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Opening gauges with sealed backs - any advice?

1K views 7 replies 3 participants last post by  the-chauffeur 
#1 ·
Periodically I see how to disassembly guides for gauges with chrome/stainless rings holding the two halves of the outer cases together - you know, the ones where you use a watchmakers screwdriver, paint can opener or other suitable picky-tool to prise one side of the ring up? Generally, they're the types of clocks you find on later CB/CL350s and the K2 SL350. Those guides are great, and I've just done something similar with a CA77 speedo so I could clean up the face.

Unfortunately, I've got a set of gauges that I need to overhaul that are different. They're from an XL350 K0, but the same outer case design was used on the SL350 K0 models (I suspect they shared the same clocks with earlier CB/CL's as well). The lens on the front of the speedo is cracked, and both the speedo and tacho faces have faded. I'd like to get them apart, tart them up, clean the number dials and sort out the lens issue by swapping in another lens. But as far as I can make out, they're sealed with no separator rings. I'm not entirely sure how they were sealed; they look as though the backs of the cases have been fused with the fronts. No photos right now; I'll try and add one or two later.

I don't recall seeing any guides for these types of clocks - and maybe for good reason - but I'm wondering whether anyone's pulled any of the sealed type apart and if so, is there a non-destructive way of getting into them? I have a nasty feeling I'm going to have to end up butchering the plastic around the area that will ultimately be hidden by the rubber cushion in the chrome housing and somehow gluing the bits back together when I'm done . . . but if there's a better way (or at least one where I'm less likely to crack or break something) it would be good to know about it before I charge in with some sort of cutting tool.

Any/all ideas gratefully received. And thanks in advance.
 
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#2 ·
I’ve opened one of the exact gauges you are referring to on my ‘74 XL350. Unfortunately I cannot find any photos of the surgery I did on it. I do remember using a small cut off wheel on a Dremel tool to cut around the base of the housing where it is hidden behind the chrome ring. Seems like I had to move quickly to cut or else the wheel wanted to melt the plastic instead of cut. I believe I used JB weld to seal the housing back together once repairs were made. The JB weld was easy to shape and sand smooth once it was hardened. The chrome base trim covers to hide the repair once it’s all back together. I consider it a successful repair and I’ve had no trouble with it over the last 5 years or so since I did it.
 
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#3 ·
Thanks 12.

Don't s'pose you noticed how the case 'halves' were originally held together when you eventually got inside, do you? I've found what I think is the joining seam close to the bottom edge, and I'm working around it with a razor blade. I've got a little way in all the way round, but I'm not convinced it's going to help much. I have a feeling the halves were either glued or fused together in some way.

Cheers
 
#4 ·
I did not notice or pay attention to how it was secured, sorry. I do remember making my cut along a seam, probably the same one you are working on with a blade. Once I was inside I just did the cleanup necessary to get the speedo working again. My inclination is to say it was glued or fused somehow as you suggested. As you know none of these instruments were really ever designed for us to get inside of. We’ve just all craftily figured out ways to get in over the years. If it helps, tomorrow I will loosen the nuts and pull the speedo out of the chrome ring and take a photo. That way you can at least see the work I did. I can also show you the photo of it installed and how it’s virtually impossible to tell the work was done.
 
#6 ·
Success. After about an hour of repeatedly running around the joint groove toward the bottom of the outer case with a razor blade, it came apart. The joint line is basically the thinnest point of the case, and just behind it sits the flared edge of the metal part of the casing. The joint itself is no more than about 1-1.5mm deep; cut through that and you're in. I persevered with the razor blade because I was a little concerned that other cutting tools might remove too much plastic, and it turns out to have been a pretty good call. The plastic ring you're left with is very thin, and despite being very, very careful, I can already see a crack in mine. Nothing that can't easily be fixed, but that stuff is really fragile.

I'm still none the wiser as to how that ring was originally sealed onto the rest of the case. There's no obvious signs of adhesive of any kind and the jointing is so clean I can only assume it was some form of heat/pressure process. I've marked a couple of places on the ring and the main case for alignment purposes, but given that the lens is badly damaged on this unit, I doubt I'll be using it again. So I'll move onto the next couple and see how I fare.

And even at this stage, I can see reassembly being a job that needs to be done carefully. Quite apart from lining everything up (like trip rest knobs and so on) the flared edge of the metal case half only fractionally extends over the outer plastic case. I'm guessing I'll need to line that up using small quantities of superglue to make sure it's central, let that set up, and only once that's set in place try sticking down the retaining ring.

I'll post some pictures when I've got better light.
 
#7 ·
Glad to hear you made it inside. Especially since I spaced today and totally forgot to pull mine apart and photo for you. I don’t guess that is necessary now. I look forward to seeing your handiwork.
 
#8 ·
Supplementary gauge question: any suggestions on safe cleaning products for the number rolls?

The number rolls - particularly the white one - have some discolouration on them. I'm not convinced it's fading, 'cos it's brown - it looks more like grease from the mechanism that's escaped over time - but whatever, it looks pretty crappy. I've tried acetone and that's turned out to be w-a-y too powerful, so before I lose any more numbers (d'oh) I'm looking for advice from anyone who's cleaned theirs as to what sort of cleaner they used. Like some old computer cases, I'm wondering if it might need some sort of retrobrighting, but for obvious reasons I want to be really careful . . .

Thanks
 
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