“I am wanting to put a bigger sprocket on a customer’s home-made trike, I have a 5/8" shaft with a 3/16” keyway. I am wanting to use a 35 chain and a 60 tooth sprocket.”

This Martin Sprocket, steel roller chain sprocket comes ready to install and includes a finished bore with keyway and also setscrews for axial retention.

Sprocket shown for pictorial purposes only.

Martin Sprocket ref 35BS60 5/8 is a simplex 60 tooth sprocket (7.165” pitch diameter and 7.38” outside diameter) for a 3/8” pitch roller chain drive.

The 5/8 reference denotes the finished bore nominal measurement in inches and in this case the hub is 1” wide.

A keyway is machined into the bore at 3/16” nominal width.

At first glance and in theory, this sprocket should work on the customers application. However, there are always other details to consider for this type of modification. This process is normally done by a mechanical design engineer and involves generating a design layout drawing of the roller chain drive arrangement.

So, let’s highlight some of the issues surrounding this retrofit example and bear in mind we don’t know any of the details of the existing sprocket being replaced. Although, we will assume the existing chain drive is also 3/8” pitch.

1.  Changing the number of teeth (or the diameter) on a sprocket will affect the drive ratio. Which on a trike will affect the acceleration characteristics and the top speed.
2.  There is a limit to the ratio of the number of teeth on the driving and driven sprockets in a chain drive arrangement.
3.  Space requirements, a change in size of sprocket may cause interference with adjacent components or structures.
4.  Shaft diameter must be precisely toleranced to suit the sprocket bore assembly fit, which in this case should be a light transition fit.
5.  Chain length will need to be revised if a sprocket diameter is changed.
6.  If a design layout drawing is not produced, other factors may present problems during installation, so proceed with caution and check function and safety thoroughly.