Auxillary Housing and Oil Pump

I think I have mentioned this unit before- it simply bolts onto the side of the crankcase. The bolts though are different lengths so I will need to sort these out carefully when refitting as I have forgotten what goes where!

Auxillary housing removed, Note cambelt drive pulley 

at front and pump housing at rear. Drive shaft visible 

though centre of body

I have no reason to doubt that this pump works fine- but I have no reason to know that it does either!  I decided to take it apart and check it for wear. The pulley nut (Allen screw) was removed whilst the pulley was held using a wooden dowel through the pulley holes to prevent rotation. The pulley could then be removed with a two legged puller pressing against the pulley screw which was reinserted about half way to prevent damage to the threads. Make sure that pulley extraction isn't prevented by this bolt as its drawn off the shaft- obviously if this happens tightening the puller won't help so check as you remove it. I am told that this removal should have needed heat as the pulley ought to be loctited onto the shaft. I didn't find a problem but its always possible my pulley hadn't been fitted properly in the first place. 

Insert wooden dowel through pulley hole to prevent rotation before unscrewing centre bolt and special washer beneath

Once pulley removed the Woodruff key is eased out...

And the circlip behind it can be removed

At the other end of the unit, the pump housing simply
unbolts from auxillary housing body

Revealing the annulus and rotor keyed to the shaft.

This revealed the working of the pump, a rotor keyed to the centre shaft around which is spun an annulus, the complex interlocking lobes squeezing the oil to provide pressure and movement in the system. Everything looked OK but I wanted to check it. This was quite difficult as the manual gives four determinants for wear- none of which were immediately obvious and all require detailed and accurate measurement.

Rotor/Annulus tip clearance- as the rotor spins the gaps between its teeth and the cutouts in the annulus narrow... this should be in the range 2-6 thou (0.05-0.15mm) but as its a highly curved structure a feeler gauge is useless. I took it to a local engineer/modelmaker who had some gauge pins. Sadly the smallest was 6 thou so all I can say is that the gap is smaller than that. As an alternative I measured some kitchen foil. I only have a metric micrometer but in my hands the foil was 0.03mm thick. I cut a small sliver of this and inserted it into the bottom of one of the annulus cutouts. I could then turn the shaft (and thus the rotor) until the gap closed. Even at its closest I could still pull the foil out smoothly so my estimate of this gap is between 0.03 mm and 0.006 inches or between 1-6 thou imperial. I think this is in range.  

Annulus End float. I had expected that this meant that the annulus would be thinner than the housing into which it fits by 1-3 thou permitting some axial lengthwise movement of the annulus along the shaft of the pump. This can be measured by fitting a straight edge across the housing and probing the gap with a feeler gauge. I was therefore very surprised to find that the annulus actually projects beyond the housing and the gap I detected (1.5 thou) was between the ruler and the housing itself! Having checked on the forum I was advised that this gap should be measured with the gasket in place and adding that showed that there was a clearance of 2.5 thou between the annulus and the top gasket surface and so I concluded therefore that this measurement was still in limit.

Straight edge across the annulus with
gasket in place

2.5 thou gauge slid smoothly
between annulus and straight edge

Annulus Housing clearance. This is the radial clearance between the diameter of the annulus and diameter of the housing wall- and this should be 7-12 thou. However this should be easily measured using a caliper to take the external diameter of the annulus and the internal diameter of the housing. Subtracting these should give the housing clearance. 

Its tricky to get accurate measurements with a caliper, but I don't have a micrometer big enough. I took 5 separate measurements and got a range of 5-10 thou and an average of 8.5. This puts the wear within limit.

Rotor End float- I don't know what this is! The rotor is keyed firmly to the shaft and can't move separately, however auxillary shaft end float (given elsewhere in the manual) isn't the same as rotor end float so I'm mystified. However Annulus end float refers to a radial clearance so perhaps rotor end float is also radial? However as its fixed to the shaft I can't see how this could be measured. 

Oil Pressure Relief Valve This valve is non serviceable as far as I can tell and is built into the oil pump housing. The valve consist of a spring loaded flap. I checked that this will push down with pressure from a screwdriver and then flushed the valve through with WD40 to shift any muck that might be jamming the valve.

Inside Annulus housing. Oil pressure relief valve at 3 O'clock, the sealing plug visible at the bottom of the opening. The bypass tunnel it communicates with is at 11.00

Overall, of those parameters that I could measure all seem pretty much in permissible ranges so I'm going to rebuild and refit the pump with new gaskets and oil seal. I'm also replacing the pulley circlip in case the old one was loosened during removal.

Reassembly
The order for this job has to be oil seal, shaft, circlip, pulley, pump  and pump housing. This is so that all forces exerted say in seating the pulley, can be transmitted down the solid metal shaft and not onto the pump housing.  The oil seal simply pressed in to the housing using a seal installation drift. I used a Draper tool but a socket would do.

Oil seal installed. Note drilling opening into space beneath seal at about 1.00 O'clock

The seal didn't bed right down onto the body which worried me until I checked the pre-strip photographs, the old seal was installed to the same depth (app 1mm below the outer edge of the recess) as well. I observed a drilling and presumed oil-way that opens into the space beneath the seal and which would be blocked if the seal did bed down fully. I suspect the is the reason. The new seal is a double lipped  type and the old one was only single lipped. I'm guessing this means you could use either.

Apply lots of assembly grease to the auxillary shaft especially over the journal areas and around the seal lips. I use Red assembly lube as its cheaper than Graphogen. The insert the shaft from the pump end right through the seal and fit the circlip to the pulley end. Dont try to open the circlip up in order to slip it over, this will bend it too far and distort it, instead push it onto the shaft end and tap it over with a mallet. It will then slide down the shaft and clip into its groove.

Insert the Woodruff key taking care that it is centralised and slips fully into its slot. Support the pump end of the shaft on a wooden block and line up the pulley keyway with the shaft key. Start the pulley gently by hand then tap home using a socket that just slips over the pulley hub. The manual calls for Loctite on the pulley. I didn't use any- I reckon its not going anywhere! It can't go backwards owing to the circlip, or forwards because of the nut and can't rotate owing to the key. I suspect I may well will be doing this job again and loctite will simply complicate any future strip.

Starting the pulley. Note assembly grease on shaft

Pulley fully seated onto circlip

I could then fit the special washer and hex plug screw into the shaft end, hold the pulley with a dowel through the pulley holes and tighten the bolt to the correct torque. I didn't have a torque wrench hex bit at the time but I've got one coming and I'll check the torque before I refit the unit.
The pump was then reinstalled using a fresh gasket. This is a plastic gasket and is installed dry. It looks like it will go in any way round but in fact it will only fit in one orientation. The rotor has to be centralised in order to fit so I used the housing to jiggle it

Fit Gasket dry in correct orientation

Fit annulus and centre using the housing without regard to the bolt holes, then remove the housing and line up the pins and holes without moving the annulus, Grease with assembly grease inside and around edge of annulus...

... before offering it back up in the correct orientation. It will be necessary to lift the pulley off the bench so that the shaft can drop back allowing the housing to fit.

Finally the bolts were inserted and torqued up diagonally to 7ft/lb. The last step was to clean the gasket mating surfaces and then wrap the pump for storage before I can refit.