Monday 20 October 2014

How to remove an Inter oilpump

1936 Model CJ cases;
note the big hole where the pump used to sit
The pump

-JdK- I have been struggling for a few nights trying to remove the oilpump from the engine of my 1936 Model CJ Norton. Like in all Carroll OHC engines, the pump is shrunk into the crankcases. Every manual and expert will tell you to heat the cases and pull the pump out using two studs screwed into the holes of the pump and a sturdy piece of steel across the bevel chamber. I managed to get it out but it took a lot of WD40, sweat and considerable force and you don't want to break the pump or cases. I discussed all this with Ian Bennett who contacted me last night with the answer:

"Yesterday I was talking to a clever old guy, Julian Harvey, who has worked on Manx engines all his life and he happened to comment on new oil pumps being made of brass. He told me the original  oil pumps made of Mazac (a zinc-like metal) have a large "coefficient of expansion" so that when the engine gets hot the oil pump gets tighter in the crankcase. I have just checked and have listed the coefficient of linear expansion of several metals below:

steel and iron: 12x10-6 m/moK
aluminium: 23x10-6 m/moK
magnesium: 26x10-6 m/moK
brass: 19x10-6 m/moK
zinc: 34x10-6 m/moK

So if you, like me, have always heated the crankcase up to remove the oil pump, you were wrong. When you heat the crankcase up with an original oil pump it gets tighter in the cases because the Mazac (zinc) expands more than the aluminium crankcases. So put the cases in the freezer to remove the Mazac pump and heat the cases up to fit it! Be aware that the new brass ones will get looser when heated! We keep learning ... "