LT85 Oil Pump problems

[lo-fi]

Following on from my rebuild thread, I had some problems with the oil pump. This manifested as a sort of ratchet noise that came from the bellhousing whenever the clutch was engaged. Not fun as I only found this out once I'd finished putting the darn thing back in, but such is life with Land Rovers. Here's the tale for those who might be interested:

The oil pump on the solid case LT85 is driven from the layshaft via a square drive in the front end. Original gears are some kind of fibre/nylon/plastic something and come in two pieces:

 

Inner and outer, inner having the drive built in. You can see this one has failed - the square has rounded off, so clearly the pump wasn't spinning. Ahem. No doubt this is why the later replacements are metal:

 

Sorry I don't have a better picture.

A three piece design, with the drive shaft being separate from the inner gear with a square drive broached in the inner gear. This is all contained in the front housing by a flat metal plate with a hole bored to let the drive through, sealed at the edge with an o-ring

It all looks great - parts from a 100% reputable supplier, so apart from checking the housing for wear, I reassembled as per the book and instructions with the kit and didn't give it a second thought. Bevelled side of plate goes towards the gears, longer square drive into the layshaft. So what happened, and why was it noisy? The problems, I found, are many....

Having removed the pump, I could replicate the noise by simply turning the pump drive. I started measuring, checking clearances, and fits, and wasn't happy with what I found. 

First up: The metal gears are smaller width than their plastic counterparts. By 0.15mm for the inner and .1mm for the outer. Which is kind of understandable, but in the case of the inner gear, this is enough to let it rock over against the force of pumping the oil and have it foul the housing internals. It's also thinner still than the outer, which makes no sense at all. You'd think it should be located in place by the drive shaft and plate, but that's not the case.. Worse still, the plate itself was found to be undersize in outside diameter, leaving .3mm clearance for it to move about in the housing. It's not machined, just a metal stamping, judging by the parting marks. But the shocker is yet to come.... The metal driveshaft is a straight dimensional copy axially of the plastic original, which itself is arguably too short. Note that the worn off part of the square drive does not extend the full length in the picture above. No doubt this is to leave room for expansion, wear, assembly tolerances etc, and is OK for the one piece design. However, with nothing retaining it from migrating, it's free to move into the layshaft leaving only a couple of mm driving the inner gear, and the square drive grinding into the cover plate, rather than the round part:

 

It's quite the cascade failure, and no wonder it was noisy. I did a lot of soul searching and research to check I'd not assembled the box incorrectly (layshaft out of position, housing wear etc.), but with an unmolested box next to me that measured exactly the same, I concluded it was nothing I'd done wrong. Now, I'm not the sort to take this kind of thing laying down, so out come the tools

Clearly a spacer is needed to keep the driveshaft from disappearing too far into the layshaft, which is easy enough. I left .6mm axial clearance, and also added a little spring to help keep it in place:

A small hole got machined in the driveshaft to take the spring too:

 

So with that sorted, I started thinking about how best to fix the inner gear side clearance... the radial bearing surface on the plate is pathetic, as evidence by the wear on the plastic shaft, and could could both be fixed by a bronze top hat bush, so I set about turning one up and modifying the plate for a good press fit:

Shown here doing a test run on an serviceable plate:

This gives 10x more radial bearing surface than the original!

The brim is 1mm smaller than the root PCD of the teeth, so no interference with the outer gear teeth is possible. It was pressed in, then measurements were taken to leave it slightly proud of the plate at its finished size, taking up the excess side clearance on the inner gear. I reasoned the the outer gear being much larger and having a smooth outer surface is able to stabilise itself well enough as was, so I left well alone. It leaves a bit of clearance which will let oil leak around, but it's just to circulate oil into the mainshaft for the needle bearings, not to create pressure, so I deem a little loss acceptable.

