Oil Pump Drive Gear

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Blimp
Posts: 18
Joined: Tue Apr 21, 2015 12:23 am

Oil Pump Drive Gear

Postby Blimp » Wed Sep 27, 2017 7:19 am

Hi all. I'm slowly putting my NC 250 engine back together. I've checked over the oil pump and was checking its alignment and smoothness when engaged with the drive gear.

My question is what stops the oil pump drive gear thrusting the small oil pump gear (inside the pump) into the pump face plate.

It seems the oil pump drive gear (the gear with the slot in the shaft) can move freely towards the oil pump and could easily apply thrust and subsequent damage to the face plate inside the pump.

Am I missing something?

Ducadini
Posts: 27
Joined: Sun Sep 24, 2017 9:02 pm

Re: Oil Pump Drive Gear

Postby Ducadini » Wed Sep 27, 2017 7:49 am

Fact is the gear CAN move freely between the case and the oilpump but, being a straightcut gear, will only do this with moderate force.
You could argue that the crank applies a force, but this has to be shimmed to zero float in the cases so that can't be an issue.
Put a shim behind it so it doens't move TOO much (if it does move) but be carefull that Youdon't apply pressure to the inshaft of the pump.
I've dismantled a few pumps where the PO didn't take care to Ensure the correct position of the coupling, and while bolting the cover down, bended the rear pump plate. Of course with loss of pressure and bigenddamage.

have fun,
ducadini

double diamond
Posts: 555
Joined: Thu Apr 28, 2011 1:20 am

Re: Oil Pump Drive Gear

Postby double diamond » Wed Sep 27, 2017 7:44 pm

The oil pump gear probably doesn't take any thrust load since the drive gear would hit the body of the oil pump before it put any thrust on the oil pump gear. The tab on the oil pump gear is not long enough to bottom out in the slot in the drive gear. I don't recall seeing any indication of the oil pump gear wearing the oil pump body due to thrust loads in engines I've disassembled. Not something to be concerned with. Oil pump wear is largely due to the poor oil filtration at the oil pickup in the sump. Abrasives in suspension in the oil wear all surfaces of the oil pump body equally.

The shim between the oil pump drive gear and crankcase is important. Without it, the bearing shaft is long enough that it can touch the crankshaft flywheel.

Matt


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