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PR: Proprietary Items Shadow Speedo Reading Low


bmetcalf

Well Known and Active Website User
VOC Member
It may be due to riding in <50F weather, but my speedo is reading low. I would surely be riding at 60 mph, but it would read ~30 mph. Do I need to squirt the works with sewing machine oil or is there more than that at work? I have looked through Whitakerpedia and searched OVR, but no help to be found.
 

timetraveller

Well Known and Active Website User
VOC Member
My advice is not to use sewing machine oil or any other thin normal oil. If you can find someone who repairs old fashioned mechanical watches then try to get them to give you some of their special oil. I do not know what it is made from but when I worked at the Observatory the Chronometer department was there to service the chronometers for the whole of the Air Force and Navy. They used this special oil which would not go thick, oxidise or otherwise deteriorate.
 
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bmetcalf

Well Known and Active Website User
VOC Member
I looked some more and found this from Big Sid at http://www.thevincent.com/vininst.htm:

Erratic Speedo: This often due just to the lubricant having dried up stiff or worn out. Remove the mechanism and place on a towel. Spray clean with arosol contact cleaner being sure to flush away the old grease everywhere seen. Lightly blow dry. Spray with 3 & 1 oil or light gun oil all moving parts, allow excess to drain, clean away excess. I've also simply applied a tiny drop of clock oil to every moving part -- but the spray method is easier. Clean the dial face plate etc., gently . re-assemble into case. It pays to clean and regrease the small gearbox on the rear - I've had shards of metal in the two gears there cause erratic flicking. Return to smooth operation by doing this. The grease was ancient and more like tar. Sid 11/29/07

Also this from Andy Rackstraw on the same page:

The trouble with the original gears is that they are too small for the job and should have been made twice as big at least - observe the same angle gear box on the back of Japanese Speedo's - much better and giving no problems - the after market Smiths gearbox is expensive and also poorly made and prone to failure (and I can say anything I like after 46 years of
Instrument Work!) the gears are made from a type 6 nylon and should be lubricated with a synthetic grease like Silicone, the original steel gears should be oiled with a high pressure (HP) gearbox oil.

The chronometric movement is the same in all chronometric Speedo's. They are fitted with different size gears for correct ratios on the odometer. The speedo part if the instrument (the chronometric movement) can be fitted with different Commander Pinion sizes and Weighted Escape Wheels for different Turns Per Mile ('TPM' on the dial of some Speedo's) so that they can be calibrated for 80 or 120 or 150 mph or kilometres ('TPK') or what ever takes your fancy. I have seen the same movement fitted to printing presses and hour meters. It should be over lubricated with engine oil not instrument oil. Never let it get dry and it will last many years if well oiled.

Andy has handled quite a lot of these, so I would put a lot of weight on what he says, although the gear oil is surprising.
 

Chris Launders

Well Known and Active Website User
VOC Member
Another problem I have had is grease migrating from the cable into the speedo and affecting the clutch (this probably can't happen with a 5" clock with the gearbox).
 

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