Wednesday 5 August 2020

Machining Titanium Valve Spring Retainers

The valve spring retainers are referred to as “top washers” in Velo-speak. Although they are available off-the-shelf in steel I decided that I would make a pair of lightweight items in titanium for this project. There is plenty already written about titanium vs steel and I won’t repeat any of that here. Rather, I will just note a couple of points from my own experience.

Firstly, titanium must be machined with sharp tools, ideally new carbide tips or, if drilling, a sharp carbide or HSS drill. If a sharp tool is not used then the surface of the material work hardens and it can be difficult to restart the machining operation.

Secondly, the swarf can catch fire! The short movie below shows a near-completed valve spring retainer being parted off from its parent bar and the heat generated by the parting tool ignites the thin ribbon of swarf.

In practice, this did not cause a problem but it’s good to be aware if it.

With a few scallops on the milling machine the final items turned out well.

I was also lacking good Velocette tappet adjusters. For their size, these are quite complicated little components. Unfortunately, neither the Velocette Club Spares Scheme nor Grove Classic Motorcycles, the two main suppliers of Velocette spares, can supply these so it was necessary to make some.

By measuring decent existing components I came up with the following dimensions:

There is a radius on the foot of the adjuster that is not shown in the sketch and the part that screws into the rocker is a collet and requires 2x slits to be made with a 1/32" slitting saw and flats for the spanner. The collet is made from EN24T and the adjuster from silver steel with a hardened and tempered "foot".

As I would need a few of these for future projects I made 6 off.


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