One of the first upgrades I made to my 1964 Harley-Davidson Duo-Glide was to change my primary drive from a chain to a belt. This upgrade provides two major advantages over the stock chain drive, less vibration at higher speeds and less maintenance. My main motivation was less vibration to make highway riding a bit more enjoyable. The less maintenance is also a big plus because adjusting the chain drive is a long process. If you haven’t adjusted a chain drive on a vintage bike, it’s hard to imagine it is a big deal, but on these older bikes there is not a primary chain adjuster like on late model bikes. Instead, you have to adjust the position of the transmission to adjust the primary chain. After you finish adjusting your primary chain, then you have to readjust your clutch and rear chain.
On a stock bike, the primary chain is lubricated by engine oil that is sprayed into the primary by an engine breather. To keep excess oil from building up in the primary, there is a drain at the bottom of the primary which allows the oil to drain out and down a tube onto the rear chain, thus lubricating it as well. This is one of the reasons old bikes seem to be constantly leaking oil, but it’s actually not a leak it’s a self oiling chain system.
Since you cannot just block off the engine breather, I decided to reroute it around the new belt drive, using a variety of copper plumbing fittings that I picked up at the local hardware store. If you know how to solder copper pipe, this is a very easy way to make a breather bypass. If you’ve never soldered copper pipe, then I would suggest checking out some of the “Do It Yourself” type websites before starting this project.
To get started, you’ll want to pick up the following:
1′ length of 1/2″ ID copper pipe
two 1/2″ ID copper 90 degree elbows
two 1/2″ to 1/4″ ID copper reducers
6″length of 1/4″ ID copper pipe
2′ length of 1/4″ OD copper tubing
6″ length 1/2″ ID rubber hose
two hose clamps
Plus standard tools and materials for soldering copper pipe.
Now comes the fun part, getting all of this to fit inside your primary cover. It took a lot of trial and error until I got everything to fit just right. Before you start cutting pipe, you’ll want to remove the small elbow on the end of the engine breather, so that you are left with just a straight piece of pipe running into the primary.
The first step is to cut about 1/4″ off the large end of each reducer. Without this step, the reducer plus the 90 degree elbow will be too long to fit inside the primary cover.
|Trim reducers by at least 1/4"|
At this point you can save a little time fitting the main length of pipe, if you can get someone to give you a hand. Basically just hold the two finished reducer/elbows at the correct locations and have your helper measure the distance between them. Once you have a rough measurement, you can start fitting the pipe, trimming as necessary, until the top reducer lines up with the engine breather and the lower reducer lines up with the drain hole. Make sure you do not solder the main pipe to the reducer/elbows until you finish the next step.
The last piece to fit is a short section of 1/4″ ID pipe. This will fill the gap between the lower reducer and the drain hole. It is essential that this piece fits exactly. If it is too long, the lower elbow will not clear the primary cover. If it is too short, the inside of the lower elbow can contact the belt.
|Here are all the pieces, cut and ready to assemble|
|Soldered and ready to install|
|Copper tubing used to route oil from the primary drain to the rear chain|
|Copper tubing positioned to oil the rear chain|
|Engine breather bypass installed and ready for primary cover to be mounted|