Advice needed: New oil pump, or stick with old one?

[Marcus OBeard]

Hi All,

I've started into my BMW R80/7 rebuild - and so far so good. I'm in the process of putting in the oil pump and it looks like it's had better days. The bike has almost 70k miles on it, so this pump has spun a few times in it's day. Question is, does it need replacing? The parts are not cheap on Boxer2Valve and will slow the rebuild down during valuable rebuild time of year while I'm off work. If i can get away with sticking these back in, I will, but would love to know what this community thinks?

Pump 2.jpeg (1.53 MiB) Viewed 679 times

Pump 3.jpeg (1.77 MiB) Viewed 679 times

Pump 6.jpeg (591.85 KiB) Viewed 679 times

I have a feeling I know the answer already, but hopeful...

Thanks for your help,

Marcus

[gspd]

It's only around $200. for a new one....
You can measure everything, it might be borderline.
It looks perfectly useable to me.
These pumps, even when somewhat scored and worn, produce ample pressure.

Airhead low oil pressure issues, although rare, are mostly with the filter o-rings and multiple check valves in the oil circuit. The actual pump is rarely the culprit, and even the rough-ish looking ones seem to go forever.
If I were still working for BMW, I would recommend it be replaced immediately for liability (and profit) reasons.

If you want my real world advice, as if it were my bike...
You should re-install it, then go for a 100,000 mile test ride and report back.
Remember, we're talking BMW, not BSA.

[Rob Frankham]

I too would re-install it. .. but... you need to examine the recess in the block where it fits. That is alloy so if the steel rotors are worn, the recess is likely to be worse. If that looks reasonable, I would reassemble and put a pressure test on the system. If it's within spec, well and good. If it isn't then you spend the money... no choice really.

Rob

[SteveD]

At a glance they look worse than mine which I replaced. Take measurements for clarity. https://forum.boxerworks.com/viewtopic.php?f=1&t=11092

This is from https://youtu.be/8SetkC3hVmg, a screen shot from one of his excellent videos.


These were my measurements. It'd be a waste of time reusing this oil pump I expect.

[Rob Frankham]

Trochoidal pumps are very resilient. My personal rule of thumb is the pump on my R80RT. When went to put it back on the road a little while ago, the rotors were badly scored as was the housing in the block... far worse than the ones shown here. Prior to dismantling, there were no perceivable problems with oil pressure. the mains and big ends weren't excessively worn...no sign that there was a problem. I did have the block machined and installed new rotors but I do wonder if the old ones would have been perfectly fine.

Of course, you also have to take into account usage. If you are intending to do long rides through death valley, then a good oil pump is far more important than if you were riding across the arctic tundra.

My advice would always be to renew but, of course, there is a correlation with how long you intend to keep the bike, the sort of use you're going to put it through and last but not least, how much you can afford to spend.

'Go not to the elves for council, they will tell you both no and yes...' (with apologies to JRRT).

(To which, the response is "Elves seldom give unguarded advice, for advice is a dangerous gift, even from the wise to the wise, and all courses may run ill.” )

Rob

[gspd]

Steve D said:
These were my measurements. It'd be a waste of time reusing this oil pump I expect.

If I were still working in a BMW $hop, I'd agree with you 100%.
I'm older and (much) wiser now.

Oil pumps do not suddenly disintegrate or cease functioning as soon as they reach or exceed the 'loose' end of the spec range; In the real world, they just keep on pumping oil forever and ever and ever, without even a measurable pressure difference. You have to remember that these pumps produce extremely high pressures; the pressure displayed on an oil pressure gauge is measured AFTER the pressure relief valve and won't exceed 150 psi cold.
Without the pressure relief valve, I'd could easily be more than ten times that.

If we were talking about a DRY SUMP motor, oil pump rotor clearances would be more consequential.
Gravity will transfer oil from the oil tank through the gaps of even a slightly worn pump and fill the sump with oil when parked overnight.
This can cause havoc when restarting. Puking oil all over and creating smokescreens sucks for some people.
Many old britishbikeguys have installed petcocks on their oil tanks to prevent this from happening because their oil pumps became 'out of spec' after only xxxxx miles. Sometimes simply removing new pumps from their packaging caused measurable and irreversible wear