SERVICING THE OIL PUMP

Section C25 of my Norton workshop manual discusses how to service the oil pump. I contend that following this procedure may cause the oil pump gears to bind in service.

The procedure calls for a "barely descernible stiffness" upon flattening the body and re-assembling the pump. This technique produces very tight clearances. The thinking here is that minimal clearance between gears and pump body results in a more efficient pump and less chance for oil drain-back.

However, these very tight clearnces may cause problems when bolting the pump to the engine case. For instance, preloading the rigid pump body against the relatively soft aluminum engine case often creates a slight strain in the pump body. This strain or movement takes up all the clearance between the gears and body that was so carefully minimized in the preceding "service" steps. And with all the clearance consumed, the gears have no choice but to rub against the end plates.

So, after servicing your oil pump and bolting it to the engine, it is important to make sure the pump rotates freely, without a trace of binding.

Regards,

Jason

The time has come to do the pump rebuild on my bike so I'm interested in hearing opinions on this. Wouldn't the gears just "break in" and establish the correct clearance as they rub? That's what I thought the manual was suggesting.

I also bought one of those inline anti-drain valves so I'm attacking the problem at both ends. I'm tired of having to drain the sump before EVERY ride!

Debby

Debby,

Yes, you are correct in assuming that the oil pump gears will "break in" after use. But this process results in the removal of metal from the pump end plates and gears. The oil pump pressures these metal particles into all sorts of moving parts, like rod bearings, main bearings, cam shaft bushes, etc.

Metal particles in these areas acdelerates wear. So, I prefer to set my oil pump up so that it turns freely, thereby minimizing the amount of metal that gets rubbed off and circulated through the oil system.

Regards,

Jason

Servicing the oil pump

Hi Jason,

I don't follow your reasoning. The pump mounts at a 90 degrees to the direction of the pump gears and the end plates. The mounting flanges of the iron pump body have no bearing on the gear cavities. How does the "softness" of the crankcase play any role?

David,

I believe that the aluminum mounting pad on the engine block distorts slightly the first time the pump body is bolted up to it with 15 ft-lbs of torque. The pump being rigid tends to pull the aluminum, perhaps in the area around the studs, out of shape. The amount that the mounting pad is mis-shapen is probably quite small but it's permanent.

You are correct, the pump gears and their bearing surfaces are 90 degrees to the mounting pad face. However, I feel you are incorrect in saying that: "The mounting flanges of the iron pump body have no bearing on the gear cavity".

You see when re-attaching the pump after "servicing," the pump body must now bend and or twist in order to conform to the slightly distorted mounting pad face. If the pump were to bend precisely 90 degrees to the mounting flange it may not cause the gears to bind. However, I postulate that the body actually twists, which causes an unparallel situation between the gear faces and the their corresponding surfaces.

Now bear in mind that the clearances between the gear faces and pump are miniscule after "servicing". So, even the slightest movement of the pump body will throw the gears out of alignment.

I have seen a freshly serviced pump that turned feely on the bench bind once bolted in place on the block. Careful flatening of the aluminum mounting pad with a small flat file and sand paper cured the problem.

Does this make any sense?

Regards,

Jason

pump body flex

Hi Jason,

Again I find it difficult to understand how there would be any flex in the pump body. First cast iron doesn't flex very well especially at the relatively low torque required to fasten the pump. Second any slight lack of flatness of the crankcase boss would be taken up by the gasket. Last, if any twist did occur the gear teeth would contact the cavity walls before the end plates.

Hi David,

At the risk of sounding impudent, here goes:

Typical cast iron has a modulus of elasticity that is about half of that of mild steel. This means that for the same unit stress, a cast iron piece will deform nearly twice as much as a steel piece.

So, cast iron will readily flex. Mild steel can be shaped into a pretzel without breaking whereas cast iron will break soon after it reaches its elastic limit. This gives the incorrect impression that cast iron does not flex at all.

Also, the gasket may not compensate for lack of flatness on the crankcase boss. The gasket is quite thin and may just follow the contour instead of filling it in.

And lastly, how else would you explain a pump that binds when torqued down to the block but turns freely once the nuts are loosened slightly? :wink:

Regards,

Jason

I have been following this thread with interest also, having never actually done the job on an oil pump.

To quote you Jason,

"Also, the gasket may not compensate for lack of flatness on the crankcase boss. The gasket is quite thin and may just follow the contour instead of filling it in."

I guess you could file flat the crankcase boss if you were VERY careful not get filings into the gallerys ? Assuming you were doing the job with the engine together, it would be simpler if the engine were stripped.

Or do away with the very thin paper gasket & sparingly/carefully use your preferred sealant ?

