Let's start this catch up with a bit of history. Right back at the start I mentioned the Standard. The Standard was a simple device and a tough wee bugger. A typically overloaded Standard, yesterday.
Brown Bailey ran their Standards, massively (and I mean massively) overloaded into the 1960s. If you know the Glasgow Transport Museum you'll know one of Brown Bailey's Standards.
It may look crude to our eyes but in comparison with what went before it was pretty bloody awesome. One day people will look at our Scanias and laugh in the same way. Anyway, the Standard was so brilliant that they sold thousands of them and Sentinel made a lot of money. By the 1920s sales were tailing off and money was getting tight which is why the new improved Super was developed. However, it was clear by then that despite their best efforts steam was not going to be viable as road haulage for very much longer so they needed to diversify. One of the things they went into was railway engines. In order to minimise risks they didn't leap headlong into building proper locos but instead chose to use as many bits from the waggons as possible. This restricted what they could build to shunters and, slightly later, rail cars. This is the quite late Sentinel Shunter that lives in the NRM
The Super engine sits vertically at the front and drive through a chain. The boiler (much bigger than the waggons in this case) is in the cab. There is a bigger version of this one in preservation that uses two Super engines. Sentinel shunters were actually quite successful and were built into the late 1950s. If you rake round most railway preservation places you'll almost certainly find one rotting into the weeds.
What is the point of all this wittering about railway engines? Well, the engines were the same as the waggons with one or two key differences namely they had a solid forged crankshaft and a differently shaped crankcase. They also ran pressure fed lubrication to mains and big ends. Why this development didn't make it onto the waggons is lost on me. They also had a slightly different (but significantly better) manifold arrangements but it is just too boring to go into that here. The upshot is that if you need a few bits for an engine then one of the first places to start is your friendly neighbourhood railway preservation yard. And we had one of those just down the road and it had not only a few shunters but also a very large pile of brand new spares. This would be just what we needed. In the end we came away with what we needed in exchange for a not exactly trivial sum of money. What will become clear over the next couple of photos is that we didn't have a great deal of choice.
Probably the most important missing pieces were the camshafts. Not satisfied with talk of railway things let's have a bit of talk about the mechanics of steam engines - apologies to anyone who is being taught to suck eggs. The reciprocating steam engine has many benefits but it also has some limitations. One of those limitations is addressed by giving it variable valve timing. On a piston valve or slide valve engine this is a pretty simple task which involves some sort of linkage - and there are lots of different types of linkage - controlled by the operator. What you are doing is controlling for how much of the piston's stroke you admit steam. To produce lots of torque you need a lot of steam so to start, for example, you will run at 90% cut off. That is admit steam for almost all of the stroke. As speed builds you need to admit steam for less and less of the stroke. The shortest cut off may be as little as 20%. The other thing is that you often need to run a steam engine in reverse so altering the valve timing allows you to do that to. All very easy to understand and handy.
However, the Super engine, like most undertype steam waggons from most manufacturers (Yorkshire being a notable exception), uses poppet valves (the same kind of thing as what your car uses) operated by a camshaft. If you have a camshaft how do you engineer variable valve timing? These days there are many ways of doing it and through the years various engineers have come up with all sorts of elegant solutions.
What we are talking about here is not elegant at all. The solution is that you have multiple lobes on each camshaft then as you want to change the cut off or go backwards you drag the camshafts from one lobe to another. Hmmmm. To illustrate here is the first prize from the trolley dash. It is a brand new, still in its waxed paper exhaust camshaft. My little beady eyes lit up when I saw this.
You have an inlet and an exhaust camshaft. Twin cam, four valves per cylinder and VTEC. There is nothing new under the sun. Each valve has four lobes. Two forward cut offs, a drain position (all valves held open) and a reverse. Because shunters tend to go forward as much as they go backwards the shunter camshafts have two forward, a drain and two reverse. Later DG and S Types waggons got three forward cut offs. Each one of the bumps you see is a lobe of a different grind. The long slot at the end take the drive dogs from the cam gears. It is long because the camshaft needs to slide within its drive gear.
This is a close up of some lobes. You may be able to make out the two forward - drain - two reverse lobes for each valve. Making these would have been tricky so it was a huge step forward to get them.
This is someone else's photo of the inside of their Sentinel shunter crankcase. It gives a pretty good idea of how things work. The engine sat upright in the shunters so they added a little tray underneath the camshafts so they always ran in oil. The things poking down are the tappets.
Enough about valves what else did we get? These are the inlet manifolds linked by the steam inlet pipe. These were overhauled spares which were nice because everything was there. Even though the valves were new they won't be used because the steel used by Sentinel was absolutely hopeless and valve seat life was close to non-existent. New ones in the right steel will be used (you'll like them when we get to them).
A pair of exhaust manifolds. You might see that one has been dropped at some point and bent the valve stem. Hardly a disaster but it broke the valve guide too. A little bit of remedial work required.
Valve adjusters. These screw onto the end of the valves and allow the clearances to be adjusted.
A pair of new pistons. Very nice. The log shaped thing is the exhaust manifold link pipe.
And lastly for the store shed was a pile of new piston rings.
There are still a few key components missing so we had to venture into the undergrowth to find the sorry remains of the two used, incomplete and mostly buggered spare engines to get the rest.
Our luck was in and one of the engines had one of its cylinders still on. This is well and truly knackered but it can be used as the basis for a pattern so that is good enough. That is the old piston next to it. We had to cut through the piston rod to get the cylinder off.
A pile of tappets. Hopefully from this pile there will be eight that can be pressed into service.
Camshaft gear train. The big one is the idler that is driven by the crankshaft and the smaller pair are the camshaft drive gears. They sit on bronze carriers which allow the camshaft to slide relative to the gear. The big bronze eccentric on the large idler gear is what drive the water pump.
This is what Honda copied to make their VTEC engines. There are forks inside this cast iron housing which engage with the camshafts. This allows the driver to move the camshafts to the desired position. You don't need to know too much about steam engines to know that using poppet valves is a really, really stupid thing to do. Suffice to say when Abner Doble designed his cutting edge steam cars and lorries he did not use poppet valves.
And the last piece of the jigsaw. A cylinder head. Only one sadly so we'll need to make another. The big bronze valve is a relief valve. If you get it wrong and overfill the boiler water can get carried over into the engine. This is called priming and it can also happen under other conditions. Priming is very bad news for a steam engine and usually results in people looking very sad and/or gulty and wondering just how all this broken thing can be made better. However, a decent relief valve at either end can save the situation. Waggons didn't have RVs but locos did. We'll keep the RVs on this one.
That will do for this time. In the next installment we go back to making patterns, a new lathe appears and some things start to look finished.