F SUPER PROPSHAFT

 Having finished the restoration I found that the propshaft had a vibration at 50 MPH that was quite annoying. I had previously built a JZR tribute Morgan with Moto Guzzi drive train. It was a known fact that the propshaft in it would begin to whip and there were even several cases of the shaft ripping itself out of the car. Triking also had this problem. The solution in both cases was to install a support bearing somewhere near but not at the center of the shaft. This will break up the harmonic vibration and allow the shaft to run without a problem.

There have been several articles in the Bulletin with various solutions for the Morgan. I have taken my experience with the JZR and together with the knowledge of other Morgan owners come up with a rather simple solution that has worked well for at least 1500 miles so far.

Clarrie Coombes also wrote, in his excellent book, a method to cut the splines using a lathe. Since I have a decent mill I have chosen a different path. This is really quite simple to do with a Chinese indexer and a slitting saw for the cutter. This photo shows the setup. If you have not used an indexer before you need to find some Youtube videos and learn as I had to.

 

The material I used was 7/8” diameter 4340 cold finished alloy steel. This is plenty strong. In one of the other articles on the subject the author used 5/8” shafting. The first step is to use the lathe to turn the end to fit the pilot bearing in the crankshaft. Then cut the splines. The same process is used to cut the two keyways in the rear end. I also cut a snap ring groove in the shaft just forward of where the support bearing would ride in the torque tube. This was in the area of the shift lever. This allow the shaft and bearing to be removed together.

Here is my Autocad drawing where I worked out all the movements of the 3 axis of the mill.

The process involves making two cuts to create each spline. This is accomplished by making all ten cuts on the bottom of each spline while rotating the indexer spindle angle according to the list on the left. Then raise the cutter .227” and make the final ten cuts to finish the top of each spline. I have a digital readout which makes this much easier but it can be done without one if you watch out for backlash in your machine. I used a 2” diameter cutter but any size will work.

Once all the cuts are made you can test fit the clutch disk. If it is too tight you can go through the process again and remove a few thousands of an inch from each spline. Watch to be sure it isn't the spline bottoming out in the disk or the disk hitting the root of the spline.

Here is how it all looked in the mill. I made a simple support for the long shaft so it would freely rotate in the indexer. The shaft was then cut to length and the key ways cut in the other end.

 

 

 

Next is to machine the support bearing housing to suit the bearing chosen. This housing should be a close fit into the torque tube.