Oil filters

As late as 1936, Harley-Davidson was still advertising the loss lubrication of the Flathead models. They wrote in their ads that the bearings in the engine only ever get fresh and clean oil. The background: the oil in the engine lubricates and cools at the same time. In doing so, it also absorbs soot particles. Of course, you don't want these particles in the engine and constantly sending them back through the bearings. For years, this was the perfect argument against closed-circuit lubrication. Fortunately, the dirt can be filtered out. The oil filter is therefore a necessary side effect of closed-circuit lubrication.

Connect the oil filter to the feed line or return line?

Wouldn't it be great if you could supply only filtered oil to the oil pump... the suction power of the oil pumps in Harley-Davidson engines is not strong enough to draw oil through a fine filter. This precludes the possibility of installing a filter in the line from the oil tank to the pump. So on Harleys, oil filters are always installed after the oil pump so that the oil is pressed through the filter. On all Big Twins up to and including Evolution and on Ironhead Sportsters, the oil filter is located in the return line to the oil tank. In Evolution Sportsters and Big Twins from the Twin Cam generation onwards, the oil filter cleans the engine oil before it reaches the tappets and crankshaft. The oil passages are located inside the engine case.

Do I have to change oil filters?

Over time, the oil filter becomes clogged with dirt particles. (That's exactly what it's supposed to do.) The more a filter clogs, the more it hinders the oil flow. Harley-Davidson recommended washing out the external oil filters of the Knuckles and Panheads and those of the Sportster and Electra Glides that were placed in the oil tank. In theory, this is still possible today for these models. But what about the solvent? The following applies to modern bikes and all old bikes with modern oil filters: washing out does not work with paper filter elements. They are much too fine pored. That is why oil filters with paper elements must always be changed.

What are the oil filter change intervals for my Harley?

With such questions, a look into the driver's or workshop manual is always helpful. In general, with Harleys, you can say that the filter is also changed with every oil change. The newer the Harley, the longer the oil change intervals. Over the years, the quality of the oils has also improved. For Panheads, Shovelheads and Ironhead Sportsters, the factory recommends 2000-mile intervals (~3000 km). For Evolution and Twin Cam engines, 5000 mls (~8000 km). Better filters and motor oils make it possible. In our experience, carefully rebuilt engines with cast cylinders can also manage well with service intervals of 5000 mls (~8000 km) if PanAm multigrade oil and Perf-Form filter cartridges are used.