When to replace piston rings?

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sculpt
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When to replace piston rings?

Post by sculpt »

I have a 1984 aero nh80. The piston looks ok and measures just within spec. The cylinder looks ok and meets spec. perfectly. The ring end gap service limit calls for .024. My upper ring is .014 and the lower measures .021. Both within spec. My compression measured 50 psi. I have purchased a new head and cylinder gasket, Boyesen reeds and 90 main jet, and a new exhaust gasket. When I was taking it apart the cylinder bolts didn't seem all that tight and there was no exhaust gasket. Also, the cylinder gasket was a bit askew and new holes were pushed into it and it was partially covering some of the ports. Cleaning things up now and want to put it back together but I don't know whether to get new rings. 2147 miles show on the odometer. Once the dirty busted panels came off it was surprisingly clean on the frame and engine. What do you guys suggest?
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Meatball
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Re: When to replace piston rings?

Post by Meatball »

sculpt wrote:My compression measured 50 psi.
Low numbers like that means youre losing air somewhere. Either the Head Gasket, Reeds, Crank Seals or Rings.

With only 2100mi, its too soon for rings to be "worn out" from normal use since their typical lifespan is much longer. If the rings are bad, its because they've been damaged by other causes.

Diagnose the issue before you start throwing parts at it. http://www.motorscooterguide.net/Manual ... Manual.pdf
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sculpt
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Re: When to replace piston rings?

Post by sculpt »

Diagnosing is what I am trying to do. Need to do the gaskets anyway since it is apart and was planning on doing the reed upgrade. I'll just go with thatsomeone didn't put it back together properly and probably reused the head gasket. Didn't run when I bought it. Thanks for the advice.
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noiseguy
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Re: When to replace piston rings?

Post by noiseguy »

... how did you measure the cylinder? That's somewhat tricky to do accurately.

Also, ensure you measured compression with throttle wide open or it will read low.

I judge "time for new rings" by a combination of low compression, hard start, and lack of visible cross-hatch on cylinder.
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