'morning,
This is to follow on from the thread in 'Wanted' about binding/stiff oil pumps.
The usual advice is to reface the end plate to remove scoring caused by the gears. I have done this and found it makes things worse. The scoring is there for a reason, clearance, and one thing I noticed is that the end plate may not be perfectly flat as witnessed when it is just lightly rubbed with fine wet and dry on a flat surface like the base of a pillar drill or with a straight edge. The first contact is with the outer edge that sits against the body of the pump and seals (?). Flattening to remove the scoring also takes this edge area away. This can result in the pump not turning at all never mind being stiff. Looking at the other end and the face on the drive body can also be scored but not showing the microscopic dish characteristic of the endplate. A bit of cleaning is ok but refacing it by hand is not easy as not matter how much you try there will all ways be a subtle rocking motion resulting in a surface that it not flat and possibly not square. The drive itself can offer some resistance and probably gets distorted over time and this can be checked separately to eliminate it from the problem. How can this be resolved?
I did find that with the pump assembled there was significant irregularity in the face that sits against the case. Flattening this face will probably do some good as this should ensure a more oil resistant joint.
The A65 pumps are far more rigid and better supported but it is worth putting the pump on with the two main bolts/studs and checking for a gap where the third one goes. There should not be one and the gasket covers this when assembled keeping things level.
Do the same with an A10 pump and check to see what gap there is under the pump where the third bolt/stud goes. There should be a fibre washer in the gasket set that goes here but is thick enough/too thick. Measure the gap and the washer you have.
Do not be tempted to over tighten the nuts in the hope that the oil will not get past the gasket. The torque for the A65 is only 7lb/ft.
The next time I fettle a pump it will be just a clean inside to check for bits stuck in the gears and a light facing of the whole pump if needed. A new pump may seem expensive but should work the best a pump possibly can and give piece of mind especially if a couple of £k have been spent on a top notch engine rebuild.
Dave.
Thanks Dave.
My own view is that the mazac bodied pumps get a distorted body and the whole pump takes a set by overtightening of the retaining nuts. The oil chambers get a bit squashed causing the gears to bind and although you may be able to relieve the high spots there will also be low spots and the result will be lower oil pressure.
This squashing of the main body may also cause the assembly screw holes to be squeezed meaning that there is some binding when they are put through.
If the body has taken a set you may find that it rotates more smoothly when fixed to the crankcase.
Use of an SRM one piece gasket on the A10 means you dont need the fibre washer (which when supplied in gasket sets is seldom the same thickness as the pump to crankcase gasket)
I have used an SRM pump in my A10 for the past 12 years (the body and nose are dowelled to prevent misalignment) and when removed for some engine work during the first lockdown it still revolved smoothly with no binding. For me proving its worth.
Just removed a cast iron original BSA pump from my 1971 A65 and that also revolves smoothly with no binding. A much more substantial pump which I doubt will ever distort.(photo below)
No going back to an old mazac pump for me, too much at risk.