Problems with Wheel Hubs/Motor

[Vacuous_One]

I've got a PT422 with the Robin 22HP engine, bought new circa 2001. I replaced one wheel motor and front hub in 2005 and now I've got one in the rear that's probably going to need both hub and motor replaced and the other's not far behind. (Haven't checked the other front one yet, but will soon...expect I'll have similar issues with it.)

In all cases, the keyway on the motor shaft is rounded over, the keyway on the wheel hub is worn away until it's virtually non-existent, and whatever key is left (if any) is essentially round. The motor shaft is scored and the wheel hubs are "extruded" around the shaft area and scored/worn at the shaft interface.

The wheel bolts and motor/hub castle nut are tight and in good shape (except for wear on the catle nut/hub from the wheel rotating due to-apparently-loss of the key).

Has anybody else had this kind of wear/issue? I'm not really pleased having to replace wheel motors and hubs every 2-3 years!

 

[SnowRidge]

Welcome to the forum. Did Power Trac use wheel motors with tapered shafts on your machine?

If so, it sounds like someone used the wrong material for the key and/or didn't torque the hub nuts properly. The wheel motor manufacturer's web site will probably have the torque spec for the hub nut posted. It should be several hundred foot pounds, and they should have been a real bear to get off.

What kind of wheel motors are they?

How many hours on your machine?

 

[ernemats]

I had the left front hub replaced on my 422 about a year ago, it was probably my fault I had taken the hub off about a year before that and I don't think I torked the nut that holds the hub as much as I should have. According to Terry it should be put on with an impact wrench, he said you cannot overtighten it. I do not have a impact wrench big enough to handle that size nut, I used a breaker bar with a 3 foot extension to put it back on the last time.

 

[SnowRidge]

A 200 lb man can put 600 foot lbs of torque on a nut with a three foot bar without difficulty, more by shock loading it. That's more than enough for a wheel motor on a small machine. Maybe they would last longer if the factory didn't use impact wrenches.

 

[Vacuous_One]

Snowridge:

1) Yes, my wheel motors have tapered shafts.

2) That "someone" was the PT factory...never touched them myself...until now-unfortunately. They weren't real difficult to get off, though...the wheel was wobbling so much with the key gone that the nut was actually rounded off on the backside and the wheel loose on the tapered shaft due to wear. (I haven't been able to find anything on the torque spec for the hub nut, by the way, from White's website. Probably have to make a call.)

I checked the front, and they both seem to be okay, although neither nut was particularly difficult to get off. With the castle nut needing to line up with the through hole for the cotter pin, there's a limit as to how much torque can be put on it: The castle nut opening and the shaft through-hole still have to line up when you're done. Once you get to metal-on-metal with the tapered shaft, there's not a whole lot of room left to move!

3) The wheel motors are the White model 200200F3013AAAAA (1" tapered shaft with castle nut/cotter key).

4) I've only got about 450 hours on the PT422. (That's in around 7 years, now.)

Ernemats:

I did much the same to put the front one back on when I replaced it 3 years ago. From looking at it, everything seems to be doing okay: No play in it and the nut was still tight. (Same with the other front one from the factory. )

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In any case, after closer inspection of the situation, it's now two new wheel motors and two new hubs for me! Oh happy day...! That'll be three new wheel motors in 7 years...not a good statement about PT quality. It's a shame, because it's otherwise been pretty good and it's quite a versatile machine.

 

[SnowRidge]

White used to have the tightening torque in their catalog, which I thought was an odd place. It seems to be gone now. I don't remember exactly what it was, but I do know a 600 foot lb torque wrench was needed to set it accurately, and a 350 foot lb model wouldn't cut it, so it's between 350 and 600 foot lbs. I think it was 400 or 450 foot lbs.

The current catalog lists the shaft as having a maximum torque limitation of 883 foot lbs, so 400 to 500 seems right.

I know one of the motor manufacturers says to use the torque spec of the hub manufacturer, and if that isn't available to use the motor manufacturer's spec.

I have to disagree on the metal to metal and not much more to move. If you really lean on it, you can get quite a bit more. I just did a tapered shaft/hub installation today on my brush cutter. I was able to get a couple more turns after I had good solid contact.

