For those unaware, the (almost invariably) cast iron cylinder needs to be machined on its underside to match the diameter of the boiler (plus an allowance for a gasket). The “stud” holes are later drilled right through the boiler shell and into the steam space. These are then tapped with the thread of one’s choice.

Although the current build is my third traction engine there are several major differences from previous similar operations. Previously the boilers have been in copper, a most horrible material to drill and tap – I found the best tapping lubricant to be full cream milk, no I am not joking it really does work. The technique I have used for these is to use no physical gasket but a generous application of Hermetite Instant Gasket, a red silicone which stands temperatures of minus 50 to plus 250 degrees C. This seals the flange and bungs up the threads nicely. Others have used a different technique but I have found this worked for me but I digress . . .

Back to the Mclaren. This is a different proposition in that the boiler is in steel. Albeit an easier material in which to tap threads but thicker than its copper counterpart. This engine is designed to operate at 175 psi – considerably higher than my previous ones. According to the Model Engineer’s Handbook steam at 175 psi is at 188 degrees C. I realise the boiler shell itself will probably not attain this temperature but it is too close for my liking to the maximum tolerance of the Instant Gasket. After taking advice I decided to use the traditional method of a proprietary gasket and Foliac Manganese jointing paste.

With the cylinder placed in the correct position on the boiler with a piece of “gasket” under it to ensure the correct position of the holes relative to the angle of the flange the first problem needed to be faced. This was that being compound the steam chests either side protrude right out over the flange, thus obscuring the stud holes so there was no possibility of using the cylinder as a jig. Some head scratching followed until I hit on the idea of using a ground up broken quarter inch centre drill (this was a snug fit in the holes) as a centre punch, using a piece of steel resting on the top where I couldn’t get the hammer to it. This worked really well in that all the holes were neatly marked. The next problem was how to mintain the correct alignment to the circumference of the boiler and ensure that each hole was at 90 degrees to the length of the boiler. With the cylinder replaced I found I could use the flange as a jig to drill and tap the four corners and the front span of holes. This was done making a little fitting which was a light push fit into the clearance hole in the flange and an M6 tapping hole up the centre in order to centralise the holes and maintain the correct angle. Studs were then screwed into these four corners and front row with a locking nut. A piece of straight wood was attached to each of these with clamps. A small engineers square placed on the boiler and leaning against the wood gave me my angles in each direction. This was repeated until all holes were drilled and tapped. Drilling 24 holes M6 tapping size through 10mm of steel boiler plate using a pistol drill is not my idea of fun but with the drill kept sharp it was not too difficult.

Now you are going to ask the question “did the holes all line up?” Well what do you think? Of course they didn’t but they weren’t so far out that slightly enlarging a few holes in the cylinder didn’t make everything fit.

Now to the “studs”. I find using real studs in this situation is not at all easy so I always make bolts that look like studs. This time this was achieved by obtaining a number of 40mm long M6 Allen grub screws (cheap as chips from Western Bolt and Engineering Supplies) and silver soldering nuts in the appropriate place. With the excess trimmed of and the end of the thread rounded no one would know the difference.

The gasket material – I was unsure what best to use so scoured the traders at the Midlands Exhibition finally settling on a sheet of 15 thou material from EKP Supplies. This was stated to be suitable for steam. On the back of the sheet was a maker’s name and product number so the following day I “Googled” it. The manufacturer’s web site stated this particular product was suitable for oil, fuel and low pressure steam. Thinking I had bought the wrong material I consulted the data specification on the web site. It was obvious that their idea of low pressure steam was different from mine. This particular material was stated to be OK up to 50 bar!

The rest is history, save to say that when I finally fitted the cylinder and used the foliac my hands, arms and even my face turned black. It is the nearest thing to oily sticky soot I ever want to get. Yet to carry out a pressure test but feel fairly confident. I am afraid I have no pictures as when I was doing the job it never occurred to me I would be asked to write about it.