Model Engine Builders - Piston Ring Question

I'm certainly no expert in ... well... anything, but could you make the rings out of mild or spring steel and then hard chrome coat them to achieve the same results or simply heat treat them?

Or... Could you HCC the inner walls of the cylinder AND the ring?

A coupla things.

Have you considered just buying rings? I know it is sorta counter to the "I made the whole thing" , but...

If you cannot find some cast stock to hog out a coupla ring blanks from, and you wish to try to use the sash weight, you are going to have to anneal it. Know anyone with a woodstove or a backyard firepit? Get the weight up to red heat and allow it to cool slowly, as in leave it in the fire while the fire burns down and fish it out in the morning. That should get it very soft. It may still be miserable to work with, as its only real requirement was to be heavy, so it may have been made with the dregs or leftovers from the foundry metal pile.

Lotsa cast in engine blocks, and Walmart sells cheap chinese cast iron weightlifting weights that may be suitable.

Cheers Trevor Jones

============= see

Given the very low duty cycle and loadings of your engine it is likely that most any iron/steel you have around with a little "spring" should be adequate.

Unka George (George McDuffee) ============================= When you give power to an executive you do not know who will be filling that position when the time of crisis comes.

Ernest Hemingway (1899-1961), U.S. author. "Notes on the Next War: A Serious Topical Letter," in Esquire (New York, Sept. 1935; repr. in By-Line Ernest Hemingway, ed. by William White, 1967).

Sash weights are usually hard as glass. Same with dumbbell weights. Tried both of them for engine building.

Mcmaster-Carr will sell you a 13" length of CI for what I think is a reasonable price.

CI is definitely the material of choice. The graphite gives it a very desirable self-lubricating property. I have heard of people making teflon rings and getting them to work well. I've never actually seen it done though.

I'm with Trevor on this, buy some rings...

FWIW I build 1.5 inch to the foot (8th scale) Live Steam, once ya get passed about 2 inch bore it's just eaiser to buy the rings than make em (meaning they are much more redaliy available than something in a 1 inch bore) A buddy just finished a nice 2.5 inch (just a touch bigger than 6th scale) Consolidated, he even bough the damn cylinder liners too... Think Briggs and Stratton.. :-)

And yeah if you do decide to make em, buy some decent CI from McMaster or who ever... why screw around with 'mystery metal'...

--.- Dave

Check out this site for material and sizes available.

What about cast iron pipe? Lots of it in old houses, and they get renovated - and it's round (sort of) to start with...

If you live in a coastal area, find a place that repairs largish marine diesel engines. Tugboat company machine shops are a good source. What you need are worn out valve guides. They are also the correct grade of moly cast iron. Some creative scrounging will do it.

Steve R.

Careful! I found a 3/4" 'T' the other day with porosity approximately equivalent to a 1/4" drilled hole. Gerry :-)} London, Canada

Don't know if DurBar CI is suitable for piston rings but Peterson Steel in Worcester MA sells it in a variety of diameters cut to whatever length you want. Nice folks to deal with too.

Errol Groff

Instructor, Manufacturing Technology H.H. Ellis Technical High School

613 Upper Maple Street Danielson, CT 06239

New England Model Engineering Society

I have heard or read somewhere that car brake discs are CI. Only some motorcycles use steel discs.

Motor-bike discs are stainless 'cause the owners like them shiny. Cast iron discs work better but you can't be a weekend wannabe and ride a bike with 'em.

Guzzis are know for their fast rusting disks. :-)

Nick

I would stay with CI. But ... Normaly, the liner and the ring are made out of different materials. What I use is CRS or precision tube (or even free machining steel) for the cylinder and CI for the ring. Now if you make the ring out of CRS, you have the same mix of material. You won't let run the engine for thousands of hours, so not much problems with wear.

Nick

How about machining a ring off the piston skirt, sliting the resulting ring and then applying heat to the opposite side of the slit to cause radial expansion thus providing some outward pressure for the ring(s). Bob Shores suggested this method for his American Eagle horizontal hit and miss engine.

I'm still strugling with Bob's kit as a first-time model engine builder and a person hardly qualified to post to this group.

JHanson