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Learning how to build Lotus Seven replicas...together!
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PostPosted: December 2, 2017, 11:35 am 
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Joined: March 30, 2011, 7:18 am
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Location: central Arkansas
"Standard" Smiths cable threads are M12x1.0, but the made-in-India reproductions are M18x1.5. Which happens to be a standard spark plug thread if you need to make an adapter; spark plug taps are much cheaper than machine-tool taps.

The square drive is 1/8", same as US standard.

The India reproductions take a 3/8" push-in lamp holder instead of the usual 1/2" or 5/8" used in most Smiths. They take a BA7S lamp, which is of course British, though apparently some French cars used them as well. The tach had a bulb, the speedo didn't. And I wanted to replace all of the bulbs in the smaller instruments so they'd all start off at approximately the same brightness. eBay and Amazon to-the-door prices for replacement lamps come out fo several dollars each. A place called partsdeal.com has 12v 2w lamps for $0.31 each. But they have a $10 minimum order plus shipping...

partsdeal.com only carries 2w bulbs. Other "standard" wattages were 1.5, 3, and 4. And the bulbs were available in 6, 12, or 24V, so make sure you get the right thing when you buy.

LED replacements are available. They generally don't work with the factory dimmer. Search "PWM instrument dimmer" and you'll find lots of people have cobbled together simple circuits to dim the lights with the factory rheostat, usually for under $10.

The India gauges and most real Smiths ground the lights through the instrument case. The LED vendors sell "positive ground" and "negative ground" lamps; unlike incandescents, polarity makes a difference on the LEDs.

Most of the LEDs I've looked at were flat-faced, whereas the stock lamp projects out past the front of the instrument face. There are some extended-nose LED lamps, but most of them are colored. Moving into geezerhood, I prefer plain white lighting.

The Smiths mechanical temperature gauge uses a Bourdon tube, a long copper tube, and a bulb filled with ether. Gauge repair and tube splicing are DIY-able; there are a bunch of web pages on how to do it. This also gives you the option of splicing on the engine end of a VDO, Stewart-Warner, or Auto Meter gauge with the correct threads to fit your engine instead of using adapters for the weird British threads. (Pegasus Racing can help you out there, if you insist on adapters)

Smiths used several different bezel designs; chrome, black, angled, or stepped, with minor variations. Replacement bezels, windows, and gaskets are available, though they're expensive. Replacement faces are available, and relatively inexpensive.

Getting the bezel off to get to the gauge innards looks to be a hassle. I get the impression Smiths didn't really intend for them to be serviced. The bezel and window on my gas gauge could stand to be replaced; I think I'll buy a dead gauge or two off eBay to experiment with first.


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PostPosted: December 2, 2017, 2:18 pm 
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Joined: July 4, 2006, 5:40 pm
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Location: Novato, CA
Bezels on every Smith gauge I've ever used just twisted until the tabs lined up with the slots, then just pulled off. The only resistance might be some of the tabs clamped down too hard, but you can lift the tabs slightly with a thin screwdriver.


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PostPosted: December 2, 2017, 6:14 pm 
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Joined: March 30, 2011, 7:18 am
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Location: central Arkansas
That'd be okay; I've taken apart some no-name gauges made that way. Supposedly some of the Smiths unscrew with a fine thread and others are crimped. But those might have been old/oddball variants.


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