loud knock coming from engine.

loud knock coming from engine.

Postby speed13 [OP] » January 23rd 2014, 10:03pm

first things first, I have a 96 Chevy Astro van with roughly a hundred ninety five thousand miles 4. 3 v 6 RWD van.several days ago I was driving on the highway for roughly 5 minutes when I lost all of pressure and engine shutdown. I pulled over on the side off the highway and realized that the oil pressure coolant line has popped off the radiator. And you would not start at that point I had a vehicle towed home and let sit for the night until the next day.

the next day I did a complete tune up including oil 10w 30 spark plugs oil filter radiator flush. After completing all this I attempted to start the van engine started a little rough but it started and ran a good. Oil pressure was around 40 to 50 psi at idle. At idle the oil pressure on a normal day is 40 to 50 psi running 5w 30 well. So I decided to install 10w 30 due to the fact that I lost all oil all over the highway. Just in case I cause slight damage to the engine figuring that would help lube bearings and so forth. Now I have a heavy in extremely loud knocking in the engine and when the engine comes up to operating temperature I go from 40 psi oil pressure to anywhere from 20 to 10 psi. I am a fairly experience mechanic ase certified with several other mechanics on call for any questions I have. I unfortunately cannot figure out where this noise is coming from. With a stethoscope I listen to several points on the motor and I cannot determine exactly where the noise is coming from but it sounds like it's coming from the lower end. If anybody has any advice I would greatly appreciate it.
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Re: loud knock coming from engine.

Postby chevymaher » January 23rd 2014, 10:25pm

I had the same thing happen.

Your ASE certified? I ask because you ran a engine dry and wonder where the knock is coming from.

Take it apart you got spun/melted bearings.
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Re: loud knock coming from engine.

Postby norohs » January 24th 2014, 12:31am

Since I just got through this same thing on my 2002, I'll share what I found on mine.

History: #2 engine with 107K miles, 196K on the truck. Oil filter fell off on the highway at 60MPH. Truck did not shut down. No SES light. I did not notice the oil gauge at zero. I arrived only 1 mile later at my destination (still didn't notice zero oil pressure). It sat for 1-1/2 hour. I got back in it and drove 300 feet. Upon a normal acceleration at 300 feet, it started to knock, though I thought for only a second or so. I listened and no knock. I went 1000 feet to a highway on-ramp and noticed the knock as a truck passed me getting up onto the highway. I thought "I sure hope that's not my truck". Then I noticed the gauge at zero. I let off the gas to pull off the highway and the engine stalled. I had it towed home. That's where I noticed the oil filter missing. It fell off. I later found the 500 foot oil slick on the road where my oil pan was emptied (to this day there is still a trace on the road - I see it every day as a grim reminder).

I replaced the (missing) filter and oil and crossed my fingers. It started right up, but had a "rod-knock" sound - not a soft one either. I figured I spun a rod or main bearing. I did drive it another 50 miles on short hops in hopes that it would go away (wishful thinking). I finally pulled the oil pan and replaced the rod bearings and inspected the mains. The mains were very good and only cylinder rod #1 showed signs of damage, though just a single grove in the center. Overall thickness of all bearings were in good shape and none were spun. Again (with wishful thinking) I replaced the rod bearings. Nothing changed. The "rod-knock" was still there. It did get quieter when the engine reached full temperature, but under accelerating load, the knock got very loud. A second pulling off of the oil pan had me looking closer.

What I found was that something let go on the #3 piston. I found scoring on the cylinder walls. At this point, I knew that the block was coming out of the truck. I also had found metal shavings in the oil. Those two together prompted me to simply replace the engine with a rebuilt long-block from a local engine shop. I never did pull the heads (I didn't need problems getting my $295 core credit from the re-builder) but I did suspect broken rings and a deformed piston. I've been told the knock was likely piston slap. I don't know.... it must sound exactly the same as a rod knock. :shrug:

Point is, I was 100% sure it was a rod-knock sound and it even had other mechanics thinking the same thing, but the problem was higher up in the engine. It had me fooled and mechanics too. I once had a Datsun 4-banger do the same kind of piston/cylinder damage and it sounded nothing like this one.

Good luck in resolving this problem. I wish mine would have gone better, but what the heck; I have to look at the bright side... I now have a new hobby! :banana:
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Re: loud knock coming from engine.

