Knock From Under Engine

Ghost23

Ghost23

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Jan 7, 2014
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My truck starting doing this a week ago, only not as bad. When I put it in gear, it stopped. Shut it off and start it again and it doesn't do it.https://www.youtube.com/watch?v=oEtTj8NDpaE

Only did it when I first start it after sitting all day.

We drove from Indiana to N. Carolina and on the way home it started doing it just like the video. I checked fluid at home because when I put it in reverse, it did not engage. It was at the bottom of add. Added some fluid, and it went into gear. Since then, the rattle is quieter and not a steady knock. Just a knock, knock knock, pause-nothing, knock. Very random. Only at first start up. Quits when I put it in gear. Doesn't do it if I put it right back in P or N. Doesn't do it after I drive to wherever and let it sit for an hour, then go back out and start it. Only after sitting many hours. Sound is coming from right under front of trans.

I just had an aftermarket trans installed back in June by local shop. Maybe put 5000 on it since then. Seems kind of soon for bolts to be backing out or billet flexplate to be cracked.

Truck starts, drives, shifts, locks up perfectly. Only hazes at idle because previous owner put early spray pattern injectors in a late 04.5. No blow by or any other know issues. Has 208000 miles.

I guess I will check the bolts to see if they are tight. I sure hope the local guy used loctite on them. He works on all the schools buses and does a lot of work for people. But that doesn't mean anything.

Just wondering if anyone else has had this issue.
 
Well there is less knock at start up now. I can start it, hear the knock, put it in gear then right back in park and the knock is gone. I'm stumped on what this could be. Oil has no signs of diesel and is not "making" oil. Starts up quick and runs like it always has. There is no top end noise. Only thing I've done different is run Rotella T6 synthetic this winter. I usually run Delo 400 or Valvoline Blue. There is no blow by when revving the engine in gear to higher RPM. Oil cap sits there and spins with engine vibration, does not jump up and down. Has not used any oil in 2 weeks since the 1600 mile trip 2 weeks ago. Oil pan does leak a bit, but it always has since I've owned the truck. I keep a good eye on oil level. It did get down to the add mark while on the trip. I don't think that is low enough to hurt the engine. Shaft in turbo has very very little play. Don't see any oil in exhaust or downpipe. I think I will change oil and adjust valves this week to see if that helps. I would think if it spun a bearing or broke something that it would make the noise all the time. Not just when I first start it after sitting, and stopping as soon as I put it in gear. Is there anyway the trans could have an issue and be echoing into to the oil pan? Everything I've read about thrown rods or valvetrain issues people have heard noises constantly and had loss of power, fuel in the oil, blow by, etc. My truck has none of that. Could it be that an injector is leaking out as it sits for a long time and causing a noise at first start up of the day? But why would it stop when I put it in gear? Anyone have any ideas? Thanks
 
Or fly wheel bolts backing off. Buddy had his do the same thing. Sounded like his was gonna throw a rod through the oil pan and it was just the fly wheel bolts had backed out and hitting. Better check it soon before it starts wearing/scuffing parts
 
Loose converter bolts or a broken flex plate will make a terrible racket. Had a stator flailing about one time that sounded pretty bad too, but it didn't last long.

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That was the first thing I checked. All bolts are tight. Sound is for sure coming from oil pan.
 
Gonna have to drop the pan then! Rod bearing most likely Hopefully you catch it before the bearing falls out and you ruin the crank!
 
Started it tonight when leaving for work, and no noise. Maybe changing the oil helped. The Rotella T6 that came out was very thin. Since changing the oil Monday, the noise has got better. Used Mobil Delvac Super 1300 15w 40 this time. I would think a rod bearing would make noise all the time. Not just at first startup, then stop as soon as I put it in gear.
 
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Pull the converter bolts and push it back and start it. I wouldn't be diving into the engine without ruling out the trans.
 
I had the same issue before and the flex plate was in two pieces. All bolts were tight. You could separate motor and trans without touching a converter bolt.
 
I broke the stock flexplate over a year ago. Just had a Firepunk trans with billet SFI flexplate installed in June. This sound is not like when the stock plate ripped the middle out. This is a dead thump/knock coming from oil pan.
 
What is your oil pressure? If you still have your old oil filter cut it open and look for material.
 
Oil was changed a week ago. No metal shavings in oil, magnetic plug, or filter. Truck has always had a haze at idle. Previous owner put 04 injectors in an 04.5. From what I've heard, this will make truck haze at idle. Oil pressure reads 38-40 at idle.
 
bar engine over cold. sounds like a cracked flex plate to me tho. if u shift from drive to reverse does the noise still exist or worsen.
 
straitsix86gmc said:
bar engine over cold. sounds like a cracked flex plate to me tho. if u shift from drive to reverse does the noise still exist or worsen.
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Did that when I checked the flexplate/converter bolts. Everything is tight, no play, no visible cracks, bars over with the engine, turns perfectly straight. Noise goes away when shifting into gear. This noise is NOT coming from the trans. It IS coming from the oil pan. You can clearly hear it and feel it. Same as me knocking on the oil pan with my knuckles. An echoing dead thump of a knock.

There was more of a grinding sound right before the stock flexplate center ripped out. Then it was a knock, but would not go into gear. It tore up the rear engine plate/cover and metal shavings/pieces all in the bell housing.
 
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