Stuck Chronometric Speedo

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clive
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Re: Stuck Chronometric Speedo

Post by clive »

I used to pour penetrating oil in the thread and sticking them face down in the freezer (In a plastic bag) and then a couple of days later take it out, and using leather gloves and a good firm mount for the speedo turn it off. Never had any success with an oil filter strap.the above worked for 95% and I took a hacksaw to the other 5 %.
When you tried the bike on the road did the odometer still work? It's unlikely to be a problem with the Speedo if neither the speed or mileage work as the systems are completely separate once they enter the system. Give that you were driving from the gearbox end of the cable you have probably eliminated a problem with the drivebox. Did you check that the cable had not snapped midway ?
clive
if it ain't broke don't fix
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thornebt
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Re: Stuck Chronometric Speedo

Post by thornebt »

Hi Clive

I did try sticking the speedo in a bag in the freezer earlier today and left it for a couple of hours. I've also tried WD40 soaking into the thread but I haven't tried both together. At a success rate of 95% though I will certainly give it a try.

I think I tried the bike on the road and the speedo didn't work. I oiled the cable as I didn't know you weren't supposed to! Put the drill on the cable to drive it anti-clockwise. The speedo went up to about 23mph and stuck there and it's been there ever since. The cable is in one piece, not snapped.

Hopefully I'll get the bezel off with the freezer / penetrating oil trick and will then see if it's got oil inside the speedo.

Cheers. Bruce.
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thornebt
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Re: Stuck Chronometric Speedo

Post by thornebt »

Clive. Excellent. Two days in the freezer with the WD40 on the thread did the trick. I didn't think it was going to work as it still took some time. However, after a struggle I finally won.

There are two things I need to do now:-

I don't understand what the nylon bush does and how it fits. It was in the top of the cable, appears to be cracked as there is an irregular split along it's length and the hole in it is marginally smaller than the cable diameter. It looks as though it should fit inside the outer cable to keep the inner cable central but as far as I can see the cable wouldn't go through the centre hole! It is stepped so slightly smaller at one end.

Rob C said about cleaning the mechanism with methylated spirit taking care not to get it on the face numerals. Do I remove the face by taking out the four tiny screws? If so how do I remove the pointer? Would isopropyl alcohol do the same job as the meths? Is there a specific part I need to clean or is it a case of immersing the whole mechanism in meths / alcohol for a period of time?

Sorry for so many questions!

Cheers. Bruce.

Edit: I forgot to mention that the speedo has now returned to 0mph. So that is at least a step in the right direction!
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clive
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Re: Stuck Chronometric Speedo

Post by clive »

Don't recognise the insert sounds like the cable may not have been reaching the head. Get a new cable and ensure it is for a Chronometric speedo. Personally I would not advise taking the speedo apart unless you are very brave. I learnt how to fix them by ruining a number but at the time they only cost £5 each or less. Now even a non working one is £160 to £200 on ebay. Basically the oil may have got into the slipping clutch which is at the bottom of the works so a slosh around in petrol, meths anything you have got might work. I would not advise it however.
clive
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Johnobirches
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Re: Stuck Chronometric Speedo

Post by Johnobirches »

My advice is don't try and clean the face at all - the lettering just wants to fall off.

The pointer levers off [gently].

Yes you have to undo the tiny screws.

Good luck.

John
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thornebt
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Re: Stuck Chronometric Speedo

Post by thornebt »

clive wrote:Don't recognise the insert sounds like the cable may not have been reaching the head. Get a new cable and ensure it is for a Chronometric speedo. Personally I would not advise taking the speedo apart unless you are very brave. I learnt how to fix them by ruining a number but at the time they only cost £5 each or less. Now even a non working one is £160 to £200 on ebay. Basically the oil may have got into the slipping clutch which is at the bottom of the works so a slosh around in petrol, meths anything you have got might work. I would not advise it however.
I'm not particularly brave so I think I will carefully rotate the cable anti-clockwise with an electric drill to see if the speedo now works. If it does all well and good. If not perhaps I'll leave it on the windowsill in the sun for a few days and keep trying it. I need to get it working somehow as I can't keep guessing my speed.

The cable has worked perfectly well in the past. In fact I think I've never replaced it so it's at least twenty years old but looks perfect. I'm going to give it a good wipe to remove any traces of oil.

Cheers. Bruce.
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clive
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Re: Stuck Chronometric Speedo

Post by clive »

If you wipe it use a rag but not soaked in petrol etc. You want lubrication just not liquid oil. On many other threads I advise to lightly grease between finger and thumb but stop greasing at least 18 inches before the cable goes fully home. Good idea to try the speedo driven directly if you can find something to drive it with. Leaving it on the window sill is unlikely to sort out oil in the slipping clutch. When I fixed speedos for members some years ago now (20 or so) I used to advise as follows
"To check the rearwheel drive box. Disconnect the cable from the speedo. Put the bike on the stand and rotate the rearwheel slowly. Grip the squared part of the cable with finger and thumb, it should not be possible to stop it turning. The usual symptom of a drivebox failure is both needle and numbers stopping at the same time, although this can also be caused by a cable broken halfway down so check this too. If you are rebuilding a bike or have just purchased a drivebox check that the cable is turning the correct way. With the rearwheel turning as though the bike was going forward the cable should be turning clockwise when viewed from above. Please note however that a few British bikes fitted anti-clockwise speedos and there are some anti-clockwise drives around. If you have the wrong match it appears that the bottom trip mileometer works but the speed and main one do not. It is also important that you have the correct ratio drivebox for your bike (all AMC machines were fitted with a 2:1 clockwise drive I think).

