Mainspring stronger than spec. Bad for jewels, etc.?

[MrRoundel]

Greetings, all.

I recently bought another pocket watch. Not that I needed another pocket watch, but we know how that goes, right? As I inspected it prior to tearing it down, I noticed that the lower center-wheel jewel was cracked. It looked like the watch would still run as it was, and the back of the arbor didn't look damaged, so with oil I figured it will be OK. I then found a broken upper balance hole-jewel. When I let down the mainspring, it seemed to have an inordinate amount of resistance. Measuring it, I found that it was a bit too strong. It was a Dennison 4 when specification is for a 5. This amounts to about .02mm in thickness. Other jewels looked OK on this 19J watch, but the two damaged got me thinking, especially the lower center jewel. Does using a significantly stronger mainspring make it more likely to damage jewels? Granted, the center jewel was probably damaged by not supporting the lower arbor when replacing the canon-pinion, and the upper balance hole jewel would have been from some other trauma, I was just wondering about whether an overly strong mainspring would put enough added stress on the jewels to actually damage them. Thoughts?

Unfortunately, the watch shows other signs that work which was carried out with less-than-finesse in the past. I guess this one won't be a quick complete fix, and  may stay on the "ticking wounded" list for a while. At least the size of the watch makes the easy stuff easier. Cheers.

[khunter]

I don't think that a stronger spring can do damage besides speed up wear. A lot of the old pocket watches were repaired using springs that just "fit", either because of expediency or lack of knowledge. I agree with your assessment that the lower center jewel was probably damaged when the cannon pinion was pressed on, I've seen a few on watches with no other evidence of foul play so it's about the only explanation. It pains me sometimes to see the shoddy work that has been done to some of these otherwise fine pieces.

[JohnR725]

Mainspring strengths are interesting specification. If your pocket watch is old which I assume it originally probably came with a blue steel spring. The original blue steel Springs are always weaker than the modern white Springs. So for the same thickness the modern spring is stronger.

So typically the wrong thickness of a mainspring worst-case will give you running problems. Either are not enough power to run the watch or too much power Which causes the balance wheel to have too much amplitude. But neither these conditions cause the watch to self-destruct and break their jewels

What are you jewels made of? Quartz crystal was popular at one time Garnet, natural Sapphire synthetic sapphire. With some of the natural stones you'll see fractures or cracks in the stone or at least they look like that they don't seem to be a problem. Anything that looks like a serious crack breakage sapphire is usually a impact. Most common impact on a pocket watches somebody dropped. Then of course unfortunately for watchmakers they're only human and accidents can occur which results at all sorts of things breaking unfortunately.