Postby chevymaher » January 24th 2014, 12:56am

Mine broke a oil cooler line drained the oil out. Zero pressure. I pulled it and had 2 melted bearings. Thickness looked correct but it was scored on the face. Crank looked good. I am running the same pistons in the rebuilt engine. Piston damage is very rare from oil starvation. They are splash lubed. Bearings bite the bullet first. I would bank metal shavings got between the piston and wall. I found shavings everywhere. And the bearing was still there and not spun.
It got to come apart and inspect all parts in a situation like this. Mine would have started again had I wanted it to. But I wanted to avoid the future damage that would be incurred. A rebuildable engine can turn to total junk in just a few minutes running.
Mine was clacking not even a knock when I looked and saw the oil gauge. I turned it off doing 65 on the freeway, coasted off the ramp and had it towed home. There was no doubt in my mind do not start it again. Take it apart and fix it.
30 thousand miles later she is a beast now.
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Re: loud knock coming from engine.

Postby Mmusicman » January 24th 2014, 1:56am

My '92 recently developed a "tick"... which over the last month has turned into more of a "knock". I have 282,000 original miles on the 4.3. Oil pressure has ALWAYS been strong, and still is. I got my money's worth on this one! I've heard engine knocks before, and this sounds a little different. I will be pulling the pan to investigate, but I'm not particularly hopeful.

I have a nice hot-rodded 350 that's been waiting patiently for years to go in... got the shorty headers and custom motor mounts yesterday...
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Re: loud knock coming from engine.

Postby speed13 [OP] » January 25th 2014, 10:22pm

to Chevy maker, I was hoping that it wasn't the bearings, most likely is though. Was hoping and praying someone had an idea what else it could be. Unfortunately its been below freezing here lately so, I have not had a chance to dismantle it yet.

To correct myself I didn't run it completely dry but, I believe you may be right.

:ty:
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Re: loud knock coming from engine.

Postby chevymaher » January 25th 2014, 11:06pm

Ah it happens. I got 2 rods hot enough they cooked the oil off the metal before I caught it. Rest all were wet looking still.
It is a pain but all you can do is take a day to get over it, Then plot and plan the recovery.
Good luck. And I mean it I been there.
Randy.

Here is my adventure in oil lines.
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Re: loud knock coming from engine.

Postby speed13 [OP] » February 5th 2014, 9:34pm

Ok, replaced all bearings, oil and, oil pan gasket. After assembling everything she starts like a dream, then oil pressure drops from 60 psi to 20 psi and she starts knoking again but not as hard or loud as before. So, I rip everything apart AGAIN too find all the bearings are shot once again. When I examined the journals on the crankshaft everyone looks excellent except for number 5 cylinder. I pulled the crankshaft and there is no warping or twisting. I've never had this problem before with new bearings new oil. I am confused on what would cause this problem ( in all my years never seen this happen before ) . If anyone has had this problem before and has any solutions please feel free to tell me, I would greatly appreciated it.
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Re: loud knock coming from engine.

Postby chevymaher » February 5th 2014, 10:16pm

Crank kit. Machine the crank and it comes with new bearings.
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Re: loud knock coming from engine.

Postby norohs » February 6th 2014, 3:41am

Oil pump? New?
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Re: loud knock coming from engine.

Postby speed13 [OP] » February 16th 2014, 8:26pm

Ok, after replacing all connecting rod bearings I ran her for around 4-5 hrs ran beautiful. The next day I took her on a 20 mile test ride and she drove like a new truck no knocking or hesitation :dance: . The following day ( valentine's day of all days ) I was on my way to secure a big contract in Manhattan when I lost all oil pressure and the engine shut down again. Had he towed back to my yard (AGAIN ) :screaming: to find out the lower oil coolant line disconnected from the radiator again. I replaced the clips that secure both lines when I did the bearings and inspectedboth lines and connections. I am lost for word and ideas on what could cuase this to continue to happen. Any suggestions would help a lot.
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Re: loud knock coming from engine.

Postby chevymaher » February 16th 2014, 10:33pm

My oil cooler leaked once and that was enough. Take it off.
I concluded hot oil is is better than no oil.
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Re: loud knock coming from engine.

Postby paulo57509 » February 16th 2014, 10:36pm

Did you use a new clip when you re-attached the cooler line? The FSM states not to re-use the clip.

Are you installing the clip onto the fitting and then snapping the line into place?

Are you installing the clips onto the fitting correctly?

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