MG Car Repair: Mechanical Fuel Pump Installation, cam lobe, different shapes

Question
QUESTION: Hello Howard, is there any trick to installing a fuel pump on a 1977 MG Midget 1500.

ANSWER: Hi Martin,
Yes, there is, first you need to determine if the arm is the same length as the old one as some were used with a spacer block and some without. If the old one had a spacer block be sure to install the spacer block on the new pump. Also it is sometimes difficult to install the new pump as the arm wants to slip off the side of the cam it rides on and if you bolt it up that way you can bend the pump arm so it is very important to keep the pump straight as you install it.
Howard

---------- FOLLOW-UP ----------

QUESTION: Thanks for the above. I thought the new pump would fit right in. As I backed off the nuts from the old pump there was quite a push as the arm extended. Would it help to crank the engine to move the camshaft a bit. I have all the spark plug leads removed and distributor cap. The pump arm is the same length, however it is wider about a 1/4 to 3/8", the deptth looks to be the same. I did notice on the old pump that one hole was round the other hole the attaching studs on the side of the block go through elliptical. The new pump both holes are round.

Cheers,

Martin

Answer
If the new pump had the same extended arm length then it is probably OK. The two holes being round don't mean anything. As long as you pull both nuts down evenly so the pump is pushed in straight so the arm don't slip off the side of the cam lobe. turning the engine over to get the cam on the low side will make it a little easier.

When the cam pushes on the lever, that is the retraction of the pump stroke. The spring action of the lever when the cam relaxes the lever is the fuel pumping stroke. The spring is then the control of the fuel pump pressure. If the cam action were to be the pumping action the fuel pressure would go sky high.

Even when these cars were new there were several different brands of pumps available so we seen different shapes of pumps too. We always worried when we would get a different looking pump to put on so we would often check fuel pressure after installing a new pump.