Smooth shaft Keyed PTO backing off / un-hooking????

[NJDiverDan]

I just picked up a used old 3 pt snowblower for my BX24. It is an open gearbox chain drive blower. The PTO shaft connects to the blower on a smooth shaft with a keyway. There is a set screw that is supposed to hold the keyway in place.

No matter how tight I make the set screw, the PTO shaft will start to back off the shaft. Most keyed shafts I have dealt with have a cross bolt that holds the shaft on but this one does not. It looks like one of the previous owners tried to drill for a cross bolt, but only dimpled the shaft (got through one side of the yoke). Should I continue to drill this out? Seems like drilling the shaft may not be the best of ideas?? Can I put lock tite on the set screw? Not sure if the set screw is backing out and that is causing the slipping or the slipping is causing the set screw to not be tight, but the set screw is easily turned every time it has slipped.

I am picking up some new keyways today, maybe that will help???

Thank you for any suggestions.

-dan

 

[kebo]

On some equipment (like post hole diggers for example that use a shear bolt) there will be a hole drilled and tapped in the yoke on the PTO shaft. There will be a set screw that goes into that tapped hole. There will also be a groove all the way around the circumference of the input shaft (to the gearbox). When you attach the yoke (of the PTO shaft) to gearbox, simply line up the yoke so that the set screw is over the groove, and then tighten the set screw down so it rides inside that groove. That way, if the shear bolt or the key breaks, the yoke just spins around on the shaft, and should stay attached to the gear box and not come off and flop around until you can shut it down. This is how my Leinbach post hole digger is set up.

Whether it uses a key, or a shear bolt, it does need some method to hold the yoke in place so that the yoke won't come off at 540 rpm's and destroy something.

It seems like the set screw is coming lose from the vibration. What you might try (if there is enough room) is drilling a tapping a second hole and add a second set screw, so that there are two set screws pressing on the key. You could use Loctite, but if you do, I suggest use the medium strength 242 first to see how that works. Good luck.

 

[kthompson]

The threads on the set screw or in the hole or both could be worn. At least take the screw with a nut and the threads internal threads with another bolt.

 

[Mendonsy]

Does the smooth shaft on the blower have a tapped hole in the end? Some of those used a cap bolt and thick washer to keep the yoke on the shaft.

 

[JCByrd24]

There should definitely be a method other than the set screw on the key to keep the yoke on the shaft. My 3pt blower has a cross bolt like you describe and the set screw just keeps the key from sliding. Yokes with a sheer bolt will have some other method like the others described.

 

[airbiscuit]

I had the same issue with a snowblower. I drilled and tapped a hole on the opposite side of the key, and then I drilled a "dimple" into the shaft so that set screw went about 1/4" into the shaft. A little locktite wouldn't hurt.

 

[Steave]

You might put another set screw on top of the first if there's enough threads left after the first is tightened and yes put locktite on them both. Sounds like the coupler and shaft are not mating with a close enough tolerance. If thats the case of a loose tolerance between the two the problem I'm sorry to say is going to be hard to patch. Drilling the shaft is one option.

 

[NJDiverDan]

Thank you for all of the replies. There is not a hole in the end of the shaft. I was hoping but no luck. There is a hole in the yoke and a dimple already. I will see if I can run a tap down it to thread it. No room for another set screw as this one is fairly flush with the yoke when tight.

As for fitment of the yoke to the shaft. It is not tight. Not sloppy but easy to slide the yoke over the shaft and key.

I will try the additional set screw in the pre-existing hole. If not then it looks like I will need to drill the shaft.

All that said I am loving the blower. I have only needed to clear 4-6 inches of snow so far but I have cut through some drifts that were probably 2 foot or so. Tractor is handling the 60" blower with no problem.

 

[Mace Canute]

I had the same issue with a snowblower. I drilled and tapped a hole on the opposite side of the key, and then I drilled a "dimple" into the shaft so that set screw went about 1/4" into the shaft. A little locktite wouldn't hurt.

Second set screws should always be at 90 degrees to the first, not 180 degrees. When they are at 180 degrees the yoke will, in direct proportion to the clearance between the shaft and yoke, rock back and forth on them...they become pivot points...and this back and forth motion will cause one or both to loosen off. When they are 90 degrees they act to press the shaft against the yolk and make full contact along the opposite side eliminating the rocking.

 

[aczlan]

I have a snowblower with the same type of connection to the shaft, but it has a through bolt and 2 setscrews 90 degrees apart both of which have jam nuts on them (they stick out enough to have 2/3 threads past the jam nut).

Aaron Z