piston ring end gap?

R

railhor5.9

cummins racer
my buddies are building there motors one a 12 valve and the other a common rail, on the 12v we cant move the piston side to side in the block its real tight. on the common rail we can move the pistons a lil. i pulled the #3 piston out and took the rings off and put them in the cylinder 1 inch down, they all have around 20 thousands end gap. just wondering what the specs were on the cr. and if i am suppost to be able to move the piston around. the cr has std pistons and the machine shop said the bores were still std, but they dont feel right. just seems like there would be some piston slap the way they are.
 
Bored to cummins spec's and with cummins rings ive found the end gaps to be in the .020 to .022" range right out of the box. Break the edge with a file make sure there smooth, at this point you could open them up a bit but it all depends on temp's the pistons will see, I know others that wont run them tighter than ~ .030" due to fear of them butting at extreme temps. While the ring pack is in new or good condition it will keep that sloppy feel from the piston in it's bore, but every time Ive freshened mine the rings are colaped and gives the piston the appearance of tons of slop, toooo much heat makes the rings loose there snap.
 
I know of a guy in Oregon who uses total seal rings for the upper rings. Keeps blow by down and your oil clean, I'm not entirely sold on the idea though. He's not much of a hot rodder, just rebuilds motor homes and such.
 
Having the extra cylinder pressure should increase hp but how do they expand when they get hot? How loose would you run the piston to cylinder tolerances with those? I wasn't comfortable not knowing the answers to those questions and how they would handle the heat. Maybe I'll try them on my next build, but for now, I just opted for the old fashioned Mahle/Cummins rings.

Out of curiosity, what are your thoughts on them?
 
cbtoyz said:
Having the extra cylinder pressure should increase hp but how do they expand when they get hot? How loose would you run the piston to cylinder tolerances with those? I wasn't comfortable not knowing the answers to those questions and how they would handle the heat. Maybe I'll try them on my next build, but for now, I just opted for the old fashioned Mahle/Cummins rings.

Out of curiosity, what are your thoughts on them?
Click to expand...

There is room for expansion. At the end of the ring, the thickness goes to half of the total thickness and then overlaps the other end that way. That’s what I found when doing a bit of research on the subject at least.

I don't think piston to cylinder wall clearance would need to be changed to run them either.

I’ve looked into running them in a few different turbo gasoline engine applications, cost caused me to steer clear of them. I don’t think there would be any problems running them as long as the area for expansion was there, just like you would need some area for expansion on a standard style ring.
 
I realy don't think the gapless rings would be much for a DD or mild performance, but in an all out race only rig...you bet it will be an advantage!!!
 
i looked into the total seal rings for my rebuild but i think ill just be using the regular rings for my truck since its just a DD and occasional weekend racer. if i was building an all out race rig, i would go with the total seals though.
 
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