Watya reckon :?:

And mate! can u not use words like "postulate", I have to go get the dictionary out ! Just kidding, I have the little oxford dictionary next to me all the time.

Nortonfan,

I was working on a partially assembled engine when I discovered the oil pump phenomenon. In addition, there was not a pump drive gear installed on the crank shaft. This gear must be removed in order to spin the pump after bolting it to the block. Chances are few people will remove this gear after installing their "serviced" oil pump. As such, they would not be able to spin the pump to check for binding.

You are correct about being careful not to get aluminum filings in the oil passages. I used a dab of grease to seal off the passages before filing. Then after filing, I carefully removed the grease with a tooth pick and bits of paper towel.

I would not use any gasket goop in lieu of the paper gasket for fear it would squish out and get into the oil passages.

I am keenly interested in what other people discover after servicing their pump. If anyone decides to tighten up the clearances in their pump, please spin check the pump afterwards and let me know what you find. Perhaps my case is an isolated instance?

"In addition, there was not a pump drive gear installed on the crank shaft. This gear must be removed in order to spin the pump after bolting it to the block. Chances are few people will remove this gear after installing their "serviced" oil pump. As such, they would not be able to spin the pump to check for binding."

Point taken & it is a good one for unwary engine rebuilders !

I spent yesterday putting my 850 frame together & will be looking at putting the bottom end together early next week. Hence my interest & I must say this thread is good timing for myself. The 850 oil pump feels "good" when I spin it but I will be checking it again once it is "mounted" !

Thanks for your timely reply.

:arrow:

Dynodave,

Did you actually spin the newly serviced pump after mounting it to the block?

I assume you mounted all the pumps you rebuilt using the gasket eliminator. Perhaps eliminating the paper gasket helps to keep everything square?

Fishing,

Jason

Your input is noted & respected DynoDave, thanks for assisting us.

I reckon u r dynamite actually mate !!!

Reg tryin hard to keep on dynos good side

Sounds like this is one of those jobs I want to give to a professional. I think I'll send the pump out for rebuild rather than (try to) deal with all of this myself. Thanks for the heads-up DD!

Debby

:arrow:

Jason,

Ignorance is bliss they say.

I have mounted quite a few oil pumps using "silastic" sealant even though many engine builders say not to use it. Used "Intelligently" it has never been a problem for myself. I also use it instead of a base gasket now & have No leaks whereas there used to be leaks with the paper gasket. Same for the rocker covers.

I postulate now that if it does that good a job on those areas, I should never have an "air" leak at the oil pump. (c postulate, watapisser :wink: )

watcha reckon bout that :?:

And Debby, I think you would be wise to have your oil pump done professionally. Surely there is an honest one that will do it for you & return "your" pump & not some pos they wanna offload. You get what I mean 8)

nortonfan said:

And Debby, I think you would be wise to have your oil pump done professionally. Surely there is an honest one that will do it for you & return "your" pump & not some pos they wanna offload. You get what I mean 8)

Click to expand...

Message understood! Thanks - I wouldn't have thought of that. Maybe I'm too naive :shock:

Debby

I removed my pump tonight. How do I know if it needs servicing? There's a small amount of axial play in the drive shaft, probably 1 mm or less. Should it have no play at all?

Mine had the paper gasket and no sealant. The mounting nuts didn't seem very tight. The spec says 15 ft-lbs but these might have been looser. Maybe that was part of my wetsumping problem?

Debby

Debby,

You should not have any play in the "drive shaft" of your oil pump. You can expect a significant increase in efficiency if you servicve your oil pump. And as a bonus, the repaired pump may slow down your wet sumping problem.

Illf8ed,

I took a close look at the oil pump mounting pad on my spare engine today and discovered that my theory about bolt torque upsetting the aluminum seal face is bogus. The oil pump bolt holes are helicoiled (sp) and the first helicoil thread is about .18 plus inches below the face of the block. As such, the mounting bolts ('75) or studs (pre '75) would have to be way over torqued to pull the aluminum around the tapped hole above the pump mounting surface.


Regards,

Jason

Well, it turns out the biggest problem is the conical oil seal - it wasn't there! Whoever worked on it last removed the seal and just applied a thin film of gasket eliminator to the mating surface on the cover. Like that's going to do anything. Probably wasn't doing my oil pressure any good either.

End play looks like 0.30mm. The screws are double-staked (two punch marks per screw) and I'm certainly not going to get them loose. Would have to send the pump out and let an expert work on it. But I'm thinking just replace the seal and put it back together. Oh and the mounting nuts weren't very tight either - maybe 10 ft-lbs instead of 15. A paper gasket was fitted, no sealant. Should I just use a bit of sealant as discussed above w/o a gasket?

Debby