Absolutely. It's funny that motorcycles so over engineered and robust must rely, in at least this one example, on such a delicate mechanism.

Once this repair is finished, quite literally the only part of this machine that I will not have repaired, refurbished, maintained or modified will be the bottom end. Wonder how long she'll go before she needs new roller bearings and a camshaft?

 

Until you get bored again, LOL.

 

Ha! Exactly...

In fact, I'm actually so oversubscribed with home improvement projects and other demands on my time that I'm not eager to have a big task like tearing down the engine added to the pile. After rolling her around on the jack for months during the initial build, I was very happy to finally have her running. But when the bottom end does need attention, which I hope will be several years from now, it'll be a fun project. Just not right now!

 

Sorry for the pause, but life is again intervening...

Got a chance to examine the new parts: I chose the J&P $11.00 kit w/free shipping, which has some differences from what was on the speedo--which looked like someone had been in there, judging from the lousy crimping job. First image shows the old and new stuff.

First, the new glass is a touch smaller because as you can see in the second image, the outermost, square-section O-ring has a groove in its center I.D., so that the O.D. matches that old glass, which merely sits inboard of the old square-section O-ring.

Second, while the opening to view the dial is the same diameter, the height of the lip into which the square-section O-ring fits is nearly twice as tall (.055" vs. .1050") --presumably to accommodate the double thickness the new style O-ring.

Third, the crimping lip is taller (.2030" vs. .1430"). However, the old lip is so chewed up from being reused that I don't know if this is true, strictly speaking.

There is still some flex in the inner round-section O-ring, so as you can see in the third pic, it looks like the case would j-u-s-t fit in sufficiently to crimp. But it's gonna be close. The inner O-ring's cross-section is .180". and I.D. of the inner reflecting ring in which it sits is almost exactly 4".

The closest McMaster Carr has is 1/8" cross section, or .139" actual (fourth pic). There are a range of materials to choose from, and it seems to me in this application a regular oil-resistant Buna O-ring will be fine. That said, I can get a soft compound, oil-resistant version in .210" actual that might squish sufficiently to work. Problem is you've got to order a pack of rings, and they're much cheaper in the .139" actual, which I know would fit--and it's hard to mash the combination down enough to get sufficient metal to crimp. So, I'm going with the .139" actual, and if it works and anyone wants one for their rebuild or lens and bezel replacement, I'll provide it free for shipping USPS (just $2 or thereabouts).

So, next step is to refinish the tin reflecting ring which also holds the round-section O-ring. I'll post again whenever the O-rings come in and I've tested the fit.

 

Update to last post: after re-micing the reflector ring, I ordered both the 1/8" and 3/16" O-rings. It's quite possible that the old, dried out one is mic'ing smaller than a new one would. We'll see which is it, but I'm kind of guessing it'll be the thicker one as it's definitely thicker than .125"... Anyway, I can always send back the pack that doesn't fit.

 

The O-rings came in and the 3/16" thickness @ 4" I.D. was spot on (see photo). However, the durometer hardness rating of these regular Burna-N O-rings is 70, and as a result you really have to mash down on the cup to get things to compress enough for the crimp. The OEM O-ring, while too old and crumbling to reuse, is (or was) quite a bit softer.

I could get a thinner, flat-section O-ring to replace the one discussed above that comes with the J&P bezel and lens kit, which is slit down the middle so as to 'float' the lens and as a result adds some thickness to the bezel stack. However, instead I'm going to return the regular Burna-N O-rings and have ordered the only softer one they stock in this size with a 50 hardness rating, which is silicone - 1173N563. That 30% reduction in hardness should allow sufficient compression for an easier crimp, and also produce a good water-tight seal for washing the bike or getting caught in the rain. They're expensive but luckily you can order a single O-ring.

We're getting there...

 

Wow, how time flies...

So, I'm making time to finish this project, at last. As you can see below, I need to make some decisions on refinishing the pressed metal ring whose recessed side contains the second, round-section O-ring--really, more like a car door's foam rubber seal with a 'skin' on it, in the case of the OEM part (first three images). I've included photos comparing the OEM ring to the silicone McMaster Carr ring discussed earlier. Just a hair fatter than the OEM part and a little firmer--but still allows for sufficient compression to crimp the bezel.

And on the flip side of the ring (fourth pic), it's painted in white for the section that reflects light onto the numbers, and black on the portion nearest the bulb and opposite the 'Harley-Davidson POLICE SPECIAL' lettering at the bottom.

First decision: I think I'll mirror the OEM scheme, so that the scale is immediately visible and the brand/model info less so.

Second decision: all of the white paint has faded to a creme color over the years. I'm making the call to leave the dial and pointer as they are because it doesn't look too bad and I don't mind the patina. However, I believe I will repaint the reflector ring, both to stop the progress of the mild corrosion and to improve the gauge's usefulness at night.

So, I think I've got some Scotch Brite-esque wheels for the Dremel, but if not there's a teensy soft wire wheel that should do the trick, together with some careful hand sanding. Then while these things are painted and drying, I'll remove the main odometer barrel to wipe it off and set the mileage roughly where the existing one was when the speedo function failed. That figure reflects miles accumulated since the top-end refresh and getting this old bike back on the road. (I've deduced that, since the odometer and trip still work on the V-Twin new unit that failed, and the reading was wildly high before finally lapsing into nothing but an occasional small jump of the needle, it's probably the clock spring that broke, followed by something else...?)

I'll post reassembly photos, since there are a couple of things you've got to note when dismantling the works to avoid damaging the clock spring. But the main drive mechanism is straightforward in design and pretty robust in construction. Not much to break or fix, frankly--and the expert told me to run the gears dry, so not even any special lube involved, other than soaking the drive shaft per the earlier post. I'll post a photo of that process tomorrow or whenever I get this thing ready to reassemble.

 

All right! The little wire wheel and cup that have been sitting in my Dremel kit for years were j-u-s-t sufficient to remove the baked-on paint and corrosion before disintegrating, as you can see in the first two images. (I used the shop vac with brush attachment to get out the tiny wires flung up into my hair - should've put on my welder's doo-rag...) Eye protection is a must with the insane rpms those things turn.

The second two pics show how the dual-gasket setup works--with the reflector ring inserted into the cup. Should be a nice water-tight seal for bike washing and the occasional unexpected shower on the road.

 

Here are before and after photos of the reflector ring. Much better. Just used Rustoleum bare metal primer for the relatively mild white color, then applied some high temp engine flat black on the bottom-of-the-dial section, both of which were leftover from various projects.

Should have the gauge back together this weekend, and I'll post some pics. Then it's on to figuring how to make this thing read out accurately on this bike...

 

Nice! Looks like that takes some patience.

Paul