FOR SALE : 1937 VH

[paul.jameson]

This PA will need a different case and bezel and different odometer cross shaft and worm gear as a minimum to make it a motorcycle PA. The case and bezel don't matter if you are not too worried about the detailed appearance. The cross shaft and worm gear make the odometer read correctly instead of recording 2 miles for every 3 travelled. Again, this isn't necessarily a big issue.

It seems that someone found a bag of PA speedos and has been releasing them via Ebay for nearly a year now. The UK location is consistent for these.

[john.davies]

Hi Paul, is it difficult to recalibrate the governor system to make it a 100mph speedo rather than 40mph and can you get a 100mph face for them?

[paul.jameson]

John,

The car speedos usually have a flex speed (rpm of the speedo cable at 60mph) of 3360. Ariel ones have a flex speed of 2240. So the 60mph car speedo is pretty close in performance to a 100mph bike one and the 40mph car one will not be too far off performing like an 80 mph bike one. When these speedos were built, Smiths ran them up individually to see how each performed and then fitted which ever face from the range of faces they used which best suited that particular instrument. 100mph and 80mph Ariel speedos have different thicknesses of wire for the governor spring. I have a couple of alternative 100mph faces available but only one 80mph face.

[andy.mcgregor]

Paul,

Are those flex speeds true of the PA version of car speedos?

Google turned up some links from Austin 7 owners which state 2240 revs/mile for the their PA speedos and 3360 for the CA and A models. See for example http://www.austinsevenfriends.com/Bruce ... Sheet.html

I picked up a car PA for my bike, but haven't yet got the bike running to see how the speedo works.
To get going, I was more interested in something that looked 'about right', especially given the price of genuine bike PAs. If necessary a bicycle speedometer can give me a correct answer.

Regards,
Andy

[john.mitchell]

Andy says "If necessary a bicycle speedometer can give me a correct answer"

And believe it - you don't want to be looking at tank mounted speedo in traffic...

[andy.mcgregor]

Fortunately in this part of the world heavy traffic is defined as more than two sheep on the road.

[paul.jameson]

Andy,

If you take your PA speedo to bits you can count the teeth on the cross shaft centre gear and on the gear that the cross shaft drives. Multiply these together and you will get 224 or 336, which is the number of turns needed to do 1/10 mile. That tells you the speedo's designed gearing. It works for KPH speedos as well for which you have to apply the 5/8 correction.

If you can't get the speedo back together afterwards, I can !

[andy.mcgregor]

Thanks Paul, but I've already put the speedo back together.

However, I dug out some photos that I took when I had it in bits. It looks to me like 14 x 16 teeth on those gears = 224.
So fingers crossed that it might work correctly.

For anyone else that's interested there is some information here: http://www.magnetic-speedometer-repair.com/new-page2/
about how these speedos work.

Cheers,
Andy

[mark.prizeman]

No regulator!

[stuart.munroe]

Now sold - sadly I wasn't quick enough! Will keep looking.