Oversized pistons with standard rings

Kaiserbailey

Kaiserbailey

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Feb 22, 2010
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In the middle of a build and found out I have standard size rings for my 0.020 over pistons. The ring gap checks out fine, but I'm wondering if it is a must have to get the correct size rings for these pistons. We ordered these pistons and rings from a popular vendor on here who has offered to take them back and send us the correct rings, but we already have 4 of the 6 installed. Is it worth it to take them out and send them off for the right ones?
 
I would put the right rings on it. What I would be concerned with is the ID of the ring and the OD of the piston not having the correct tolerance. A smaller ring in a bigger hole would cause the ring to not have enough outward force on the wall and intern not be completely round causing it not to touch all the way around. Im confused how its gapping correct.
 
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We checked all rings in the holes they were going in. They were all within range specified in the manual
 
Soooo........ After installing and then uninstalling 4 pistons, turns out they were the right rings in the right box with the wrong parts guy on the other end of the phone. :bang Called a cummins dealer local to us and found out they were the correct rings. Not very happy about this.
 
Sorry...
I built a little cheat sheet for Tbone and he looked at the incorrect number. Hate to see you inconvenienced.

Can I ask what lead you to believe the gap was wrong in the first place?
 
Snedge said:
Sorry...
I built a little cheat sheet for Tbone and he looked at the incorrect number. Hate to see you inconvenienced.

Can I ask what lead you to believe the gap was wrong in the first place?
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The gap was correct. I had called to confirm the pistons were correct and just happened to have him check the rings as well.
 
Kaiserbailey said:
The gap was correct. I had called to confirm the pistons were correct and just happened to have him check the rings as well.
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Again. I'm sorry for the miscommunication. Tyler has been doing a good job for me, but honestly, I don't expect him to bat 1000 for me after a year on the phone. There is more than a lot to learn.
The good news is the parts were on the money.
 
Let me get this straight how did you figure out you had STD rings when everything they sent you was right and the gaps checked out to boot?

Edit: In fact unless something's changed Cummins marks the boxes as to size. It's in mm so other than the conversion it's hard to screw up there.
 
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Joesixpack said:
Let me get this straight how did you figure out you had STD rings when everything they sent you was right and the gaps checked out to boot?

Edit: In fact unless something's changed Cummins marks the boxes as to size. It's in mm so other than the conversion it's hard to screw up there.
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There is no indication on the box. There is "0.5" marked on the piston itself. I didn't realize what that was until I got off the phone. These pistons have been sitting for a long time waiting to be installed. That is the reason for double checking the part numbers. First engine build here, and very much a learning experience. Mumau has always provided me with excellent customer service, products, and pricing. All 6 pistons are back in the engine.
 
Ok no problem, I'd like to think a guy can learn something from every thread on here....(trouble is there's a ****load you can't pull a damn thing from). So here it is the .5 is in metric mm which converts to a **** hair shy of .020".
 
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