View Full Version : 48-53 Chief Oil Pump Rebuilding

06-14-2005, 12:05 AM
Hello fellow enthusiasts.
Have any of you had good results rebuilding your aluminum oil pumps your selves?
I would like to install the complete pump gear kit and bushings for the distributor shaft, that Kiwi or Greers sell.

Any tips, tricks for assembly or recomendations on part suppliers would be appreciated!

As you can see I am in the early stages of restoration!

10-12-2005, 03:35 PM
have some real good advice on 48 pumps,i just aquired a barn fresh 48 that has been sitting since 1968.after freeing up the pistons and starting it .it would start to seize after 3 min of idling.noticed minimal oil return to tank , i took off the oil pump and after taking off the cover i noticed this strange little woodruff key that looked like it belonged somewhere.sure enough it belonged inside the pump body.makes me wonder how the bike went down the road back in the day.top of pistons were spotless ,fresh motor?anyway dont drop the keys!

12-31-2005, 02:38 PM
I took mine apart, then cleaned and inspected the gears and shafts. The shafts had some rust and pitting, so I chucked them in my lathe and polished them with emery cloth. I also power wire brushed the gears, some of which had pitting. I put all the gears and shafts back in and had a slight bind. After switching gears around, I located a spot in the housing that was causing the binding. A little emery cloth took care of that. Then I disassembled/cleaned everything again and re-assembled things. I still had a slight bind, but swapping gears around got rid of it. I buttoned it up and did a flow test using a makeshift oil reservoir and turning the pump with an electric drill. Got good oil flow, so I quit at that point.

T. Cotten
12-31-2005, 09:45 PM
You can test your pump on the bench.

Using a battery-powered drill that turns a perfect 500 rpm to spin it (fudge an adapter somehow), it should feed somewhere around 200 cc a minute on 50wt at room temp from an elevated reservoir.

(Unfortunately, not enough folks with test benches have compared info under the same conditions to set a firm baseline.)

Of equal importance is the return side. After drawing oil and then allowed to **** air, the pump should produce a minimum of 30 psi on the return line when blocked at the exit.

To improve flows, worn pump covers can be dressed to flat, and new gears installed if blemished.

Beyond that, most reported comparisons of pump performance have been anecdotal. It seems the only concensus is that castiron models produce fatter results.