oil pump service
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An acknowledged expert thinks so:
oil pump maintenance
Postby dynodave » Mon Oct 18, 2004 1:31 pm
Just a reminder. Lapping the body of the pump to reduce excessive side clearances is normal maintenance of this style pump. But be advised it adresses only one of 4 pump leak-thru paths and should not be thought of a complete pump maintenance, but rather as a improving a dying pump.
4 leak paths.......
These three feed out to the crank ......
gear ends to body (lap body)
pump gear teeth end to body
pump gear to gear clearance
and last
cross cavity leakage down the shaft to the scavange side of the pump and back down to the sump
oil pump maintenance
Postby dynodave » Mon Oct 18, 2004 1:31 pm
Just a reminder. Lapping the body of the pump to reduce excessive side clearances is normal maintenance of this style pump. But be advised it adresses only one of 4 pump leak-thru paths and should not be thought of a complete pump maintenance, but rather as a improving a dying pump.
4 leak paths.......
These three feed out to the crank ......
gear ends to body (lap body)
pump gear teeth end to body
pump gear to gear clearance
and last
cross cavity leakage down the shaft to the scavange side of the pump and back down to the sump
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Hehe just keep in mind Norton quilckly quit putting oil guages on Commandos after about a season of horrified reports of Zero pressure at hi way speeds, so may not even require an oil pump but to feed your head. My thinking if mine wet sumped so much it hindered an easy step down cpld start I'd drill hole in the slump plug and stick on a super magnet with a bit of rubber seal glued on, then just slide off, drain and let magnet snap back on, as sure ain't gonna pull it straight off. A valve may get knocked off or bent to foul its valving. Here's a few more upgrade details I collected for the areas concours pointed out.
oil-pump-ways-wet-sump-mods-t9312.html
oil-pump-ways-wet-sump-mods-t9312.html
hello. hearty good wishes to all.
Just a small point regarding gear pumps.
Backlash, the amount the tooth space exceeds the tooth width, has no bearing on the efficiency of a gear pump, unless it is a really really excessive amount, so don't be concerned about about a bit of tooth thickness wear.
Backlash is controlled at manufacture and by the time the tooth thickness are worn excessively, the pump is worn out anyway.
All other advice on these pumps is very good and should be followed. Backlash is the least of all problems
Bradley
Just a small point regarding gear pumps.
Backlash, the amount the tooth space exceeds the tooth width, has no bearing on the efficiency of a gear pump, unless it is a really really excessive amount, so don't be concerned about about a bit of tooth thickness wear.
Backlash is controlled at manufacture and by the time the tooth thickness are worn excessively, the pump is worn out anyway.
All other advice on these pumps is very good and should be followed. Backlash is the least of all problems
Bradley
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Might not affect the pumping efficency , as the oil goes outside the gears , rather than through them like a ( mangled ) finger .
BUT :
Would explain the insideous drain down when parked giveing the smokey start up from a sump full og oil . :mrgreen:
BUT :
Would explain the insideous drain down when parked giveing the smokey start up from a sump full og oil . :mrgreen:
Hello all.
Matt, respectfully a few more comments to your post.
the backlash is not the most likely and single cause of the dreaded leakdown. to be the main cause, the pump would need to come to rest with a pair of teeth having no contact with each other. in other words one tooth exactly in the middle of the tooth space. as there is more than one tooth in mesh at any given time, this is unlikely and also provides more restriction.
Oil does indeed get carried in the tooth spaces, around the pump from the inlet side to the discharge side and is prevented from escaping by the limited radial clearence between the gear OD and the pump chamber. it is forced out under pressure when the teeth actually come into mesh and the path of least resistance is the delivery orifice.
Radial clearance between the OD and the casing, provides an lesser path of resistance and will affect effiency also.
Axial clearance is the most likely cause of leakdown, as the clearance is critical and the most likely wear point.
The shafts are well lubricated and are usually the least likely to wear and give trouble.
reducing the axial clearance will in most cases restore effiency, and reduce leakdown, if done correctly. Reconditioning a worn pump requires a focus on a couple of things. I start with ensuring the pairs of gears are the same thickness to a couple of tenths. also the bore depths must be the same to a couple of tenths. this can be achieved by lapping. only then can the axial clearance be completed. the best clearance I have found is 1/2 to 1 thou with no signs of sticking or friction. on pumps that have never passed solids, wear on shafts and bores is neglible. if repaired properly, these pumps are very reliable.
