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MG Midget and Sprite Technical - Smiths Speedo Numbers

Hi every one,
Can anyone point me in the direction of a list of serial numbers for smiths speedos fitted to midgets. Mine has a number of 6142/0685 1376 and it reads at least 10% slow (as measured on Peter Baldwin's dyno). I am not sure it is correct for the car - it is a 1972 round wheel arch 1275.
I am not sure what is best to do, find a correct one on ebay (if I can find out what serial number i need) or get mine rebuilt and calibrated correctly (four or five weeks away at speedy cables.
Thanks
Dave
Dave Brown

Dave you want a copy of Terry Horler's excellent book - http://www.amazon.co.uk/Original-Sprite-Midget-Restorers-Austin-Healey/dp/1906133336/ref=sr_1_1?s=books&ie=UTF8&qid=1308751648&sr=1-1

page 96

looks like you've got the correct gauge

as you probably know a gauge is just that a gauge plus a change of wheel and/or tyre size or g/box and/or wear and tear will give errors

just checked mine - SN 6142/06A 1376



N Atkins

Dave I also meant to put book shows:

SN6142/06 (3.9:1, MPH, RHD, from GAN4-66226)

so yours sounds like it might be the correct one (?)

and on page 112:

Jan '72, GAN5-113617, firstcar built in 1972

Jun '72, GAN5-123644, last 1972 model built followed by a break in numbers

Jul '72, GAN5-123731, numbers restart, first 1973 model on 13 July

Jan '73, GAN5-129951, first car built in 1973

(also forgot change of diff ratio effect on speedo)
N Atkins

mine's on my desk and has the same number: SN-6142/06A 1376

from a 1972 RWA

what size tyres are you on?
Rob Armstrong

The suffix number after the part number on the dial, is the calibration, revs per mile. In this case 1376.
Thats IIRC from my time at Lucas. Terry probably tells you that, but my copy's under the bed.

Andy
Andy Pie-Crust

that last bit made me smile Andy :-), the thought of Terry under your bed that is ;-)
DW Warren

Thanks everyone,
Nigel what would you do without a manual. I have got the Haynes one, I thought that may be the only one I needed, but I need more. I guess a men can't have enough manuals ;)

Tyres are 155s. I would not have thought they would have made a huge difference. I am sure I have read that they only make a few % difference. Not enough to make a gauge go from several % points under reading, as most do as standard, to 10% over.
Is a speedo refurb soomething that can be done at home by a semi competent mechanic?
Dave
Dave Brown

"Not enough to make a gauge go from several % points under reading, as most do as standard,"
eh, where does that come from?
I've always understood that old-car speedos OVER-read by up to 10% so that when doing an indicated 77 you are actually only doing 70 (for instance).
David Smith

...and 'modern' cars seem to over-read by 3-4MPH.
Dave O'Neill 2

Dave, Haynes is OKish for repairs, for owning it's the owners Handbook and for originality and nerdy facts it's Terry's :)

get yourself this DVD and you get the Workshop and Parts manuals too - http://www.motoringclassics.co.uk/mg-midget-and-austin-sprite%3Cbr-%3E1964-to-1974/p21737

right back to speedo - tyres, also depends on (sidewall) ratio too see - http://www.carbibles.com/tyre_bible.html

and - http://www.kouki.co.uk/utilities/visual-tyre-size-calculator

speed calibrating info here - http://www.speedycables.co.uk/
N Atkins

This thread was discussed between 22/06/2011 and 23/06/2011

MG Midget and Sprite Technical index

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