John Wise wrote:
> A colleague at work has a nice MGA (which he has owned for
> many years) sitting in his garage in need of a good engine. He
> said he could not find some basic engine parts, e.g., a good
> crank. During our discussion about getting it back on the road,
> the question came up as to whether he could replace his engine
> in his A with one from a B.
>
> I said I thought he could (to me they *look* the same...), but that
> I would check the source of all valuable MG knowledge and get
> back to him.
I'm sure that we could locate the bits to rebuild his 'A' engine ...
this will probably cost him less than fitting a 'B' engine. What's the
engine number and what's he missing?
Having said that a 'B' engine will fit, however the ease of the swap
depends on the 'B' engine that you use ... retain the 'A' tranny and
everything is easily switched back.
Fitting the 'B' 3-main engine (18G, 18GA -> '62-64) is actually
quite simple ... just a matter of bolting the 'A' back plate on
the 'B' engine. The 'A' flywheel bolts up to the 'B' crank so
the 'A' clutch bits can be used ... however, fitting the 'B'
flywheel (18G, 18GA) in conjunction with the release bearing
lever and front plate (the bit that retains the release lever) from
a 'B' 3-synchro tranny ('62-'67) allows the use of the superior 'B'
pressure plate and release bearing.
Fitting the 'B' 5-main engine (18G through 18V -> '65-'80) is
a bit more difficult ... commencing with the 5-main engine, a
modern rear seal was fitted in lieu of the ol' reverse scroll or
'slinger' type, the diameter of the input shaft was increased,
the bolt pattern for the flywheel changed, the water pump was
uprated, and an electronic tach was fitted ... commencing
with the 4-synchro tranny, the diameter of the flywheel was
increased. The crank hole in the 'A' back plate must be
machined (increasing its diameter to approximately 4.125")
to accept the 5-main rear engine seal. A special spigot bush
(pilot bearing) is required to allow the 'B' 5-main crankshaft to
accept the 'A' input shaft ... Moss stocks this bush. The 'A'
flywheel will not bolt up to the crank without modification and
the 4-synchro 'B' flywheel ('68-80) is too large ... the 'B' 5-main
3-synchro flywheel ('65-'67) and 'B' pressure plate is fitted in
conjunction with the release bearing lever and front plate from
a 'B' 3-synchro tranny ('62-'67). The radiator must be shimmed
forward (approixmately 5/8") to accomodate the larger 5-main
water pump. The 5-main block is not machined to accept the
'A' mechanical tach drive so the 'B' electronic tach (with an
'A' face) is fitted ... *rumor* has it that the block can be
machined to accept the mechanical tach drive. Changes did
occur to the 5-main engine as it was "federalized" (thermostat
housing, crank pulley, carbs, emmission equip, etc.), but
these can be negated by swapping them for 'A' or early 'B'
bits ... the cylinder head combustion chamber volume, port
diameter, and valve size changed quite a bit from the early
'A' to the late 'B' so be careful swapping heads.
Holler if da above don't make no darn sense nohow ... ;^)
Safety Fast! ... larry.g.unger@lmco.com
'61 MGA 1600 MkII
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