Not trying to make a mountain out of a molehill here, but most damage is done by pump passing solids or forigen bodies. in 90% of cases reducing axial clearance will restore a pump to good operation for many years. these are simple external gear pumps, well balanced hydraulically, and are very reliable for normal street use. racing applications I am not able to comment on.
Best wishes Bradley
Matt, respectfully a few more comments to your post.
the backlash is not the most likely and single cause of the dreaded leakdown. to be the main cause, the pump would need to come to rest with a pair of teeth having no contact with each other. in other words one tooth exactly in the middle of the tooth space. as there is more than one tooth in mesh at any given time, this is unlikely and also provides more restriction.
Oil does indeed get carried in the tooth spaces, around the pump from the inlet side to the discharge side and is prevented from escaping by the limited radial clearence between the gear OD and the pump chamber. it is forced out under pressure when the teeth actually come into mesh and the path of least resistance is the delivery orifice.
Radial clearance between the OD and the casing, provides an lesser path of resistance and will affect effiency also.
Axial clearance is the most likely cause of leakdown, as the clearance is critical and the most likely wear point.
The shafts are well lubricated and are usually the least likely to wear and give trouble.
reducing the axial clearance will in most cases restore effiency, and reduce leakdown, if done correctly. Reconditioning a worn pump requires a focus on a couple of things. I start with ensuring the pairs of gears are the same thickness to a couple of tenths. also the bore depths must be the same to a couple of tenths. this can be achieved by lapping. only then can the axial clearance be completed. the best clearance I have found is 1/2 to 1 thou with no signs of sticking or friction. on pumps that have never passed solids, wear on shafts and bores is neglible. if repaired properly, these pumps are very reliable.
Not trying to make a mountain out of a molehill here, but most damage is done by pump passing solids or forigen bodies. in 90% of cases reducing axial clearance will restore a pump to good operation for many years. these are simple external gear pumps, well balanced hydraulically, and are very reliable for normal street use. racing applications I am not able to comment on.
Best wishes Bradley
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It occurs to me that any "normal" vehicular oil pump would wet sump under the same conditions - the oil reservoir above the pump - regardless of how tight the clearances are in the pump. The only way it can be avoided is by providing a valve SOMEWHERE. Obviously on the Commando, it is usually placed on the input (suction side), which most engineers would say is NOT the place for any sort of restriction.
But there is nothing inherently wrong flow-wise with having a non-restricting valve - like a standard ball valve of proper I.D. in the suction side. The issue, as has often been debated here, is the possibility of forgetting to open the valve or the possible failure of whatever electrical device may be installed to prevent starting if it is closed. There is, of course, the appearance issue as well -ball valves are pretty obtrusive. I suppose if you painted it black it might "blend in." But then it is less noticeable to the rider as well, and thus easier to forget about.
But there is nothing inherently wrong flow-wise with having a non-restricting valve - like a standard ball valve of proper I.D. in the suction side. The issue, as has often been debated here, is the possibility of forgetting to open the valve or the possible failure of whatever electrical device may be installed to prevent starting if it is closed. There is, of course, the appearance issue as well -ball valves are pretty obtrusive. I suppose if you painted it black it might "blend in." But then it is less noticeable to the rider as well, and thus easier to forget about.
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Shouldve made it clearer . the thought was that - If the teeth are severly worn , say 15 or 20 thou backlash -
as one gear is a free idler , the weight of the oil would tend to equalise ea side of the messed teeth .
So thered be clearance for flow . even if the rest of the pump were refaced and clearanced .
The point I was trying to make is that if there were yards of slack in the mesh of the two return gears , its unlikely to not bleed down thus giveing smokey starts .
Dunno if they ever refined ( or cheapened
) pump metalurgy , machineing & finish . The thing seems to have been passed down from before the war .
The Original / first ones might be real quality - though youd need to fit the six start drive gear . :evil:
as one gear is a free idler , the weight of the oil would tend to equalise ea side of the messed teeth .
So thered be clearance for flow . even if the rest of the pump were refaced and clearanced .
The point I was trying to make is that if there were yards of slack in the mesh of the two return gears , its unlikely to not bleed down thus giveing smokey starts .
Dunno if they ever refined ( or cheapened
) pump metalurgy , machineing & finish . The thing seems to have been passed down from before the war . The Original / first ones might be real quality - though youd need to fit the six start drive gear . :evil:
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