Bunn Special demonstrating low amplitude problem

The 60-hour Illinois Bunn Special on the left is diagnosed as having a so-called low amplitude balance problem, poor motion or not a full enough swing of the balance wheel, while the Bunn Special on the right demonstrates the right kind of amplitude. The difference is clearly visible. Í have read somewhere that the swing should ideally be around 1 1/2 turns (270 degrees to either side of rest), or at the barest minimum at least a full turn (180 each side of rest). With such a low amplitude the power from the mainspring is not being transferred wholly through the train to force the balance to have good full swing. It can have many causes, from a bad mainspring to dirt in the jewels, pivots, wheel teeth, barrel and so on. A movement with such a low amplitude is in need of service.

[@jafi8120]

I have a few antique and vintage American pocket watches and I can set down and watch these movement's tick away all day.

[@stearman]

When a watch or aircraft clock comes in with this issue it is most often gummed up oil and dirt being the cause. After it is properly cleaned and reassembled and you still have this problem, the cause is most often a weak or "set" mainspring.

[@Wepouaout]

Yes, the spring needed to be replaced. At the same time gave it a normal overhaul with cleaning, oiling, timing and such. It is working again like clockwork.

[@Limou551]

SOmetimes looks like it is fixed and later the problem appears. Sometimes clean/oiling is just hidding the problem..

[@innocentoctave]

"Like clockwork"...

[@Mars-zgblbl]

@@Limou551 Is it best to put the watch on the timegrapher before any service begins? What types of problems can be masked by servicing?

[@TheTinker6871]

In my 40 plus years in the trade, underpowered mainspring is not the most common cause of low amplitude. Dirty, dry and gummed up is the first thing I look for. I almost always clean the watch before I replace parts. Many old mainsprings have plenty of power to do the job.

[@Limou551]

Indeed.~
They are only useless when they break.

[@user-wv1pj6wh4h]

mainspring is not the cause but its the barrel..

[@mrrobot6757]

If this were my watch id first clean the cap jewels on the escape lever bridge and the same jewel onnthe dail side... also the escape wheel also has a cap jewel... also balance cap jewels are a must clean for alll 100 year old watches... ✌🏽🇨🇦

[@mnpd3]

I've heard all kinds of reasons for low amplitude, and while I'm not the most experienced watch dude, every case of low amplitude I've seen was caused by an underpowered mainspring. But, this is true only for old pocket watch movements. The more modern wristwatch movements with the problem usually wasn't the mainspring. Just being dirty with old oil seems to be the number one cause there.

[@Limou551]

sometimes overlubed, or bad lubed

[@lordofbees9067]

@@Limou551 Or something bent

[@user-wv1pj6wh4h]

@@lordofbees9067 most aprt of time wear in ger train

[@Limou551]

thas not barrel for sure...