Miyota stem and crown question

[Jeremy67]

I'm just trying to fix a friends Gul diver which he is very fond of and has lost the crown for.

Presumably the blob on the top of the stem is part of the old crown, yes?



Any tips for unscrewing the remains of the crown?

What measurements do I need to take to find a new crown? How do I find out the thread size of the stem or do crowns come untapped and you have to tap them?

Any advise would be much appreciated, I've changed batteries and crystals but never tinkered this deep.

Thanks

Jeremy

[Bry1975]

Hi,

A decent digital caliper or micrometer will be sufficient to measure the stem diameter which will give you the thread size.

[Jeremy67]

Thanks Bry. Calipers and micrometers I have though after my Aldi digital failed after a mere 10 years I decided to go mechanical so I now have some lovely dial calipers.

So do I understand correctly that there is only one thread spec. for a given diameter of stem so a 0.7mm thread is a 0.7mm there's no fine vs. coarse or similar compexity?

Do crowns come tapped or will it need tapping?

Is it likely the old crown has some sort of thread locking glue on, would some heat help get it off?

[Bry1975]

Generally speaking a 0.7mm thread is usually one pitch size.

Most crowns are already threaded, don't forget you can get stem connectors from Cousin's means you can use diff sized stems.

[Jeremy67]

OK thanks, it looks like the stem is 0.9mm.

There was the remains of an o ring sitting in the tube above the stem. Does this mean I'm look at the sort of crown with the threaded tube that descends 'below' the inner face of the crown, or can the 'flush' ones have o rings too?

Sorry for all the newbie questions!

[walkerwek1958]

Firstly, you need a strong magnifier to see what's what and be certain what you're seeing is part of the old crown; from you picture it looks like a stem extender but it can`t be, I assume the bit in your fingers is the business end of the stem that fits the movement!

Heat, plus two pairs of small pliers, is the way to unscrew the remains. Ideally, use brass-faced pliers to grip the thread, you don`t want to mark or damage it. You can get away with ordinary pliers provided you grip the thread where it isn`t going to be used. Two points to remember: don`t bend the stem and don`t use too much force. That's where heat comes in, a quick flash in a gas flame will soften any Loctite on the remains of the crown.

Measuring the diameter of the stem with a vernier caliper will determine the diameter; it's likely to be 0.90mm which is referred to as 'tap 9' when choosing a crown. If it's 1.0mm it's tap 10. If an identical crown isn`t available the job starts getting complicated, particularly if it's a screw down. If a generic crown's needed the stem may have to be trimmed to fit; taking a bit off's easy but adding length requires a stem extender to be fitted and that's why it pays not to damage the thread oon the stem.....now's when you may need to use it.

You may find yourself in deep water on this job if the correct crown isn`t available and it might be better to send the watch to a repairer.

Paul