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Discussion Starter #1 (Edited)
So I am trying to figure out if an OEM (and used) oil pump I have is still good. I have done the basic checks and perhaps that is enough, not sure. Here's what I have done (according to attached spec):
  • All gears look good
  • Internal oil pump gear end float in spec (.08 mm)
  • Internal oil pump gear teeth clearance to body of pump in spec (.05mm)
Three things I am not sure about:
  • Pressure relief valve operation smoothness: The relief valve piston has some slight scoring (enough to very barely feel with a finger nail). Is this piston supposed to baby skin smooth? Also, when I slide the (oiled) piston in the (oiled) relief valve cylinder bore it moves smoothly for the first 1/2", then sort of catches before moving smoothly again. Normal or not good? If not good, can I just take fine emery cloth to the cylinder and polish it smooth?
  • Pump drive shaft: This is the shaft that connects with the distributor. When I turn it it seems like it has something like a slight "compression" stroke halfway through. That is to say, it does not turn with the same torque all the way round, but instead sort of slightly hiccups like a much smaller version of turning an engine crankshaft with a compression stroke. The entire rotation is smooth, it just has that slight "compression" stroke feel. Is that normal?
  • Clearance between main drive gear & body: The clearance between the brass drive gear to top of body is .15mm. On this thread it states clearance should be between .2mm-.5mm. So is .15mm a problem?
Thanks.
 

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86 Veloce
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905 Posts
Gordon Raymond is our pump pro. PM him or he will probably see this sooner or later. So8nds to me like that pump is due for an overhaul or the trash bin. Take a bunch of close up pics and send them to Raymond, he will give you the low down skinny....
 

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The lumpy feel when you turn it is normal if it is filled with oil and it is the cause of spark scatter with these motors. A slight irregularity in relief valve operation should not be a problem provided it it is not due to something that is likely to get worse. The forces on the piston from oil pressure and the spring will overcome any light stiction.
 

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Discussion Starter #4
Yeah, the repro pump I have on the bench also the same sort of "lump" when I turn it, so was thinking it might not be unusual.

Not sure if Gordon will make it over to this thread, but lots of good discussion from him on pump specs over here: Bad Batch of Oil Pumps
 
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