| For more than
35 years I have stuck to 2 Six Volt batteries without thinking
about it until our “C” would not start for our club run on the
13th of August. So once again the BMW was called into service.
Next day I rang Century-Yuasa only to find that they had no Type
03 (MGB & Early VW) batteries available. So it was time to think
about a 12 Volt battery to replace the traditional MGB six volt
units.
First I made a
ring around to discover that a couple of “C’s” were using a 12
Volt battery without any problems, including a 4.6 L V8 on 9.7:1
compression. Step 1; carefully measure both battery boxes,
which turned out to be identical, to discover that the maximum
length is 202mm, width between mounting rubbers 175mm and height
up to 225+mm.
Step 2: Look
up the B & C “Workshop Manuals”. The B has a lock in current of
340 amps and running current, at Starter speed of 1000 rpm, of
250 to 270 amps (cold cranking amps, expressed as CCA by battery
manufacturers). The C has a lock in current of 465 amps and
running current at Starter speed of 1000 rpm of 260 amps.
I have always
fitted the biggest capacity battery to fit the mounting and
usually get 6 to 7 years life, so without thinking assumed that
the 2 sixes would have a similar capacity to a 12 of slightly
less length. This was a very incorrect assumption as applies to
Type 03 traditional batteries.
|
Step 3: Check
with Century about battery capacities. Type 03 have a CCA rating
of 270 amps only; why don’t you fit a single 12 said the helpful
person at the end of the phone. Because the battery box will
only take a 200mm long battery says I; that’s no problem said
the phone we have 2 batteries that long, one with 280 CCA and a
European type with 300 CCA. The battery most suitable is type
“M96-12” 200mm long 175mm wide 175mm high. With both terminals
on the same side: + on the outside and – on the tunnel side. The
distance between the mounting rubbers is 175mm so this battery
fits perfectly with one small modification. Most cars these days
(European ones anyway) mount batteries by clamping to the base
of the battery. The – end clamp needs cutting off, with a
hacksaw, as the overall length at the base is 206mm. Cut off 5mm
and the battery fits perfectly.
Remove the
interconnect cable and move the chassis cable from the passenger
side box to the driver side box, the hole already exists (scrape
off the paint). The + terminal is as before. To hold the battery
down cut a piece of 2” by 1” by 1/8” aluminum angle to the width
of the battery box and mount at the back of the battery and the
sloping uprights of the box. The battery cannot move with this
mounting. Total battery cable length reduces from 8ft to 6 ft
and 2 connections disappear. Our car turns over better than ever
before and I should have done this years ago. The M96-12 costs
about the same as 1 type 03
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