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 tank. Notice the oil lines on this bike flow smoothly from the tank to the engine.
When an oil tank, such as this horseshoe style tank, has the oil lines exiting the bottom of the tank there will be tubes (arrow) inside the oil tank for the oil return and the breather line. The feed fitting will be flush with the bottom of the tank because you want “all” the oil to feed the engine. The oil return and the breather lines should be above the oil level inside the tank. The oil returning from the engine is hot, and there’s less resistance if the oil returns to the tank freely, without having to push past the oil already in the tank. The breather should exit above the oil level also for the same reasons. Because if it was below the oil level, the oil in the tank would run down into the engine and cause it to sump.
Some oil tanks like this round aluminum tank on another rigid shovel have the return and breather fittings (arrows) located on top of the tank. The oil feed line is the line coming from the bottom of the tank. When using an oil tank such as this one, you have to pay more attention to the path the oil lines take going to the top fittings on the tank, because they will pass close to the exhaust pipe.
The oil lines are fastened to the fittings on the oil pump and the engine case. The breather line from the tank goes to the breather fitting (A) on the engine case just above the pump. The oil feed line from the tank goes to the feed fitting on the pump (B) and the return line from the pump (C) goes back to the return line on the tank or if you have a remote oil filter it goes to the “in” fitting on the filter mount.
On most Harley-Davidson big twins (pre-evo) the oil filter was located in the oil tank. The return oil line from the oil pump, connected to the tank at the filter (arrow), the returning oil went through the filter before entering the oil supply in the tank. The oil filter shown in the photo is an aftermarket item.
Our bike features a remote oil filter mount located behind the transmission. The return oil line from the pump goes to the “in” fitting on the filter mount. If the filter mount is not marked, the oil return line always goes to the outside fitting (A), where the returning oil will pass through the filter material before returning via the center fitting (B) to the oil tank.
Here we have a remote filter mount that H-D used on some touring models. This filter mount is not marked. Oil from the pump would enter the filter through the top fitting (A) and enter the filter, returning out through the center of the filter (B) and back to the tank. Oil filters on shovels and evos are always on the return side of the pump, never on the feed side. The simple reason for this is that the oil feed is by gravity and you don’t want anything impeding the flow of oil to the pump. The oil requires pressure from the pump to be pushed through the filter element and the return line to the tank.
Another important part of the oil line system are the oil line fittings. Originally, H-D used two fittings side by side like on this factory oil pump cover (arrows). With the introduction of the evo engine and remote oil filters there were different oil pump covers used with different oil line fitting locations, our shovel features an S&S oil pump with the option of two oil feed fitting locations.
Here is just a small sampling of the various oil line fittings for either the oil pump or oil tank. The standard thread of these fittings is 1/8-inch pipe thread, pipe threads are tapered, and they are a smaller diameter at the end of the threads and increase in diameter as they wind up the fitting. The benefit of using pipe threads is they are self sealing, to a point. As you tighten the fitting, the threads mesh together, slightly deforming, preventing fluid from passing by the threads. It is still a good idea to use some type of thread sealant as an added precaution and to aid as a lubricant.
As we said earlier, all fittings are not the same, even though they may appear the same from the outside. Here are four different fittings for oil lines, the outside diameter of the fittings are suitable for a 3/8-inch oil line, however the inside diameter varies. The inside diameter of the fittings are .250-inch (A), .265-inch (B), .295-inch (C) and .299-inch (D). The inside diameter of the fitting determines how much fluid will pass through it. Fittings (C) and (D) have the largest inside diameter you can run while still maintaining enough strength in the fitting for clamping the oil line. If you find yourself with some of the small inside diameter fittings, you could enlarge the inside diameter by drilling them out with a 19/64-inch drill bit. 19/64 equals .2968-inch, the easiest way to drill the fittings is in a lathe, but careful work with a hand held drill and bench mounted vise will work just as well.
After sorting out the fittings for the oil tank and pump, cutting you oil lines to length (avoiding sharp bends) you have to clamp the lines in place. The factory uses a band clamp that uses special pliers to crimp the top of the clamp (arrow) over the oil line. This type of clamp is permanent, meaning you have to cut it to remove the oil line.
The more popular style of clamp is the reusable screw clamp, which is known around the world by many names, screw clamp, worm clamp, hose clamp, jubilee clamp, (just to mention a few). We will call them screw clamps, come in about any size you want, we have personally seem them up to 2 feet in diameter. With proper care, a good quality screw clamp will last indefinitely. Here we have cut an oil line in half and inserted a oil line fitting, you can see how the clamp squeezes the hose over the barb (A) preventing the hose from sliding off the fitting. Over tightening is the screw clamp’s greatest enemy, a good rule of thumb we learned over the years is to tighten the clamp until it sinks into the oil line where the surface of the oil line is just above the metal band of the clamp (B). Screw clamps will require little maintenance, other than an occasional check with a screwdriver.
