The MGA With An Attitude
MODIFY ENGINE BLOCK to Accept 5-Main Water Pump - CO-301

These photos and notes come from out friend Tom Baker, currently residing in Japan. He is the only person I know who has done this modification (but there could be others). He had procured a supercharger kit that came with a water pump from an MGB five main bearing engine, so decided to take the plunge and modify the MGA engine block to accept the larger impellor. While the four attachment bolts are in the same location on 3-main and 5-main blocks, the later and larger impellor is positioned lower and slightly off center from the early one. This then requires removal of a lot of iron around the bottom of the opening and not so much at top. With the later impellor being deeper, it also requires removal of iron from the web near the back of the opening on the early MGA blocks.

Original opening in block
Original MGA Engine Block
Modified opening in block
Modified Opening for "5-main" Water Pump

At 07:33 PM 6/29/2008 -0700, Tom Baker wrote:
>> As for the water pump, the SC kit I got was for the early MGB with a generator. With it came an MGB cast iron water pump and a spacer. The impellor is 73mm, the MGA is a bit smaller although the opening is just a bit undersize. The MGA block also has a scroll in the back with a diameter that matches the front. I consulted with Kelvin [Kelvin Dodd of Moss Motors], and from his experience, the larger MGB impellor flows better (more volume) and may assist in cooling and recommended using the MGB pump as it was with the kit anyway. Even with the modification the original MGA pump would still work fine.

At 06:01 AM 7/5/2008 -0700, Tom Baker wrote:
>> I have started installing the supercharger. I modified the block to accept the MGB pump with its 73mm impeller no less. Used the same router and stones I used to cut the eyebrows (cranked over the engine by hand and no binding!). Took some time, made a mess, and some noise but its OK.

At 12:47 AM 7/20/2008 -0700, Tom Baker wrote:
>>It did take a lot of grinding and made a mess but it was easy. I just had several wheels handy and changed them out when they got hot or less effective. At about $1.50 each it's no big deal. I think I bought 4 and used 3. They all still look fine, though. Let the wheels do the work. Cut for a while, stop and let the motor cool and my back rest, start again. Maybe a couple hours total with setup, measuring, recutting and fine tuning. The only part that concerns me is at the bottom right. Seems a bit thin on the block casting but there is enough mating surface for the gasket so it should be OK.
>>The pump is the short type for the 18V and it is a couple of mm's shorter than the A. When I finally got it to fit, I found that the supercharger pulley was inline, but the stock v-belt pulley was too far in rubbing the case. With the sc pulley, the fan sat too close to the hoses etc. and needs to be shimmed a bit to fit. Kelvin has told me there is a spacer (for the sc setup that will provide the proper offset but I tried a thick wide washer on each bolt with a 1/4 hole and they worked fine.

At 09:39 PM 7/20/2008 -0700, Tom Baker wrote:
>>Kelvin said the early castings for the 1500 had the scroll in the back, newer castings don't so that took a bit more effort.

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