Walkthrough of a Dixmont Guangzhou DG2813 Service
Why is amplitude Important
- Amplitude is most desirable at least 270 degrees in the DU and DD positions
- A high amplitude indicates that the watch is clean overall and watch components are healthy
- A high amplitude diminishes the biasing effect of poise errors
- Poise errors are largest when amplitude is low
- Poise errors are equalized when the amplitude is 220 degrees
When servicing a vintage movement, always, always use a new modern alloy mainspring. You just pop them in, no cleaning, no lubrication needed. If you are not doing this, there is no reason to read any further. Nothing else matters is you are not starting off with enough power from the barrel.
If installing a new manual wind mainspring, there is no more lubrication needed. Automatics need braking grease, but we will get to that in a minute. And for God’s sake, do not drizzle oil over the mainspring while it is in the barrel like I have seen some people do on the Tube.
The Mainspring Barrel
You can play around with mainspring sizes.
Do not be afraid to experiment with different mainsprings. Do not assume that the mainspring you are taking out is of the correct size either. Vintage watches have usually been worked on many times and you cannot assume everything is correct.
If needed, you can use a higher strength than what was originally used. You may need to reduce the length a little and give up some power reserve, but who cares if you are only getting 180 degrees for 50 hours, right? Using a mainspring with more torque can help overcome the inevitable wear in vintage wheel teeth and pinions which robs amplitude. More on that later.
Use a stronger braking grease on automatic barrels.
If you are using 8213, step up to a stronger grease like 8217. This will give the mainspring a little more holding power before the mainspring slips and more amplitude.
The barrel requires a close examination of the side and end-shake, not only with the barrel inserted into the plates but also between the arbor and the barrel drum’s bottom and lid.
Start by looking for wear above and below the barrel which would indicate excessive side shake. The arbor holes in the plates can become oval in shape robbing amplitude. Depending on how bad it is, arbor holes can be closed up, but will usually requires either replacing the bushing, if it has one, or by reaming the hole and installing a new bushing. If the problem is in the bridge or main plate hole, it can be replaced, if you can find a good bridge that does not have the same problem.
Check the side-shake of the arbor inside the barrel.
With the mainspring out of the barrel put the arbor back in and test the shakes. The arbor hole in the barrel lid and drum can be closed with a staking set. When you close a barrel hole like this, broach from the outside of the hole in. Since the smoothing broach is tapered, this creates an oil reservoir between the arbor and arbor hole.
Check the end-shake of the arbor in the barrel
Hold the arbor in a pin vise and spin the barrel on the arbor. Is it spinning freely? It is not uncommon for the bottom of the drum or the lid to be bent out. This is often caused by pushing on the arbor end when opening the lid. When bent out, the lid or drum bottom can rub on the plate and bridge, robbing amplitude. When they are bent in, the added friction on the arbor and/or mainspring creates friction and will reduce the available amplitude.
If the barrel drum bottom or lid is pushed in, it can be corrected by pushing on the opposite side of the arbor so that the arbor pushes against the lid or bottom, returning it to its correct flat position. If the bottom or lid is pushed out to far, that is best corrected with a staking set if you have one, but you can use a piece of peg wood in a pinch.
Polish the Barrel Holes
Today in watch repair changing the barrel complete is often standard practice. That is fine for newer calibers but what about vintage movements. Since most vintage watches do not have jeweled arbor holes, you have to deal with the wear between the two metal parts. When you look at the wall of the barrel holes you will see the micro scratches from dirt and grim and these need to be polished out. Using a .5-micron diamond paste works well for this. I insert a toothpick into my rotary tool and load it with diamond paste and polish away. Be careful not to use anything to heavy as you do not want to make the hole larger, increasing the side shake. You just want to polish it.
Same with the arbor itself. Hold it in a pin vice if you do not have a lathe or old school screw polisher which is what I usually use.
Inspect the barrel lid and bottom for wear
Wear in the barrel and lid come from dirt and grit that was left inside when the mainspring was put in. I do not know of a good fix for this issue other than just replacing them.
Another cause of this wear is from the mainspring being coned. This is caused by the mainspring being hand wound into the barrel which is obviously bad. When you hand wind a mainspring, it loses it flatness and cause the mainspring to ride higher in the barrel and rub the lid, robbing amplitude, and wear.
Inspect the barrel teeth
Since the barrel transfers the power from the mainspring through the barrel teeth this is your next inspection point. Dirt and grim can cause wear between the brass barrel teeth and the steel leaves of the center wheel pinion. Usually, this wear will be on the barrel teeth, but it could be both.