To check the cable. Check the last 1/4 of an inch of the cable at the head end. If it is worn this will be slightly rounded. Usual symptom of failure is a steady speed reading until about 40 mph at which point the needle will begin to swing wildly across the scale. This fault is usually caused by a pattern cable that has the wrong length of screw fitment for the head. Both Johnson's Cables and the AJS and Matchless Owners Club Spares Scheme supply the correct sort provided that you specify that it is for a Smiths Chronometric speedo and the year and bike. When screwing up the cable it is important that the inner cable is slotted into the drive and that the outer cable is held firmly in place without any movement. This is particularly important if you speedo is the sort with a very short thread. Your speedo is / is not that sort.

N.B. Cable lubrication. DO NOT use oil to lubricate the inner cable. Pull it out and then use a pinch of grease between finger and thumb as you push it back in. DO NOT grease the last 18 inches of the cable. Failure to observe these rules will result in grease or oil being forced up the cable by Archimedes screw action which rapidly causes the slipping clutch to slip at the wrong moment and hence no speed reading.

To check the speedo. Insert a spade end electrical screwdriver into the drive. Looking from below flick the screwdriver anti-clockwise as fast as you can. The needle should move up to around 20 mph (more with practice) and stay there most times. If you then rotate it slowly (still anti-clockwise) it should fall back to zero (well 5 mph actually). If it does this the speed is probably working OK. If you have the drive part of an old speedo cable you can use a drill with a reversing feature. The cable has to turn clockwise when looked at the chuck from above. Depending on the speed of your drill the speedo will probably show between 40 and 100 mph (1600rpm is 60 mph). Again when you stop the drill it will probably not stop at zero until you turn it slowly again. It is rare for both mileage and speed to fail at the same time so please check the drivebox and cable first. Faults which usually mean an overhaul is necessary include a wildly fluctuating reading throughout the range, winding up to 120 mph and staying there, or returning to zero erratically. The mileometer readings are particularly susceptible to vibration which can stop them turning over or even to turn backwards. I cannot always guarantee to solve this unless you do something about the vibration too! Headlight mounted speedos should have a rubber grommet fitted (available from the spares scheme) and it is a good idea to put a rubber washer under the fork mounted ones.
Safe riding"
clive
if it ain't broke don't fix
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thornebt
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Re: Stuck Chronometric Speedo

Post by thornebt »

Thanks Clive for so much information. You say in your post:-

...you can use a drill with a reversing feature. The cable has to turn clockwise when looked at the chuck from above. Depending on the speed of your drill the speedo will probably show between 40 and 100 mph (1600rpm is 60 mph). Again when you stop the drill it will probably not stop at zero until you turn it slowly again.

This is exactly the situation I have.

Perhaps I need to try it in the bike again as it might work correctly now. I guess the difference between using the reverse drill and the bike to drive it is that the drill stops almost instantly with the result that the speedo sticks until slowly rotated again - whereas the bike decelarates more slowly which enables the speedo to gradually tick down to zero.

I'll do as you suggest with the cable as well.

The speedo looks incredibly complex in its construction. Especially when you compare it with something like the wireless pushbike speedo I bought recently! Just a small 'computer' on the handlebars and a magnet on the spoke. It probably won't be working in sixty years time but when it costs about a fiver who cares!

Cheers. Bruce.
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Rob Harknett
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Re: Stuck Chronometric Speedo

Post by Rob Harknett »

clive wrote:Don't recognise the insert sounds like the cable may not have been reaching the head. Get a new cable and ensure it is for a Chronometric speedo. Personally I would not advise taking the speedo apart unless you are very brave. I learnt how to fix them by ruining a number but at the time they only cost £5 each or less. Now even a non working one is £160 to £200 on ebay. Basically the oil may have got into the slipping clutch which is at the bottom of the works so a slosh around in petrol, meths anything you have got might work. I would not advise it however.
For delicate mechanical parts, I use Electrical switch cleaner spray. Sevisol super 10 is a brand name found in Maplins stores. It will clean switches etc. that have become intermittent, due to muck oxidisation etc. I've sprayed lot's of bike bits with it. Electric terminals, bullet connectors, CVC unites, Dynamo / Mag brushes etc. With the 150 mm plastic tube that comes with it, stuck in the spray nozzle. You can reach areas where you want the spray to go.
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Harry44
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Re: Stuck Chronometric Speedo

Post by Harry44 »

That nylon spacer that's broken. Is it meant to be attached to the inner cable to stop it sliding down inside the outer cable too far and no longer drive the speedo ?
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