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17th December 2004


Opinion: AMC Anorak Part 4

Have you ever wondered how the lubricant in your engine gets from tank to sump and back again? Frank Westworth gets pumped up, and then strikes oil...

It's not easy to work out how long I've been smitten by things AMC (I have to include Norton here, for secret reasons which are not entirely a well-kept secret), but it is certainly a long time. And in all that time, I have occasionally found myself wondering how and why the heavy AMC singles' lubrication system works. OK, I entirely accept the idea that I should give up all this at once and Get A Life, but sometimes, on long dull train journeys, or while lying awake in the silent, bleak hours celebrating the excellence of the BBC World Service, my mind wanders towards … the AMC single and its oiling. Oh well, there's no hope…

Just in case you are not entirely familiar with the remarkable world of single lubing, can I remind you that what happens goes a little like this. Proud AJS or Matchless Owner pours glittery golden clean oil into his bike's oil tank. I will make no comment on what kind of oil Proud Owner uses, because it seems that every time I remark that I tend to use whatever is cheapest on the shelves of my local garage, and just change it a lot, I get shot down in flames. This is A Change, in fact; in those distant days when I was more involved with Matters AMC than today, I often remarked upon the cheap thrills of using Tescoil to ease my frictions, and those folk who cared about such things, and they were thankfully few, tended to agree.

These days, when old bikes are ridden less and slower than a decade and a half ago (in general; I understand fully that you, gentle reader, ride everywhere at 100mph on your Bantam), it feels like every time I raise peepers above the parapet I get shot at! Plainly, either cheap oils have got worse than they used to be, or our bikes have become somehow more classic and picky.

One of my remote acquaintances runs his 1954 Matchless G3LS on a diet of fully synthetic oil, oil which was originally intended for modern multi-cylinder, multi-valve, etc, etc engines revving to 100,000rpm, and capable of propelling bike and rider around a race track at 200mph. The fact that he rides his G3 only twice a year - MoT and Jampot Rally - and that he never revs it over 2345rpm suggests to him that this oil is crucial for mechanical longevity. And who am I to argue? His suggestion that I insult the mechanical heritage, integrity and the spirit of long-dead designers by feeding my Ajays on Noname 20/50 is plainly correct. I just can't see why…

But I digress. Proud Owner (and that could be you!) pours in the oil, and gravity, one of the few truly free things in life, dribbles it down to the timing side crankcase, where it encounters The AMC Oil Pump.

A late G80 engine. Oil pump not shown. And we are given no clue as to why it's late. Did it sleep in?Now this is a chucklesome thing. Some sort of desire for eccentricity saw a distant engineer invent a cunning way of combining two pumps (feed and scavenge) into one. Good thinking. Much more elegant thinking for example than the twin plunger type of pump employed by some lesser marques; Ariel and Triumph spring to mind here.

He then enjoyed another brainstorm and understood that while using both ends of the same plunger to provide both sides of the lubrication system was mighty clever, driving the single plunger from a single skew gear on the timing end of the crank was very clever indeed.

And if that was the case, then machining an eccentric groove into the pump plunger and inserting a fixed peg into that same groove was genius! This groove and peg arrangement forces the plunger to slide backwards and forwards as it rotates, thus providing a fine pumping action.

Genius indeed.

It works pretty well in practice, too. And I'm sure that no-one in those distant days justified this cleverness by pointing out that it cost less than all rival designs simply because there are so few moving parts. There is just one…

But there are a few drawbacks. I have been amusing myself with a little maintenance on a pair of G80s. The first is a 1947 rigid, and it is an object lesson in how little oil an engine needed to survive in those distant post-war days. Take off the oil tank filler cap and observe just how much lube returns to the tank. Hmm… Then do the same when the engine's really hot after a bracing thrash along the Atlantic Highway, say, and take a deep breath!

Matchless Stuff on eBay.co.uk

If you really want to raise your blood pressure over the lack of oil pressure, detach the rocker oil feed pipe and observe how much of Mr Shell's finest heads north to the rockers. I was so surprised at this that I ended up whipping off the rocker inspection cover to take a closer look at Lube In Action, and discovered that there was no danger of drowning in the sea of oil flooding from that wide aperture. At tickover, in fact, there was no oil coming out of the rocker feed pipe at all! How's that for confident engineering? But there was plenty of oil in the rocker box, so all remains well, while the rest of the engine sounds sweet and quiet, too. Those old engineering fellows knew their stuff.

Then I performed the same gentle surgery upon a 1966 G80. This late beast, as you know, propels its lube using a Norton twin gear-type pump; a hint that someone in charge at AMC was slightly unhappy at their own oh-so-elegant design. Or perhaps they changed pumps to permit a better timing-side main bearing?

Anyway, I detached the rocker oil feed on the late engine, confident that I would be pressure-blasted to the walls of The Shed by the unleashed energies…

Guess what? There's no feed at tickover, although I was entertained to watch oil plodding slowly along the transparent rocker feed pipe, and highly amused to see the level stop long before oil reached rocker box. A blip of the throttle saw it rush higher, and then fall back when I reinstated tickover.

Meanwhile, back at the oil tank, the late pump revealed its true virility by blowing great big bubbles once it had pumped the sump clean. Thrilling stuff, and always a winning topic of conversation down at the Rat & Cockle.

And in case you had wondered, this is a small demonstration of the entertainment offered by ownership of a classic motorcycle. Who needs to get wet and cold by actually riding the thing when there's so much fun to be had watching oil drip slowly onto the floor? It's plain too that by the time AMC invented the parallel twin engine they had understood that hiding all the oily gubbins away would force owners into riding more. Mind you, the twin oil pump is a thing of wonder, too. Let me tell you a story…

An early G80, and two early owners.

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