Cummins ISL compression percent

[Kiko]

Hello All. I am wondering if anyone on here knows what the compression should be on a ISL engine. Cummins does not like to use compression psi but wants to use blowby tests. This is all fine when testing but does not tell me what cylinder it might be. I am getting blowby excessive codes and engine was taken to cummins to test. They reported that the blowby was to high. I want to check compression at the cylinders first before condemming the engine for a rebuild. Also would like to eliminate everything else first like compressor and turbo. We inspected both all ready and don't see a problem just jumping out. Engine appears to run fine and operator said no loss on performance. I have an old injector that we converted into a compression tester but can't find actual specs. The only thing I can go off is that a diesel engine should be 300 plus and relatively close on cylinder to cylinder. Thanks in advance.

[Rawze]

If its only blow-by and nothing else wrong ...

== Do an overhead valve adjustment and ensure there is plenty of clearances ... and that no valves are recessed in the head.

== Eliminate/remove the crank case filter from the engine. Let the damn crank case breathe properly!. - Actually this should have been done years ago, as its the primary reason for overhead cam failures, the turbo bleeding oil, and other oil starvation issues ... but that is a different story.

- After removing the CC filter and doing overhead valve adjustment ... Run it until it is consuming more than a gallon of oil every 3,000 miles. - Otherwise, if literally nothing else is wrong... there is no need to inframe it for blo-by alone.

And if your concerned that its really worn out badly .. then pull a rod/main bearing instead of trying to figure out how much compression losses there are.- In fact, that engine is due for rod/main bearings replacement at the 600k~ish mark any ways. Not doing it is asking for a window thru the block at some point in its future with zero warning.


And if you really really want to get technical with it because you can't leave it alone.. then pull injectors and boroscope it, look for excess wear on the thrust side of the liners, and for scars down the cylinder walls as this is a sign of a cracked ring.

And Worrying about cylinder compression is the last/least thing you should be looking at. In fact, before even considering it ... it would be far easier to remove the turbo and overhead rockers, then pressurize the intake (and then exhaust) with 30-psi with all valves closed, and checking the intake manifold, and then exhaust manifold, check all valves for ANY seepage/leak-down instead.