Oil Tank Installation

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Oil Tanks

  The H-D factory has used several different designs of tanks over the years to suit specific models of cycles, but the original ‘Horseshoe’ tank introduced in 1936 is a hallmark of the Harley image up until modern time. From an engineering standpoint the tank was considered a brilliant solution to the problem of keeping the oil supply as close to the oil pump as possible but it served a dual purpose in also housing the battery thereby keeping the bike relatively uncluttered.

The Horseshoe tank has gone through minor modifications over time but is basically identical from 1940 up to 1958 and then had the rear mounts modified for the 1958 to 1964 tin primary frames and again for the 65 through 84 frames using the larger cast primary covers.

The aftermarket tanks being sold today will be of three basic types. Those for use with tin primary bikes (1936-64), those for use with cast primary bikes (1965-85) and those for use in the ‘Softail’ frames that is wider and has a unique mounting system.

The filler can be had either mounted on top as originally designed or located on the side which many riders prefer. You can also get the tank with an integral oil filter but in general all horseshoe tanks follow the same theme.

Softail horseshoe tanks are seldom used on choppers due to their mounting system and the extra weight it entails.

A cheaply made, painted Horseshoe tank can be had for around $150 while a high-quality chromed tank will set you back almost $400. Custom tanks range in price from $120 to $800.

Custom Tanks

There is a significant number of custom-made tanks on the market in all types of shapes and sizes but in every instance, they will require that you fabricate special mounting brackets to suit any particular unit and there are too many alternatives to cover here so you’re on your own if you go that route.

Horseshoe Tanks

  I’ve laid out three tanks on my improvised work bench in the photo below. The tank on the left is a ‘soft tail’ horseshoe. The tank in the middle is a modern repop of the classic Horseshoe and the tank on the right is an authentic Harley horseshoe I’ve had on several bikes that needs a lot of work to be put back in service.

Note the different front mounting system used on the Softail tank. The snapshot below shows the same tanks when viewed from the rear.

Note the rear mounting brackets on the Softail tank as opposed to the simple system used at the rear of the original styled tanks. Also note that the Softail tank has a ‘floor’ built into it where the old-style tanks are just ‘open’ on the bottom.

 There is reason for this and that is that batteries back in the old days were leaky, sweaty acid containers and combined with standing rainwater rapidly disintegrated battery pans in short order. To prevent riders from buying new oil tanks every few years the factory came up with a separate battery ‘tray’ that fits in under the tank as seen in the picture below sitting to the right of the tank.

This is a nice chrome unit I bought at a swap meet still in the packaging for only a few dollars. To the right are the two 5/16-18 bolts needed for installation. The small dark round object is a spacer, and these fit in under the tray and on top of frame mount tab, Unfortunately I’ve already lost one.

Installation is fairly straight forward but it’s made a lot easier if you have a helper. You can install the tank before or after the transmission is in place, but I prefer to finish up the tranny before adding the tank. Be sure the clutch release lever is in place prior to fitting the tank as it’ll be impossible after the tank goes in.

Not shown, since I didn’t have one in time for these pictures, but if you’re using a cable type clutch release there is a small bracket that fits on the forward tank mounts.

The one shown here is for a Panhead bike and the type I prefer.

By the way the fastener holes in the tank mounting tab welded to the seat post can be found with either threaded holes or simple bored holes. If your frame has the threaded mounting holes, you’ll find it much easier to deal with future tank work if you drill theses out to 11/32” and use bolts with nuts.

The stock rear mounts on the original tanks consisted of a bent metal strip that contained two holes in each leg of the bracket as see below.

The bracket was bolted to the two holes in the lower cross bar at the rear of the tank as seen below. The bracket served a dual purpose in that it not only held the rear of the oil tanks in position but also functioned as an upper mount for the forward part of the rear fender.

Since chopper fender mounting locations don’t favor this type of bracket it is seldom used nowadays.

The following picture shows a rear view of a pre-1958 oil tank and holes for the bracket in the lower cross brace. To mount these tanks in a chopper, frame most builders use two sections of 5/16” all-thread rods with washers and nuts on each end that run upward from the brace to tabs welded onto the upper wishbone cross tube.

Tanks made for bikes built between 1958 and 64 had two additional mounting tabs with bolt holes fitted high up on the rear face of the battery recess making installations sometimes easier and cleaner and sometimes harder depending on exactly where your frames wishbone brace is situated.

The upper tabs are visible in the web snapshot below.

With our particular frame geometry, we could have fabricated mounting tabs for either type of tank, but we’ve elected to use the old style that used threaded rods to hold up the back end.

Once we positioned the tank in the frame it became obvious that the best alignment for the ‘rods’ put them directly in line vertically with the wishbone crossmember.

Here’s few from behind showing one piece of uncut all-thread running all the way through.

I have worked on bikes where people have simply drilled through the crossmember but that’s really low class so what I decided to do was to weld threaded lugs on the underside of the tube.

Here’s a shot from the rear of the bike showing the proposed concept. In application the lugs will of course be on the underside of the crossmember then the threaded rods, having nuts on the lower end, will run up from the bottom of the plate mounting bar. It’s not the slickest but it’ll work.

The side view snapshot illustrates the two mounting tabs for the tin inner primary, if you’re going to be running an enclosed primary.

We’ll come back to this article once the lugs have been installed and then go over piping and fittings.

Before you get to the point of filling the tank with oil take a good look inside and make sure it’s clean and rust free. Even new tanks can have a surprising amount of debris inside.

In some instances, in certain aftermarket frames, or hard-tailed swingarm frames or if you’re using an electric starter, you’ll find that there simply isn’t enough space above the transmission to permit the use of a stock tank and you’ll be forced into buying a custom unit. If you like the looks of the old horseshoe tanks however several manufacturers make a tank modeled after the original Harley TT racing tanks that’s about 1-1/4” shorter in height. The electric-start tanks are shorter as well.

This snapshot came from the Jockey Journal site and provided a great comparative view of the two options, short or tall.

The shorter tank also makes it possible for you to run a ‘raised’ tranny which is a great modification on any bike. (See the Raised Transmission section on the main site).

As you're installing the tank take a look at both sides where the top of the tank edges are near the rear wishbone tubes and also look at the gap between the front of the tank and the seat post.

It's not uncommon to find that the tank mounting tab on the seat post was welded in place being slightly skewed in either the longitudinal or transverse plane and the tank wants to set a little cockeyed. This problem can be fixed by a little shimming and tightening the rear support fasteners before the fronts are cinched down.