Bushing Wear: Where is the biggest loss of power?

[MuensterMann]

When a pivot wears its bushing to an oval shape (actually a key hole shape), is the biggest loss of power between its wheel and the pinion of the next wheel by being tilted? Or is the problem with the pivot not rotating in its original round bushing, thus rubbing on the worn plate hole? Or both? If both, which one causes the biggest loss of power?

On the same topic of loss of power, of the 4-6 wheels of the train, which ones being out of alignment (worn bushings) amount in the greatest lost of power?

 

[Willie X]

Both ... either defect can cause a train to stop cold in it's tracks. But it would be difficult to have one without the other.

The more robust lower part of the train can tolerate much more wear (in linear measurement) than the top. I've see barely perceptible flaws in the upper part of a train cause all kinds of trouble, including a dead stop.

Willie X

 

[MARK A. BUTTERWORTH]

keep in mind that every wheel ones goes up in the train there is a power reduction of 8-10 to 1. As a result going up 3 wheels can cause a reduction of up to 1,000 to 1 on the power.

 

[MuensterMann]

Willie: You are saying that the higher wheels (away from mainspring) are more important to tend to worn bushing than the lower wheels. Is this correct?

Mark: Are you saying the same thing?

 

[Willie X]

Yes, if we're talking about a linear measurement. Example, a .005" wear-over on a tiny French escape wheel pinion will probably be a problem where the same .005" wear at the barrel will cause no problem.

I think it's best to measure wear-over as a percentage. Example, a 10% wear-over is slight and probably won't cause any problem anywhere but it does indicate that wear has reared its ugly head. Conversely, a 50% wear-over is severe and can cause trouble in the present, or near future.

Attached photo is a 60% wear over on a Urgos UW66 @ T1B. This was enough to allow the weight to drop. Willie X

 

[MuensterMann]

Now, that is one obviously worn big time bushing! Is the percent worn calculated by the linear distance of the wear to the diameter of the original hole or pivot? For example, a 2mm original pivot and the distance from the original circumference edge across the new worn hole to the end of the new worn hole - thus another 1mm would signify 50%?

 

[Willie X]

I just 'eyeball' it. That one is over half the hole diameter, so 60% is a close guess.
Willie X

 

[POWERSTROKE]

That clock was still running willie?

 

[Willie X]

Yes, until the last split second, when the weight drum lost mesh with it's pinion.
Willie X

 

[TEACLOCKS]

I've see gear mesh come apart from pivot wear.
Amazing It could still run.

 

[roughbarked]

Yes, until the last split second, when the weight drum lost mesh with it's pinion.
Willie X

You waited that long to bush it?

 

[Willie X]

Peter,

Actually, when I was checking that one, I was looking at a badly worn center shaft and the customer (a good friend of mine) pointed to that T1B in the photo! Ha

That one ran 22 years and never had any attention at all.

Willie X

 

[RJSoftware]

Why are most worn bushings in top plate?

 

[shutterbug]

Speed increases wear. The lower gears run slower, but under more power. The upper run faster, but under reduced power. Gears under a greater load tend to wear more, but will overcome it more easily by sheer strength. Less wear in the upper, weaker wheels will have a greater effect because they are not able to power through it. As a pivot wears into a plate it cuts a groove the size of the pivot. And just like a tight bushing, it creates more resistance and eventually stops the train. Also wear is compounded when present in more than one wheel.

 

[RJSoftware]

bushings wear in the attempt to escape force. High pressure seeks escape into low pressure.

The gear bushings that wear out first are the one closest to power source yet have pivot/bushing/gear size ratio designed/favored for reduction of friction.

This relationship is not linear. The tinsel strength of bushing to pivot size seems to have been chosen by some convienience of manufacturing process becoming a norm. Certainly not linear progression as logic would dictate.

The slope intercept between the source escape force and bushing hole diameter tinsel strength seems to correlate 3rd and 4th gears up train.
If it where simply speed then the most bushing repair would be escape wheels and flies.

This also means resulting mesh tend to bind as force pushes too deep the mesh. A proper mesh is approximately 90% engagement and 10% relief. Teeth actually slide across each other's surfaces.

Proof is power is robbed not released as a slipping mesh would do.