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Self starting steam engines

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michael howarth 126/07/2018 15:31:24
34 forum posts
4 photos

I recently bought a small marine steam engine with 2 x 5/8" single acting pistons with 11/16" bore. The cranks are set at 180 degrees so that when one piston is at tdc the other is at bdc. The engine runs sweetly on low air pressure and will self start about 25% of the time. Unfortunately this is not good enough as I intend to use the boat on a river and a midstream stall would be mighty inconvenient.

Other than remaking the crankshaft so that the cranks are at 90 degrees is there any other wheeze i can use to encourage self starting?


Tony Hadley26/07/2018 19:06:55
914 forum posts
559 photos

Two thoughts -

Send a copy of your message to Richard Simpson who writes the monthly Boiler Room column in MB magazine. Contact would probably need to be an email to the magazine editor or as a message to Colin Bishop, website editor.

As you say, 90degrees (quartering) is the normal method for self-starting a steam unit. For sailing in a high-risk environment, might it be worth fitting an auxiliary electric drive system. These were a simple on/off system fitted to some i.c. powered models as a 'get you home'. Whether a separate drive line or as some kind of clutch/gear system to disconnect the steam and engage electrical drive to the existing propeller shaft.

Ray Wood 226/07/2018 21:24:05
2838 forum posts
988 photos

Hi Michael

I'd agree with Tony about the auxiliary motor and prop to get you home if it stalls and the burner keeps going! Quartering only really works with double acting cylinders. The single actiing twin should self start in theory :-!

Regards Ray

Charles Oates26/07/2018 23:25:46
663 forum posts
52 photos

This is not my field, but I remember seeing an unusual arrangment. A gear wheel was put into the drive line, about 2 cm diameter. Then a simple push rod was connected to a servo so that it gave the gear a nudge to start it. I think he usually used the mechanism to start the model so it certainly worked.

michael howarth 127/07/2018 10:19:50
34 forum posts
4 photos

This ai the plan of the engine I am referring to.marine engine jpeg.jpg

michael howarth 127/07/2018 10:26:36
34 forum posts
4 photos

I have been playing around with it this morning and I have found that the only position for repeatable self starting is when No.1 cylinder is at 45 after tdc. I can achieve 100% self starting on very little air (5-10psi) at this setting. What does the forum think of inserting, say, a round headed rivet into the circumference of the flywheel with a very lightly sprung plunger bearing on the surface of the flywheel circumference (plunger could have say .020" clearance) to encourage the crank to stop in the desired position? Experiments continue.


michael howarth 127/07/2018 14:22:51
34 forum posts
4 photos

I have received a suggestion on the MEW forum which sounds good and is pretty much the opposite of my idea above. It involves making a small disc which is fitted to the crankshaft and a dimple. of a depth yet to be determined, drilled in to the circumference of the disc. A spring mounted plunger with a tip that will match the dimple can then be mounted so that it engages the dimple when the crank is at optimum position for self starting. I wondered about the "click, click,click....." that will occur when the plunger engages/disengages but a teflon tipped plunger should sort that I think. Any thoughts on this very simple proposal?


Andy Stoneman28/07/2018 20:00:35
128 forum posts
12 photos

Hi Michael,

What makes you think your engine will stall midstream, I think prior to making the changes your intending you might before trying a river for cruising carry out some steam testing of your engine out of the water.

You will gain more confidence in its operation. When your happy it runs well you'll gain more confident in it, after that try a few bath tub trials, if all goes well you know the next step


michael howarth 128/07/2018 21:37:22
34 forum posts
4 photos

Thanks Andy. Perhaps my lack of confidence derives from a lifetime of falling foul of Sod's Law but your good wishes and advice are appreciated.


Richard Simpson15/12/2018 10:44:28
1015 forum posts
256 photos

Mick, There have been numerous ideas on this very theme. My own favourite is to use a controllable pitch propeller, they are being made in brass again by a supplier in China, but there are also reversing gearboxes to consider as well as an electric motor connected to the shaft that free wheels under normal operation and can be powered to turn the engine if it stops in a dead spot. I would love to see someone use the motor as a generator when it is being turned by the steam engine to charge up the battery!

By the way your disc with the hole and the plunger idea I am sure will sap a huge amount of power from the engine that will reduce running time as well as performance.  The electric motor idea will as well but it should have a lot less drag.

Edited By Richard Simpson on 15/12/2018 10:46:31

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