Submitted by: TCSTD
Routing the oil lines from the oil tank to the engine is simple task. There are only three oil lines needed to make your bike run: the feed from the oil tank to the oil pump which is located on the engine, the return line from the engine to the oil tank, and the breather line from the engine to the oil tank. Shovelhead and evolution engines share the same lower end assemblies with slight variances, depending on how the cylinders and heads are bolted on. Both engines use an oil filter to keep dirt particles and contaminates to a minimum. The main difference between the two filters is the oil filter on the shovel is mounted in the oil tank, while the evo has the oil filter mounted externally, first on the right frame rail and then on the engine, below the front cylinder.
The design of the oil filter on the shovelhead uses one oil line, which feeds the oil back through the filter and into the oil tank. The evolution’s external filter requires two oil lines; one line feeds oil into the filter and the second line takes the filtered oil back to the oil tank.
Both the shovelhead and evolution use a gravity fed oil system, which means the oil going from the tank uses gravity to find its way to the feed side of the oil pump. The oil pump has a check ball held against a seat by a coil spring which prevents the contents of the oil tank from just running into the pump and consequently filling up the crankcases with oil. This condition is called sumping and makes starting the engine very difficult. When the engine does start, it tries to pump all that oil back to the tank, which is virtually impossible. Some oil will return to the tank but a lot of it will escape through the crankcase breather onto the floor.
The coil spring in the oil pump holds the check ball in place preventing the oil from entering the engine until there’s three pounds of oil pressure in the engine. Once the pressure is up the check ball lifts off of its seat and oil flows unhindered into the pump and through the engine and then back to the oil tank. We will deal with this pressure check ball in another article.
In the photos we’ll show you what fitting on the engine goes to what fitting on the oil tank and how to plumb the lines for positive oil flow to and from the oil tank. Speaking of oil lines, the minimum inside diameter of oil lines for a big twin engine should be 3/8-inch regardless of what material oil line you chose, rubber hose or braided steel. This size oil line will allow a sufficient supply of oil to feed the engine even in cold temperatures when the oil is thick. Straight weight oil such as 50 or 60 weight thins out and flows free when it warms up to operating temperatures. Multi-weight oil, such as the 20w50 oils, for most evo’s flows free, even in cold temperatures, but will still get a little thinner as the engine rises up to operating temperatures.
Our subject for this article is a rigid frame shovelhead with a remote oil filter. Evolution engine oil line systems are pretty much the same (i.e. the oil feed line from the oil tank goes to the oil feed fitting on the oil pump). There are two main things to keep in mind when routing oil lines, first, no sharp bends in the oil lines, sharp bends restrict the flow of oil. Second, oil lines should be kept clear of any hot or moving parts. This means keeping the oil lines away from the exhaust pipes and the drive chain or belt, even if you run braided steel oil lines, the braided steel sheath will abrade other metals it comes in contact with.
Our subject motorcycle uses a horseshoe style oil tank with three welded steel tubes exiting the bottom of the tank. These fittings are oil feed from the tank to the pump (A), return oil from the pump to the tank (B) and the breather line from the engine to the