I have had wheel hubs off at least twice on my PT-425. I never have purchased that 600 lb torque wrench. I tighten the hub nut up with a 42" breaker bar on the ratchet and give it everything I have. I figure I am good for about 600 foot lbs with that setup.

I always clean the hub and shaft real well, then grease the dickens out of things. It helps when torquing it down, and it also helps to keep them from rusting together.

It does sound like it was PT that didn't torque them tight enough. It also sounds like the other two need to be tightened, too.

 

[ponytug]

Hmmm. Thanks for all the tips.

I am curious, when I was taught to torque things, I have this vague memory of someone telling me that the torque settings were always dry. The rationale that I recall was that greasing made it easy to over torque the nut/bolt...Are tapered hubs a special exception, or did someone feed me a bunch of...

Times like these, I wish I had gotten a formal education in mechanics, rather than a real world education in mechanics, if you know what I mean.

(Like the time we were 200 miles from the nearest gas station, when the gas tank got ripped open by a boulder, with a six inch ribbon of gas flowing out the bottom...of course, the fix worked so well we drove another 1000 miles before we had the gas tank fixed...Bonus points for catching and reusing the gas.)

All the best,

Peter

...I always clean the hub and shaft real well, then grease the dickens out of things. It helps when torquing it down, and it also helps to keep them from rusting together.

It does sound like it was PT that didn't torque them tight enough. It also sounds like the other two need to be tightened, too.

 

[J_J]

Hmmm. Thanks for all the tips.

I am curious, when I was taught to torque things, I have this vague memory of someone telling me that the torque settings were always dry. The rationale that I recall was that greasing made it easy to over torque the nut/bolt...Are tapered hubs a special exception, or did someone feed me a bunch of...

Times like these, I wish I had gotten a formal education in mechanics, rather than a real world education in mechanics, if you know what I mean.

(Like the time we were 200 miles from the nearest gas station, when the gas tank got ripped open by a boulder, with a six inch ribbon of gas flowing out the bottom...of course, the fix worked so well we drove another 1000 miles before we had the gas tank fixed...Bonus points for catching and reusing the gas.)

All the best,

Peter

I was going to say the same thing about lubing things that are to be torque down. There should be metal to metal contact or you will over torque the product and twist the shaft or strip the nut. You never lube wheel nuts. On the castle nuts, You either over tighten them to match the hole or back off one notch. If you have enough threads, you might be able to double nut the axle shaft.

 

[SnowRidge]

Hmmm. Thanks for all the tips.

I am curious, when I was taught to torque things, I have this vague memory of someone telling me that the torque settings were always dry. The rationale that I recall was that greasing made it easy to over torque the nut/bolt...Are tapered hubs a special exception, or did someone feed me a bunch of...

Dry unless stated otherwise for common fasteners. The coefficient of friction of a dry fastener is a known entity. Different lubricants would require different torque values. For the engineers to specify lubricated torque values, they have to also specify the lubricant. There's little reason for them to do that for ordinary fasteners.

For tapered shafts, I don't know of a specific rule, but as an example, on one of their tapered shaft products, Eaton specifies lubricated threads and nut face, but doesn't mention the tapered part either way.

The hub nut on the new Parker motor on my brush cutter came precoated with a locking compound, which of course would provide thread lubrication. The cutter's drum was bolted to the hub with lug bolts that had been coated with locking compound by the factory. I did the same thing when I reassembled it.

I do know that greasing the taper helps to keep the hub from rusting on. To me, that is an important consideration.

 

[ponytug]

That sounds like a certified exception to the dry torque rule.

Having removed tapered shafts, I can appreciate how useful it is not to have rust. I once had six foot cheater bar on rusted 10mm nut on the brakes on my car. I wouldn't have been using it, but a friend who used to service them professionally was standing next to me, telling me not to worry. He was right, too!

All the best,

Peter

Dry unless stated otherwise for common fasteners. The coefficient of friction of a dry fastener is a known entity. For tapered shafts, I don't know of a specific rule, but on one of their tapered shaft products, Eaton specifies lubricated threads and nut face, but doesn't mention the tapered part either way.

I do know that greasing the taper helps to keep the hub from rusting on. To me, that is an important consideration.