Kirk Cowen wrote:
>>You cannot mate a "B" five main bearing engine to
>>an "A" transmission unless you are prepared to do
>>custom machining to the flywheel. You MUST keep
>>the plate that the "A" tranny bellhousing bolts to,
>>because otherwise you cannot fit the starter to the
>>transmission. You have to modify that plate to
>>match the "B" 5 main block.
>>
>>I don't know anything about the "B" three main
>>bearing block, but I suspect you will find that it will
>>not match up with the "A" tranny either. BMC
>>changed the pilot shaft tip size, so you have to
>>look at changing the pilot bearing in the end of the
>>crankshaft as well.
>>
>>The best bet is to buy the "B" 5 main block WITH
>>a 5 main tranny, and thrash out the minor body work
>>problems. You will need to enlarge the transmission
>>hump. The front motor mounts are the same, so no
>>problems there. You might have a problem matching
>>the rear transmission mount to the new tranny, but it
>>will be minor. You may have to "dimple" the firewall
>>to clear the new starter position, because bmc
>>moved the starter position around a bit.
If the 'swap' is done properly (retaining the 'A' tranny) then
welding, cutting or other modification of the 'A' frame and/or
body is *not* required ... in fact, if the external bits from the
'A' engine are fitted to the 'B' engine, the only way most folks
will be able to distinguish it from the original is the engine
number and 1800 casting on the block ... ;^)
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.
The stock 'A' cast iron exhaust manifold can be fitted, but it
is IMHO quite restrictive and should be replaced with an
aftermarket 'A' tubular header.
Safety Fast! ... larry.g.unger@lmco.com
'61 MGA 1600 MkII
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