Tech W/ Kyle: Making (And Repairing) A BSA Gear Shift Quadrant

• Making a new shaft 
• Cutting splines
• Repairing and modifying an original gear change quadrant 
• Finishing 

The modification 

Supplies

I will be making my own splined shaft, however we do sell them new on the site so you do not have to make your own - since I had the material on hand I decided to make my own 

The material used must be weldable (4140)

Below are the supplies needed to be able to make your splined shaft 

• Lathe
• Mill
• Rotary table

Machining a shaft - #1 (the lathe) 

Cutting the splines - #2 (the mill) 

Now that the 1/2” shafts have been machined on the lathe, it is now ready for cutting splines

I first have to set up the rotary table by ensuring that the rotary table is perpendicular to the table 

For the splines I’ll be cutting, we need to cut a total 36 splines, which means each spline will be 10° apart 

Now that the splines are tight in the 3-jaw chuck we are ready to cut the splines 

Goal is to make 1 pass per each cut to the proper depth…

After 36 rotations and passes using my cutter, we now have a successfully made splined repair shaft 

Quadrant Repair

Now that we have our new splined shaft made, it’s time to dive into repairing an old gear change quadrant

This specific quadrant on hand is for my 1962 BSA C15S project that I plan on building soon..

Although the quadrant is in decent shape the splines for the gear lever are worn down (see photo above)

To execute this repair job, I highly recommend using a lathe as concentricity is very important..

Measuring

Before we do any cutting or machine work on this quadrant, we must record the shaft protrusion (length) from the shoulder of the casting to the end of the shaft 

Record and document the correct measurement on a note pad

Each gear change quadrant will be slightly different, however, not ALL quadrants are the same spec - for example, a B44 quadrant will have a different shaft protrusion than a A65 quadrant..

Cutting

Now that we have the length documented, we will have to cut the shaft off using an angle grinder

Try to get as close as you can to the casting flange - make sure you keep the cutting wheel straight and true

I do NOT recommend parting this shaft off on a lathe

Machining

The best way that I have found to mount the gear change quadrant in a lathe is to use a 3/8” 5C collect

Once mounted we will face off the shaft until it cleans up all the way down the casting flange

Now that the face is cleaned up, we will use a spot drill to start the drilling process

Starting with a 1/4” drill bit, we bore the quadrant to the proper depth followed by a metric drill bit just shy of 1/2"

Once we get near 1/2", we will lastly use a boring bar to size the hole no more than .001” larger than the 1/2” shaft (.501" approx)

Using our spline shaft we will test fit the shaft into the quadrant

If you are happy with the fit, you are ready for welding

To aide with welding and penetration, I do recommend adding an undercut on the splined shaft to allow the weld to build up

Welding

Now that our shaft is made and the quadrant machined it is now time for welding

You can choose to weld or braze

I’m not a welder, but I can braze confidently 

For this repair I opted in for brazing because the convenience for me, and the fact that the braze can "fill in"

Once the shaft and quadrant are brazed together we will have to mount the quadrant back into the collet to allow a quick face off the weld build-up

Only clean up what is necessary 

Job complete