Author Topic: Piston rings-How many?  (Read 3060 times)

Offline John Rudd

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Piston rings-How many?
« on: May 04, 2012, 09:56:54 AM »
The piston rings I ordered have arrived...

They seem quite thick at around 1/8th inch...

Could I get away with using just one per piston or should I use two?

Piston is based on the Webster design but is bigger at 1.000in diameter ( cos I could get rings to fit   :D )
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Offline Lew_Merrick_PE

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Re: Piston rings-How many?
« Reply #1 on: May 04, 2012, 12:09:57 PM »
John -- My "vote" would be for two rings.  It does not take much of a "gap" to lose a significant amount of air through a single gap and the labyrinth effect will cut that loss by a rather large factor.  Not having done one of these equations in many years and speaking through my hat, my guess is that you will cut your pressure loss by a factor of 4-5 by using two rings.

Offline John Rudd

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Re: Piston rings-How many?
« Reply #2 on: May 04, 2012, 01:08:07 PM »
Lew,

Thanks for the advice...It appears that the rings have an overlapping joint as opposed to just having butt ends if you see what I mean?

I'd have thought that because of this then leakage would be reduced....?

What about ring gap?

I bored my liner to 1.001-1.002, but the ring gap is just perceptible..Should I bore the cylinder liner a slightly bigger diameter to accomodate the rings?   :dremel:

This may render my piston useless as the skirt clearance will be greater... :scratch:

Certainly a steep learning curve..
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Offline 75Plus

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Re: Piston rings-How many?
« Reply #3 on: May 04, 2012, 09:22:23 PM »
John, A few decades back, before we had today's metallurgy, it was common practice to replace all the piston rings without doing any thing to the cylinders except maybe removing the ring groove at the top of the bore. In order to keep the pistons from slapping in the cylinder the skirt of the piston would be either knurled or Kotherized, a process where by the piston skirt would be shot peened, to expand it. This was only done on the two sides parallel to the wrist pin. Some if not all new pistons were cam ground to provide a better fit also.

This method could prevent your pistons becoming useless. The rings would take care of the top and a little bit of egg shape will keep the skirt snug while providing clearance for lubrication.

Joe