The Fire Drake Files No.4 - McLaren tandem cylinder compound

Colossus is back together again at last. I just love all that ironmogery on top of the boiler.

For the last 18 months, whenever I’ve passed through South Petherwin on my way to Launceston, I’ve noticed a traction engine in a yard and workshop. One day I went slowly enough to see a nameplate on its smokebox door – Colossus. Like any steam engine, it had a certain presence, especially confined within four walls and looking over a gate.

At the Great Dorset Steam Fair, I was delighted to come face to smokebox with Colossus and to find out what a remarkable engine it is.

Its most striking feature is the tandem cylinders on top of the boiler behind the chimney. Most traction engines have them side by side, which makes for a more compact arrangement. I’d only ever seen tandem cylinders before on a conversion of an old single cylinder Fowler ploughing engine. The idea of souping up some great lumbering leviathan by strapping on another pot and making it more efficient, powerful and more impressive to look at, appeals to me hugely.

Colossus dates back to 1905 and was built to burn straw by J & H McLaren as their Works No. 897. It was exported to Argentina but repatriated after a hundred years abroad as a bare boiler with only the cylinders and the trunk guide in place. Its condition and status as the only surviving tandem cylinder McLaren inspired the present owner John Atkinson to reconstruct Colossus to full working order. This took the amazingly short time of 28 months and the result is an absolute credit to all involved in this engine’s resurrection.

The extra low pressure cylinder is mounted on an extra wide boiler band. The advantage of the tandem arrangement in a rebuild is that it doesn't need any alterations to the motion of the original cylinder, which used to live alone but is now promoted to high pressure work.

It is thought that Colossus was originally a single cylinder engine but was converted by Robert McLaren, brother of founders John and Henry and resident of Rosario, the principal city in the state of Santa Fe. He either obtained from Britain or sourced locally a second cylinder block and mounted this ahead of the other one to re-use the waste steam in a larger cylinder. It looks to me that the boiler was extended to make room for the new block and the result is a long, low, racy machine that looks faster than it is. 

Part of the bigness of this engine is the firebox - you need a lot of straw compared to one burning coal - and the water tanks - the pampas can be a grassy desert. With fuel and water in scarce supply it makes sense to get the most bang per buck by bolting on that extra cylinder.

Well, when I say low, it’s actually quite tall and lives up to and beyond its name.

I like its plain black livery, too. This is a no nonsense machine built for work that could have been anything but elegant. However, in its no frills black it looks better than many gaudy showman’s engines. 

McLaren are not one of the most famous of the steam engine builders. Their engines lack the glamour of a Burrell or the smiley face of a Fowler but there is an earnest intent about them. Their ploughing engines were said by the men who operated them to pull harder than Fowlers of an equivalent size and weight. 

The 2010 Great Dorset Steam fair gave these quiet giants the recognition they deserved by featuring the engines of J & H McLaren and bringing together as many survivors as possible. It's a fascinating firm and at the show I marvelled at the earliest engine brought back from Australia (thought by those who know to be Works No. 2!) and another that had been recreated from worn out parts hauled out of  a river bed. You could trace the development of the steam engine if you wanted to, by looing closely at the various exhibits in order of works number. McLaren went on to devlop the diesel engine and designed a road haulage engine to rival their steamers in performance but none of these survive - unless anyone knows any different (he added hopefully)

Respect for these quietly benign giants of steam is now assured, even if they are tiddlers - a small McLaren seems bigger than it is. Black is the best colour for them. It's understated and refined.

Hero is the little brother of Colossus. The conventional arrangement of the two cylinders shows the difference in diameter of the low (large) and high (small) pressure cylinders. I wonder if anyone tried a four cylinder arrangement, with two tandem blocks of two cylinders. Hero almost has room.

Colossus makes an interesting comparison to Hero, which was also present at this year's show. Hero is McLaren Works No. 1552, a double crank compound ploughing engine with the cylinders in the usual place. Hero is world famous in Cornwall and has been a favourite with my family for many years. It’s the massiveness, the plainness and the blackness that appeals of engines like these and I think I’m going to enjoy seeing Colossus around for many years into the future, thanks John Atkinson’s hard work and resurrectionist skill.