Maintenance and technical information

Motor  Oil

What oil to use in what engine is one of the most discussed questions in any Harley BBS or club. Let me add my wisdom to the fury: Use multigrade, no matter what the 1962 repair manual for your beloved Panhead says. I can explain why:

The viscosity of an oil is given in numbers, the higher the number, the "thicker", the more "honey like" the oil. A lower figure stands for a more "liquid", a "thinner" oil. Everything was OK until the mid seventies; Harley Honey was 50 weight or 50 grade. A pretty "thick" slime, resistant enough against "shearing" when hot and pretty much like butter from a fridge when cold. People riding their sled in the winter used 30 grade and changed back to 50 in early spring.

Mono Grades / Single Weight

Now what do we want our oil to do? Lubrifiate all moving parts and put a thin molecular film between any two metallic parts in the engine. A pretty difficult task if you think cylinder wall vs. piston ring or the crankshaft in it's bearings. The oil has to stay in place under very high temperature  and must be able to take up against the high speed difference of the moving parts. All this without suffering too much from dirt particles that come with explosions or metallic wear. The best remedy is a "thick" oil. It can take more temperature abuse and stays in place under extreme pressure. One pretty common reason for engine failure is an "oil shearing". The oil film will be torn apart from pressure or, even more common, from the high speed piston against the cylinder wall. You lose lubrification and metal starts scrapping on metal. No good. Use some thick honey!

All this comes with a high price tag. Thick oil is a sucker to get moving, especially when cold. You start your engine on a cold day and during the first few turns there is no oil distribution happening. Your oil pump woks, your pressure gauge goes berserk, but no oil in the heads or on the cylinder walls. The honey is simply too thick to be pumped through the small oil lines, through the paper filter and all the small openings in the engine. So you build up an oil pressure that is largely in the red zone, pump the slime through the lines at any price (the pump works!)  and abuse your parts. That's life. We could use a "lighter" oil, like 20 or 30 grade, but it would be critical once the engine (and the oil) is hot. Our starts would be fine from the beginning but after 30 minutes in warm weather we risk an "oil shear" and that means we risk our engine. And because it's "smaller" molecules, we would have our sled spitting oil through every little gasket. Ever found your sled just leaks oil when real hot? Once the oil is "thin" it comes through every little hole? Put in some lighter oil and it starts right from the first few revs!

Multigrade

It IS the solution. Multigrade oils are (simply put) oils that are as liquid, as thin, as their first indication and "thicken up" to the second indication at high temperatures. Our celebrate 20 W 50 is a 20 W (winter) 50 (normal conditions) oil. Now the truth of the matter is that it doesn't really change it's liquidity but rather it's viscosity, meaning the molecules stick together a lot better when hot. You get the advantage of a smooth start with a good resistance and sturdy film when hot. That's what you want. Modern additives allow oil to have better "cleaning" abilities, meaning they keep up the work even when badly polluted. 20W50 is recommended by HD for some yers now (even for old bikes) and I know some Flatheads and a 1947 Knucklehead that run this oil without any problem.  For those bikes who still "mark their territory" you can go up to 25W60 (RevTech). It simply works.

Mineralic, Semi-Synthetic and Synthetic Oil

Forget about Mineralic oil. It is not sold anymore (or only very rarely); Semi-Synthetic is by far the most common. It is mineralic oil (so has been pumped out of the Earth at one stage) that has been treated and enrichened with modern molecular additives and stabilizers and performs pretty well, though it gets old (it "ages") and loses a lot of it's performance when in use, partly because of the water molecules that come with a cooling engine after a day's ride.  You have to change it on a regular base and you can encounter big differences in quality.

Nearly every mid-price oil can you buy is half full of recycled slime. The old oil (that you brought back to your garage) will be treated, the carbon chains will be cracked up and made longer again and then the syrup gets filtered and re-conditioned. That's what the different API specs are for; the higher the spec, the lower the "recycled" percentage. While this sounds horrible, a mid priced 20W50 API SE or SF from Pennzoil, Castrol, Igol or other "brand" is good for 5000 miles in any street legal Harley, provided you change the oil filter with the oil and the engine is still healthy.

Synthetic oil comes from labratories. They are chemical art objects and have very precise specifications. Their major advantage is an unlimited lifespan because they do not age from temperature or pressure. The limiting factor is the amount of dirt they can transport. So as long as your oil is not all black, it is still 100% OK. Oil change intervals can go up to 20000 miles or more for a healthy engine. So there is really no need to do it every 5000 mls.

Oil Filters

These cheap little things can tell you all about your engine's health and condition. The trick is to get the paper filter out, "unroll" it entirely and hold it against the sun or a strong lamp. On a perfect day you see nothing except a fine grey or black, greasy smear. That's your cylinder walls and piston rings with a little combustion acids in addition.

Fine, dusty silver grains are normal and if the size is real small, don't be afraid. Copper or brass particles tell you that you have bearings and bushings coming unglued and are a sign for immediate repair. If these particles ar bigger than grains of sand, it's pretty safe to say you are in trouble and a substantial part of your wealth will change hands in the near future. The picture above shows the filter of my 1200 Shovelhead (more than 200 000 km on the counter!) It's the first time that I found brass, and I am not particular happy about it.

last updated 04-May-2001