Chronometric instrument repair.

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
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Pharisee
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Chronometric instrument repair.

Post by Pharisee »

I've recently rebuilt a '54 G3LS from a few boxes of bits (has been mentioned in other threads). The speedometer that came with it was obviously damaged and not the correct one anyway so I sent it to Chronometric Instrument Services in Nottingham who rebuilt it and recalibrated it for my bike. Well, I had problems with it... The speed indication part worked fine but the trip and main odometers were not keeping in step with each other and were 'missing miles'. To cut a long story short, after sending it back twice and then me taking it back to Nottingham personally again, we put it down to vibration causing the ratchet pawl to miss teeth on the ratchet wheel. Russell at CIS changed the mechanism at least twice and we had it running on test rig for a considerable time and it worked perfectly. Put it on the bike and the odometers were missing miles and generally unreliable. I've now got it back for hopefully the last time as Russell has made up a tiny custom steel leaf spring to keep the ratchet pawl in contact with the ratchet wheels on the end of the number roller banks.
I would just like to say a public thanks to Russell for all the time and effort he has put in to solving the problem (at no extra charge, I might add). Wish we could get the same service from all suppliers...
John

EDIT... sorry, I meant to post this in the General Topics forum.
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clive
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Re: Chronometric instrument repair.

Post by clive »

The problem of mileage and trip being affected by vibration is a pretty frequent one. If you have a headlight mounted Speedo it's I'mportant to have the partial rubber shroud to help damp it. The fork mounted Speedos may benefit from a pad of rubber between bracket and Speedo. The thread form on the Speedo mounting bolt is very similar to a metric one (think it is 8 mm) allowing the fitting of a modern nylock nut. Internally the fault is caused either by weak ratchet pawl springs or wear on the face where it impacts the wheel. Replacing both often does not solve the problem unless the vibration is tackled too.
clive
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Pharisee
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Re: Chronometric instrument repair.

Post by Pharisee »

clive wrote:The problem of mileage and trip being affected by vibration is a pretty frequent one. If you have a headlight mounted Speedo it's I'mportant to have the partial rubber shroud to help damp it. The fork mounted Speedos may benefit from a pad of rubber between bracket and Speedo. The thread form on the Speedo mounting bolt is very similar to a metric one (think it is 8 mm) allowing the fitting of a modern nylock nut. Internally the fault is caused either by weak ratchet pawl springs or wear on the face where it impacts the wheel. Replacing both often does not solve the problem unless the vibration is tackled too.
This speedometer is mounted on the right-angle bracket that bolts to the top yoke. I've put a piece of 2mm rubber sheet between the bracket and the yoke and put a rubber washer under the bolt head. The bolt is assembled with Loctite so that there is a little 'compliance'. The holes in the bracket that the speedometer studs go through have been opened up to 8mm diameter and rubber grommets fitted. The speedo studs (appear to be M6) go through the grommets and as you rightly say, are secured with Nyloc nuts. These mods, along with the internal modification that Russell made, will hopefully go a long way to curing the problem.
I'm from the Fens.... Gimme six.
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