Cast iron cylinders

[BOB BLACKSHAW 1Participant @bobblackshaw1]

[BOB BLACKSHAW 1Participant @bobblackshaw1]

Hello, I am making a French design twin cylinder marine engine with reverse which fits on a base 62mm x 50mm so is quite a small engine but has 13mm dia bore.

I am making my first cast iron cylinders, I usually use brass but I haven't got any so cast iron was in the box. With brass I use to polish the bore and use viton rings, as they are not used much I got good compression with the engines Ive made so far.

The cast iron cylinders have been finished with a new 13mm reamer, and float reaming was done, the finish is dull with slight score marks under a eye glass.

My question what is the best material for the piston, Ive got bronze,brass, and cast iron. I made atmospheric engine some time ago with cast iron cylinder and piston but with the condensations it rusted up, so that is what Im worried about making it all in cast iron.

Thanks Bob

[noel shelleyParticipant @noelshelley55608]

Good lubrication will help and when not in use turn the crank from time to time. Noel

[not done it yetParticipant @notdoneityet]

Either way, it is generally accepted that wearing surfaces are of different metals? So cast iron on cast iron is to be avoided.

I would expect the items to be honed, so those surface ‘irregularities’ should be removed.

Your choice of brass or bronze, presumably comes down to cost and longevity?

[Anonymous]

Posted by not done it yet on 07/09/2021 10:28:44:

Either way, it is generally accepted that wearing surfaces are of different metals?

An exception is cast iron on cast iron due to the graphite. On my traction engines the pistons are cast iron running in cast iron liners. Similarly I've re-designed the slide valves to be cast iron, in a cast iron cylinder, to reflect full size practise.

Andrew

[Ramon WilsonParticipant @ramonwilson3]

Bob,

My first engine was a ST Twin Vic with cast iron pistons – after a lay up between it's first and second displays it was siezed solid. A strip down revealed rust was the culprit but it had not affected the bore surface. Fitted bronze pistons with PTFE impregnated yarn packing and never ever had any further issues. Ran like that on steam then air for many years before parting with it. All other engines built since have the same set up

That's not to dispute Andrew as cast on cast is a good wearing combination but cast on cast with condensation present in much smaller bores isn't a good idea in my thoughts.

Brass would be okay but bronze would be better

Hope that helps – Tug

[JasonBModerator @jasonb]

As Andrew and Ramond say cast on cast is OK and lets face it many a cast iron ring running in a CI bore.

Talking of which are you going to use rings/packing or more likely at that size just a plain or oil grooved piston would be fine.

If kept fed with steam oil iron will be OK or brass bronze will be a bit safer if you get some moisture left inside. Aluminium also works and can help with balance if your small crank has no counterweights and is what I usually go for.

On the little engines I tend to lap them rather than hone as my brake cylinder hones won't fit 12 or 16mm bores.

Edited By JasonB on 07/09/2021 12:49:31

[BOB BLACKSHAW 1Participant @bobblackshaw1]

Thanks for the replies, I shall go for bronze pistons and just oil rings.

Bob

[not done it yetParticipant @notdoneityet]

While wear may not be important with most model engines, cast iron on cast iron will wear well but both will wear, hence often needing both to be replaced/restored when worn.

Obviously, piston rings wear more than the bore (area:area ratio), but rebores were a common occurrence with internal combustion engines. Some old engines I have wear out the rings but not the bore (to any great extent. The liners are made from a Nickel cast steel.

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