Engines (2) Cylinders

Before looking into the cylinder tops, a brief digression. I've occasionally been asked about the four 'pips' on top of 7109's engine cowling; some enquirers had assumed these were a peculiar type of chimney where the smoke would rise from.

7109's four 'pips'

However, this is far from the case. In fact they are merely an adjunct to the cylinder covers to allow space for the top-of-cylinder automatic drain cocks. One wonders whether the 'pips' were an after-thought on the designer's part rather than a feature. Oddly enough, later designs did not have them!

Beneath each of the two covers is a pair of engine cylinders.

Rear engine's cylinders showing auto-drain cocks

When a lid is removed, inside it looks like this:...

Front engine RHS cylinder lid

... and inside the cylinder, it looks like this:

Front engine RHS cylinder

The muck is well stuck on and must have been there a long time. I've cleaned out some of it but it's hard to dislodge and will have to stay put.

The cylinder wall looks like this (the others are similar):

Front engine RHS cylinder wall

Some years ago, in my ignorance, I cleaned the cylinder walls with light machine oil. The variation in colour shows where I washed away the brown cylinder oil which probably would have been better left as it was.

On this occasion, however, I drenched the cylinder in new cylinder oil in preparation for running.

Guess who took the photo!

I did the same for all four cylinders, The piston is right at the bottom in the photo below.

Rear engine LHS cylinder

Finally, I got a bit arty and captured the picture below.

It was a fine day!

Then I put the cylinder lids back on as in the second picture from the top. Job done.

The rectangular holes in the cylinder walls are the steam inlet and outlet ports.