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Clarkson Twin Horizontal Steam Engine

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Mike Bondarczuk:
Hello all,

Have finally started on the Clarkson Tandem engine build as per the Blackgates castings, which I had purchased some two years ago from Jo.

The kit was incomplete but I have ordered the missing castings, where appropriate, and will collect them at the Midlands Exhibition in two weeks time, and I am planning on building it as a tandem with 2 LP cylinders and not a tandem compound with HP and LP cylinders.

However, to get things rolling I have started on the build and it seemed that the first action should be to keep Jo happy, so I decided that the cylinder block assembly with steam chest and cover should be held together with studs and nuts, and I trust that she approves.

The next series of interconnected parts are the crank discs, con-rods, crank pins and axle, and these are all from stock as per the drawings.

I have started on the cylinder blocks and got them down to within 25thou of the finished size, all nice and square and just waiting for the steam chest to be able to confirm the cylinder bore centre.

Hopefully work will progress at a  faster rate once I have the remaining castings though already have some questions regarding the main bearings and bearing caps as from the drawings the castings seem to be extremely tight in machinable material.


Look forward to following along.

Just one point a "tandem" engine is one that has the two cylinders in line with each other ( think tandem cycle), what you have there if it was built as a compound would be a "cross compound" or with the steam going straight into both cylinders will be a "twin" or double high" as the steam will be classed as high pressure from the boiler rather than low (expanded) steam from a HP cylinder.

I think I would be tempted to add some bronze bearings rather than run straight in the cast iron which would allow you to put the bearing in at whatever height you wanted if the base casting was too low, you have double the amount of bearing caps so can split them off ctr if required.

I'd also go for a 2 bearing crank not 4 and swap the baseplates over putting the flywheel into the inside of the "L" shaped base castings but that is probably a bit further than you want to go ;)


I tried reversing the baseplate castings on my 3D CAD assembly as you suggested, but it does not work out very well in practice.
I think on mine I will remove the existing bearing lugs from the castings and make up some new ones to form a single bearing either side.


I'd only traced it off the drawing quickly to see if it would work, i seem to recall that one of the pads for the cylinder would need building out to help line things up . New bearing supports would make it easier and you could beef them up a bit which would look more appropriate maybe 4 studs per cap.

If I do one then it won't be a problem as I doubt I will use castings, maybe just a couple of 4" flywheels. I'll draw something up at some time maybe twin 24mm bores to go with my other engines or 18/30 compound that could be plumbed either way so you can run as a compound on steam and double high on air.

Anyway back to your thread Mike.

Back to the main bearings I notice there is a bit of an anomaly in the drawings (Clarkson Drawings).

The cylinder casting ctr height is shown as 1 1/16" and this sits on a pad that is cast into the top of the bed casting so lets say the pad stands proud by 1/16" after machining. This gives the engines ctr line at 1 1/8" above the top of the base casting.

The ctr of the main bearing is shown as 1 1 /16" above the top of the bed casting and it has no pad being part of the bed casting.

This gives an error of 1/16" which could be sorted in a number of ways depending where the casting has more metal than needed or where it may seem a bit tight but the extra 1/16" may help matters. Without a set of castings in my hand it's hard to say, maybe as they have been fondled a lot by Jo's hands she could shed some light on this unless it was one of the reasons she parted with them ;)


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