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piston rings

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tom hardy09/11/2019 09:15:03
11 forum posts
5 photos


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


Nigel Bennett09/11/2019 09:34:28
337 forum posts
11 photos

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.

JasonB09/11/2019 10:11:59
17864 forum posts
1954 photos
1 articles

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.

Ron Laden09/11/2019 10:35:43
1874 forum posts
346 photos

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

Paul Lousick09/11/2019 11:11:40
1377 forum posts
532 photos

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.


Phil P09/11/2019 11:43:44
622 forum posts
165 photos

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


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

JasonB09/11/2019 13:10:00
17864 forum posts
1954 photos
1 articles

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.

Ron Laden09/11/2019 14:04:56
1874 forum posts
346 photos

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..?

JasonB09/11/2019 16:04:47
17864 forum posts
1954 photos
1 articles

That's the ones.

tom hardy09/11/2019 23:12:52
11 forum posts
5 photos

amazingly quick and useful information

thank you

XD 35110/11/2019 02:40:37
1419 forum posts
1 photos

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 .

John Vietti12/11/2019 16:29:41
22 forum posts
3 photos

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.

Martin Johnson 112/11/2019 17:25:41
129 forum posts
1 photos

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!


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