ENGINE/TRANNY-BOLT/NUT PLACEMENT

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amiabledave
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ENGINE/TRANNY-BOLT/NUT PLACEMENT

#1

Post by amiabledave » Mon Jan 17, 2011 3:53 am

OK, I'VE GONE THROUGH A GALLERY OF PICTURES AND HAVE SEEN THE ENGINE AND TRANNY MOUNTING BOLTS (HEX HEAD) ON TOP AND THE NUTS WITH COTTER PINS ON TOP. WHICH IS THE OEM AND WHY? I HAVE, BY HABIT, PUT THE HEX ON TOP.

THANK YOU FOR YOUR TIME......DAVE



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Re: ENGINE/TRANNY-BOLT/NUT PLACEMENT

#2

Post by FlatHeadSix » Mon Jan 17, 2011 4:10 am

general rule of thumb; nuts up (but not always). You're going to get responses for both. I think john HD posted something a while back about the physics of this, it seems that the natural tendancy in a system that vibrates is for the nuts to loosen if they are on the bottom, they self-tighten if they are one top. But I guess that's why they also drilled the bolts and put a cotter pin in them.

Let's see what the "experts" have to say......

like I said: nuts up

mike

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Re: ENGINE/TRANNY-BOLT/NUT PLACEMENT

#3

Post by caschnd1 » Wed Jan 19, 2011 5:20 am

Don't know how the factory did it, but I put the nuts on the bottom. With castle nuts and cotter pins you're not likely to ever lose one, but if you do, the bolt won't fall out. Motor will be loose but if the bolts fall out it's gonna be all over the place.

-Craig

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Re: ENGINE/TRANNY-BOLT/NUT PLACEMENT

#4

Post by beets » Wed Jan 19, 2011 1:30 pm

I bought a neglected '54 pan several years ago that had a terrible vibration. Inspection revealed three of the motor mount nuts were gone and the fourth was loose, held only by by a cotter pin. Nuts down for me.

Robert Luland
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Re: ENGINE/TRANNY-BOLT/NUT PLACEMENT

#5

Post by Robert Luland » Wed Jan 19, 2011 2:14 pm

Actually if I remember correctly, 47 was the last year the castle nut and carter pin were used. 48 and up used a Flexnut even though the bolt sported the carter pin hole up to about 63 when CP bolts were being fazed out but I have a couple of CP mounting bolts in cad with out the hole. They also used the rear mounting bolt on the early Due-Glide rear left side crash bar lower mount. Guess it was a good size. Bob L

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Re: ENGINE/TRANNY-BOLT/NUT PLACEMENT

#6

Post by Panshovevo » Wed Jan 19, 2011 3:35 pm

I don't personally know how Harley did it, but in aviation, the FAA specified rule of thumb, unless a manufacturer specifies otherwise, is that the bolt head always goes top or front. The reasoning is as expressed by Craig, if the nut comes off, the bolt should still remain in place, and may get you home.

Think about the fact that in an airplane, you can't just pull over to the side of the road if you break down...

To further confuse the issue, all the general aviation aircraft I have worked on have the engine mounting bolts installed from the rear, with nuts in front. I have never been able to get an answer as to why.

Regards,
John

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Re: ENGINE/TRANNY-BOLT/NUT PLACEMENT

#7

Post by panz4ever » Wed Jan 19, 2011 10:35 pm

How I did mine on my 49 based on info from a very old timer who worked at Sam Arena HD in San Jose CA until it closed in the 70s

Motor...
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panz4ever
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Re: ENGINE/TRANNY-BOLT/NUT PLACEMENT

#8

Post by panz4ever » Wed Jan 19, 2011 10:36 pm

And tranny...
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Re: ENGINE/TRANNY-BOLT/NUT PLACEMENT

#9

Post by FlatHeadSix » Thu Jan 20, 2011 3:32 am

Panz,
When this thread first started my first response was based on an earlier discussion we had about this, that's where John HD mentioned the "nuts up" lesson that the power company learned when assembling their towers.

I went out and looked at my '49 FL and everything is assembled exactly like yours, front bolts are nuts up on the engine, heads up on the rear, and the transmisson is also mounted just like yours is.

The '57 Parts Catalog diagram shows it the same way (but you can't always trust the parts books or the pictures in them).

Dave Swanson should jump in here and tell us how the bolts on his '56 are oriented.

mike

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Re: ENGINE/TRANNY-BOLT/NUT PLACEMENT

#10

Post by john HD » Thu Jan 20, 2011 10:36 am

mike is correct about my earlier position on this topic.

when a nut and bolt is installed vertically and subjected to vibration the nut travels down the threads. the bolt captured by the parts it is ment to fasten does not rotate.

once the nut falls off the bolt is useless.

obviously, in a critical application some type of locking device is best.

john

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