Oil - pump and ways

[Geordie]

Advice would be much appreciated.

Pump from a '62 Mototrans Elite.

IMG_pump.jpg

The pump was sealed with wired screws and lead seal but opening-up showed that it had run with an end load on its drive shaft leading to significant wear on its ported plate. All is not lost if the teeth are OK - I cannot see any difference in profile from their driven sides to their trailing sides but there is significant angular 'play' between gears. It is not a high pressure pump but flow rate is important.

Question 1 - are the teeth worn past serviceability or not much different to as first fitted?

There is a flow restrictor in the drive side of the crank. It is an aluminium tube which shows its outlet to be mangled which reduces its bore.

Question 2 - Should it be opened-up or is there a recommended exit size to further restrict flow?

Ian

[Jordan]

I think it's normal to have play between the teeth of a gear type oil pump.
When it's working, there is no leakage (in theory), because play is taken up.
If not needed, why go to the expense of "perfect" gear mesh?

Dry sump engines were often fitted with non-return valves to prevent oil passing the gears when not running, emptying the oil tank into the engine.
No such issue with wet sumps.

[Geordie]

Jordan, thank you for that. Logic suggests there will be more flow per 'toothfull' with greater clearance so I'm with you on your reasoning. And it is flow we want. It was looking at the Nigel Lacey high output pump that made me wonder if that logic was sound.

pump ho.jpg

There would appear to be no play in its gears. I could not find a photo of the meshing online or elsewhere of a standard pump for comparison.

Edit.
There will be a pressure difference between output and input side of the chamber so the closer the gear fit the less the loss through the meshing teeth, should there be any of significance at the operating pressure. Nigel Lacey's high output pump wins on that point.

[DBDBrian]

( It is not a high pressure pump but flow rate is important.)


Hi Geordie
A gear type pump is permanent displacement, a gear pump in good condition will generate pressure to the point of destruction if the flow is dead ended, hence the incorporation of a PR valve in the system.
Accepted in this application, flow not high pressure is the primary requirement, but, a worn pump will still generate flow against zero resistance. The true indicator of the condition of a pump, is it's ability to generate pressure against a resistance to the flow output.
As Jordan said, tooth contact clearance between the gears is not the critical point, as this will be taken up as the slave gear is put under load, The gear shaft in the housing, tooth tip to body clearance, (very critical,zero ideal) and gear end clearance are the important points.
Oil viscosity and temperature will also come into play.

[Geordie]

Thank you Brian. With the tooth profile acceptable, the only significant wear I can detect is that caused by the axial force on the gear shaft causing metal loss to the end plate and to a lesser extent, the driving gear in contact. The plate is easily replaced but the gear, not so. I was hoping that the whole assembly could be skimmed down to a depth to remove the wear (with a small loss of output). Unless I can lay my hands on a pump at reasonable cost as alternative.

[Geordie]

I have been lucky and obtained a pump in good condition for a modest price. For the record, the gap between teeth is 0.2mm whereas the old pump is 0.5mm.

I have one question about mounting the pump. The new gasket has one circular hole and one D shaped hole for the ports. Parts diagram shows two circular and the old gaskets were as that. Does the D serve the inlet or outlet port or should it be cut circular?

As for my question on the crank flow restrictor, I have opened its bore to parallel - it's likely to have been a bodge in a past attempt to get lube to the head.