OT: Angular Contact Bearings for Right Angle Gearbox?

[The Metal Butcher]

Hi all.

I helped dad rebuild a 5 foot yanmar tiller. The power comes in via a driveshaft and then through a bevel gearbox. The issue is that after about 20 minutes of hard running a bearing on the input shaft was completely destroyed, to the point where it had filled the oil with metallic shavings. It appeared to have failed due to the thrust load from the bevel gear to me. I'm figuring it should have been rebuilt with 7 series angular contact bearings (7207 vs 6207). He found a part seller on the internet and their diagram showed a standard 6207. However, he's a notorious cheapskate and uses Chinese bearings on everything. Still, I'd believe a 10x shorter lifespan, but it was probably junk before two minutes are up making me think it's more than just a quality factor.

We'll definitely be putting quality bearings back in, but I see no disadvantage to angular contacts and I think they'd handle the thrust a lot better. But you all are smart folks so I thought I'd ask here.

Thanks, MB.

[Mcgyver]

On converting to AC's is there a way to tighten something on the AC races? You can't just put them on a shaft, you have to squeeze them together (or if sepereate with spacers on the inner and outer reace) so you need a way to load them - i.e. a nut on the shaft sandwiching them to a shoulder. I've replaced ball bearings with AC's once in boley headstock, but it was already set up with the mechanical arrangement to essentially clamp together the inner and outer races. You may have all this present or know all this, just saying if you didn't....its not going work.

What might work if it wasn't setup to properly hold AC's would be double row AC's, but not sure if they come in that size and it greatly increasing the width - may not fit.

Has the design be modified? Seems like there's something piece of the puzzle missing....I mean it must have lasted longer from the factory? what was the OEM arrangement?

[JoeLee]

I would think you would have head or felt that bearing going. Buy a quality bearing. Angular contact bearings are probably used because of the outward force the beveled gears place on it.

JL................

[CCWKen]

Perhaps the angulars were installed incorrectly. They MUST be installed in pairs and they MUST have the thrust direction opposing each other. At least one must be adjustable. They will come apart if not installed correctly. Just ask me about my TPG.

[MattiJ]

I’d suspect some sort of butchering during installation 😅

[AntonLargiader]

I work with a lot of right angle gearboxes where the axle is supported by a tapered roller and a ball bearing. When assembled properly, they last well. Assembling them properly is not straightforward, though.

Before re-engineering it, I would be sure that the original engineering was faulty. Yanmar isn't a ChiCom who is likely to send out poorly engineered crap. Setting the tooth contact, backlash, and preload is critical to getting these to work, as in a differential. If it wore out because it wasn't set up properly, and the person who repaired it just copied what was there before (which is VERY likely with people who don't really understand the work) then you don't really have a viable repair. Throw in a mistake (wrong bearing, wrong shimming) and I can see having a repair that lasts ten minutes in that environment.

Are the teeth still OK?

[nickel-city-fab]

I would vote angular contacts with meticulous assembly. Evert right angle box I ever got into has them, and they had lifespans measured in years of daily use.

EDIT my mistake, I meant tapered rollers.

[JCByrd24]

I’m in the minority here I guess but this is farm machinery and not a machine tool spindle. I’d bet a paycheck the original setup was not angular contact bearings and was simple ball bearings or tapered rollers. These gear boxes are very common and not that expensive. Old Yanmar designs are great (I have a beautiful 1981 186D tractor) but part of that is their simplicity. Either a crap bearing or an install issue.

[J Tiers]

I'm with JCByrd, this is a tiller. And bevel gears do not develop THAT much thrust, it is not a helical gear. it's a bigger tiller than I deal with, but I just do not see a spindle quality bearing being needed.

Much more likely that some damage was done putting it in, or that dirt got into it and started it getting chewed up.

So, what was the REASON for replacing the bearing? Just precaution? Or was IT chewed up also?

A little bend in the shaft can bust up a bearing, depending..... Tillers have a rough life. Does it operate under oil? Are you sure it GOT oil? How does the gear look now?

[JoeLee]

Perhaps the angulars were installed incorrectly. They MUST be installed in pairs and they MUST have the thrust direction opposing each other. At least one must be adjustable. They will come apart if not installed correctly. Just ask me about my TPG.

How would you install them incorrectly?? You would have to be blind and pretty stupid. Not to be insulting or anything but they are pretty straight forward. Were not talking grinder spindles. This is (stone knives and bear skins) here.
The OP might also consider tapered roller bearings. Like Timkin.

It would be a lot easier to diagnose with pictures.

JL....................

[Doozer]

How would you install them incorrectly??

JL....................

Maybe you have never seen the work of a factory maintenance department.!.!.!

-D

[chipmaker4130]

On converting to AC's is there a way to tighten something on the AC races? You can't just put them on a shaft . . .

Sure you can. Why does everyone seem to think that angular-contact bearings are 'spindle quality'? If the operating load always yields thrust in one direction, and if the installation doesn't allow significant movement in the other direction, these bearings can be used without any kind of preload. Think jackscrew with weight always on or other similar situations.

While the design characteristics of these bearings make them easily suited for precise preload and the elimination of longitudinal slop, the main benefit is their ability to handle comparatively high thrust load, precision or not.

[J Tiers]

Sure you can. Why does everyone seem to think that angular-contact bearings are 'spindle quality'? If the operating load always yields thrust in one direction, and if the installation doesn't allow significant movement in the other direction, these bearings can be used without any kind of preload. Think jackscrew with weight always on or other similar situations.

