A friend's 650cc T120 oil-in-frame Triumph Bonneville wasn't getting much use. The bike had turned into a spider hotel.
Maybe once a month, said friend was taking the bike out for some exercise, then returning home and covering it up under a tarpaulin and leaving it for the next four weeks or so, the battery on trickle charge, the tyres slowly deflating.
Most times, his afternoon ride-outs started with a centre-stand warm-up outside the garage; a warm up that included a murderous cloud of smoke and half a pint of oil squirting from the breather onto the dirt. Maybe a little less than that. Something was ailing the Triumph. But these bikes go on forever, don't they?
And then one day the T120 refused to start at all and dumped some 20W/50 and merely gurgled at him. He shrugged and rolled it back into the garage and left it there for another month; unloved, untouched, unridden.
Not good at all.
Another friend was called in, the bike was dragged out, the spiders were evicted, the usual preliminary checks were made, and wet-sumping was quickly suspected.
A lot of people mistakenly think that Triumph 2-valve and 4-valve plunger pumps preclude the possibility of wet-sumping. But not so. Wet-sumping is what happens when oil drains through the pump into the crankcase. Normally, there's not much clearance between the crankshaft and the crankcase. But you can still get a surprising amount of Texas tea down there where you don't want it.
When the bike is restarted, the piston comes down, pressurises the crankcase, and pumps the crankcase oil either out of the engine breather, and/or forces it up the bore past the piston into the combustion chamber. There, it burns (if you can get the bike started at all) and then fills the atmosphere with smoke. It won't help the spark plugs much, and it will help jam up the valves with carbon.
Often, however, there's too much oil in the combustion chamber, and the bike simply won't start. In this instance, the first thing to do was check the oil pump and see what was going on. The bike was fitted with the 2-valve Triumph plunger pump. This is an old design, but is generally reliable and trusted. Dirt and grit in the oil can prevent the check-balls from sealing/seating. Also, the springs will soften over time causing the balls to lose effectiveness. But with correct maintenance, these units will carrying on for years returning good service.
The pump on this bike was found to be leaky. Also, it wasn't seated properly on its flange/base and had some free play. Actually it was amazing that it worked at all. But relatively low-tech Triumphs (like many low-tech British bikes) will chug on competently when more sophisticated machines have self-destructed.
If the pump doesn't seat properly, air can leak into the suction/scavenge side of the pump; i.e. the side that pumps oil from the crankcase and clears it. Or it can leak on both sides and deprive your internals of the required lubrication.
This T120 pump looked like it had had a hard life. Rebuild kits are available (new balls, springs and nuts). But the pump was a mess and might have been fitted with a hammer and chisel. The decision was made to fit a new one, but possibly upgrade it to a more reliable 4-valve design.
▲ Morgo unit twin 2-valve oil pump, 1961 bikes onward. These are made in Bradford, and are the ones favoured by many Triumph owners. No engine modifications are needed, Morgo say. And they're said to deliver more oil than rival pumps.
▲ Another view of the Morgo plunger pump for Triumph twins. Morgo never made a
4-valve version for Triumph twins. All theirs are two-valve. The next move up, they say, are rotary pumps which deliver more oil and lubricate those hard to reach places.
The original better quality Triumph pumps don't turn up often. But L.F Harris (Les Harris) and Morgo still make replacements. Four-valve for Harris. Two-valve for Morgo. Either will do the job okay, although Morgo promises higher oil delivery. However, some say that too much oil can cause problems on older engines and add to general leakage woes. We wouldn't have thought that the extra 20% or so that Morgo promises would be a real problem, and it will help cooling. But we haven't bench tested anything. Like everyone else, we have to base our opinion on what we're told and through long experience. And we've always had Meriden pumps on our bikes.
But what does Morgo say?
We spoke to Graham at Autovalues which makes the Morgo pumps. Graham is of the opinion that the Morgo pumps don't cause leaks through too much pressure. Why not? Because the pressure is ultimately controlled by the oil pressure release valve in the crankcase. If the pressure rises, the valve opens. However, Morgo pumps, he says, flow more oil, and that oil can reach places (such as the cylinder head) that often gets starved by a weaker/older pump.
A starved cylinder head can mean dried out gaskets that bake hard. And crack. And cracked gaskets leak. Think of a wooden ship's hull than dries out and leaks, as opposed to a wet wooden hull that swells and seals.
Makes sense to us, but you can form your own conclusions. Morgo did experiment with 4-valve oil pumps, but they found little or no benefit in them. The feeling is that as the 4-valve pump is essentially two pairs of valves inline, a block on the first two means a blockage on the second, and vice versa. Instead, Morgo moved straight to their rotary pumps.
Oil pump prices
There are cheaper pumps on the market than Harris or Morgo, usually from the Far East, but many are rubbish and badly machined (or made using the aforementioned hammers and chisels). Buy online, and you'll get whatever is dumped on your door mat. Be warned.
In the end the owner of this T120 opted for a slightly cheaper Harris pump, largely because it was available exactly when he wanted it (bought at a show). The 4-valve pumps are, however, slightly larger than the 2-valve pumps. To fit the 4-valver into the timing case, you sometimes have to grind away a small amount of material from the inside of the timing cover. It's not hard if you've got a Dremel, or similar. Or you could use a very small scraper. Or you might get lucky and find that it fits straight on.
A small amount of aluminium was removed from the cover; in this instance, a very small amount. The engine oil was drained and flushed. The oil tank was also flushed. The new, 4-valve pump was fitted together with a new gasket and nuts. The oil feed pipes were checked and found to be okay (not cracked, split, etc). Everything was tightened. Fresh oil was put into the tank. The bike was started (fourth kick) and it smoked for a bit as the combustion chambers cleared. But after that, it was fine and stopped wet-sumping. However, the bike didn't get any more regular use, and a few months later it was sold.
You should take wet-sumping seriously. In itself, it doesn't necessarily cause too many problems, except stress the engine, dirty the atmosphere and waste oil. But it could point at underlying problems with the oil pump. And if the pump fails on the road, you might be looking at big beer bills.
The 2-valve plunger pump was fitted to 650cc Triumph models, but the later 4-valve pumps will fit all the 650s and the 750s and can be retro fitted (given a little grinding). Just ensure you grind the aluminium well away from the engine, clean the swarf thoroughly, and never grind more than you really have to. The later 750s had the 4-valve pumps as standard.
Either way, always fit new gaskets and trash that old pump if it's dead. No sense putting that onto an autojumble table where some unsuspecting buyer will latch onto it and put it back into dangerous service.
The average home mechanic can sort this one out without too many problems. Expect to spend a few hours mucking around with it. We'd recommend removing the spark plugs and cleaning them up or fitting new items. Fit a new sealing washer on the crankcase drain plug. Tighten it, but go easy. You won't want to strip that thread.
Think you know better? Good, drop us a line at Sump and we'll include your thoughts/experience.