3 liter knocking noise VIDEO

Redwing4900

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Aug 21, 2012
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i have a knocking noise coming from the oil pan area used one of those stethoscopes to pinpoint where it was coming from. All compression readings were great 140-145 PSI, engine fires right up. Here is a link to a YouTube video: https://youtu.be/RW4aRk9_A_U
Just loaded up today since I'm thinking it could be an oil pump? Is this something that will go bad? I have had this boat on the lake and she runs perfectly with good power, just can't figure out where this could be coming from inside the pan.
 

Bondo

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Ayuh,.... Sounds like the crank or a rod to Me,.....

Have ya pulled the plug wires, one at a time to see if it changes,..??
 

Redwing4900

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I was afraid that it was the connecting rod bearing. I'm curious what would taking the plug wires off do? Assuming that it is the rod bearing Is it probable that the crankshaft is going to be damaged as well? I have never done this repair, do I change all of the rod bearings while I'm in there? I was all set to relaunch her and just put up with the noise, and do the repairs in the fall, but that's probably not a good idea, huh? Thank you for your help.
 

998cc

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IMHO. Running that motor in this condition will only lead you down a dead-end bad road. You have to determine what you want out of your boat; you can have the crank ground and replace the rod and main bearings as an absolute minimum. However, if you are looking for reliability and possible better resale value, rebuild the entire motor. Anything less, you are taking chances that you'll end up doing it all over again at even more expense. Russ in Ca.
 

nateo

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Are you sure that isn't burnt exhaust flappers (i.e. with the rubber gone)? those are very easy to check and or replace and fairly cheap. If it runs great then I would check these for sure. Those were toast when i first bought my boat but only cost about $40 to replace both of them.
 

Watermann

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Sounds like a spun rod bearing to me. Did the knock just suddenly develop or was there an issue prior to it? Water intrusion in the oil will cause it down the road after it's repaired. Do what Bondo suggested, with the cylinder not firing it should change the sound of the knock.
 

flipbro

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No way that's exhaust flappers... That is 100% failed bearing sorry
 

Redwing4900

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As an update I pulled the motor and put it up on a stand so I could seewhat was going on with the rod bearings. I couldn't find any movement or burning with any of them. Could it be a main bearing? The knocking now that I think of it was a singular knocking noise not like I thought a rod bearing would sound like. It seems like the rod bearing noise would be double time of the knock I am experiencing. I did not pull the spark plug wires,I totally forgot to do this and now I regret it. Any thoughts on where to go from here? Thank you in advance.
 

Bt Doctur

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not a main, a rod bearing. you should check for and rod movement up and down . If the motor is in a stand ,simply rotating the crank and watching the rods will show you the bad bearing by a up and down rod movement on the crank , Then remove that bearing cap remove the bearing caps to visually check the bearing
 

nateo

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Did you ever check your exhaust flappers? If you have engine out they should be right there in the Y pipe. would probably only take about 60 seconds to look at them. Sounded to me as though that engine was idleing fine. burnt exhaust flappers knock just like that, fairly slow interval.
 

Redwing4900

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Did not check the flappers will do it tonight...how do they look when they're bad? I did turn the motor with the oil pan off couldn't see any connecting rod movement, took off the end caps no scoring on them or the crank journals. Mechanic friend of mine said possibly a stuck valve? I believe I have push rods and hydraulic lifters he said I should pull the valve cover and turn the motor see if there is any gaps by the push rods before taking the main bearing caps off and checking them. Never did it before hope I'm explaining it correctly.
 

nateo

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No Title

Not sure what year you are working on. I think I remember reading that y pipe has to come off for older models. On my '86 there were at top of y pipe and very easy to get to. They are coated in rubber. They can be burned up during a overheat situation, etc. The rubber melts off and all thats left is steel, they tap up against the cast exhaust pipe. Here's a picture of what a brand new one looks like.
 

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Watermann

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Yeah his 3.0 L is a 4 banger with a single pipe and flapper.
 

Redwing4900

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Well I checked the exhaust shutters they look okay to me although they don't look like they're closed completely. All of the rubber is intact. Before I pulled the engine
I used a stethoscope to listen for that sound and it wasn't coming from anywhere but the oil pan. the valves, seemed to be okay too. I have yet to hear what a bad oil pump sounds like. I'm still hoping that is my culprit. I will continue the search and update as I go. Of all the YouTube videos I have looked at with engine noises -about thirty I would say- none of them sound like mine. Picture file is too large to post here of the shutters. Sorry I tried.
 

Watermann

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Haul that chunk of cast iron out and start digging into it. No matter what the motor has to come out for the repairs. One thing on that last car video, everyone commenting says that their oil pressure is all wonky too along with the noise. Those con rod bearings are pretty much in the oil pan too.
 

biggjimm

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I've never heard a oil pump sound quite like that. What was your oil pressure? When the head is off, you can put each piston at TDC & strike it with the end of a wood handled hammer or something similar that won't damage the piston & you can hear the bad rod bearing, that's with the head off. I've never tried it from the bottom end but put the piston all the way down & rap the rod cap with hammer handle, probably need the plugs out so your not fighting compression. Good bearing will just kinda go thud but the bad bearing will make a noise. You'll hear the difference if it's a rod bearing.
 

Redwing4900

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When I put the motor on the engine stand I pulled the oil pan and rotated the engine and was tapping the pistons from underneath to see if there was any movement and found none. I am going to open up the oil pump today and see what it looks like in there. The only indication for a bad oil pump while running would be reduced oil pressure or oil overheating as far as I know but I didn't really run the boat too hard, because I was worried about causing more damage. Also,I didn't see that the oil pressure was too low. I don't mind tearing into things, but don't want to open up a can of worms where I didn't have to. I think I will take off the main bearing covers and see what they look like under there. Don't want to rule anything out while the motor is in this state. Thank you all for your input.
 

Redwing4900

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Today I took the head off, turned the engine right side up and put each piston tdc and gave each one a tap with no movement. I also checked each main bearing cap and found no grooves or damage to the crank. I made sure to torque all cap bolts prior to the tap test. I even put my oil pan up temporarily to see if there might be a dent that's causing a rub and the noise, shot in the dark, and no sound. Any other suggestions? When dumping out some residual oil in the pan, I found a piece of the number three cylinder the tab on the underside broke off, but no apparent damage to the jug or the piston. I don't know where to go from here. There is a whole lot of carbon buildup, so I'm probably going to clean it up change the oil pump put her back together, and see what happens. I can't find anything else wrong.
 
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