Stripped threads

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greasypants   10 W

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Stripped threads

Post by greasypants » Apr 21 2007 9:32am

While replacing a flat (screw) before my ride home from work last night I was unable to fully tighten one of the axle nuts on my rear 5304. After removing the nut it looks like I stripped a portion of the threads on the axle. I guess I was a bit overzealous tightening the nuts due to not having any torque arms . I was able to partially tighten it and rode home carefully with no problems . How hard it is to replace the axle ? Do I have to take the entire motor apart ? If I use a few extra washers I could move the nut farther back to where there are some good threads temporarily but would be better if I could replace the axle .

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fechter   100 GW

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Post by fechter » Apr 21 2007 10:24am

Hmmm.... not good.

I think the axle is pretty much integral with the whole stator assembly. I don't think it will be easy to replace (even if you could find the part).

If you can make a spacer or stack of washers to get the nut on a good spot as you suggested, it should work OK. Make sure the nut is OK.

Another possible approach might be to build up the stripped part with some welding or brazing and re-machine the threads. This might be pretty challenging since it would be hard to put the axle in a lathe. You might be able to do it by hand with a dremel grinder and a thread cutting die.

Another possible approach would be to grind off all the threads and use a die to cut new threads that are one size smaller.

Yet another approach would be to saw off the damaged threads completely, drill and tap a hole into what's left of the axle, and insert a stud (threaded piece of rod) into the new hole. This method would allow you to use hardened steel for the new threads. Loctite the stud in place.
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Post by greasypants » Apr 21 2007 10:54am

Thanks for all the suggestions Fetcher, I was afraid it would be difficult to change . I will try the washers and keep a close eye on it and try not to reef on it so hard , if I use a torque wrench any idea how many foot lbs to tighten ?

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Post by Drunkskunk » Apr 21 2007 11:22am

Throw Away that nut.

most likely if the axle threads were damaged, the nut's threads were either damaged or weaked as well. it may "look" ok, but it shouldn't be trusted.

your washer idea should work fine. However, in a laminated compression fitting like this, were you have not just the drop out, but several layers of spacer, the torque required to hold everything in place will be higher. You've exceeded the torque once, So you can reduce whats needed by adding a torque arm to this side to help keep the axle from moving, and also using a Nylock nut instead of the conventional style. If you are going to be using more than 3 washers, try using grade 8 washers, as they're less likely to have a squash effect over time.

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Post by 29a » Apr 21 2007 11:30am

Hi greasypants,
I had a simillar problem i went with a torque arm the thickness of which does the job of the washers.I made mine with 3/8 steel drilling two 9mm holes and filing to fit and used "u"clamps to bolt it to the frame.[/img]
Idon't know how to rotate pic but if you tilt your head to the right you can see thats it's bolted to my front fork's
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Post by greasypants » Apr 21 2007 11:54am

That's a great idea to fill the space with a torque arm . I was planning to add one eventually anyway. I will use the washer spacers for now and fab up a torque arm when I have time and be more carful when I tighten the nuts. Will try and find some new nuts and washers at home depot on the way home today .

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Post by 29a » Apr 21 2007 12:01pm

Don't procastinate it only takes an hour to make this torque arm, a lot quicker than repairing the wires if you spin the wheel in drop outs.
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Post by Lowell » Apr 21 2007 12:04pm

A Porsche wheel nut will thread on, and the longer thread engagement should grab the threads on the unstripped portion of the axle. An M14x1.5 rod coupler would do the same thing, although might be difficult to find. 100ft/lbs should be plenty for the axle nuts.

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Post by Lessss » Apr 21 2007 1:36pm

Rotated
Use locktight as well on whatever you choose to repair with.
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tesco   100 µW

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Had the same problem

Post by tesco » Apr 22 2007 12:18pm

Had the same problem as you with my X5 but its the thread on the nut that strips, the steel is softer on the nuts so thats what ususlly goes first. If you clean out the swarf from the shaft threads with somthing that has a point on it. You can then use a wire brush to get the small bit out. Then put on a new nut it will be OK. I think its a funny thread somthing like 1" 3/8 pitch X 12mm, I got one from my local garage spares dept.

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Post by CGameProgrammer » Apr 22 2007 6:20pm

Loctite is what Less means.

Hey Less, can you post pictures facing forward/backward so we can see what exactly those bolts on your torque arm are bolted to?

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Post by BrendaEM » Apr 23 2007 2:44am

Please, be careful. If that thing breaks it won't keep it secret.

This is a head joint failure, but if you loose the front wheel, the physics would be about the same, perhaps worse if the fork ends dig into the pavement.
http://video.google.com/videoplay?docid ... e+accident

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Reid Welch   10 MW

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Post by Reid Welch » Apr 23 2007 6:46am

I've never been a fan of extreme torque, particularly not when the threads are -cut thread- v. rolled threads. I don't like torque wrenching. Hand wrenchs are made to standard lengths for the very reason to prevent stripping, except by gorilla mechanics.
Torque wrench specs standarize and work ONLY for dry, clean threads.
Dry, no oil, no dirt on the threads, or the results skew drastically.

