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MG MGB Technical - speedometer

HI
CAN I USE THE SMITHS NON OD SPEEDOMETER SN6144/00 WHICH WAS FOR CARS FROM DEC 64 TO SEPT 67, FOR MY CAR WHICH IS NOV 67 AND USES SN6125/06A OR SN6125/04A ,
SN6125/04A IS FOR OCT64-NOV64 .
SN6125/06A IS FOR OCT64-NOV 64 .
THANKS
VIGNES

QUOTED FROM MOSS CATALOGUE
vignes pillai

hi
just for clarification , i always thought my car mgb roadster,WAS NOV 1964
CHASSIS NUMBER CHN3/53843
ENGINE NUMBER 18GB-U-L-4639.

AM I CORRECT, I HAVE TO BUY SPARES AND MOSS CATALOGUE SAYS GB ENGINES ARE 1965ONWARDS.
THANKS
VIGNES
vignes pillai

vignes

GB engines are 5 brg so if yours is 3 brg its before november.
there is a small change is rpm between the 2 but nothing to worry about between the 6125 and 6125a .
first one is jaeger and second is smiths then rpm changed for the 5 bearing engined cars so diff speedo.

Steve
Ste Brown

Sorry forgot to say that the sn6144 is near enough to change over
Ste Brown

Chassis number 53843 (GHN3 by the way) dates to about Jan 65, not 67. Sometimes the a '1' is interpreted as a slash and if it should be 153843 that would date it to August 68. 18GB-U-L-4639 dates to between Oct 64 and Apr 65 by which time engine numbers had got up to 11876, so if original fits with a Jan 65 chassis number.

Speedo needs to match the gearbox, not the engine, as it is in the gearbox that the speedo gearing varies. The suffix number is also significant, as this varied between OD and non-OD on 3-synch boxes and indeed between Jaeger and Smiths even when the prefix stayed the same. The confusing thing is that Jaeger 3-synch non-OD speedos (SN6125/04) were 1060 tpm but Smiths (SN6124/04A or SN6144/00) were 1040. On OD boxes they were 1040 (SN6125/06) and 1020 (SN6125/06A or SN6144/02) respectively. The gearboxes changed from 3-synch to 4-synch in Dec 67 with the MkII, and from here on OD and non-OD speedos were the same tpm even though the reference numbers were still different for some reason. If you do have a 3-synch box then the difference between the two speedos is only about 2% (or 4% if going from a non-OD Jaeger to an OD Smiths)so can be ignored, as they can over-read by up to 10% anyway.


Paul Hunt

hi
am confused. my engine is a GB ENGINE. MOSS SAYS 18G AND GA ARE 3 BEARING, AND GB IS A 5 BEARING.
STEVE SAYS MINE IS 3 BEARING. MOSS SAYS GB ENGINES ARE 1964 ONWARDS. AND PAUL SAYS GOING BY MY CHASSIS NUMBER GHN3/53843 IT SHOULD BE JAN 65.
GOING BY ENGINE NUMBER DO I ORDER PARTS FOR A 5 BEARING OR 3 BEARING.

THANKS FOR THE HELP
VIGNES
vignes pillai

While on speedo's, I'm still looking for a kilometer version of those used in the early 70's. Part #SN6144/24 I believe.
Gary Lock

Steve says GB is 5 bearing, which is correct. 18GB engines started in October 64, which means 18GA engines went up to that date (actually July 64). 18GB went up to August 67, which means an 18GB could have been produced any time between Oct 64 and Aug 67. The serial number refines it to between Oct 64 and Apr 65, and the chassis number dates to Jan 65, which is within those two dates.

But in any case you can't go by the date, you have to go by the spec of your engine for engine parts, and not even the chassis number as the engine could have been changed. Yours seems correct though, or at least is of the correct era, you will only know exactly which engine was supplied with your car and the car build dates if you get the BMIHT certificate. But as far as speedos go it is the gearbox that is important, not the engine number, let alone the chassis number.

As far as Gary's early 70s KPH speedo goes strictly it depends on the market and whether it was OD or non-OD as they had different part and reference numbers, even though they had the same turns, which was 800, although that is turns per kilometre which is the same as 1280 turns per mile. SN6144/21 for non-OD, SN6144/24 for OD, with or without a BS suffix, for LHD except Sweden and Germany which were SN5227/20 for non-OD and either SN5227/22, SN5231/08 or SN5230/09S for OD.
Paul Hunt

Were't the GA engines still using a mechanical tach that was driven off the camshaft? RAY
RAY

Yes.
Paul Hunt

thanks PAUL.
vignes pillai

This thread was discussed between 23/01/2009 and 27/01/2009

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