12v Cummins knock after pulling. - Dodge Cummins Diesel Forum
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post #1 of 11 (permalink) Old 08-12-2019, 05:07 PM Thread Starter
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12v Cummins knock after pulling.

I have swapped a 12v into a 89 chevy c30. I was pulling my camper up a hill and as I went to shift from 5th to 4th the truck sounded funny. I pushed the clutch in and the truck died. I tried to start it and the motor just maybe turned over once but then the starter just ticked. I had to pop the clutch to get the truck to start. Well I pull over and check everything I noticed some blowby more than normal but the oil level was fine. The egt was at 1100-1150 pulling up the hill I never lost oil pressure and fuel pressure was normal. Every since then I have developed a knock. I drove the truck all the way home over an hour drive pulling a camper. I get the truck home and turn it off. Go out to check it the next day and the knock is a lot louder. I thought it might be injectors so I pull them and have them tested and the guy said that I needed new ones that a couple were sticking and recommended 6 new nozzles. I took this opportunity to buy Industrial injection 80hp injectors and installed them yesterday and that did not help. Knock was still there and just a loud. I decided to drive the truck down the road to a diesel mechanic to have him look at it and by the time I got there the knock was no where as long as when I had started it this morning. Im guessing that getting the truck warm has something to do with quieting the knock down. Tomorrow I plan to remove the valve covers to get rockers. I am wondering if I have spun a bearing. What makes me think its not a rod is it should have blew by now after towing a 7500lb airstream over an hour home. I have pushed the prime on the lift pump making sure that it hadn't wore but it didn't change the sound. What else could I be looking at? only thing that is done to the truck is a ground fuel plate and blocked wastegate and now new injectors.

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post #2 of 11 (permalink) Old 08-13-2019, 12:04 AM
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Sounds like a bent rod or slipped timing. Check both and report back.

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post #3 of 11 (permalink) Old 08-13-2019, 05:07 PM Thread Starter
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I will do. It will take till the weekend to pull the motor. Today I checked the valve lash and every thing there seemed fine. I went and bought a bore scope and will check the cylinders tomorrow and let you know.
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post #4 of 11 (permalink) Old 08-13-2019, 06:51 PM
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How does slipped timing cause a knock? It cause backfiring sounds as you rev the engine and produces a crap ton of white smoke.

Itís possible some valves loosened up. Whenís the last time you did a valve lash? How oldís the engine? Need some more background information on the engine.


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post #5 of 11 (permalink) Old 08-13-2019, 10:15 PM
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Quote:
Originally Posted by Volunteer93 View Post
I was pulling my camper up a hill and as I went to shift from 5th to 4th the truck sounded funny. I pushed the clutch in and the truck died. I tried to start it and the motor just maybe turned over once but then the starter just ticked.
My guess is you overheated a piston because you waited too long to downshift. The knocking is probably the wrist pin.

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post #6 of 11 (permalink) Old 08-13-2019, 10:48 PM Thread Starter
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I would say you are right. Ill post back tomorrow. I am going home and checking after work tonight.
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post #7 of 11 (permalink) Old 08-13-2019, 10:57 PM
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Im not sure why we went immediately to wrist pin failures, bent rods, and failed bearings...

Did the engine overheat during your tip? Has it been overheated before?

If no, then there is a better chance than not the bottom end is fine.

First thing I would try is to figure out what hole it's coming from. I would start by figuring out if it's a fueling issue. Crack each injector one by one at idle and see if it goes away. If it does, swap that injector into another hole. If the knock moves you've found the bad injector. If the knock doesn't move then you know which cylinder it is and now you can perform some inspection of that cylinder, it's valve train, and possibly that barrel on the P7100.

I know you say the nozzle was replaced but a new nozzle does not equal a new injector. You injector guy could of missed something in the body that is the source of failure. Swapping holes will point to a bad injector if that's the case.

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post #8 of 11 (permalink) Old 08-13-2019, 11:21 PM
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Originally Posted by hemirunner426 View Post
Im not sure why we went immediately to wrist pin failures, bent rods, and failed bearings..
The fact that the engine died when he pushed in the clutch and then the starter couldn't turn it over were the key issues that don't make sense except for a partially seized piston
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post #9 of 11 (permalink) Old 08-14-2019, 12:29 AM
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Originally Posted by Truefat View Post
The fact that the engine died when he pushed in the clutch and then the starter couldn't turn it over were the key issues that don't make sense except for a partially seized piston
I agree. It sounds like a melted piston. Listen to some youtube videos on these motors with a bad piston. Sounds like a knock.

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post #10 of 11 (permalink) Old 08-14-2019, 12:49 AM Thread Starter
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I agree on the piston. I only looked in #6 with a bore scope. I'll try to attach some pictures but it doesnt look melted but scratched pretty bad. I apologize for the bad pics. I guess I'll start pulling the head tomorrow.
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post #11 of 11 (permalink) Old 08-14-2019, 10:49 PM
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Quote:
Originally Posted by Truefat View Post
The fact that the engine died when he pushed in the clutch and then the starter couldn't turn it over were the key issues that don't make sense except for a partially seized piston
Looks like I skipped over that for some reason. The pictures tell the story.

It will be interesting to find the reason for failure.

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