Here it is assembled and being tested on the bench:

 

I learned a lot from this! Firstly, that the forces are impressive, even at moderate speed. Those original washers holding the plate down bent in moments! Also that once freed to move a little and rock over against the pressure, the inner gear really tries to push the driveshaft out with considerable force... But it was still noisy even when clamped correctly  This was the point that I found the cover plate to be undersize, so my only real option was to make a new plate and another bronze bush:

 

This worked like a charm on the bench, so back on it went and the box got put back in. I'm happy to report, it's quiet as a church mouse, so I'm very happy. There you have it - I hope it's interesting! I could have waited, spoken further to the supplier etc. And indeed it's possibly just a bad batch, but it was Christmas shutdown, and I think my solution is better and should be longer lasting anyway. Gave me something interesting to do, and you guys to read about too!

Happy new year

/Ian

[Retroanaconda]

Impressive fix, thanks for sharing. 

[Davo]

7 hours ago, lo-fi said:

Now, I'm not the sort to take this kind of thing laying down, so out come the tools

I really like your attitude - I dread big jobs like this! 

By the way, I think you've discovered the future: just buying new parts and fitting them is so hit-and-miss, so with the machine tools you've got, you can make and modify what you need. That's the way most of us will have to go if we're going to keep our old heaving wrecks cherished classics on the road. 

[Mutley]

A great read, very impressed with your knowledge and abiliy to resolve the problem.

There is no greater sense of satisfaction than when you accomplish something that is better/more practical than the original design. Knowing it was an idea from your head that you then make happen! Well done Sir.

The difference between being a mechanic and a fitter.

[lo-fi]

5 hours ago, Davo said:

I think you've discovered the future: just buying new parts and fitting them is so hit-and-miss...That's the way most of us will have to go if we're going to keep our old heaving wrecks cherished classics on the road. 

I could not agree more! I've spent many years now working on steam engine projects surrounded by inspiring engineers for whom this is a way of life because there simply isn't another option. It's impossible not to get swept up with it. The bronze bush is classic steam era tech, for which I make no apology...

3 hours ago, Mutley said:

The difference between being a mechanic and a fitter.

Owning an old landy should challenge us to be more fitter than mechanic, I think! As Davo points out, pulling parts out of a bag and assuming they're 100% is becoming increasingly hazardous. Not necessarily because the parts are poor quality (though sadly this is often the case), but because the parts surrounding them may well not be to spec in some subtle way not pointed out in any manual, and you're left with no option but to get creative.

Thanks all for the kind words. I'll try and remember to photographise and write up my next bout of tinkering. 

 

TTFN

/Ian

[Davo]

Ah, steam engines . . . that explains it!!! You've hit the nail on the head there; that's the new era we're entering with these cars. (And even these days I already have enough trouble trying to explain that my Range Rover has carburettors on it . . . oh, those looks of confusion.) 

[cackshifter]

Inspiring fix. Thanks for posting, and glad it worked out Ok, nothing worse than spending a lot of time on it and still having a problem.

[Soren Frimodt]

Another great piece of Tech lo-fi So I take it you gather that you actually would have been better off with a set of Genuine fiber gears in the first place? Obviously with the fix you've made now your much better off, but for someone else fixing up an old LT85 that doesn't have your skills?

[lo-fi]

17 hours ago, Davo said:

...trying to explain that my Range Rover has carburettors

I feel your pain! 

2 hours ago, cackshifter said:

nothing worse than spending a lot of time on it and still having a problem.

Sounds like Land Rover ownership to me! lol  But I wouldn't have it any other way; it's part of the charm.

 

In all honesty, I'm really not sure Soren. It's possible this particular box has a buildup of parts that on its own are in tolerance, but added up across many bits causes this problem with the pump drive. Having said that, the other box appears for all intents and purposes to be exactly the same, so all other things being equal I'm not sure how it's ever supposed to be what I'd consider "right". I did look at getting a set of plastic gears, but they didn't seem easy to find, and I wasn't sure the places that advertised them actually had stock or would just turn around and say they're no longer available having been superseded. If anyone is doing DIY rebuild, I'd encourage them to pop the cover plate on, put the drive through and see how it looks. An engineering firm just about anywhere could probably whip up something like I have just given the parts, photos and a quick explanation, so it's not out of reach even if you don't own a lathe or feel confident to tackle. I'd be interested to see how anyone else gets on!

Once again, thanks for all the kind comments.