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Motorcycle Primary Drive

with 3 comments

Since my main focus is on chopper style bikes, this blog post here will be focusing on V-Twin engines. This is important to note since primary drives are configuration specific.
So, to begin with… Primary drive is what transfers the rotation of the engine’s crankshaft to the transmission (which in turn transfers it to the wheel but this is out of the scope of this blog post). To get you started let’s have a look at various types of primary drives…

This is a photo of a Harley-Davidson Softail. As you can see, it is a “closed” type. In fact, it is covered with this metal plate because it uses a chain that is lubricated. Imagine the mess of having this open. Below you can see a photo of a Harley-Davidson Sportster’s primary (along with the engine and the transmission) laid on a workbench.

Nowadays, a very common type among long, fat choppers is the so-called open type which uses a belt instead of a chain and looks like this:

The first type that was using the chain is the most common on stock bikes. There are numerous reasons behind this. First of all, it’s more secure, well lubricated since the primary cover is sealed but produces more noise. However, in this type the clutch is also inside the the primary drive. The overall installation process could be considered complicated.

Well, I know, it’s not rocket science but if you’re not mechanically inclined it is very likely that you will screw it up. Another advantage of chain primary drives is that they can work for ages with minor maintenance. Finally, they function perfectly with high RPMs.

And now… The other side…

The belt type now. This makes less noise and it is very straightforward to install. Also, you don’t have to lubricate it and adjust it from time to time. On the downside, it can overheat easier and depending on its size might be uncomfortable for everyday riding. It is usually cheaper than the chain one but it doesn’t perform well with high torque engines and they require riders attention (mostly to not catch his/her clothes) since they are open.
Here is a diagram of a belt primary drive:

So, I guess that this will be useful to some people out there.

Written by xorl

April 26, 2011 at 22:01

Posted in motorcycles & cars

3 Responses

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  1. Newbie-to-Harley-Repair/Maintenance here. Looking for an exploded diagram / chart [poster-size… the bigger, the better] w/ the basic V Twin parts labeled – – – to hang in the garage over the Sled. Know where any such critter may be had??? zencruzer@gmail.com


    January 8, 2012 at 17:51

  2. Unfortunately I don’t. Sorry man.


    January 11, 2012 at 17:05

  3. that was a great explanation. Thanks


    July 21, 2014 at 09:46

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