I know the answer is emissions related. But can any expert engine builders out there explain this to me in terms of advantages/disadvantages and also engine reliability??
12v:
Top 0.016 to 0.0275
Intermediate 0.010 to 0.0215
Oil control 0.010 to 0.0215
24v, common rail 5.9 and 6.7:
Top 0.010 to 0.014
Intermediate 0.033 to 0.045
Oil control. 0.010 to 0.022
We know the top ring is the one that will get the hottest under high EGT or continuous load, thus a tight top ring gap is asking for problems in those situations. At the same time we want engines that don't produce much blowby or burn oil. There is no doubt that the common rail engines seem to break rings fairly commonly.
So with all of that. It seems to me that the 12v had it right? Have the bigger gap on the top ring to allow for lots of thermal expansion, then have the tighter gap on the intermediate ring to keep blowby in check. And at the same time having a tighter intermediate ring would allow more pressure at the top ring to help seal against the cylinder wall?
At the end of the day, one of the compression rings has a tighter gap and the other a bigger gap. The only thing Cummins changed was the order... The way my brain works the 12v specs just make more sense in terms of how the engine is supposed to work.
Am I out to lunch here? I'm no expert. Opinions would be appreciated.
Thanks
12v:
Top 0.016 to 0.0275
Intermediate 0.010 to 0.0215
Oil control 0.010 to 0.0215
24v, common rail 5.9 and 6.7:
Top 0.010 to 0.014
Intermediate 0.033 to 0.045
Oil control. 0.010 to 0.022
We know the top ring is the one that will get the hottest under high EGT or continuous load, thus a tight top ring gap is asking for problems in those situations. At the same time we want engines that don't produce much blowby or burn oil. There is no doubt that the common rail engines seem to break rings fairly commonly.
So with all of that. It seems to me that the 12v had it right? Have the bigger gap on the top ring to allow for lots of thermal expansion, then have the tighter gap on the intermediate ring to keep blowby in check. And at the same time having a tighter intermediate ring would allow more pressure at the top ring to help seal against the cylinder wall?
At the end of the day, one of the compression rings has a tighter gap and the other a bigger gap. The only thing Cummins changed was the order... The way my brain works the 12v specs just make more sense in terms of how the engine is supposed to work.
Am I out to lunch here? I'm no expert. Opinions would be appreciated.
Thanks
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