Wednesday, 8 May 2013

Camshaft Surface Finish (1)

In April 2009, I first began investigating Sentinel 7109's engines. The reverser lever was seized so I started tracing the cause (and this is actually why I got so interested in the subject of Sentinels in the first place).

Initially, I found on both engines that the cam followers (the things that actually rub against the camshaft surface and push on the push-rods) were stuck fast as the oil on them had dried over the years and set like varnish.

However, the main problem bothering me was the corrosion at the end of the rear engine's camshaft in the cavity where the cam-selection finger is located.

The following photo shows how it looked in 2009.
Camshaft surface in April 2009
Ironically, I used diesel fuel to remove the corrosion (sad that diesel has to be used to repair steam equipment!).

It now looks a lot tidier as in the photo below.
Camshaft surface in April 2013
The surface was still not very smooth so I made enquiries as to whether this level of roughness was going to be a problem.

I was reassured that, so long as there was nothing standing proud of the surface, then there should be no problem as crankcase oil is so thick that it will be able to protect any pitting from causing trouble.

This was a considerable relief as I had envisaged having to take the whole caboodle apart for re-machining.

To remove anything standing proud of the surface, the easiest way is to turn the engine using compressed air and hold a file (gently!) against the roughness as if using a lathe - a lot easier than taking it all apart!

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