Care of Tachymeter and other plastic chapter rings.

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Seiko7A38
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Care of Tachymeter and other plastic chapter rings.

Post by Seiko7A38 »

I've recently posted a couple of examples of Seiko 7A38-706x's fitted with non-original replacement Tachymeter rings in this thread in the eBay section - as salutary warnings, to highlight their non-standard elements to potential buyers. :idea: One remains unidentified; the other evidently came from an Orient / Racer J39908-70 donor. It begs the question why the sellers needed to fit something else. The simple answer is: like many other vintage Seiko parts, the correct original spare part is obsolete and no longer available. Here's what may have become of their missing original components ....

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Re: Care of Tachymeter and other plastic chapter rings.

Post by Seiko7A38 »

Seiko 7Axx Tachymeter - or other plastic chapter rings (e.g. minute marker) usually get accidentally cracked, damaged or broken by inexperienced tinkerers, novice modders, franken builders and wilful bodgers alike, for various reasons.

As we know to our cost, most 15J quartz chronographs need serving at some point. The 35+ year old oil in the jewels, originally intended to lubricate, gradually picks up dirt, thickens and the watch eventually succumbs to 'old sticky oil' syndrome and refuses to run. A quick means of establishing this, though only ever a 'temporary fix' is to leave the watch somewhere warm overnight (I use the airing cupboard above my hot water tank). Others have been known to leave the watch on top of a radiator, or use a hair dryer / heat gun. This may give a more immediate result, but the rapid heating of the watch case can cause the plastic dial ring to warp and shrink. There are a few examples in this old forum thread:
3 W's - a Warning about Warming and Warpage. Although patience is not one of my virtues, I've never personally made that mistake in haste. However, a few years ago, I inadvertently bought a watch off eBay that had suffered at someone else's hands. This is (or was) the plastic dial ring spacer from a 7A38-713A (the main reason I never rebuilt that watch):

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Here's what looks like another example of heat-induced warpage in this new UK eBay listing for a well-worn 7A38-704C:

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As a general rule (though certainly not in all applications), the plastic Tachymeter rings in Seiko 7Axx's are sandwiched between the upper case flange and the bezel - effectively fixed in position, but free to rotate. They have various small locating lugs molded into their undersides, designed to mate with matching cut-outs around the perimeter of the dial plate. Careless folk will sometimes remove the dial / movement (for whatever reason); not notice that the Tachymeter ring has slipped and replace the dial / movement without correctly re-aligning it (with '60' above the 12 o'clock mark).

This does generally not hold true for most Orient and Racer J38 / J39's and Yema N7's and N8's. In the majority of these watches, the Tachymeter ring sits inside the watch case, immediately above the dial, similarly located by molded lugs and cut-outs, so that when the dial / movement is withdrawn, the chapter ring drops down with it. However, they don't always cleanly come right out. Usually, I've found with most Orient / Racer J39's, that the plastic dial ring fouls on the ends of the pusher tips and the crown tube. I suspect it might be persuaded to pass these obstacles, by squeezing and twisting it, but for the sake of a couple of minutes extra work and peace of mind, I always remove at least two, if not all three pushers, to facilitate its removal. Here is a classic example of 'how not to remove it' from an eBay listing in September 2020, for a possibly franken Racer J38906-70, by Spanish watch botcher scufutzz.

Racer-Orient-J38906-70-7A48-Franken-HeadOnly-eBay-Sept2020-2.jpg
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Yema N8 dial rings usually come out cleanly, dropping down with the dial / movement. Risk of fouling hands as they do. Particularly Kamatz and Jaz N8's (smaller diameter rings). However handling them requires care. The slim Tachymeter rings used in dressy white dialed variants frequently yellow with age. Meaning they're likely to be brittle.

Disregarding the 'diver' variants, which sometimes need their rotating bezels removed, to enable you to replace a crystal, with conventional case designs, there are two ways of going about it.


Here's a possible example: an otherwise decent 7A38-702H listed recently by a US eBay seller; its description included:
The tachymeter is broken at the 3:00 position. I am selling for parts and/or repair because of the tachymeter.
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Cleaning underside of crystal (sometimes slightly fogged), from inside the watch case, with the Tachymeter ring still in situ. Beware of using proprietary household glass cleaning solvents, e.g. Windolene. Contain vinegar = dilute acetic acid. See this thread: viewtopic.php?p=1043#p1043

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Taking longer than I thought. :roll: Finish editing next week. ;)

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