Hi Folks. I have a 16 size 15 jewel Waltham pocket watch which I have completely rebuilt. I have meticulously cleaned and oiled, but unfortunately the watch is running about 2 minutes every 24 hours slow, even on maximum adjustment. The balance wheel, hairspring look perfect and amplitude seems excellent. Here is my question: Is it possible for the watch to run slow if a stronger than normal mainspring is fitted?, I was thinking about increased amplitude?.
Thanks, Steve.

Check to see that the regulator pins aren't too far apart and the hairspring is not bouncing very far between the pins. You may just have to close up the regulator pins a bit and that will speed up the watch. If that doesn't help, assuming all else is good, then the balance vibration needs to be checked.

The short answer to the increased amplitude question is no, increasing amplitude does not slow the watch. Think along the lines of a tuning fork. It always has the same pitch regardless of how strongly it vibrates.

Stephen, after you make sure the regulator pins are properly gapped to contain the hairspring without free-play, adjusting 2 minutes a day fast or slow is easy because your 16a Waltham should have at least 1 pair of mean time screws which to speed it up 2 minutes can be adjusted in 1 full turn. If you have a higher end 15J with 2 Pr., you need only adjust each of the 2 pair in 1/2 turn and this should bring your time in closer. if that makes the watch run "too fast", just back them out a bit.

ALWAYS remove the balance cock, mount the Cock/Balance wheel assembly on your watch makers pin, carefully hold the Balance wheel and adjust the M.T. Screws with a timing screw tweezers as pictured below.

Hint, when on the watch makers pin as pictured, adjusting the regulator pins are also very easy.

Well guys, I learn something every day!. Thank you Roger and Dave for taking the time to reply and I will remove the balance cock and carefully tweak the screws one full turn inwards. The balance wheel has one of these at each end of the cross shaft.
As you can gather I am no expert but am learning every day.
This is a superb site and I am in gratitude to you both.
Warm regards from the UK.....Steve (wyvillman).

As usual, Dave supplies a great graphic for the meantime screw adjustment. Glad your watch has these screws...it makes it a lot easier than going thru the vibration checks and deciding whether to shorten the hairspring or lighten balance screws.

Stephen, although your comment indicates your watch only has 2 meantime screws at the balance arms, for the future you should know that adjusting meantime screws that are 90 degrees from the arms (on a cut balance wheel as shown above) will affect the temperature compensation and should not be done (assuming they haven't been touched since they left the factory).
Mike

Michael makes in interesting point as Hamilton's Mean time screw adjustment chart refers us to all 4 screws when timing watches. There has been much discussion about those "mid" screws along with the importance of understanding consistency of "Rate" error as opposed to "Daily Deviation" . . .

Thank you all very much indeed. I have today succeeded in regulating the watch, but it took two goes. I ended up having to turn the meantime screws two full turns (720 degrees) and now she is running beautifully with the micro adjuster in the middle.
I will carry the watch around with me over the next few days and see if any small adjustment is required...........top site, top people.
Thanks so much......Steve.

The finished watch!!

Another pic.

Magnificent! The dial and hands present handsomely

A top accolade indeed from a top watchman David. I assembled the watch in bits and bobs really and was thinking of giving it to my son who gets married next July. The watch has a new mainspring all greased and ready to go. Steve.

One more, with matching blued hands....

Very nice Stephen! Glad you were able to get it adjusted nicely.

Thanks Roger.....