Loud knock 97 VIP 5.7

wulfcomp · Jun 15, 2012

So we just picked up our first boat on Memorial Day weekend. Got it in the water the next weekend, Sat, everything was great, not a single issue. Sun all day was great and smooth, then when into a small cove, came out and took a lap around the small lake, on the way back to the ramp, started to hear a knocking noise, shifted back to neutral and the motor shut off. Looked at temps, they were at 240 or so. Never got it restarted. Took it to the shop, they replaced the water impeller, though it didn't look bad, and the housing as it had melted. I think debris from the cove blocked the water intake. They also changed the oil, as we wanted to make sure the previous owner used the right type. After service, we get the boat back in the water, go out to our little sitting spot... everything seemed normal again, then back to the marina to pick up some friends, no problems. After we picked up the passengers, and were headed back out, the knocking noise came back. There is no sound at idle. And I can't get it to reproduce the noise while on the hose. It only happens above 2000 rpm, and only while in gear and moving in the water. Originally the techs thought it might be the exhaust flappers, but we checked those, and they still seem covered in rubber, and don't think they could make this sound. We got a tech to listen to it in the water, and he thinks maybe a loose rocker, or bent push rod. Just thought I would ask the opinion of other experts before we started tearing it apart.

http://www.youtube.com/watch?v=HRyOwnhQwgE

Thanks for your help

HT32BSX115 · Jun 15, 2012

Re: Loud knock 97 VIP 5.7

wulfcomp said:
So we just picked up our first boat on Memorial Day weekend. Got it in the water the next weekend, Sat, everything was great, not a single issue. Sun all day was great and smooth, then when into a small cove, came out and took a lap around the small lake, on the way back to the ramp, started to hear a knocking noise, shifted back to neutral and the motor shut off. Looked at temps, they were at 240 or so. Never got it restarted. Took it to the shop, they replaced the water impeller, though it didn't look bad, and the housing as it had melted. I think debris from the cove blocked the water intake. They also changed the oil, as we wanted to make sure the previous owner used the right type. After service, we get the boat back in the water, go out to our little sitting spot... everything seemed normal again, then back to the marina to pick up some friends, no problems. After we picked up the passengers, and were headed back out, the knocking noise came back. There is no sound at idle. And I can't get it to reproduce the noise while on the hose. It only happens above 2000 rpm, and only while in gear and moving in the water. Originally the techs thought it might be the exhaust flappers, but we checked those, and they still seem covered in rubber, and don't think they could make this sound. We got a tech to listen to it in the water, and he thinks maybe a loose rocker, or bent push rod. Just thought I would ask the opinion of other experts before we started tearing it apart.

http://www.youtube.com/watch?v=HRyOwnhQwgE

Thanks for your help

Howdy,

Normally, you cannot hear knocks and other strange noises in a video good enough to identify them.....

That said, It sounds VERY metallic, and to diagnose further, you need to get yourself an automotive stethoscope like the following

http://www.sears.com/shc/s/p_10153_...21x00003a&ci_src=14110944&ci_sku=SPM213831552

and get a little closer to the sound.

Let me say right now that it sounds very expensive (because I think unless you find something externally obvious, you're pulling the engine)

Sometimes exhaust leaks can sound metallic. Using the stethoscope, you should be able to get close to a metallic knock... If you cannot, then use a small covered microphone and move it around the intake and exhaust manifolds. If it's an exhaust leak that only occurs at the higher power setting (loaded RPM) the mic will easily identify the noise when you get very close to it. (the steth might too)

Sorry about that,

Rick

mjfink · Jun 15, 2012

Re: Loud knock 97 VIP 5.7

Again, to second what HT said, it's hard to tell for sure in a video..

But, the sound is almost exactly what I heard when I had the following issue:

http://forums.iboats.com/showthread.php?t=546922

The problem, in my case, was there was a rod bouncing around because it had unseated from the lifter. The boat needed a valve job (and, in my case, a new exhaust as that's what caused my problem). Pulled the heads off, machined them, reseated the valves (replaced a few of them), replaced the exhaust (most expensive part of the whole thing) and the boat is running just fine again.

