Tip & How-To about Watches
-One of the most common stoppage problem is caused by increased friction and mostly due to lack of incorrect amount of or lack of oil. If discovered in time, the movement can be cleaned and oiled with only high quality Clock oil, then it will be good for another 5 years or so. Insufficient lubricants eventually cause wear in the pivot holes and/or bushings.
-After a pivot is worn it will change the depth of the wheels and pinions to such an extent that the power train will stop due to improper gear meshing. Wear causes a pivot hole to become egg shaped.
HOW TO TEST
-One testis to completely let off the power from the power train and rock the main wheel back and forth. Then you will clearly see the pivots that have the problem jumping back and forth.
Examples of EGG Shaped pivots above.
WHEN DO YOU NEED BUSHING REPLACEMENT?
-One rule of thumb used by many repair persons, if a bushing is worn one third or more the diameter of the pivot it needs to be replaced.
-Above is Two example of a worn pivot's [note the black gum med up oil around the pivot in photo above]. This is a dead give away of a potential problem.
-Before disassembly, mark all bushings that need replacement in the correct geometrical direction of centerline.
-Complete disassembly of movement is required.
-Then you will need to file out the exact opposite direction with a small file, this will ensure that when you start drilling out the hole it will be centerline.
-Set-up the drill press and lock the plate on to the drill press making sure you find the centerline of the original pivot hole. Use a steel short stock the same diameter of the old pivot and chuck it in the drill press after the plate is secure, select the proper bushing that you intend to press in.
PRESSING IN THE BUSHING
-With a small broach taper slightly the inter plate before the insertion of the bushing. Do this from the inside of the plate, this will ensure that the bushing will never fall out.
-Select a bushing that is a bit undersized after it is pressed into place, then open the hole up to the correct diameter.
-Use the drill press to push in the new bushing from the inside plate out.
-Be sure to broach out the pivot bushing in both directions, this will leave the hole in an hour glass shape ”===)I(===” and will reduce friction.
- Counter Sinking is very important and not only needed to hold the oil in place but also to reduce the amount of actual friction on the pivot. [Note:] don't get carried away the first gears tend to have a lot of torque on them and a lot of bushing surface is needed; however, the final pivots do not and are very sensitive to friction.
-Barrel Bushings, these are often overlooked. This is an example of a bushing before and after replacement.
Hope this tip helps.
Posted by David... on
Jun 11, 2011 | Watches
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