The Steamboating Forum

My engine is a Stuart Turner Swan, 2 cylinder double acting simple, 2.25” bore x 2” stroke. First steamed on the water in September 2025 and operated about 18 hours since then. Boat is back in the shed for winter (Southern Hemisphere), and, of course, since it all seemed to be working so well, I had to open everything for a look (that’s what Engineers do to avoid gardening duties). There had obviously been problems with cylinder lubrication, due mostly to my use of the wrong grade of cylinder oil. That can be easily solved. Both cylinders had “sticky” piston rings and greasy deposits, with the fwd cylinder being worse. Both cylinders, their pistons and rings have cleaned up nicely, showing no scoring or adverse markings.
More serious though was the corrosion, pitting and scoring of slide valve and port faces, the most affected being the fwd cylinder port face - that nearest the steam supply end of the inlet manifold. I am confident that the scoring is due to corrosion debris in the valve box rather than ingested material. Deepest pitting is yet to be measured but it looks to be about 20 thou (or half a millimetre – take your pick). Port faces are cast iron, as are the slide valves. The slide valve faces should clean up with a bit of work on the lapping plate, as should the aft cylinder port face, but the fwd cylinder will need a skim in the mill.
Normal steaming is at 90 to 100 psi. with no superheat, and I am yet to fit a drier coil to the boiler. I don’t believe there has been any significant carry over while steaming, and boiler water has been kept to Ph 9.5 to 10.
I operate my boat on a tidal estuary, and have not been brave enough (or foolish enough) to risk her sitting in the mud between tides, so after each session on the water, it’s back on the trailer. Prior to taking her out, I allow the engine to drain boiler pressure to around 30 psi, open cylinder drains until the engine stops, then shut the main stop and throttle, leaving drains open. Generally I turn the prop daily for a few days after each session on the water.
So what am I not doing correctly? I have tried to ensure extra lub goes in prior to shutting down, and there are indications that oil is getting to most places it should. How can I shut down and cool the system without leaving a wet, corrosion inducing atmosphere in the valve boxes? For those who believe cylinder lub is not needed with LP sat steam – how do you keep corrosion out?
Any and all advice will be most welcome.

I've had good luck w/ preventing/reducing corrosion by drilling and tapping the cylinder and piston valve covers for small 1/8" brass pipe plugs. I remove these and squirt in some compounded cylinder oil (600W) and turn the engine over by hand to distribute the oil. I do this when the boat is to be laid up for a while; I've found that it's not necessary if the boat is going to be used the next day.

Recently I've picked up some "Fluid Film"; this is a lanolin-based product. I'll give this a try this year and see how it works.

Thank you for your advice. I will give that a try and let you know how it goes - will be some time though as I have all the other "take it apart to see why it's working things" to do before heading back to the creek late September.