The Power Train
Inspecting wheel teeth, pinions and pivots should be part of every service regiment. The wheel teeth and corresponding wheel pinions are designed so that when the tooth and pinion are going out of contact a new pair (tooth and pinion are coming into contact. This provides a smooth almost effortless transmission of power resulting in high amplitude. As the brass from the teeth wear, the geometry is changed resulting in a gap between the tooth and pinion which causes a binding between the teeth that was not present when new and loss of amplitude.
Gear wear can be expected in a 50-year-old watch which is one reason I suggest using a stronger mainspring when needed.
With the barrel and wheels in place and before the pallet work is installed, check for backlash.
When you spin the barrel, the wheels should move in one direction then reverse to the other direction. This lets you know the pivots are straight. If you are not getting the backlash, then you need to take the wheels out and starting with the barrel and center wheel check their rotation. Add another wheel and check it again until all the wheel are in place, or you have found the faulty pivot.
Inspect the pivots
Pivots in jeweled holes do not usually have the same problems with wear around the pivot as in a non-jeweled hole, but they will not be as polished as when they were new, robbing amplitude. adding friction Pivots can be polished on a lathe or a Jacot pivot polisher. Pivots that are turning in non-jeweled holes tend to be worn down thinner at the contact point of the pivot, causing excessive side-shake and lower amplitude. This has to be corrected by either re-pivoting the wheel or filing and burnishing the pivot so that it’s straight again. Of course, if you reduce the size of the pivot, you then need to correct the pivot hole size.
Straightening Bent Pivots
Trying to bend hardened steel usually results in a broken pivot. Seitz and Bergeon pivot straighteners should be renamed Pivot breakers as I have never been able to use on successfully. In theory, you could temper the steel, try to bend it back into position then re-harden the steel but who does that. The biggest issue is really being able to make a 0.01 mm adjustment by eye. Replace the whole wheel or repivot it.
Inspect Pivot Holes
When inspecting jewels shine a light under the jewel. This illumination will make crack stand out even more. A jewel does not need to be shattered to cause an amplitude problem, even one that is cracked will increase friction and should be replaced.
Make sure all pivot holes have been pegged.
Non jeweled holes that are out of round from wear will need to have a bushing installed. This goes hand in hand with the worn pivot, so if you see one then look closer at the other.
Since the forces of the two horizontal positions are the same, the amplitude should be within a few degrees of each other. This is required to be able to regulate the rate in multiple positions.
If the horizontal positions differ you likely have an issue with either one of the end stones which is not flat or is pitted from non-lubricated operation, the end-stones have been mistakenly put on the wrong side or the balance wheel/spring is rubbing on something in one position but not the other or the lubrication differs from one side to the other. All of these can be seen through both rate variation and loss of or fluctuating amplitude.
Other Possible Causes
- One pivot is bent.
The tip of the balance pivot is domed and rotates on the end stone. If one pivot is bent, it creates added friction that should not be there and a loss of amplitude.
- A Jewel is dirty or lubricated differently.
You have to clean and polish the end or cap stones. I have demonstrated this many times and it
only takes a minute. Oiling the end-stone is fiddly work and take patience to do correctly. Microscopes come in handy for this type of work.
- The balance jewel is cracked, loose, pitted or out of flat
- One pivot tip is flattened, and the other is domed
This can happen when lubrication has been drawn away from the end stone and the tip of the pivot runs dry. They make tools for both rounding and flattening pivot tips. I prefer to round them instead of flattening them out.
- The regulator pins are not parallel or flat to the regulator
When the pins are not parallel, the balance rides differently in between the pins when changing the horizontal position, effectively shortening the balance spring in one position.
- The hairspring is out of flat or not centered on the collet
Same as above
- The banking pins are not perpendicular to main plate, so the run-to-banking varies
The run to banking is the distance between the “End of the Drop,” when the escape wheel tooth, “Drops” onto the locking plane of the exit jewel and when the pallet lever makes contact with the banking pin. If this distance varies, there is a loss of amplitude. This is most common on adjustable banking pins and can be adjusted either by turning the eccentric screw or bending the banking pin back to the correct position.
- A variation in the end-shakes between the escape wheel, pallet, and balance wheel can create an array of DU/DD differences
One of the more common issues is that the pallet fork guard pin is dragging or hitting on some part of the main plate, or the guard pin is hitting the safety roller and causing friction and loss of amplitude.
- On high beat movements, wear on the pallet forks point of contact area with the solid banking, (milled into either the main plate or pallet bridge) can cause big loses of amplitude.
- The impulse pin is too small for the pallet fork slot
If an impulse pin was replaced and is too small for the fork slot, there is a loss of energy and of course loss of amplitude.
You May Also Like...