Unfortunately.. It wasn't cheap.. But I didn't need to pull the engine, there was no damage to the lower end of the engine. If you have a compression tester, you might want to try a leak down test. But, honestly, with that noise, I'd pull the valve covers and take a look; I think you'll find your problem is quite evident.

Also, given that you had an overheat, take a good look at your exhaust when you pull it off; the reason your motor could be clanking (in my case, anyway) is because water got into a cylinder though the exhaust and, because it's non-compressible, broke something in the valve train. You'll have to pull it anyway to get at the heads, make sure to examine it closely.

HT32BSX115 · Jun 15, 2012

Re: Loud knock 97 VIP 5.7

But, honestly, with that noise, I'd pull the valve covers and take a look; I think you'll find your problem is quite evident.

You might be right. A stethoscope will probably lead there too. It's very possible that a lifter is leaking down but I am sceptical of that. It would likely do it at the same RPM whether the engine is loaded or not.

A severe exhaust leak at the intake manifold or exhaust manifold would be quite different under load vs a neutral run-up (you might not even hear it with the engine unloaded)

wulfcomp · Jun 15, 2012

Re: Loud knock 97 VIP 5.7

Thanks for the input so far guys. I am going to try and take the valve covers off tomorrow, see what I can find. I've just gotten so many possible answers from experts, I guess its best to start where ever its cheaper and work my way to the expensive stuff down the line. I could see the possibility of an exhaust leak, as possibly the overheating ruptured the gasket. A very odd thing that no one has been able to answer. When the motor overheated, we checked for oil, none was found on the dipstick, after it was trailered home, some was found at the very end, the next day when we took it to the shop for the impeller change, it was all back. no one knows where the oil was hiding at. Some motor guys I have talked to think it could be a rod bearing that burned, or slipped. It just sounds awful solid to be a rocker or anything in the top end. I guess it was easy to figure out, we wouldn't have to pay mechanics so much to fix stuff. I just wish there was an easy answer, instead of all this guessing and speculation. I'll keep diggin and let you guys know how it turns out.

mjfink · Jun 15, 2012

Re: Loud knock 97 VIP 5.7

When my top end went it was a VERY "solid" sound. I'd compare it to someone hitting the valve cover with a light hammer. I would have guessed "valve/piston contact" from the sound.

Please do let us know what you find, I it helps everyone if you give the resolution when you find out where the problem lies.

wulfcomp said:
Thanks for the input so far guys. I am going to try and take the valve covers off tomorrow, see what I can find. I've just gotten so many possible answers from experts, I guess its best to start where ever its cheaper and work my way to the expensive stuff down the line. I could see the possibility of an exhaust leak, as possibly the overheating ruptured the gasket. A very odd thing that no one has been able to answer. When the motor overheated, we checked for oil, none was found on the dipstick, after it was trailered home, some was found at the very end, the next day when we took it to the shop for the impeller change, it was all back. no one knows where the oil was hiding at. Some motor guys I have talked to think it could be a rod bearing that burned, or slipped. It just sounds awful solid to be a rocker or anything in the top end. I guess it was easy to figure out, we wouldn't have to pay mechanics so much to fix stuff. I just wish there was an easy answer, instead of all this guessing and speculation. I'll keep diggin and let you guys know how it turns out.

rickryder · Jun 16, 2012

Re: Loud knock 97 VIP 5.7

mjfink said:
When my top end went it was a VERY "solid" sound. I'd compare it to someone hitting the valve cover with a light hammer. I would have guessed "valve/piston contact" from the sound.

Please do let us know what you find, I it helps everyone if you give the resolution when you find out where the problem lies.

If you had valve piston contact it would bend the valve and you would have a miss in the engine.

wulfcomp you have the right idea...pull the covers and look around

FreeBeeTony · Jun 16, 2012

Re: Loud knock 97 VIP 5.7

You might also try this...........

While the engine is making the noise, remove the plug wire 1 at a time.
It might help determine which cylinder the noise is associated with.

spdracr39 · Jun 16, 2012

Re: Loud knock 97 VIP 5.7

Sounds like you lost a rod bearing to me. If you keep running it to diagnose it better i bet you will find out soon enough. It could have burned a piston and your hearing it slap around in the hole but my money is on lower end. That isn't a valvetrain noise

If you had saved your old oil you could have it analyzed for metal particles and that would tell you if it was a bearing issue.

