It wont take much of a flaw in the head with the valves to cause compression loss. May take a valve regring. Lets hope for that. That will be the best scenario.

 

and worst case scenerio?? cracked head?

 

they shoulda done a leak down test before they pulled the head that would've told you if it was a valve leaking, it's probably rings ,I did not look at your signature but if you have a k&n type 3 layer oil filter and you're driving in any kind of dusty conditions you probably have a bad hole ,I'm seeing it more and more as the years go by ,I did 2 motors last year do to it ,I use to sell those filters like candy and have had to eat my words ove r the last couple years and give up a bunch of labor to fix things for the customers I sold them to.......good luck man hope it's not a bad hole but if it is pm okay I can either rebuild your motor for you or at least make sure no 1 ripd you off cool?

 

With no visible issues, my thought would be broken rings on that piston.
A valve or crack in head would be apparent. Incomplete diagnois. Did it have blowby??

 

a broken ring would scar the cylinder wall

 

a broken ring would scar the cylinder wall


Wrong.

 

Defr should have done a leak down then you would know for sure what was leaking.... Now it's up in the air you could throw a fresh head on, and stil have low compression. I've personally seen/had engines with bad/ broken/ glazed rings that the bores looked fine. Fuel that washed down a cylinder coulda glazed up the walls enough allow leakage.

 

Also what were the readings ? Failing a compression test doesn't mean anything did they do a wet also what about balance that will tell u more then just it failed.

 

dozer wins this one

running an oiled cyl compression test is CRAZY dangerous on a diesel if the hole is even half way good.
Oil turns to fine mist under 17:1 compression, fires.
suddenly static compression cyl. pressure goes from approx 400 psi to
a nuts blown off 3000>5000 psi combustion dynamic pressure.

can one say, good by compression tester.
diesel techs loose arms and heads from that kind of stupid shiiittteee

will NEVER see a certified Cummins diesel shop run a cyl oiled test.

 

im not sure if they did a wet down test, they just told me that it was something in the head and the cylinder was fine, so im assuming maybe they did? ill wait and see what they say on monday.

 

finally got news back after 3 weeks. They told me that all the cylinders were around 480 - 500 psi of compression except hole #4 which was about 100 psi less. Machine shop said the valve guides are very loose on the cylinder causing the valves to not seat properly.

So they are regrinding all the valves, replacing all the springs, valve guides, retainers. Then they will do another compression test with the head back on.

 

the valve seats on common rails have been known to come loose and pop out so if you're gonna go to all the trouble to have that head rebuild you should upgrade the valve seats while you're in there, would suck to have a valve seat drop down the road !.........I still can't believe they didn't do a leak down test!..... that woulda told them if it was in the head or rings, 100psi is a lot to lose through guides ,I mean it's possible but usually guides wear equally, I think all signs still point to rings ,I hope I'm wrong ! ......good luck address the seats now so your not sorry later

 

thanks for the heads up! i asked them about the leak down test and they said that on most diesel engines a leakdown doesnt come back very accurate because the end gaps are so wide on the rings.... this shop has built some pretty high HP trucks around here so im trusting him on his diagnostics.

 

I'm watching this thread. Have an 05 that seems to have waaay to much blowby coming out the crankcase breather hose, gets crummy fuel mileage, and gulps motor oil....but I'm a bike guy, diesels are new to me.

Thanks for the info gents!

 

Interesting

 

(fly on the wall)

 

i guess i never updated but it turned out to be a cracked ring that hadnt let go completely yet. I was just somewhat lucky to catch it when they did the test having the inkectors out. I ended up putting a new long block in. Truck runs like new now