While the design characteristics of these bearings make them easily suited for precise preload and the elimination of longitudinal slop, the main benefit is their ability to handle comparatively high thrust load, precision or not.

Yah.... I have seen the results of using one A/C and one standard together. With no particular effort at or provision for preload.

It was not pretty. The A/C got banged up and failed (quite possibly the way this one did, but of course this one did not HAVE and A/C bearing in it, so ...)

Pictures of the assembly here, and the failed bearing, would be good to have any chance of figuring it out.

Personally, without more info, I'd suspect assembly damage, or dirt, or possibly lack of oil. Pics could change that.

[The Metal Butcher]

Thanks for all the responses, I knew you guys would have some good stuff.

So backstory: Dad bought this tiller I guess knowing that it had issues thinking he could fix it. It was all tore up so he bought another and married the two. It also sat for a few years which doesn't help reassembly. Certain things were missing I guess, so he had no reference for what bearings were installed before.

On converting to AC's is there a way to tighten something on the AC races? You can't just put them on a shaft, you have to squeeze them together (or if sepereate with spacers on the inner and outer reace) so you need a way to load them - i.e. a nut on the shaft sandwiching them to a shoulder.

What might work if it wasn't setup to properly hold AC's would be double row AC's, but not sure if they come in that size and it greatly increasing the width - may not fit.

Has the design be modified? Seems like there's something piece of the puzzle missing....I mean it must have lasted longer from the factory? what was the OEM arrangement?

Shouldn't the gear provide constant thrust force? Nothing will ever force it inwards.

Can't do double row. OEM arrangement is unknown, but probably 6200 series bearings.

I would think you would have head or felt that bearing going. Buy a quality bearing. Angular contact bearings are probably used because of the outward force the beveled gears place on it.

JL................

Tillers are not exactly quiet. 2 Cylinder Kubotas wide open are much louder.

Perhaps the angulars were installed incorrectly. They MUST be installed in pairs and they MUST have the thrust direction opposing each other. At least one must be adjustable. They will come apart if not installed correctly. Just ask me about my TPG.

It doesn't have angular contacts ATM.

I’d suspect some sort of butchering during installation 😅

Lol!

I work with a lot of right angle gearboxes where the axle is supported by a tapered roller and a ball bearing. When assembled properly, they last well. Assembling them properly is not straightforward, though.

Before re-engineering it, I would be sure that the original engineering was faulty. Yanmar isn't a ChiCom who is likely to send out poorly engineered crap. Setting the tooth contact, backlash, and preload is critical to getting these to work, as in a differential. If it wore out because it wasn't set up properly, and the person who repaired it just copied what was there before (which is VERY likely with people who don't really understand the work) then you don't really have a viable repair. Throw in a mistake (wrong bearing, wrong shimming) and I can see having a repair that lasts ten minutes in that environment.

Are the teeth still OK?

Agree to disagree. Every single bearing fit in the secondary gearbox was loose by at least 0.001. The case off the other tiller was worse, at nearly two thou. You could spin the race in the bore no issue. I realize under load that's unlikely, but it's bad practice. We used bearing retainer on every single one. I am quite underwhelmed by the quality.

You may be right about the shimming. The bull gear is spaced outward with a small shim on the inner race. There is a huge amount of tolerances stacking up though. The bullgear is against the shim, against the bearing which floats, which is held by the shoulder on a drive shaft, the other end of the driveshaft is shouldered against bearings in the secondary gearbox. So there are about 10 different fits which determine the position of that gear, two of which are gaskets. The pinion gear seems to be depthed via the gasket thickness as well, and maybe ours was too thin. It spun ok by hand, but there was a few small catches.

I would vote angular contacts with meticulous assembly. Evert right angle box I ever got into has them, and they had lifespans measured in years of daily use.

EDIT my mistake, I meant tapered rollers.

Impossible to do here without large amounts of re-engineering and machining.

Much more likely that some damage was done putting it in, or that dirt got into it and started it getting chewed up.

So, what was the REASON for replacing the bearing? Just precaution? Or was IT chewed up also?

A little bend in the shaft can bust up a bearing, depending..... Tillers have a rough life. Does it operate under oil? Are you sure it GOT oil? How does the gear look now?

Complete rebuild as said above. Dad did say the shaft was undersized so the race is not a great fit on it. We felt another one of the brand new bearings and they felt kinda ehh, even by Chinese standards. But give us some credit, we install probably almost a bearing a week. We've got an entire bucket of junk bearings, it's unlikely that we installed the bearing incorrectly. Something else incorrectly? Maybe. Probably.

Brand new oil. I haven't seen the gears, but dad said they're fine.

Sure you can. Why does everyone seem to think that angular-contact bearings are 'spindle quality'? If the operating load always yields thrust in one direction, and if the installation doesn't allow significant movement in the other direction, these bearings can be used without any kind of preload. Think jackscrew with weight always on or other similar situations.

While the design characteristics of these bearings make them easily suited for precise preload and the elimination of longitudinal slop, the main benefit is their ability to handle comparatively high thrust load, precision or not.

Exactly. Angular contacts were looking at are low precision American or Japanese bearings on ebay for $10-15.

--

I'll get your some pics, JT. I'll have to was the metal off the bearing first lol.

[CCWKen]

"How would you install them incorrectly?? You would have to be blind and pretty stupid." If you're not familiar with them, it's pretty darn easy to install them wrong. Or you may not know what you have. Most are not marked at all. All you have to go on is the minute difference in the inner race thickness from one side to the other. And most my age ARE blind. If you think we're talking about tapered roller bearings, then you're stupid.