slide valve material

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lostintime
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slide valve material

Post by lostintime » Tue Apr 17, 2018 1:22 am

I'm ready to start machining my engine. Whats best :cast iron, brass (leaded or non) bronze, mild steel? I'm leaning towards leaded brass but I don't know if that's right. I have the capabilities to cast it so I'm tempted to do everything except the crankshaft in it.
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Re: slide valve material

Post by marinesteam » Tue Apr 17, 2018 1:10 pm

What's the material of the block?

With the rare exception of cast iron on cast iron, generally a metal sliding on the same metal will lead to sadness. There are times that you can get away with mating similar materials but it's dependent on velocity, pressure & lubrication.

The tried & true combination would be cast iron valve on nearly any other material.

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Re: slide valve material

Post by DetroiTug » Tue Apr 17, 2018 7:34 pm

As Ken says, cast iron is well proven, however only grey cast iron, not nodular cast iron. Nodular cast iron is not good for pistons and logically slide valves, sliding surfaces.

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Re: slide valve material

Post by Lopez Mike » Wed Apr 18, 2018 4:27 pm

Iron on iron on every surface of my engine except the connecting rod big end. Running for years with no problems on saturated steam with no internal lubrication except water condensation.

I would machine your cylinder valve face on a raised mesa so that long term wear will not find your valve living in a valley.
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Re: slide valve material

Post by barts » Fri May 25, 2018 6:46 am

Lopez Mike wrote:Iron on iron on every surface of my engine except the connecting rod big end. Running for years with no problems on saturated steam with no internal lubrication except water condensation.

I would machine your cylinder valve face on a raised mesa so that long term wear will not find your valve living in a valley.
Or more easily, machine a groove in the face such that the valve overtravels the ends and along the sides... you can do this after you measure the actual valve travel on the assembled engine

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Lopez Mike
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Re: slide valve material

Post by Lopez Mike » Fri May 25, 2018 12:36 pm

As the old Inuit said in Never Cry Wolf, "Good idea!"
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Re: slide valve material

Post by fredrosse » Fri May 25, 2018 5:37 pm

I am considering placing a plate on the slide valve seating surface, about 1/4 inch thick, maybe stainless steel, and making the slide valve from filled Teflon. This would allow replacement of the simple flat plate (with some ports cut thru) with various materials, and no need to resurface the cylinder casting due to wear.

Has this arrangement been used with success? With other material combinations?

Thanks in advance for any information here.
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Lopez Mike
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Re: slide valve material

Post by Lopez Mike » Fri May 25, 2018 6:16 pm

The only experience I've had with Teflon tells me that the finish on your metal plate has to be good. Maybe very good. I've used Teflon rings and even a whole piston on display engines meant to run on air with no lubrication. The first time when I tried to used the cast iron bore as machined the rings went away very rapidly. A polished surface using felt pads and abrasives working all the way down to rouge worked much better.

I don't know what the temperature v.s. deformation curve is like on your Teflon. Worth a try at any rate. It would be nice to have a setup where you could experiment with different port locations.
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Re: slide valve material

Post by Mike Rometer » Fri May 25, 2018 6:22 pm

I can only reference you to my long running thread "And now for the Twin". On page 2, a photo shows the ones I've made in M.S. with the intention of using gun-metal slides. Almost inevitably the plate will wear first and worst. but an easy thing to replace.

I'm sure the plate would take a good polish finish if required.
Last edited by Mike Rometer on Fri May 25, 2018 7:46 pm, edited 1 time in total.
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Re: slide valve material

Post by TahoeSteam » Fri May 25, 2018 6:45 pm

Teflon does deform quite a bit with temperature... We made a Teflon piston for the condensate pump on the big boat. We had an issue with this when we were testing the machinery before launching the boat. Due to the proximity to the exhaust on the engine and the conditions of running on the hard with only some lawn sprinklers on the condenser, the pump got very hot causing the piston to expand in the bore.... We had to open the thottle more, un aware what was slowing the engine down until BANG!!!! Linkage pieces from the walking beam flying around the engine room and the engine running away to nearly 400rpm before we shut it down. Luckily noone was hurt and the linkage pieces were easy to replace. After that we put the piston in boiling water for a long time then machined and fit it until we found a happy medium. It was a cheap lesson, and another testimony to testing out all systems multiple times before ever putting your new boat in the water.
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