Torque wrenching dirty, used nuts on bolts of unknown composition quality is a blind endeavor, imo.
I say, employ a hand wrench of standard length and -feel- the nut tight.

If you have a torque arm like 29A has so well-made, then the thing to do in general practice is keep the nut tight.
No need to brutalize threads;
the torque arm is what's keeping the stator from spinning.
I like to retighten things by feel, to moderately hard tightness, several times over a period of service. Eventually the clamped joint beds down and holds torque.
That is to say: a little and often is kinder to threads than one massive torquing.

__________________
_________

The longer the torque arm, I suppose the more graceful-looking it may be made to look; I like the notion of exploiting leverage.

_____________
__________

Loctite, blue, is good for axle nuts.
Always use a new nut if the old nut has been abused.



Main point: tap or die cut threads are inherently weaker than rolled threads.

Most all bolts and screws today have, in effect, forged threads which preserve the grain-strength of the steel.
However, a hub motor axle is a machined affair,
and so, it probably offers die-cut or lathe-cut threads, which all engineers know are weaker by nature. Corn shucks.
So do machine cut threads if overstressed.


Image

http://www.rolledthreads.com/why_rolled_threads.htm

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Post by Matt Gruber » Apr 23 2007 8:44am

Reid is very lucky,
he has a "clicker" wrist :D
i use a torque wrench on axle nuts as i'm not able to get my wrist to click.
I did some tests years ago
oiled vs. dry vs. loctite red vs bolt stretch.
had to increase the torque 10# to adjust for the loctite on chevy rod bolts. loctite isn't necessary on rod bolts, but i wanted to try it.

MY advice: if your car mechanic uses a clicker wrist, go elsewhere.
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Reid Welch   10 MW

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Post by Reid Welch » Apr 23 2007 2:41pm

"Ach!" says old Herr Flash. "Rid has just been impugned, 'clicker wrist'.

Der Matt gonner pay mit feet wiped on his face befur dis is offer.
Vaitinsea."


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Post by Lowell » Apr 23 2007 3:03pm

BrendaEM wrote:Please, be careful. If that thing breaks it won't keep it secret.

This is a head joint failure, but if you loose the front wheel, the physics would be about the same, perhaps worse if the fork ends dig into the pavement.
http://video.google.com/videoplay?docid ... e+accident
That failure was probably avoidable if the frame had been inspected regularily. High performance machines should get visuals at the very least, and preferrably dye penetrant or magnafluxing. Thick paint/coatings are a no-no in high stress areas as they mask surface cracks. (unless you have access to xray equipment)

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Reid Welch   10 MW

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Post by Reid Welch » Apr 23 2007 3:04pm

I'll make this real simple.

A) a screw thread is a wedge, a ramp, an immensely powerful wedge driving itself down with force limited only by the resistance of the thead

B) tight is tight. Going more than tight is done for one of two purposes, or for both these purposes:

I ELONGATE the bolt or stud in dynamic tension, by which to create an elastic, lasting clamping pressure. This is done to keep head bolts, for instance, tight, over the range of operating temperatures where a gasket must follow the movements and seal between two dissimilar surfaces. Squirm requires tension.

II DEFORM the threads themselves into an interference fit so they should not loosen. This is why rod bolts will be torqued to spec. These should be one-use only. Should best be thrown away.

----

At best, at best, the torque wrench is an indirect measuring device.
The variablility of thread friction is -huge- in real life.
Torque tables are based upon one condition: dry, unlubricated threads.

----

The ONLY genuine measure of bolt thread deformation and/or bolt elongation is direct measurement. This can be done with a micrometer on con rod bolts with heads, but not on cap screws.

-----

Finally, here's what really counts to a C-Lyte axle thread:

-It is ONLY a stub-bolt or stud and is very stout*, and so, if we TORQUE it hard we are NOT stretching it, but only deforming the CUT threads, which are SOFT steel and NOT elastic*.

How many times does one want to heavily bend a tiny metal wall: ^^^^^

Each turn gets the same pressure. IF we overtighten: mmmm

ALL we should do is clamp the parts together, tight, so they cannot rattle.
Recheck axle nut tightness at intervals. Use blue loctite on cleaned threads.

And if we have a torque arm, there's certainly no need to do more than -tight-,

hand-wrench tight.

And if we're not using a proper, THICK or HARDENED torque arm (see 29's good example), then we are foolhardy to bully the axle threads by brute wrenching,
relying on inelastic pressure* to maintain an immovable clamping force to resist a -rotating force-.
That's so very unmechanically correct, friends.

And if a mechanic has no "feel" for what metal is doing when
the mechanic uses a too-long wrench like a breaker bar handle,
the mechanic should use a hand wrench.
Breaker bars are for loosenings, not tightenings.

I can't "feel" accurately with a breaker bar.
But I can "feel" with a box end hand wrench.
Or even if could not "feel" threads going bye-bye with the hand wrench,
that's for good reason: the hand wrench is designed to prevent idiot overtightenings by hand power alone;
the hand wrench is not wrenching off threads, see?

