Oil pump rotor clearances?

[mole42]

I'm refurbishing a couple of Hobourn Eaton oil pumps I grabbed at Stoneleigh. Refacing the rotor pair is possible, and refacing the alloy pump body cap is easy, but is there a preferred clearance between the rotor pair and the cap? ISTR a maximum clearance between the inner and outer rotor lobes of 0.008" which seems reasonable, but I don't remember the rest.

Can anyone help?

Richard

[DJT]

From the ROM

[Guest]

I have been blueprinting HE pumps for the Triumph Spitfire for donkey's years.
The early Spitfire had a weeny little cast iron housed pump that never wore out the housing, but was not good enough at all in hot weather

The later car had an alloy body with a considerably longer rotor, which would score internally but still pointed straight down.

They then changed to a totally stupid design with a long angled neck which everyone and their dog claims is an "uprated" competition type thingy.
Of course they haven't the brains to work out an angled neck pump will give ZILCH pressure under heavy braking, and give the most magnificent oil surge.
Cars always brake with much heavier G forces than they can ever accelerate!

In the process of assembling pumps that are actually any good for those cars, I opted for the 2nd gen pump with a new rotor kit.
This is because the bore wears badly on the alloy pump housing so the alignment of the rotor is rubbish, never mind the end float!

Next thing that happens, "county" that wonderful branding operation from XRN turns out a "copy" ostensibly of this pump, whereupon I am only to find, the new repro body has so much clearance on the shaft-rotor it's already way out of spec out of the box, and there's so much clearance in the rotors, I regard them as junk.
These are the "county" repro pumps you will see everyone selling on EBAY, and of course everyone else sells them.

In the end, I had to opt for sifting thru a big pile of recon pumps at TDF, finding 1 or 2 out of 10 which actually had decent repro rotor kits in them, then grinding them in on a face plate myself until they hit a clearance of about 0.002".
The result is convincing, the engines routinely run a hot pressure of 1-2 bar HIGHER than normal, which is particularly useful on the little Spitfire Mk3 1300 which is quite easily capable of knocking out the same power (bhp) as the Stag 3L engine.

(sadly I no longer do this stuff, cos I ran out of patience, with the current spares situation, which is shared with clutches, engine bearings, gaskets and goodness knows what else...)

why this lesson?
because reading between the lines, and seeing the ongoing train wreck which appears to be the Stag/Dolomite 16V/TR7 bullet oil pump saga, it would appear to me you have EXACTLY the same problems, bearing in mind, a decent Sprint 16V or Stag V8 engine is capable of hitting 200bhp...

[milothedog]

Does that answer the OP's question ?

[mole42]

From the ROM

Silly me, I forgot to look at the ROM

Thanks!

[mole42]

Does that answer the OP's question ?

It goes somewhat towards answering my question - if Gareth is using 2 thou on the faceplate I can use that as a working measurement. The ROM gives the maximum, but I really wanted the preferred clearance - GT has given me his preferred clearance which is good enough for me.

By selective assembly I can probably achieve something that's suitably better than the worst case, the two areas that are difficult to resolve are the outer rotor to body clearance and the shaft clearance in the upper bearing. Both will be poor if the alloy casing has worn.

Richard

[richardthestag]

I think Gareth is saying fit a spitfire pump but dont drive in the summer. or brake gently.

Not sure

Anyway where do you get replacement shaft and rotor from Richard?

I have a pump with a good case and cover but the rotor and its cage are outside tolerances in the rom.

I see that SOCspares list the parts but are out of stock

[mole42]

I'm mixing and matching parts I've pulled from used items, the manufacturing tolerances are such that it's possible that a rotor made to maximum size will fit into a housing that used to have a rotor of minimum size. If you see what I mean....

[richardthestag]

I'm mixing and matching parts I've pulled from used items, the manufacturing tolerances are such that it's possible that a rotor made to maximum size will fit into a housing that used to have a rotor of minimum size. If you see what I mean....

I do indeed,

On my worn out pump the rotor and cage have worn but NOT the body or even the cover. i.e. put another rotor combo into the body and it is bang on.

[Guest]

Most people don't realise oil pump rotors are made out of sintered material not solid.
Also usually the drive shafts are knurled not splined to get them to bite & so as not to distort them.

When the 2 are mated together the centre sintered rotor "grows" a little bit to get final clearance.

Lots of engines don't use eccentric lobes pumps at all, they use gears clamped between 2 machined plates,
a bit like on a rootes blower....same as on a Lucas pi fuel pump btw.

Also certain engines (eg the Jaguar V12) use a crank driven pump, not a cam driven pump.
This has the advantage of running twice the speed.

The sworn enemy of good engines is oil cavitation.
It happens a lot more often than most people might imagine.

[stagmuffin]

Gareth any usefull tips on how to avoid cavitation in the stag system

[72BLUE]

Gareth any usefull tips on how to avoid cavitation in the stag system

Fit a Jaguar engine?










........only kidding

[Guest]

I have no idea, you would have to check which level of the engine is prone to poor oil control and foaming.
That's why so many modern engines have plates in the bottom end to redirect flows and oil galleries that are well designed, and have been viewed through perspex inspection holes during dev.
You might be shocked to see the kind of things going on in there.

I am guessing there, but engines really aren't made with that construction any more, and modern turbo diesels have to be absolutely bomb proof.
+
I would hazard a guess, one of the causes of overheating on the Stag is cavitation on the water pump, but that's altogether different problem area as we know.