At the beginning of motorcycle production, the oiling systems were rudimentary at best.  Often times the rider was required to pump much needed lubricant into or onto the engine components via a handle mounted on the fuel tank! In fact, exposed valves and total loss oiling systems could still be found on machines manufactured in the 1950s (Nimbus). Interestingly, it was 1941 before Harley Davidson introduced a recirculating oiling system in place of the unpredictable and messy total loss system.

In the modern world, riders and mechanics are used to motorcycles that have sophisticated oiling systems and, besides new filters and oil changes, need very little maintenance. In fact, most of us would be hard pressed to name the last new motorcycle that had an oiling issue. However, when dealing with older machines it is imperative to understand the different requirements of earlier motorcycles compared to the modern day cousins.

A Worked Example

The Triumph 'C' series was designed in the 50s by Edward Turner and comprised of T21, 3TA, 5TA, T90, and T100 models.

For this article we will consider the oiling system from a 1964 Tiger 90.

The biggest difference from more modern designs is the basic configuration of a dry sump, as opposed to the wet sump. In the dry sump layout, the oil reserve is located in a separate oil tank (instead of the engine's sump).

Engine Oil Flow

The engine's components receive oil from the oil tank via a mechanical pump mounted on the inlet camshaft gear.  The pumped oil is then fed into the crankshaft main bearing (on the right side) before flowing to the connecting rod (big-end) bearings having passed through the sludge tube.

The pressure to these critical bearings is controlled by a pressure release valve, which, once the pressure has reached 60 lb's., releases oil into the crankcase to ultimately be scavenged back into the oil tank.

Oil that has passed through the crankshaft bearings is thrown by the crankshaft rotation around the crankcases before flowing to the base of the crankcases through a wire filter. This oil is then collected into a small container (the oil drain plug housing) at the lowest point of the engine. From this collection area the oil is pumped back toward the oil tank; however, an additional line feeds oil to the top of the engine into the valve gear. Having passed into the valve gear, the oil is gravity fed to the push-rod tubes, onto the camshaft followers, and then along the camshaft to the timing gear case.

One unusual aspect of the Triumph's oil system is a breather from the end of the inlet camshaft. This breather supplies a small amount of oil to the final drive front sprocket, and it is often this area that produces the dripping oil often associated with Triumphs and is not an actual leak.

Do's and Don'ts

The design of the Triumph oiling system is simple and effective, but the mechanic working on one of these engines must be aware of some unique but very important tasks to perform after an engine rebuild or even after just an oil change.

During an Engine Rebuild

During the building of an engine of this type, the mechanic must lubricate liberally all bearing interface items (crankshaft bearings including the connecting rod - big-end - bearings).

The camshaft bearings must also be lubricated along with the timing gears and oil pump slider.

The oil pump and all associated oil lines and feeds must be pre loaded with oil.

The valve gear must be pre loaded with oil and assembly lube must be used on the valves (where they interface with their guides) and the push rods must have assembly lube on both of their ends.

Before attempting to start the engine it is imperative that the oil is fully circulated. To achieve full circulation, the mechanic should remove the spark plugs, remove the oil tank's filler cap then (having filled the tank to the appropriate level) kick the engine over until oil can be seen returning inside the oil tank from the return line. Once the oil is seen to be returning to the oil tank, the mechanic should then loosen the domed end nut on the exhaust vale rocker shaft, place a finger over the oil tank's return line hole and then kick over the engine again until oil flows from the domed nut area. Once oil is seen to be flowing from this area, the nut must be re tightened to the correct torque.

Having refitted the spark plugs, the mechanic can now start the engine. As soon as the engine starts, the mechanic should place his finger over the hole in the return line to force oil under pressure to the valve system: this will take only a few seconds to achieve.

Note: The mechanic should be aware that over tightening the oil pipe domed nuts on top of the rocker feed lines can crush the copper washers which can restrict the flow or block it completely.

During an Oil Change

Some of the guidelines mentioned above also apply to oil changes. For example, having drained the old oil, cleaned the filters (there is a gauze filter inside the oil tank and the sump collection area) and filled the oil tank with fresh oil, the mechanic must ensure oil circulation before attempting to start the engine.

To drain the engine oil, the mechanic must remove the lower drain plug from below the crankcase, along with the gauze filter (for cleaning) and also the feed line from below the oil tank (the large nut under the oil tank is for this purpose—this also secures the oil tank's gauze filter). 

Notes: It should be noted that for those not familiar with the older motorcycle's oiling systems that the gearbox, primary drive, and engine oils were all separate (as is the case with the engine considered here).

The Triumph factory recommends replacing the engine oil every 3,000 miles; the primary chain case every 1,000 miles, and the gearbox oil every 1,500 miles.

 The crankshaft on some British motorcycles contained a sludge tube inside the crankshaft journals. Removing this tube, for replacement, requires a complete engine disassembly but this is essential if the owner does not know when this tube was last replaced or cleaned. With modern oils, the sludge tube will require replacing less frequently, but riding conditions, climate, and oil types will greatly affect the buildup of sludge making each machine unique in the amount of buildup.