The Tale of my Old Dumper, Part One

A 1960’s Thwaites Orion dumper rated to carry 15 hundredweight or ¾ ton load

The beginning

This story starts roughly six years ago when we moved to Cumbria having purchased a small farm cottage with adjoining derelict barn which we planned to convert to domestic accommodation. Firstly a warning, I should point out this story is of a technical nature and probably only interests the hobbyist and keen DIY types.

My builder and I set about this task, partly aided by a labourer who was invaluable when I was away with work. It was a big job, probably bigger than bulldozing the whole lot flat and starting from scratch largely due to National Park planning stipulations. All new roof with green oak trusses, holes made in walls for new windows, excavating the ground inside to gain headroom for an additional floor and the necessary underpinning of the stone walls with concrete foundations. This work created a very real need for my dumper and it was earning its living again shifting a few hundred tons of spoil, sand, gravel and concrete.  One thing soon became evident, the little single cylinder air cooled Petter diesel engine was perfectly adequate for running around building sites but I was now asking it to climb steep banking on the hillside that we live on and traverse soft fields when laden.  Both of these tasks showed that the engine was totally inadequate and was woefully short of power and even first gear was sometimes not low enough . Common sense says I should have purchased a more modern dumper with a larger engine but the experimental or crazy side of me decided that I would fit a bigger engine. I discovered that Petter made a PH2 engine which is simply a 2 cylinder version of the PH1 currently installed. But would it fit in the space? That was a good question and some preliminary measurements indicated that it would be tight. Eventually an engine appeared for sale on ebay near to me at a sensible price, so it was purchased and carted home.  I discovered that the sump was full of around two gallons of water, no doubt due to it standing outdoors, but these engines are solid simple beasts and after removing the crankcase inspection doors I soon had it cleaned out and the old filthy black sump oil had done its job and protected all the surfaces from rust. I dismantled the big ends and found the bearing shells to be in good condition and so shoved them back together with the standard Puff torque wrench tightening method employed of ‘’5 white knuckles.’’  The specification of engine that Thwaites purchased from Petter for their Orion model was the version where the power output shaft is driven by an extension of the camshaft and thus rotates at exactly half crankshaft speed, the reason for this is to achieve the correct overall gearing for the dumper. The output shaft has a sprocket on it and a chain drive takes the power down to a clutch assembly mounted on a remote gearbox. The engine I purchased was from a more modern machine with conventional drive from the crankshaft so the main job was swapping the camshaft extension, and tail shaft housing over onto the new engine having removed all the unwanted components from that.

Next was the job of fitting it to the dumper, and I discovered that it wasn’t going to fit as hoped for. But by removing an inch or two of surplus crankshaft that protruded forward of the flywheel  with my trusty 9” angle grinder and by trimming the rear decking away I had it sitting in place. Four new holes for the mounting bolts were marked out, the engine removed from the trial fitting with my 2 ton chain block and A frame, new mounting holes drilled and engine bolted down and so it was time to see if it would fire up. I bled the fuel system and amazingly it started first time but rather worryingly it was throwing out large amounts of blue smoke suggesting stuck or worn piston rings.  Another period of thought ensued regarding pulling the cylinder barrels and pistons off to do a top end overhaul, but I noticed that the smoke situation appeared to be improving slowly and I was no longer choking quite as much inside the barn. After an hour or two of running it fixed itself, so most likely due to stuck oil control rings that freed themselves.  We British do build exceedingly rugged engines.

The new two cylinder PH2 engine in position and ready to go. This boasts a stunning output of 19.8BHP at 2200RPM

The dumper was transformed and it thought itself to be a thoroughbred chomping at the bit during the start of the Grand National. It would pull away from a standstill in top gear unladen and romp up hills and soft fields fully loaded with just the regular tell tale trail of black smoke from the exhaust indicating that it was working hard.  I was very pleased with myself after that episode.

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