nut may be over tightened to permit lining up the next slot with the cotter pin hole. The torque loads specified may be used for all unlubricated cadmium-plated steel nuts of fine or coarse-thread series which have approximately equal number of threads and equal face bearing areas. These values do not apply where special torque requirements are specified in the maintenance manual."

Van's RV-12 Maintenance Manual does not give a specific torque for the motor mounts. They simply have torque table showing the torque range for AN-6 bolts as 160-190 in-lbs.

Rotax refers you back to the aircraft manufacturer.

So I guess by juggling washers or adding torque one should be able to get those holes lined up.

Art Pennanen

What are you using to mount. The Lord Bolts? And weren't those AN7 bolts? As I recall the instructions Van's provides says torque to bottom out the bolts on the metal sleeve, then "back off and torque to AN7 specifications."

I vaguely recall this being something like 40 foot pounds, though.

Bob Collins said:

What are you using to mount. The Lord Bolts? And weren't those AN7 bolts? As I recall the instructions Van's provides says torque to bottom out the bolts on the metal sleeve, then "back off and torque to AN7 specifications."
I vaguely recall this being something like 40 foot pounds, though.

Click to expand...

This thread is relative only to the Rotax 912 and the RV-12.

Right. Just noticed that....the dangers of clicking the "new posts" link.