Honing a steam engine cylinder

[Jennifer Edwards]

I have a question regarding preparing a steam engine cylinder for service.

When I worked in a marine diesel engine rebuilding shop I was taught to hone the cylinders with a nice crosshatching pattern before final assembly.

My question is: should I do the same with a small steam engine, or just the opposite and leave a nice polished finish?

 

[Cogsy]

Just my opinion but I don't think we have the equipment to leave surfaces smooth enough that they wouldn't retain the sub-micron lubrication films needed at the scale we work with. So I don't think we need visible cross-hatching. From what I've seen with some full-size production IC engines, it seems crosshatching is not used in OEM anymore either. So I wouldn't worry about it, but again, just my opinion.

 

[abby]

Jeniffer there are many variables such as what are the cylinders made of and what piston rings are you intending.
Traditional graphite yarn and synthetic 'O'rings run well in polished bores , cast iron rings in cast iron cylinders might benefit from cross hatching.
Personally I run a flexi-hone through my cylinders with some light oil , I continue to do this until the 'O' ringed piston will pass through very easily.
The use of the flexi-hone produces very fine cross hatching , does this retain oil ? very doubtful I think.
Bear in mind that we are using wet steam with a steam oil feed in our locomotives.
High speed boat and hydroplane engines using flash boilers and superheated steam pose a different situation and cross hatching could possibly save seizing.
Dan.

 

[Charles Lamont]

For piston rings, if the finish from the boring tool is reasonably fine, and the bore parallel, there is no need for any further treatment. If you are using an o-ring or yarn, I agree a smooth surface is good.
Dan, if you can see cross-hatching, the surface texture is a lot bigger that a molecule of oil.
If by flexi-hone you mean the thing with balls of abrasive, personally I wouldn't use one anywhere near a model.

 

[Jennifer Edwards]

Thanks for all the input everyone.

To clairify I used silicone bronze for my cylinder, made cast iron rings and a brass piston. I was thinking I should hit it with a three stone hone, like the type used for brake cylinders.

Presently I have lapped the cylinder to size down to a 1500 grit finish. I am worried that the surface my be too slick, so that the rings will never really "bite" and allow steam to get by.

Any further thoughts?

 

[Jasonb]

For Iron rings I tend to just go straight to a bake cylinder hone as there is no point lapping first unless you have a tapered or oval bore that needs correcting.

For gland packing or o rings I lap to 1000grit with Sic powder and oil. Same for iron on iron or iron on steel with no rings

Having said that for display on air I often leave the rings out and just run the piston in the bore, the much reduced friction allows for a nice slow turning engine that barely lifts the needle of the compressor off zero, prabably 2-3psi in reality.

 

[Jennifer Edwards]

For Iron rings I tend to just go straight to a bake cylinder hone as there is no point lapping first unless you have a tapered or oval bore that needs correcting.

For gland packing or o rings I lap to 1000grit with Sic powder and oil. Same for iron on iron or iron on steel with no rings

Having said that for display on air I often leave the rings out and just run the piston in the bore, the much reduced friction allows for a nice slow turning engine that barely lifts the needle of the compressor off zero, prabably 2-3psi in reality.

Jason,

Thank you for the validation that I am on the right track

Thanks again,
Jen