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+--- Thread: Smiths PN 80mph speedo - anyone fiddled? (/showthread.php?tid=7732)
Smiths PN 80mph speedo - anyone fiddled? - JonE - 12-07-2022
The PN is the same 2240 turns as the PA but has the canted exit at the back of the instrument.
The insides are subtly different and there appear to be less balls to get lost than with the PA. (I've read all the helpful PA instructions from various parties on the web).
I've got a PN in bits and would like to know if anyone has disassembled one so I can see if there is anything missing. I think it all has the prospect of working, but the sitting of the conical end into the bush next to where the speedo cable screws... that is where I'm wondering if all is correct. Pics... anyone remember fixing one? The brass thing seems odd as the whole of the bit on the right is going to be spinning. I can see it has a stop for the gimball-like things, but surely its going to snag on the inside of the case casting?
RE: Smiths PN 80mph speedo - anyone fiddled? - Robert Foreman - 12-07-2022
Were there any balls in the bottom end when you dismantled it Jon? Looks to me that someone has fitted the weird 'shim' as a replacement.
RE: Smiths PN 80mph speedo - anyone fiddled? - JonE - 13-07-2022
no - no balls, but no securing in the same way as the PA has either. Which is why I'm wondering.
RE: Smiths PN 80mph speedo - anyone fiddled? - Parazine - 13-07-2022
I built a PN/A type hybrid for my Chummy to get an angled back, silver faced, 2240TPM speedo. There are a few angled back PA's in existence but I didn't know that then (that's probably what was fitted for a short time in 1927).
There should be ball bearings at both ends of the governor but I believe, with different size balls?
RE: Smiths PN 80mph speedo - anyone fiddled? - JonE - 13-07-2022
well, I've used the same size... as that's all I had. The balls do appear to be sticking in the groove in the pictured section I was worried about, and the conical bit DOES seem to run on them. So I'll omit the brass thing.
The upper end ballrace is much smaller, but most importantly there is no possibility to get rid of end float like the PA, with the different internal structure. Whether it actually all goes together, I'll let you know.
RE: Smiths PN 80mph speedo - anyone fiddled? - Robert Foreman - 13-07-2022
The Smiths 45° drive speedo is adjustable. The top cup is threaded and when set clamped with the screw through the jaw.
RE: Smiths PN 80mph speedo - anyone fiddled? - JonE - 13-07-2022
Thanks Robert - now that you've said that, I can see it all! (mine is partially hidden behind the trip dials - I just hope I don't have to remove them)