Servicing The Oil Pump

What is the result if the conical seal is bad? Will this result in more oil being pumped into the crankcases than can be returned to the tank by the pump?

The return side is double the capacity of the feed, even if the seal is missing you will still have a low oil level in the sump. This is assuming the oil pump is not worn out more on the return side than the feed but a quick check is to look at the return flow and make sure its intermittent or has bubbles showing the return side is keeping up with the feed side plus a bit more. If the seal is missing the top end does not get oil so another check is the crack open a rocker feed banjo and see if oil escapes as it will be at big end pressure, if the seal is missing this will be nil.

If you are worried by the seal then get an oil pressure gauge temporarily on the bike by using the banjo joint to pump in, low pressure can also be caused by a maladjusted or worn pressure switch which is under the large domed nut on the rear of the timing cover.

Dirt2Oil said:

What is the result if the conical seal is bad? Will this result in more oil being pumped into the crankcases than can be returned to the tank by the pump?

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IMO, Yes what your saying is correct, eg, "bad" meaning split, not there, buckled, cracked ..

But more information will encourage a lot more response like,

Is there oil returning to tank at a "steady flow" rate?????????

Is there "no Oil returning" to Tank ?????????????

How long do you run it and then "Panic" cos no oil is returning ????????

Was the pump working before "servicing" and why was it serviced ??????

Its a bit like saying to the Doctor, "i feel sick"..

olChris said:

Dirt2Oil said:

What is the result if the conical seal is bad? Will this result in more oil being pumped into the crankcases than can be returned to the tank by the pump?

Click to expand...

IMO, Yes what your saying is correct, eg, "bad" meaning split, not there, buckled, cracked ..

Click to expand...

No, it isn't correct.
The scavenge side has considerably more pumping capacity than the feed side, therefore if the pump is operating normally, the scavenge will empty the sump at a faster rate than the feed side is capable of filling it.

I have the head and barrows currently off to determine reason for excessive smoking on left cylinder and to replace leaking gaskets. So while I am at it thought it would be a good time to look at the oil pump. Appears I can't stop from going deeper and deeper into this thing.

The seal was there but squished up pretty good. Before I replaced the rocker feed lines to SS oil was observed circulating through the hoses. A new seal has been ordered just in case.

Oil is returning to the tank but I am wondering if it is all through the breather hose. I have placed a piece of tygon tubing firmly over the holes in the case where the oil pump mounts. I can get air to pass through the inlet and return lines but not the scavenge hole ( the round hole furthest on the right). I have been grasping at straws trying to avoid the crankcase breather mod suggested in another thread but looks like I may have to go deeper still.

Should I be able to blow air through the scavenge hole with the cases empty of oil?

Combat's don't need an oil pump to return oil to the tank via the factory breather hose. Combats have long thin internal sump passage that can get blocked by Combat shedding its cam thrust washer tabs. Thrust washer tabs get beaten by crank till size-shape to get stucked into return side of pump which can damage pump gears. Oil pumps have twice the sump size gears & out flow than pressure side. The TS cover gasket and the oil pump nipple seal come in 2 combo's of thicknesses that are supposed to match to give correct crush to seal w/o damage or significant pressure leaks. Call or search Old Brits for the correct combo of seals to buy. Easy enough [if messy] to top off oil tank and pull its return hose into a jug and start up and rev a bit to see if it blasts out mixed oil/air adequately.

Dirt2Oil said:

Should I be able to blow air through the scavenge hole with the cases empty of oil?

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Yes.

I have the head and barrows currently off to determine reason for excessive smoking on left cylinder and to replace leaking gaskets

Click to expand...

Depending on when it smoked you can make a fair analysis, on acceleration would indicate rings need replacing, on deceleration would indicate inlet valve guide or seal. You would need to check bores for size in case new pistons were needed but 2 sets of rings per piston size seems to be the norm on Commandos.

Should be able to blow bubbles through over filled crank cases by two routes in Combat, oil pump sump path and breather hose path. If internal case passage clogged its hard to clear as stuff enters with passage heat swollen then extra trapped when cool enough to handle. Moving Combat drain to rear bypasses this Norton oversight and some hi rpm wet sump too though the factory breather wont like very much oil accumulate as can return way more oil volume than the pump can. Combats are wet sump damage immune, may leak at hi throttle rpm, but not at risk like all the other models of blowing out an "especially weak" crank seal fitting fault.

You can see if most or all the oil is returning by breather hose just looking in oil tank, oil pump spits and spatters out against side of tank, while breather shoots a pencil thick solid jet - until sump lowered to mostly air left. Breather return can hit ceiling if testing blipped too much over fast idle, pump only splatters a mess close to cap.