Leaky Mamod cylinder

The cylinder assembly of my TWK1 leaked steam. I knew about the problem before I bought the engine as it was mentioned in the eBay description. 

The first job was to remove the cylinder from the engine and take a good look at the mating surfaces. Here's the back of the cylinder;

I then 'blue'd' the mating surfaces with a marker pen, re-fitted the cylinder and then gave the flywheel a few turns before removing the cylinder. Looking at where the pen marks had been rubbed away gave me an idea of how well the cylinder and bracket mated together;

Note how the pen marks revealed where the steam was escaping, they should be completely rubbed away around the steam holes. I took the problem to a Mamod Facebook group (Facebook has its uses!) and I was advised that the bracket might be bent. So, armed with a pair of pliers, I gently bent the bracket, a bit at a time, until the wear marks looked like this;

I then removed the bracket from the engine, made easy by the fact that this is a kit built example so the bracket is screwed rather than riveted in place and the steam pipe isn't soldered to the boiler but is held in by a screw fitting and seal;

Note the threaded inserts in the firebox top. I've also given the pipework a wee polish.

I then lapped the two mating surfaces following the method detailed here, although I used 600 grit wet & dry rather than 400 as I didn't have any;

Success! The engine now runs without any leaks between the two faces, although there is some leakage from the cylinder bore itself. I may yet try turning up a new piston.

Here's a close up of the boiler pipework; 

The union where the steam pipe joins the boiler relies on a seal, I've used a 3mm i/d x 1.5mm cross section O ring.

I'm quite pleased with this job, and it will be good practice for when I re-assemble by Mamod loco. The next job will be to sort out the leaking whistle and then strip the engine down for a repaint.

Paul.