Holmes Racing - MGB MGC classic car racing
This is a new, County brand oil pump, available from all major parts suppliers. We will start our modification process by removing the two bolts seen in this photo, socket size is 10mm.
After removing the two bolts shown previously, we place a 1/4-drive socket extension into the pump drive bore
The socket extension is used as a drift to drive against the pump rotor and knock the cover plate loose. We use a small, soft faced mallet, as a light tap is all it takes
Disassembling the pump leaves you with the parts seen here
Starting with the cover plate, we see sharp edges present where the incoming oil makes the turn into the pump body. Also note that the hole is not round (but should be).
By spending time with a small carbide burr on a die grinder, we open the hole to the proper round shape and radius the sharp edges. This work eases flow of the oil from the pickup, into the pump body itself
From the cover plate, the oil will travel up the pump body until it meets this transfer junction. The sharp edges presented to the oil flow in this view are obvious
Our goal is to smooth the transition of the oil from the pump body, to the rotor cavity by physically smoothing this junction area. A comparison with the previous photo shows a dramatic improvement
Looking at the same area from another angle shows how restrictive the stock castings can be. All the pumps we've taken apart have exhibited varying levels of obstruction, similar to this one
Comparing this photo to the previous one will give an idea of the dramatic increase in port opening size
Looking at the same port from the rotor cavity side, again shows how restrictive a stock pump can be. Comparing the last photo to this one, shows a vast increase in port opening area
Just as with the pump inlet port, we also modify the pump outlet port for equal flow capability. Both the entry and exit of this passage are smoothed and enlarged.
After cleaning all pump parts spotless and making the clearance checks outlined in the factory manual, all parts are coated with assembly lube and reinstalled
One critical check to make, is clearance of the oil pump with the block. As can be seen in this photo, a sharp ridge left from the block machining process is interfering with the oil pump. While the gasket thickness may take up some of the difference, removing excess pump material with a file is a better idea
A closeup of the ridge in the block shows where interference occurs
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