B40 Speedo - wots the right one ?

[hoogerbooger]

Looks like I may have a speedo off a C15 on my 1965 B40 Star. I've got a Smiths 'grey face'  SSM2001/00 16000 (goes up to 80mph on the dial) I think SSM2001/02 1600 is the right speedo (goes up to 100mph on the dial (presumably just to impress rather than any need!)

Does anyone know if mine is definately the wrong speedo ? Were they ever fitted to B40s ?

With the different wheel sizes on C15/B40's I may find I have the wrong speeds showing ( if I get it to work) But  presumably with the right drive gear  (on the back wheel) it wouldn't matter as it's that that allows for the  wheel size  ?

So If, in due course, I find I have the wrong speeds showing ...is it possible to get parts to change the gearing in the driver unit or is there a code number or pattern part I could look out for  ?

[JulianS]

The 1965 Smiths list shows the B40 (18 inch wheels) as being fitted with SSM 2001/2 and the 2001/00 as being fitted to the C15 (17 inch wheels) and D7 Bantam (18 inch wheels)

It also shows that the SSM2001/2 as being fitted to the C15SS80 (17 inch wheels)

All above fitted with the same rear wheel gearbox.

So if SSM2001/00 is OK for the D7 then it should be OK for your B40 unless you want to go over 80.

See list below.

[AWJDThumper]

I personally wouldn't worry about using a C15 speedo on a B40. It's unlikely you'll want to go over 80mph and the only problem will be that the speedo will read 6% too high. That means that at 30mph, it will read 1.8mph too high; at 60mph, it will read 3.5mph too high. Those errors are easy enough to compensate for, if necessary.

[AWJDThumper]

Sorry, I got it the wrong way round and the C15 will read -6% on a B40. However, fortuitously, since speedo's are required by law to have an error of up to +10%, the C15 might actually end up being more accurate than a pukka B40 speedo

[hoogerbooger]

Over 80 !!  I recall being alarmed at 50 with a corner approaching!! Lower speed limits are the only thing I was concerned about. ( but can calibrate/check the  error against the car - or temporarily rig up a bicycle computer).

Never had it connected on the bike itself, but I did test it running on a  drill 19 years ago & it seemed ok. Just tried again on a drill and it was ok to 10mph but above that makes a whirring sound and the needle jumps up and down by 20 mph or so. I can't remember it doing this before (although I am getting more senior ! so can't be sure)

Anyone have an idea what sort of fault it is ? looks like they are supposed to be maintenance free/no need to lube. 

I'm wondering if this may be an intake of dust/cack through the open port that looks like its a bulb holder. Anyone taken the bezel off & cleaned/refurbed themselves? I'm wondering whether I may as well have a go at some point  or whether it's a don't bother leave it to a professional restorer/get a replacement ?

[AWJDThumper]

There's actually nothing much to go wrong inside except for a build up of crud over time although the drive spindle can become stiff through lack of lubrication. They can be overhauled once the bezel has been hacked off but it would need to be recalibrated afterwards which needs the correct test equipment (ie a driven input at a precisely known rpm).

[hoogerbooger]

just found something on repairing them/how they work.

Sounds to me like lack of lubrication on the needle bearing......so may be able to address that without full dismantling/affecting calibration.

However....it can wait to some later date.

[AWJDThumper]

From memory, I think the needle rotates in a self lubricating brass bearing. However, if it's not that, it may be a build up of crud stopping the aluminium plate attached to the needle from rotating freely. Either way, if you pull off the needle and unscrew the dial, you can then get at the needle mechanism and clean and lube it as necessary. It's only when you need to get at the drive spindle or the odometer mechanism that you are likely to disturb the calibration.

[JulianS]

I would use the bike and give the speedo chance to settle down after its period of hibernation.

Often dismantling and reassembly of a speedo is more difficult than anticipated and the result can be disappointing.

[AWJDThumper]

I rebuilt a C15 speedo last week which was in very poor condition after not having been used for many years. One of the main problems with it was that, as well as having accumulated a lot of crud inside, the lubrication of the main spindle had dried out. I had to strip it completely to refurbish it and, of course, I had to re-calibrate it afterwards.

[hoogerbooger]

Noted.

I will give it a chance to see if it sorts itself out. (There currently a metalic screetchy sound when the rotation speed goes above  circa '10mph' It's then that the needle flickers)   

If I dismantle... it's a)look for crud and remove. But b) if crud doesn't look like the reason what lube is used where ?

Sounds like the needle bearing is not lubed ?

By the main spindle do you mean the part the drive cable goes into......i.e if that is jamming the cable head twists off ?   

[AWJDThumper]

I've got a needle mechanism in my workshop and will pop down and check what the bearing looks like.

Screetchy sounds are not good and are  not likely to get better. It's unlikely to be the needle bearing and is either the drive spindle or the rotating magnet touching the aluminium needle disk directly or via foreign matter. The drive spindles interfaces to the speedo cable and has an odometer drive cog and circular magnet attached to the upper end. It's unlikely that the odometer gear train is making a noise because it's all made of plastic. Normally, you can tell whether there's a problem with the drive spindle by seeing whether or not it rotates freely.

[AWJDThumper]

Having just dug out my bag of speedo bits, I can see that there isn't a needle bearing as such - just a hole in the support plate through which the needle spindle passes. There's nothing to lubricate and it is unlikely to give a problem.

If there are nasty noises coming from the speedo mechanism then that must be associated with the part of the mechanism that continuously rotates. If the drive spindle lubrication has failed, then that could become noisy. Alternatively, the rotating magnet could be coming into contact with the aluminium plate attached to the needle, as said, due to a build up of crud or because the clearance needs adjusting.

[hoogerbooger]

many thanks.

The screeching noise could well be from a thin aluminium plate. I will revise my diagnosis to the magnet touching the drag plate/aluminium needle disk.... although not so sure why it doesn't make that sound at lower rotation speed.

So I won't connect it up/until I've ventured inside to try to sort.....at probably a future point. Man at my MOT place said as long as he has something to note a mileage down from that'll do to get it on the road ! [my testing of it running on the drill now gives a reading 1.2 miles higher than the last MOT in 1998 (!!!) .....that'll do !]


It's a crimp on bezel. As long as I'm patient and careful uncrimping ( prizing up with a flat head screwdriver.....it looks like I should be able to re-crimp by just pressing with the screw-driver.....any tips?

[AWJDThumper]

You can easily buy a new bezel which is just as well because it is normally impossible to remove the old one without damaging it irreparably.