Oil does more than lubricate. It cools, cleans and seals, and an old engine often asks more of it than a modern one does. Oil choice for a classic is rarely a mystery if you follow the manual, but there are a few traps worth knowing.
Start with the manual
The workshop manual or owner's handbook gives the viscosity and the quantity. Many classics were designed for monograde oils such as SAE 30, 40 or 50, chosen for the season. Many owners now use a multigrade oil, often 20W-50, that is sold as a classic or motorcycle oil. Either works if it suits the engine. Do not use a thin modern car oil because it is cheaper.
Zinc and flat tappets
Many old engines have flat tappets, which slide against the camshaft and need an anti-wear additive, often a zinc and phosphorus compound (ZDDP). Modern car oils contain less of it because it harms catalytic converters. Classic and motorcycle oils are often formulated to keep it. If your engine has flat tappets or high spring pressures, choose an oil sold for classic engines.
Wet clutches
On most motorcycles the clutch runs in the same oil as the engine. Car oils with friction-modifying additives, often labelled "energy conserving", can make a wet clutch slip. Choose an oil with a motorcycle specification such as JASO MA or MA2, or one sold for motorcycles. If the bike has a separate primary case, the manual may call for a different oil there.
Mineral, semi-synthetic and synthetic
Synthetic oils are fine in most engines in good condition. Some owners of old engines prefer mineral or semi-synthetic oil, partly because of traditional practice and partly because an engine with worn seals can leak more with a thinner oil. There is no general rule: use a good oil of the right grade, change it on time and watch for leaks.
Change intervals
Oil in a classic ages by time as well as by distance. Many owners change it once a year or every 2,000 to 3,000 km, whichever comes first. A bike that runs short trips or is stored is harder on its oil than one that covers long distances. See winter storage.
Dry-sump engines and wet-sumping
Many classic British engines use a dry sump with a separate oil tank. When such a bike stands, oil can seep past the pump and fill the crankcase. This is called wet-sumping. On the first start, the pump has to clear that oil, and the tank level may look low or the bike may smoke. Check the manual for the right way to check the level, and ask your owners' club about the fix, which is often a check valve or a seal in the pump. See waking up a bike from storage.
Total-loss and premix
- Total-loss oiling. Some early machines feed oil to the engine and let it escape, so oil use is normal. Keep the tank topped up, and do not expect a clean floor.
- Premix two-strokes. The oil is added to the petrol in a set ratio. Use the ratio in the manual and an oil made for two-strokes.
- Oil-injection two-strokes. A pump feeds oil into the engine. Keep the oil tank full, and check the pump cable setting.
Leaks
A thin film of oil around the joints is normal in an old engine. Dripping is not. Fix leaks with new seals and gaskets, not with sealant on every surface. Check the breather: a blocked breather pushes oil out through the seals.
Oil checks
- Check the level before each ride, warm or cold, as the manual says.
- Look at the colour: milky means water, glittering means metal.
- Change the filter, or clean the strainer, with the oil.
- Record the date and distance.
