Thursday, February 13, 2020

Oil Pump

(Posted on FB 1/14/20)

PROJECT 51: Oil Pump. Once again, something that I thought only needed cleaning held surprises. Apparently, when Brutus got done rebuilding the engine, it still had low oil pressure. That would not be surprising as there was .003 to .004 too much clearance between the connecting rod and main bearings and their respective journals on the crankshaft. So, he bought and installed a new oil pump. (The old pump came with the car in the new pump's shipping box, which still held the receipt, so I know exactly when it was replaced.) Unfortunately, that would not have solved the problem.
To get still more oil pressure, Brutus stretched the spring in the pressure relief valve. This would have done nothing, as the "relief" only kicks in when the pump is producing too much pressure; which it was not.
I also thought that he had plugged the hollow bolt that passes the oil from the engine block (where the pump is) to the cylinder head, with a slug of brass with a smaller hole. The oil pressure gauge on the dashboard is connected to one end of this bolt, so I believed he had done this to show higher oil pressure on the gauge. It turns out that the restriction was added by the folks at MG after engine #31942 "... to prevent the possibility of a hydraulic knock in the oil pipe which was encountered on some earlier models."
Inspecting the pump's internal clearance with feeler gauges per the vintage (1952) shop manual, showed that it was well within tolerances, so after replacing the spring with a new one, and drilling out the oil bolt, the pump just needed cleaning, masking off of the mating and gasket surfaces, and painting. The brass hole caps on the pump would have been painted red at the factory, but I like the look of the polished brass too much to cover them up.
The assembly will be getting a new set of bolts during installation, as long bolts like this can become fatigued over time, especially if they might have been over-torqued to start with … not that I would suspect Brutus of that!

Disassembled and cleaned oil pump parts.

Receipt for new oil pump in December of 1968.

Stretched vs. new pressure relief spring.

Hollow bolt to send oil to the cylinder head. This end
connects to the pressure gauge on the dash.

This end was restricted by MG to prevent
hydraulic knock in the oil pipe.

Ready to inspect the clearance of the pumping gears.

Page from vintage shop manual.

Finished product.

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