At 03:54 PM 11/10/03 -0800, Dodd, Kelvin wrote:
>....
>1. I have heard tell that the MGB 18V 5 main short water pump (1972-80)
>can be fitted to the MGA, and 3 main MGB if the mounting surface is
>machined out to fit the larger impeller.
>
>True or False??
Not even close. And man, are you a glutton for pumishment, just for
thinking about it.
The impellor is not only larger, but on a slightly different center of
rotation. It would take a LOT of tricky machining to recreate the block
pattern for the snail chamber of the 5M engine in the front of the 3M
block. Not even sure there's enough material in the right places for
simple material removal without material addition required somewhere. At
least two of the four mounting bolts are in a different location, and I
probably don't need to elaborate on how hard it is to relocate a tapped
hole in an iron casting (not impossible, but a royal PITA). I suspect
there may also be a difference in depth of penetration of the impellor into
the block, and not sure if there would be enough material at the front of
the water jacket of the 3M block to cut far enough into that area without
breaching the wall between the pump cavity and the water liner area.
>2. Is there a difference in the crank pulley Internal Diameter between
>the 3 main and 5 main MGB??
No. Single and double row timing sprockets are interchangeable, so the
pully bore is also the same. Timing covers are also interchangeable,
except that if you want to use the MGB cover on the MGA you have to also
use the MGB oil thrower. The Moss slight of hand with MGA and MGB oil
thrower part numbers a few years ago is another gray area, but not a
problem here. (Would be happy to review that one with you later).
>You can probably guess why I am looking for this information.
Guess? Uh, looking to put the SC kit on a 3M engine, maybe? Wanting to
increase coolant pumnping capacity with the 3M block?
>I know what the pulley part numbers are, and they are different, the
>question is why.
Harmonic balancer on later engines, not on the earliest ones. Different
timing mark location, bottom on early engines, up top on later
engines. Not sure of some of the later crank pulleys had more than one
belt groove. I know the '68 and later air pump ran off a second groove in
the water pump pulley. Also understand there was a 3-groove water pump
pulley on some models, maybe 68-71. Just guessing that would be used with
a 2-groove crank pulley, maybe for air conditioning belt drive.
>Unfortunately I don't have a 3 main MGB to hand to figure this out.
You can swap crank pulleys if you use the timing cover with the timing
pointer to match the position of the timing mark on the pulley. Pretty
much stuck with using the original type water pump on the 3M block. If the
belt grooves in the 5M crank pulley don't line up with the 3M water pump
pulley, then you may have to fiddle with the mounting of the pulley on the
water pump. I have a really stale and vague recollection that machining
away about half the thickness of the 3M water pump hub (about 1/4 inch)
might be the solution there. I never took the time to figure out if the
generator and alternator belts all run in the same plane.
The question of possibly installing 5M water pump on a 3M block was hashed
over a few years ago (maybe even farther back). I got into it because
there was a tech article published several years ago in MGA! magazine by
NAMGAR purporting to show how to machine the 5M water pump hub to allow use
of the 5M pump on the 3M block. When that question came up on the mgs
list, I had a feeling it wouldn't work. To resolve that question, some mgs
list members conspired to send me 4 or 5 different models of water pump for
comparison. The first question was supposed to be about the extension
length of each pump, and what to do about pulleys. Second question was
which pump(s) had longer or shorter noses, as the short nose pump has to be
used when installing the 5M engine in the MGA. Third question was whether
a 5M pump would even bolt up to a 3M engine.
A little measurement quickly revealed that the 5M pump was never going to
fit on the 3M block. The impellor is larger diameter and on a different
axis, and the bolt patern is different. That pretty much killed the
purpose of the original intention, as required machining modification of
the 3M block to fit the 5M pump would be prohibitively expensive. Solution
to using the 5M engine in the MGA is to use one of the short nose water
pumps and the whatever water pump pulley was used in the same year as the
pump. I seem to recall that the 5M short nose pump comes a little closer
to the radiator, so it is adviseable to shim the radiator forward about 1/4
inch.
For follow up, I had contacted the NAMGAR editor and the NAMGAR tech writer
to let them know that their published article was in error in stating that
the 5M pump could be mounted on the 3M block. Their reaction was a mutual
shrug, something about the small print disclaimer in the magazine saying
tech advice was never guaranteed to be correct, or even safe or
functional. I think they had just published an article submitted by a
member without checking the validity of the information. No retraction or
correction note was ever published.
If my guess about your intention is correct, you are probably stuck with
using the 3M water pump on the 3M block, and may have to make a different
water pump pulley to suit your special application. If water flow MUST be
increased, then I can imagine the prospect of trying to manufacture a
special water pump for this new application. That could have a pretty
developement high cost for only limited production. Maybe think about
using a smaller diameter water pump pulley to run the original 3M pump
faster. That may be feasible with a flat belt drive.
Barney Gaylord
1958 MGA with an attitude
http://MGAguru.com
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