I just had another thought. If it burned the top of the piston could we be hearing detonation from the hot spot ? A borescope in the sparkplug hole could determine that.

mjfink · Jun 16, 2012

Re: Loud knock 97 VIP 5.7

I'm not saying your wrong (I thought the same thing when I started tearing mine down), but, I will say, my noise was almost exactly the same sound that this engine is making and it was upper end. The rod was bouncing around in the valves and made a very "deep" noise.

Either way, I'm curious and sounds like we'll know soon enough, hopefully the OP will be back to tell us what he finds when he pull the valve covers off.

spdracr39 said:
Sounds like you lost a rod bearing to me. If you keep running it to diagnose it better i bet you will find out soon enough. It could have burned a piston and your hearing it slap around in the hole but my money is on lower end. That isn't a valvetrain noise If you had saved your old oil you could have it analyzed for metal particles and that would tell you if it was a bearing issue.

I just had another thought. If it burned the top of the piston could we be hearing detonation from the hot spot ? A borescope in the sparkplug hole could determine that.

wulfcomp · Jun 16, 2012

Re: Loud knock 97 VIP 5.7

Not to worry guys, as soon as I know an answer, you will know. I've been dying to figure this out since last weekend, It seems to be more of an issue of finding time to get to it. With it being fathers day weekend, it seems alot of my time has been allocated. There is a possibility I can get some time tonight, if not I'll try again tomorrow. Happy Father's day to all those that meet the requirements.

joewithaboat · Jun 16, 2012

Re: Loud knock 97 VIP 5.7

wulfcomp said:
Not to worry guys, as soon as I know an answer, you will know. I've been dying to figure this out since last weekend, It seems to be more of an issue of finding time to get to it. With it being fathers day weekend, it seems alot of my time has been allocated. There is a possibility I can get some time tonight, if not I'll try again tomorrow. Happy Father's day to all those that meet the requirements.

Some guesses in no particular order... wrist pin, cracked piston, or spun rod bearing that has worn the crank enough that the piston is hitting the bottom of the head.

I think the last one is most likely.

Of course give the valve train a good look before tearing everything apart! To me it sounds like it is at crank rpm not cam.

Good luck, keep us posted.

Oshkosh1 · Jun 16, 2012

Re: Loud knock 97 VIP 5.7

I think I can tell you what it's NOT...
It's not valve train nor exhaust related.

It's "deeper", low end...I agree with "joe" in the above post.

mjfink · Jun 16, 2012

Re: Loud knock 97 VIP 5.7

I'm keeping my money on valve train (the sound, maybe not the actual cause of the issue). But that's just because I JUST completed a repair on my engine that was making a very similar noise (the recency bias).

Oshkosh1 said:
I think I can tell you what it's NOT...
It's not valve train nor exhaust related.

It's "deeper", low end...I agree with "joe" in the above post.

wulfcomp · Jun 19, 2012

Re: Loud knock 97 VIP 5.7

mjfink, what we the cause of water in your cylinders?? We have her apart now, and we had water in 3&5. We are still taking her apart.

mjfink · Jun 19, 2012

Re: Loud knock 97 VIP 5.7

Exhaust failure. It wasn't all that visible by looking at it, but, from the rust inside the exhaust, it was clear that water had been intruding on the hot side and drained back down into the cylinders. 3&5 are common places to get it because they are in the middle of engine. Take a look at the manifolds and risers, that's almost certainly where your problem lies.

Did you find the knocking sound yet (the water, by itself, won't do that; the water broke something and that's what's causing the knock).

wulfcomp said:
mjfink, what we the cause of water in your cylinders?? We have her apart now, and we had water in 3&5. We are still taking her apart.

wulfcomp · Jun 25, 2012

Re: Loud knock 97 VIP 5.7

Well, our exhaust was ok, seems the only problem we had was a blown head gasket. Got everything torn down, the heads checked and milled. new gaskets, flushed the motor of all the water in the oil, did two oil changes and everything seems good to go now. I want to thank everyone for all the help with our problem, and hopefully this thread will help others who find themselves with the same problem

Loud knock 97 VIP 5.7

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