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Antique Gas Engine Discussion

Use an O-Ring for a Piston Ring?


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  #1  
Old 08-25-2007, 10:36:55 PM
OldironJeff OldironJeff is offline
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Default Use an O-Ring for a Piston Ring?

Has any one used an o-ring for a top ring in an engine with blowby?
A guy told me he has had success with an engine that tends to wash down the cylinder with fuel while trying to start.He maintains that the o-ring should
fill the groove but not fit tight only act as a squeege.He says you may have to use a ring spacer.
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Old 08-26-2007, 12:44:31 AM
John G. Simpson
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Default Re: O-Ring for Piston Ring

Old.
unless the o'ring is teflon or other heat resistant mat'l it will probably melt.
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Old 08-26-2007, 05:05:30 AM
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The Engineer The Engineer is offline
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Default Re: O-Ring for Piston Ring

have used an oring 6x 95 mm on the last ring groove on an associated chore boy engine with good results has only 4 hrs run so far but still no blowby and easy starting cheers
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Old 08-26-2007, 09:07:50 AM
Patrick McNallen Patrick McNallen is offline
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Default Re: Use an O-Ring for a Piston Ring?

I would deal with the flooding problem first. It shuld not be necessary to flood the cylinder with gasoline to start the engine. It is not difficult to put rings in the engine if needed. If your bore is in such bad shape that rings won't help the situation, o-rings aren't likely to last long either.
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Old 08-26-2007, 09:38:37 AM
vern0n vern0n is offline
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Default Re: Use an O-Ring for a Piston Ring?

Many people use O-rings in model engines.
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Old 08-26-2007, 10:51:59 AM
Patrick McNallen Patrick McNallen is offline
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Default Re: Use an O-Ring for a Piston Ring?

Some oilfield downhole pumps are made with no rings at all. They pump liquid at very high pressures. The piston/plunger just has a number of grooves in it, and the grooves somehow interfere with the fluid getting past the plunger. The ones I have seen have shallow grooves with chamfered sides and a flat bottom. The grooves would be about 1/16" deep and around 3/16" wide at the top on a 1 1/2" plunger. It might be possible to do some experimenting and adapt this principle to a model engine. The profile and placement of the grooves and the piston/cylinder clearance would probably be critical. Using teflon plugs in the wrist pin holes, synthetic oil, and an extra long piston skirt would probably be helpful.
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Old 08-26-2007, 12:11:57 PM
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George Vaughan George Vaughan is offline
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Smile Re: Use an O-Ring for a Piston Ring?

The escaping compression with piston blow goes around under the rings not down the outside face of them. When they become excessively worn they no longer have enough depth to hold the compressed air/fuel mix at the top of the piston. It is escaping around the bottom of the shallow worn ring through the space between the groove and the bottom of the ring. An O ring might very well fill enough space in the groove and out towards the cylinder wall to deter blow by for however much time that the O ring material holds up.
For my own personal use I cannot see using rubber/synthetic when good economical cast iron rings are so readily available and easy to install.
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Old 08-26-2007, 11:39:41 PM
OldironJeff OldironJeff is offline
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Default Re: Use an O-Ring for a Piston Ring?

Patrick,your idea of dealing with the flooding problem first gave me thought.
In looking at photos of similar engines I noticed that my intake pipe is to long putting the carb inlet level with the bottom of the tank.I have a horizontal
check valve near the carb but this may not help.The cylinder mic's good and it has new rings and the cylinder was honed just enough to clean it up.The ring grooves are tight.I'm going to shorten up that pipe an inch an see if that
makes the dif.Thanks
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Old 08-27-2007, 02:43:36 AM
Redwing Redwing is offline
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Default Re: Use an O-Ring for a Piston Ring?

I seen people using in some scale model engines, and now this full size I never tried before. or thinking may ok for low rpm & smooth bore?
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Old 08-27-2007, 01:44:35 PM
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Forrest A Forrest A is offline
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Default Re: Use an O-Ring for a Piston Ring?

The model guys use them but not for very long. Do this as a test, get an o-ring that will fit (One of the hardest parts of using o-rings is finding one that will even fit...) the piston and soak it in gas. What you will find is that most o-rings you can buy for a reasonable price will turn to goo. Now go to your local bearing supplier and buy gas/oil resistant o-rings (These may not be easy to get in large sizes or the size you will need.) and be prepared to pay a good sum for them too.

My opinion is that o-rings are not the way to go in engines over 1 inch bore especially if they will run more than 5 minutes.
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