Reusing Rings

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Reusing Rings

Post by KDXGarage »

Can one buy a new piston, then reuse the old rings? This is strictly a technical question. What are the reasons why one could or could not reuse the old rings?

Try to focus on the question, not me recently noticing my top end was messed up. :grin: Iam still in the gathering information stage, so bare with me.

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Post by Indawoods »

Sure... you can run it without rings if you wish... how long is it going to last? Anybody's guess. You do know how the rings seal correct? They wear into the cylinder walls to create a seal. If you are using exactly the same type piston with exactly the same forging or casting, install the rings exactly as before and you rings are in tolerance... it would work fine. If any of those things are off even a little bit... it won't seal. Also, when you remove the rings from the old piston, you are re-stressing them, causing hairline cracks ultimately and very possibly causing ring breakage, they will never be the same. It would pay to use new rings... especially considering the cost. :razz:
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Post by T-Roy »

Now that you have heard the politically correct version, let me give you the other version. HELL NO... :lol:
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Post by canyncarvr »

Why not? Because said used rings have already mated to the cylinder they were in.

They aren't just used, they are used up.

Sure...you could re-use once used rings and the engine they were used in would probably even work.

Not well. Not as it should. Not for long.

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Post by KDXGarage »

Again, just on the technical side of things, if it is the same cylinder, same rings and a new OEM piston, how does that affect the wear? I am not doubting anyone's opinion, I am just curious as to how all this works.

For example, my rings have a ring end gap measurement of less than .33mm. That just got me to thinking about the technical side of things.

From canyncarvr: "Sure...you could re-use once used rings and the engine they were used in would probably even work.

Not well. Not as it should. Not for long."

How could it not work? Why would it not work? Why would it not work well, like it should, not for long?

Again, I am wanting the technical reason.

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Post by fuzzy »

This brings up a question. How could(did) you come upon the scenario where the piston was bad, but rings were fine?

I would suppose that IF the rings were going back into the cyl they came out of, and the piston needed replacing due to some wierd failure where NO damage was done to the cyl AND rings....You could reuse them. IMO, this would be close to the same as just doing an inspection--I know the piston would have to break back in, but I don't really see any harm/performance/longevity issues with this. This is the only scenario where I think it would be jusifiable, but I would never personally change a piston out and reuse rings...Especially when the KDX's go SO long between rebuilds....
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Post by Indawoods »

Indawoods wrote: Also, when you remove the rings from the old piston, you are re-stressing them, causing hairline cracks ultimately and very possibly causing ring breakage, they will never be the same. It would pay to use new rings... especially considering the cost. :razz:
There's your reason.... good enough for the girls I run with! :grin:
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Post by KDXGarage »

fuzzy, I am just going through options. I looked at the cylinder and piston again. I looked at the cylinder with a 5X and 10X magnifying glass / loupe. What I thought was a crack in the cylinder was actually a crack in the plating. It doesn't go below the depth of the plating. I thought it was all along a bridge support of the cylinder, but that was just a radiused edge. The other side was symetrical. It is not perfect, but it is not as bad as I first thought.

The rings didn't go down as far as where the damaged area on the cylinder is.

I never checked the top end until now. For all I know, the damage could have happened before I bought it and put 500 miles on it. Since I didn't tear it down earlier, I have no idea when it happened. It could have been 5 miles ago, 50 miles ago, 500 miles or more. It seemed to run fine, and I have no date in mind that I can look back on and say, "You know it ran bad after such and such."

I know that the best option is new, new, new, but I am just interested in knowing more about the technical side of why. Thanks for your reply.
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Post by canyncarvr »

A generally considered proper part of any top-end job is going to include scuffing the cylinder surface (usually with a scotch-brite). That scuffing is going to allow piston to cylinder sealing and ring sealing.

So...in your case...you're not going to clean your cylinder? You're putting a new piston in a cylinder that the old piston was ruined in? But...you have to remove whatever aluminum is stuck to that cylinder...and wherever that has happened, the rings have been rubbing up and down on that spot....a whole lot! Maybe the rings don't go down to the 'crack' spot..but you piston shows contact/wear all the way up and down, don't it? Your 'piston3' and cylinder shots look like the rings have been in a metal-transferred area.

How is that a good thing?

Not a good plan. You need to consider using something like muriatic acid (dilute HCL) to get the aluminum off that cylinder.

I guess I have no technical input for you in regard to 'why not'? Seems anti-sensical to me. Why bother taking the time to mess with it and not use new parts to mate with clean, properly prepared parts?

Ha! I'd likely re-use the rod bearing in your case, though.

Go figure....

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Post by KDXGarage »

From just looking at it, I don't think there is any aluminum stuck to the cylinder. The piston looked like it had a couple of flakes on it, though.

The rings ALMOST go down to the crack in the plating. I checked it and it is DANG close.

Again, I am just wondering about the technicalities of all of it. I'd hate to wait for a replate and piston kit if a new piston kit would suffice. I don't know how long it has been like that, but the cylinder must have some mileage on it, in that condition. Of course, if I had the money, I would have mailed it to Eric Gorr the next day with a "give me the works" note tossed inside. :grin:

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Post by canyncarvr »

To heck with the tech part of it.

I'm back to my original point of view.

Clean it.

Run it.

Check it next year to see how it's doin'!


I'd run my scotchbrite over the rings, too. Roundy'round like...not up-n-down.

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Post by KDXGarage »

Seeing that the crack did not go deeper than the plating made me get to wondering again.

Are you suggesting to use the Scotch-Brite in a cross hatch method on the cylinder?

The fine emery cloth and 400 grit sandpaper made the piston look real nice. :grin:

If I ran it for a year at my current average of miles per year, I would only have to hope it held up for 200 miles. :oops:
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