piston rings

hi

i am building a 1/2 size barn engine from e j winter in australia can i use rubber o rings for the piston instead of cast iron if so what should i be asking for at the o ring shop

tom

I'm not particularly into IC but there aren't many IC engines I've seen that use O rings. This is probably because of the heat involved. IC engine pistons can get quite hot, particularly if close to the piston crown.

I suggest you use cast iron rings. Making your own is quite straightforward. The idea is that you turn the rings to be a good fit in the bore, split them. and then heat-treat them by heating them up with a suitable piece of material in the gap. When the rings cool down, the gap is maintained and they behave in the same way as a bought one. You make sure, of course, that you make a couple of spares! An article by G Trimble in ME in 1984 V153 No. 3735 p 210 Heat Treatment of Piston Rings is a good start.

Good luck.

The last three IC engines that I have done, two Alyn Foundry open crank engines and one of my own design have all had a single Viton O ring and they make very good compression and run well.

For your 1.5" bore engine I would go with a BS number 125 ring which is 3/32" nominal section and 1.5" nominal OD, actually 0.103" section and 1.505 OD. make the groove 0.125" wide and the bottom of the groove 1.304" dia. You will want a fine honed finish to the bore.

I would never have imagined that, a Viton piston ring in an IC engine you learn something everyday.

Is there a misprint in the original question for "a 1/2 size barn engine". Should it have been a beam engine instead.

In which case it is a steam engine and not an IC engine. Rubber O-rings are used in model steam engines but I am not sure of suitable size and material.

Paul.

The info below is from the E.J. Winter catalogue. So it is probably the one in question I would think.

Phil

No IC/14 1/2 Full Size Roseberry Type A Hit and Miss Petrol Engine 75CC 1 1/2” Bore by 2 1/8” Stroke 3/4HP Two Stroke Air Cooled An accurate half size version of an example of a once common small stationary power unit. The original plans were prepared by Mr Russell Paynter from a full-sized engine in his possession and includes some unique features. Engine Data Length 14 1/2” Height 7 7/16” Width 10 1/4” Flywheels (2) 7 1/4” Uses “Victa” points and standard 10mm spark plug Plans: 1-2820 Castings: 7-8000 E and J Winter – Bolton Scale Models PO Box 9440, Bathurst NSW 2795 Australia

Yep that's the engine I understood it to be, hence my suggestion for a ring to fit a 1.5" bore.

Forgot that one I'm working on at the moment uses a Viton Quad Ring so interesting to see how that goes.

Thats interesting Jason, I looked up some images of quad rings are the ones you are working with X shaped in section with rounded ends on each leg of the X..?

That's the ones.

amazingly quick and useful information

thank you

I'm currently building the same engine and ended up increasing the bore diameter to 40mm so i can use the rings off a mini dirt monkey bike that are sold on ebay , they are dirt cheap to buy and you can get the pistons cheap as well .

I made my own cast iron piston as per the drawing but had to make a couple of adjustments as the 40mm rings are thicker .

I was originally going to use the 1 1/2 bore size and have the rings for that( costly little things they are !) but when machining the cylinder from cast bar it relieved itself and went oval so i had to rebore it and then i lapped it .

I too was surprised by the inexpensive nature of those foreign rings and pistons so I bought a few. A caution regards the pistons. Because they are for two stroke engines, the ones I got were far from round or consistent diameter top to bottom. I assume this is because they are two stroke pistons and made for high rpm and heat.

i did buy a piston for a Honda four stroke about 1 3/8” bore and it is beautiful with very nice oil rings etc. consistent dia. Top to bottom. Not as cheap as the others though.

Another vote for adjusting the bore size to suit a commercial piston ring. My traction engine runs on a chain saw ring (High pressure) a Ural motorbike ring (low pressure) and I have just built a much modified Southworth steam pump that runs on a petrol strimmer ring.

Have a trawl round e-bay to see what you can find. If you go for non OEM parts, they can be dirt cheap - probably cheaper than the cast iron bar to make a ring.

For steam work, you can close a ring up slightly if you need to. Make a hollow ring to hold it in, cook the whole lot up to dull red and you will find the gap will close up nicely. A bit like the old trick of springing them open and heat treating, but in reverse!

Martin