Possibly silly question: Tachometers

[PHPaul]

The bezels on the tach and speedo on the GT are VERY yellow and crazed. I buffed them up with a headlight polishing kit and it helped a lot but they're still pretty nasty.

I have a really pristine set of gauges off my parts Yahama XS650.

The question is, what are the odds that the tachometer will be suitable for use on the GT? I'm guessing they're much like speedometers and it's all about the gear ratios that drive the cable.

[bpeck27]

I cleaned up the lenses on my tach and speedo last winter by wet sanding the lenses, THEN I finished them off with headlight restorer. I started with 600 grit and went progressively finer down to 2000. I changed the water every time I changed to a finer grit. It took the better part of a Sunday afternoon, but it was worth it. I can actually read the gauges at speed now, even at night.

[PHPaul]

Okay, so a bit more surfing comes up with this tidbit: The tachometer drive on an XS650 uses a 1:5 ratio. That is to say, for every 5 revolutions of the crankshaft, the tach cable turns once.

So the next question is, how does one go about finding the drive ratio of the GT550?

I suppose I could get a ballpark figure by watching the tach cable connection while turning the crankshaft with a wrench. Easy enough to do with the engine on the stand.

Edit: It's pretty clearly 1:4 on the GT. Poop. So much for that idea.

[Coyote]

Done it several times. Take the gauges out of the shroud. Work where you can be messy. Get a bowl of water to keep things very wet. As said above, start with 600 grit paper and sand in a circular motion till it looks evenly destroyed. Move up a grade, get fresh water and start again. The trick is every time you move to a finer grade, get all the scratches out from the previous grade. After the 2000, I use plastic and plexiglass scratch remover. You won't believe it. they will look brand new! Don't rush it. Takes about1.5 hours per gauge.DO NOT use power equipment. You will melt the plastic. Ask me how I know.

Here's a before and after. So bad I had to start with 400 grit.

[PHPaul]

That's about what mine looked like. I did a quick-and-dirty with some very fine rouge and a rag wheel (being very careful not to melt the plastic, BTDT) and they look much better, but not nearly as nice as yours.

My problem is the crazing/cracking deeper in the plastic. I'll see if I can get a decent picture of it.

Edit: Looking closely at yours, I'd say mine is about the same. I have the various grades of wet 'n dry paper from polishing the cases on the 650 project. Perhaps I'll get bored enough to try your method, it's going to be a looooong winter...

[Coyote]

My problem is the crazing/cracking deeper in the plastic

You can't get those out. You won't see them if you look at the gauge straight on, but they show big time at an angle. Replacement is the only fix for that. It is however a lot more work. Glass is preferred but I did a couple with Lexan that came out OK. You need access to a lathe to face off the amount you are adding back, plus you need to remove the gauges from their 'cans'. If you look at the back of the gauge you will see a hardened ring of green glop near the outer edge. You need to scrape all that off and the guts will come out. I replace with 2 part epoxy paste.
Here's a pic of the ones I replaced with Lexan. Scuffs a little easier than I thought it would:

[Alan H]

Or you can do as I had to with the clocks on the 550K which had completely opaque one side, and the other had a hole in.
Cut the non see through polycarbonate 'glasses' out with a dremel and make sure the lip that they are glued to is clean, then get some 3mm glass cut to the correct size to fit nicely. These can then be bedded with a smear of silicone to keep any moisture out. Glass never deteriorates and it's a helluva lot easier than polishing.
Of course, if you're a purist it might not 'do'. I'm not, I'm a practicalist, so it's fine.

[PHPaul]

Oh, I'm all about practical. I'll look into that option as well.