Example: Regular bike with QR skewers: Impossible to ruin them or their threads. They do not super-torque themselves.
Nor need they be super torqued.

Key point: use competent torque arm on every hub motor axle.
Make it fit well. Make everything firmly tight and keep it tight.
Allow no movement of stressed parts.

___________
_______

I never spoil threads anymore. Never.
Nor do I suffer catastrophic failures. Ever.

Not E er. Damn!
the " " key just quit working on this keyboard.

Serious content, but I am kidding about being insulted or insulting,

Reid
Last edited by Reid Welch on Apr 23 2007 3:20pm, edited 1 time in total.

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Post by Lowell » Apr 23 2007 3:19pm

Probably not a bad idea to use a castle nut or nylock on the rear axle. Safety wire would be good too, but a PITA for servicing.

http://www.nutty.com/metcastlenut.shtml

http://www.whizwheels.com/Tips/safetywiring.html

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Reid Welch   10 MW

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Post by Reid Welch » Apr 23 2007 3:30pm

Yes, agreed.

Castle nuts, cotter pins: useful (I've done many hundreds/ Model T Fords are cottered-pinned together)

Downside is minor annoyance and limited range of adjustability.

In practice, blue loctite on cleaned threads holds well and provides lasting friction that still allows for periodic re-tightenings, while preventing working-off of the nut.

This is why so many bolts in critical places (Vee brake levers) come from the factory with a stripe of
blue threadlocking agent in the hole or on the bolt.

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Post by Drunkskunk » Apr 23 2007 3:39pm

Reid Welch wrote: (((ehh, too long. read it above. )))
Exatly, Anyone who's built a big power motor knows to measure the rod bolts to determin when they are tight. one bolt to the next might be +5LBS diffrent, but .05 inch streach is a good, solid, direct measurement.

Furthermore, using threadlock inside a combustion engine is a bad idea. that stuff melts under heat, pressure, and the solvent action of the oil. Its also ment to harden by anarobic action, and petrolium products interupt this. So what happens is you build your motor with locktight, torque it to what you think is right, then run it. over time, that Locktight works its self free, and causes the bolt to be "lose". A very bad thing on a Rod bolt. It also tends to find its way into other areas, and can build up in oil pasages and bearing surfaces. Probably not a problem on a 350 Chevy, but that kind of thing can Kill a Honda.

Any good mechanic can tell how much torque he's putting on a bolt by feel, with in, say, 10%. By the same token that anyone who's ever held a can of beer knows how much pressure to exeret on the can to keep it from falling, but not crush it.

As for these motor shaft bolts, tight is as Reid said, tight. A little tighter for aluminum, or soft steel. less tight for hard steel. And use Nylock nuts on anything with cut thread.

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Post by Matt Gruber » Apr 23 2007 4:44pm

Watch Heros tonight on NBC!
New hero!
tightens lug nuts perfectly using his bare fingers! don't miss it!
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greasypants   10 W

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Post by greasypants » Apr 23 2007 4:52pm

I think my problem was the only wrench I had that was the proper size was way to long and it didn't feel like I was overtightening it because of the extra leverage.

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Post by Ypedal » Apr 23 2007 5:01pm

Cotter Pins : Only good on splined or shaped hubs, no good on a Hub motor.

I got me one of those click-wrists.. has served me well over the years lol..
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Reid Welch   10 MW

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Post by Reid Welch » Apr 23 2007 5:27pm

DS, amen. Glad my self-taught-the-hard way T-learnings jibe closely with your experiences in the mainstream mechanical world.

Gaston: You may drill an axle end for a cotter pin.
The thing with cotter pins: the castles notches are too coarse for fine adjustments, about half of the time.

Soft metals embed under pressure as DS notes.
This is why it's always good to recheck tightness over time.
Eventually even soft metal takes a permanent seat/bearing of the clamping pressure and the joint remains tight.


Interesting to ponder: A QR skewer is thin steel. It locks into elastic stretch
(a dynamic tension) because it's thin enough for the cam lever lock to stretch it a bit.
That's how I see it, though I have no facts to back up the presumption.

_________

Q: how to figure the theoretical clamping pressure of a threaded device being turned by a one foot long lever.

Presume the torque is ten pounds at the end of a one foot lever (10 foot-pounds).

Presume the thread is 24TPI?

Think of this as a massive gear reduction. Now, neglecting friction,
how do we translate the lever torque into bolt stretching force?

Will it be 240lbs of tension? No. How about 2,400lbs? Much more????

????

(I don't know)
Last edited by Reid Welch on Apr 23 2007 7:18pm, edited 1 time in total.

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Post by Matt Gruber » Apr 23 2007 6:23pm

My hats off to u guys!
Last time i checked to see if i had that skill(click wrist),
i swore it was 35,
checked it and it was 20.
I'd be in awe of anybody that consistant(that could pass a test).
IF u have checked, u deserve congrats!
If not U R FIRED :lol:
ASE CERTIFIED IN ELECTRICAL SYSTEMS 1984- retired
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Testing various foods.
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