The other thing

In our last episode your local horologist was fretting over corrosion on the Peter Green clock. Paul, the owner, had decided to pull us up out of that rabbit hole.

There was another issue that presented itself rather early in the examination of our Danish friend that was both more concerning and far more subtle to see.

This brass jockey was gaining a richer understanding of what he lovingly referred to as the "snail unit" ie. the whole gizmo that encompasses the inner and outer snails and the wheel behind them. 

It was that large wheel at the back of the snail unit and the little pinion gear above it that caught the eye.

There was something off... in there.

In the photo below the pinion is hard to see as it is covered by a hand cut brass washer with a copper wire to anchor it.

But can you see the issue? 

Here's a tighter look at another angle.

See it now?

What we have there is a rather severe depth problem with the meshing of the teeth of the big wheel and the little pinion.

Here's how a wheel and pinion should align and make contact:

from Advanced Watch and Clock Repair by H. G. Harris

See how the teeth from the pinion and the wheel are meeting at the pitch point. This is the optimal "depth of engagement" for the meshing of those gears.

When that meshing is too deep it can lock up the gears. Too shallow and the gears can lose power, create considerable wear on the pinion or it can even slip and fail outright.

from Advanced Watch and Clock Repair by H. G. Harris

The depth of engagement between the pinion and wheel on our Peter Green... 

Way, way too shallow.

Look from this angle.

That is considerably worse than the Too Shallow example in the diagram above. Furthermore, and almost certainly as a result of the shallow engagement, there is a LOT of wear on the teeth of the pinion. There are grooves cut in each tooth of the pinion, almost filing each one down to a sort of point.

This is not good. 

If left unaddressed, that pinion could become severely damaged and a repair to it would be a considerable effort.

Zo!

A. What is causing the depth problem?

B. What to do about it?

C. What does Paul want to do?

A call was made. A discussion ensued and an agreement was realized that the problem was serious and needing remedy.

But what was causing this and what to do?

YLH said he had an idea and would get back to Paul.

There's a clue in the very first photo of this post.

Here's a slightly different and tighter version of that photo.

What's that gap about?

Well...

Remember our snail unit? (Technically it is the hour wheel.)

Its center is a hollow tube such that the whole unit slides over the center arbor and cannon pinion.

A little blurry but you can see here the tip of the center arbor and its squared edge to which the minute wheel attaches. Then below that the center arbor passes through the barrel of the cannon pinion. 

When seated in the movement the hour wheel bridge barrel slides over the center arbor and cannon pinion continuing over the hour wheel bridge barrel and coming to rest against the base of the hour wheel bridge. 

It's that hour wheel bridge barrel that seems to be... drooping and creating the gap which misaligns the hour wheel barrel when it is slid onto it.

How did that misalignment come to be?

The reason is likely lost in the past. 

Back to our problem…

If that hour wheel bridge barrel could be angled up a bit (closing the gap) then properly centering around the cannon pinion, it might have the effect of lifting the hour wheel upwards enough to increase the depth of engagement between the pinion and the wheel.

Here's a composite of two pictures of the hour wheel bridge removed. 

How to adjust the barrel to bend upwards just a bit?

This is heavy duty brass. Butter hook* might break something.

The clock doc needs to tilt that barrel angle upwards just a smidge.

Wait! Ah ha!

A shim.

A call was made to Paul with a proposed repair. Not a perfect solution but one that should ameliorate the issue considerably and would be non-destructive.

Thumbs up!

The solution?

YLH loves painters tape. 

Cut to fit and layered along the bottom edge of the hour bridge feet. A couple of tests were made and two layers of tape did the trick.

Then the cannon pinion was screwed back down and the snail unit slid on top and...

Voila!

The gap is effectively eliminated.

Now how about the depth of engagement between the pinion and the wheel?

Clearly improved.

Could it be even deeper? Sure.

Will it suffice for now? Yes. 

A couple decades of use? Probably.

Paul was thrilled. 

YLH was thrilled.

This being the final, approved repair on the Peter Green by YLH, the clock was fully reassembled, tested and then returned to the happy owners.

For now.

YLH misses the bell chimes.

* An obscure reference to a line from Live and Let Die