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MG MGA - Water pumps as the cause of poor cooling ?

I ran across this when looking for some other information and wondered what others think.

Quote

"My Morgan suffered from what a lot of TR engined Morgans suffer from, namely radiator boil-over and slight overheating after a brisk run. I removed the pump and its housing to do some flow testing using a hand drill to spin the pump at different RPMS. I determined that the stock pump will not pump at all when the engine is slow idling, and will not even begin to pump at almost twice slow idle speed. I'm compensating for the speed increase given by the larger crankshaft pulley. I took the pump off the housing and measured the end clearance using some plumber's putty and discovered that without a gasket, the end clearance was 80 thousands of an inch.

We have quite large pumps where I work and the end clearance on some of those pumps are only a few thousands of an inch. In particular, we have a set of pumps that need to have discharge pressures matched, and one, one thousands of an inch will result in a 20 kPa difference on a nominal discharge pressure of 1100kPa. So, 80 thou without a gasket on the tiny TR pump? No wonder it doesn't work. Apparently, an end clearance of 75 thou is recommended. I can tell you, that even at 40 thou, the clearance is still so large it won't pump effectively.

I added a 77 thou steel spacer to the recess in the pump housing and riveted it in place with flush steel pop rivets. With a gasket, the end clearance is now 7.5 thou and the pump works like a pump should. I repeated the experiment and the pump starts pumping at about 400 rpm on the drill with 4 times the flow it had at full speed on the drill before, and double that speed at full drill speed (about 8 times the flow). I must mention too, that this was with the stock 4 bladed impeller. I do not think that the 6 bladed impeller offered by some would be much more effective without the end clearance corrected. The experiment I did was rather crude, but it did definitely show that the pump was not working as it should. Also, my experiment was done with cold water, not hot water mixed 50/50 with antifreeze which requires even higher speeds to obtain the same mass flow"

I have no idea what the clearance in a B-Series head would be, but it is logical that a poorly designed impeller and high clearances are not going to do a lot for coolant flow around the pump, and could account for cooling problems that were never apparent when the cars were new.....
Dominic Clancy

I reckon anyone blaming impeller clearance for overheating problems are clutching at straws (assuming you have the correct pump installed for the engine). The impeller design on B series engines have the efficiency of slurry pumps (around 50%) compared to high efficiency centrifugal pumps like boiler feed pumps etc where clearances are very important. Just my 2 cents worth.
Mike
Mike Ellsmore

There are 2 styles of pump impeller in the B series pumps, the original cast type and a pressed steel one in some of the aftermarket pumps.

The clearance between the impeller and the casting is often too large as it comes in the box and I reset it in a press to the factory specs of 20 to 30 thou - clearance C in the attached image.

I have no idea what the TR pump set up is, but B series pumps fit in the block, not the head and end clearance between the impeller and the number one cylinder wall is only an issue if the impeller touches it!!!




Chris at Octarine Services

Yeah, usually when I'm doing a B or similar pump I push the impeller on 'til it just touches the housing and then when the press is let off it 'just' clears
Interesting with the cast v tin impellers
On Ford V8s if you have an original cast one you're a lucky man-If you have a tin one the impeller cavitates and rots the timing cover out
I have a little problem with the pump in the elan, it's fitted with a small dia.race crank pulley which slows everything down-- At idle the temp gradually climbs but give it a blip on the throttle and down it goes--not really a problem, just something to be aware of
William Revit

This thread was discussed on 12/10/2018

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