Speedo drive

Helpful information and requests for assitance and advice
MalcW
Member
Posts: 626
Joined: Tue Oct 24, 2017 12:05 pm
Location: DEVON UK

Speedo drive

Post by MalcW »

Hi

The speedo drive on my 1960 Model 31 decided to fall apart - the rear cover for the drive spindle came adrift and the drive spindle itself came out. I actually found the spindle, but that's all. I've seen item 392083632190 on Ebay which says it's from an AJS 650 - the only difference is that the drive on mine is on top, but this is underneath. That shouldn't matter as long as the drive direction is correct. Did they vary from year to year? Does it look OK to you? I believe that the speedo drive boxes used on a bike with a full width hub needs the centre hole reaming out; something I don't have the facilities to do. I was therefore thinking that either I could use this one as a straight replacement, or make one from two. What do you think?

Cheers,

Malc
User avatar
Rob Harknett
Member
Posts: 11236
Joined: Mon Jan 01, 1990 12:00 am
Location: ESSEX UK

Re: Speedo drive

Post by Rob Harknett »

The cable will appear to go to the bottom, to exit going towards the back, if viewing it back to front.
User avatar
thornebt
Posts: 488
Joined: Sun Apr 19, 2015 9:13 am
Location: Somerset, UK

Re: Speedo drive

Post by thornebt »

The hole can be reamed out with a file as the metal is quite soft. I used a Dremel with a small flap wheel to do mine, obviously it's worth using some adhesive tape to keep the filings out of the mechanism.

I've got a couple of unserviceable speedo drives and could probably send you a rear cover for the spindle. Does it just unscrew or does it push out? I think one is a grey metal torpedo shape and the other is a flat brass type plug.

Cheers. Bruce.
User avatar
clive
Member
Posts: 5657
Joined: Mon Jan 01, 1990 12:00 am
Location: LONDON UK

Re: Speedo drive

Post by clive »

Rob Harknett wrote:The cable will appear to go to the bottom, to exit going towards the back, if viewing it back to front.
Cannot follow what you mean Rob. The ebay item, if mounted so the drive is at the bottom will be perfectly usable with the cable orientated to the front of the bike, regardless of whether viewing it from the front or back!

On the other questions raised
Yes the speedo gearboxes varied over time. Before 1960 the rear cover was flat and screwed into the body. From 1960 on the rear cover was torpedo shaped and and pushed on. To get the cable going forward these torpedo shaped ones would usually (but not exclusively) be slung under the spindle rather than above on our bikes. The boxes could come in different ratios and different rotations but the overwhelming majority were 2:1 ratio and clockwise drive which is what you would want for your 650 (by clockwise drive Smiths meant the direction the cable turned, viewed from above at the speedo end as its easier to understand which way its turning) . The ratio would normally be stamped on the steel ring on the inside of the speedo gearbox if it was not 2:1 and i cannot see that on the ebay item. Anticlock driveboxes were rare as are other ratios and most of those are 19:20 which is pretty close.
clive
if it ain't broke don't fix
oldandsmelly
Member
Posts: 114
Joined: Tue Aug 30, 2011 4:35 pm
Location: DEVON UK

Re: Speedo drive

Post by oldandsmelly »

On my model 31 the speedo drive appears underslung, i.e. the cable comes out of the bottom of the drive gearbox when looking at the wheel.

The ebay item looks to have the wrong ratio as it seems to have 'ratio 19/10' stamped on it and I think they were always 2:1 for singles and twins right up to the change to Norton bits. The same part number - 024448 is quoted for the drive gearbox for 1960 singles and twins.

The suggestion about reaming the central hole is because a batch of new gearboxes were (or are) available which had the hole a smidgen too small. I bought one of these and reamed it out and, has been mentioned, it was very easy as the metal is very soft.

If you don't fancy that, AMC spares list a new drive gearbox that has been already reamed to size. If you can't face the cost of a new drive box, the ebay item might do but your speedo would be slightly out and as always with these used ebay things, you don't know why it was removed from the bike in the first place.
MalcW
Member
Posts: 626
Joined: Tue Oct 24, 2017 12:05 pm
Location: DEVON UK

Re: Speedo drive

Post by MalcW »

Hi, since it is so easy to ease the hole out to the correct size I have decided to order a new one via the club spares. Bruce, thank you for offer though. Although my bike is a 1960 model it has an overslung gearbox with a screw in brass rear cover. Perhaps it's from early 1960 and they were using old stock. At least with a new one I can be sure of what I'm getting. Oldandsmelly, how's yours going since we met on that wet club run? Apart from this small issue mine has been fine, and completed 140 miles in total on the air ambulance charity ride very nicely.

Malc
User avatar
Rob Harknett
Member
Posts: 11236
Joined: Mon Jan 01, 1990 12:00 am
Location: ESSEX UK

Re: Speedo drive

Post by Rob Harknett »

clive wrote:
Rob Harknett wrote:The cable will appear to go to the bottom, to exit going towards the back, if viewing it back to front.
Cannot follow what you mean Rob. The ebay item, if mounted so the drive is at the bottom will be perfectly usable with the cable orientated to the front of the bike, regardless of whether viewing it from the front or back!

On the other questions raised
Yes the speedo gearboxes varied over time. Before 1960 the rear cover was flat and screwed into the body. From 1960 on the rear cover was torpedo shaped and and pushed on. To get the cable going forward these torpedo shaped ones would usually (but not exclusively) be slung under the spindle rather than above on our bikes. The boxes could come in different ratios and different rotations but the overwhelming majority were 2:1 ratio and clockwise drive which is what you would want for your 650 (by clockwise drive Smiths meant the direction the cable turned, viewed from above at the speedo end as its easier to understand which way its turning) . The ratio would normally be stamped on the steel ring on the inside of the speedo gearbox if it was not 2:1 and i cannot see that on the ebay item. Anticlock driveboxes were rare as are other ratios and most of those are 19:20 which is pretty close.
Clive, It appeared to me the drive on ebay was viewed from the back, but when a drive is fitted to a wheel, we view it from the front. It was this, that I thought had mis leaded to person asking the question. Or did it miss lead me?
oldandsmelly
Member
Posts: 114
Joined: Tue Aug 30, 2011 4:35 pm
Location: DEVON UK

Re: Speedo drive

Post by oldandsmelly »

Hi Malc, my model 31 has done another 6-700 miles since the Exe Valley run. I don't like to tempt fate but it is running really well. I fixed a small oil leak from the oil filter housing but other than that I've just been riding it. If you're ever stuck for something to do on a sunday, we meet at the Imperial weatherspoons in Exeter at 1000 for a tootle round the countryside.

My theory is to ride bikes as much as possible before they wear out.
SPRIDDLER
Member
Posts: 8542
Joined: Wed Sep 01, 2004 1:00 am
Location: WEST SUSSEX UK

Re: Speedo drive

Post by SPRIDDLER »

oldandsmelly wrote:My theory is to ride bikes as much as possible before they wear out.
or we do. :(
'There is a tide in the affairs of men
Which taken at the flood............'
MalcW
Member
Posts: 626
Joined: Tue Oct 24, 2017 12:05 pm
Location: DEVON UK

Re: Speedo drive

Post by MalcW »

The idea of a Sunday run sounds good. You're way ahead of me, I've only done about 300 since then.
I have removed the wheel ready to fit the new Speedo drive, but how do you get the old one off the wheel?

Cheers,

Malc
Locked