motors knocking! where do i start?

WHITE-NOISE

WHITE-NOISE

rollin coal, chasin hole
Joined
Apr 17, 2009
Messages
68
ok so i thought i had a rod knocking in my truck, i havent tore it apart yet because i had another motor lined up, but guess what, the guy sold it even after i gave him a $1000 deposit on it!!!

so now im just gonna have to tear into this one and find out whats wrong....

heres what happend... i was cruising down the highway (haulin a$$). started to smell oil so i pulled off the exit and checked it out, well the oil dip stick was pushed out of tube about 5-6 inches and oil was blown everywhere and now theres a knock coming from the motor, still had plenty of oil in it though wasnt even halfway down the fill mark.

heres my question...

1.what would cause the dip stick to blow out of it??? high crankcase pressure?

2.whats the common failures of this happing? could i have a whole in a piston?

3.the knock kinda deafens itself after 1200rpm....would a rod knock stay concistant throughout the rpm range??

4. what else should i consider before i start dismantleing the motor? i am by no means a newbie mechanic, but this would be the first cummins ive owned thats started knocking on me.

any and all help would be greatly appreciated
 
When you idle the motor, is there a lot of blow-by when you remove the oil fill cap?
 
no, ive been as far as taking the valve cover off with it running to see if may have lost a rocker bridge and all was good.
 
What oil filter were you running?

There are oil nozzles that help cool the piston, and they are sometimes plugged causing a failure. Generally, it is the 6th piston that fails. This will score the cylinder wall and trash the piston, which could explain the extra crank case pressure.
 
I agree with the piston cooling nozzle getting clogged. Sounds just like my roommates truck and that was his problem. Not sure why it would blow your dipstick out?
 
thing is the stupid thing runs fine still, everyone thats come out to listen to it says it not bad enough to really tell where its coming from but its bad enough to know theres something wrong..???
 
Justin Price said:
I agree with the piston cooling nozzle getting clogged. Sounds just like my roommates truck and that was his problem. Not sure why it would blow your dipstick out?
Click to expand...
When the oil nozzle gets clogged, the piston will overheat and melt. When this happens it will put a hole in the piston or deform it so that you get blowby. Blowby causes the increase crankcase pressure which will push out the dipstick.

I hope it is something simple but it doesn't sound good.
 
well ive checked the valve lash and that was still good...the head has only been on it 1500 miles or so....and i got ahold of a borescope and shoved it up in oil pan but couldnt really tell anything, the screen display on it sucks. guess i could pull the head and see how the pistons look. i know when i put the head back on this last time i noticed you can still make out the cross hatching in the cylinder walls, this motor only has 125k on it. but who knows chit happens, you pay to play!
 
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I broke a piston ring on my truck and It made a similar knock with blowby... would seem to smooth out and run ok in higher rpms but would knock at idle. Take the valve cover off and idle the truck with it off. I could see blowby coming out off # 5 so I knew where the problem is... if its not a bent pushrod or valve, then its a melted piston or cracked ring.

Lavon
 
pull the injectors and have a look in the cylinders with your bore scope...
 
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