HELP---Strange Engine Noise is very puzzling

[datzenmike]

If the oil pick up was loose the engine would be seized by now. It'll be something external I would think

[raythomas]

On 3/8/2023 at 6:18 AM, Crashtd420 said:

Or are you talking about the pickup tube in the oil pan.. if so yes it has a typical flat gasket... 

I believe it's with any gasket kit you buy.... 

Yes sir, I looked but was unsure.

Thx

Ray

[raythomas]

On 3/8/2023 at 7:04 AM, datzenmike said:

If the oil pick up was loose the engine would be seized by now. It'll be something external I would think

No sir, not loose. I had to remove the pickup tube to get to the crank and rods when I was checking bearing clearances with plastigage.

Thx

Ray

[raythomas]

Got the oil pickup back on, the pan back on and the cross member mounted. I removed the drive belt so the water pump, fan and alternator are not turning in the background of this audio file I'm attaching. The file size ended up being huge. I had to trim it down so I picked the best part of the whole clip where you can hear the noise the best.

I re-checked the clip below and you can hear it at 7 second mark and then at 14 seconds it really cuts up good.

If you fellows hear anything interesting let me know.

Thanks

Ray

Edited March 12, 2023 by raythomas

[datzenmike]

Got old ears, sounds like an L series to me. I hear no change at 7 or 14 seconds.

 

What are you idling at 3,500?????????

[thisismatt]

I hear it, but it isn't apparent what it could be.  Still kiiiiind of sounds like an exhaust leak...or maybe a sticking valve?

[EDM620]

All I hear is what could maybe be a slight exhaust leak, but it isn't a loud or obvious sound.

[raythomas]

11 hours ago, datzenmike said:

Got old ears, sounds like an L series to me. I hear no change at 7 or 14 seconds.

 

What are you idling at 3,500?????????

I think it just sounds like that. The engine was dead cold when I started recording so it was idled up some. But its amazing just how noisy it is under the hood of a running engine. By "L" series I assume you mean engine type? This is a Z24i engine in this truck.

Thx

Ray

Edited March 12, 2023 by raythomas

[raythomas]

9 hours ago, thisismatt said:

I hear it, but it isn't apparent what it could be.  Still kiiiiind of sounds like an exhaust leak...or maybe a sticking valve?

Is there a way to test for a sticking valve? I've had the valve cover off and everything in there looked super clean with no apparent broken parts.

Thx

Ray

[raythomas]

1 hour ago, EDM620 said:

All I hear is what could maybe be a slight exhaust leak, but it isn't a loud or obvious sound.

I do apologize for the audio. I understand it's not the greatest. But believe me when I say, when it makes the noise you DO hear it. And it just started this a few months back. Before then, it NEVER made this noise, or any noise for that matter. It's hard to describe the noise. It sounds like something knocking or banging against something big and hollow, like hitting a empty steel drum with a shop hammer. Its not a hard clunking noise. Like I've mentioned before, the noise at first sounded like old fashion valve knock or clatter to me.

Thx

Ray

Edited March 12, 2023 by raythomas

[datzenmike]

It's OK my ears are not the best quality.

[thisismatt]

6 hours ago, raythomas said:

Is there a way to test for a sticking valve? I've had the valve cover off and everything in there looked super clean with no apparent broken parts.

Thx

Ray

 

You could turn it over with the plugs out and rocker cover off and see if any are sticking, but seeing as it seems intermittent it may not show up even if that was the case.

[EDM620]

9 hours ago, raythomas said:

Is there a way to test for a sticking valve?

Have you performed a compression test across all cylinders?

 

A "sticking" valve generally translates to a bent valve stem, and a slight bend could give an intermittent "stick". Use a compression tester and stick the release open, then watch as the engine is cranked over - if all is well, each compression stroke should peak about the same PSI, a "stick" would show as a low read. As the engine runs, the valves rotate a few degrees so the valve and valve seat don't land on the same spot every stroke. I can't recall how many degrees that is, but it will take many engine rotations for a valve to make a complete rotation, so expect to crank it over many times.

 

This test method would identify which cylinder but not which valve.

 

Once you know which cylinder, then the next step is to check both intake & exhaust valve. The sticking valve should show some blow-by on the valve edge grind opposite the side it is bent to, more evident on the intake than the exhaust valve.

This illustration is exaggerated but helpful.

 

Initially, use the solid stick against the ear method (or a mechanics stethoscope) and poke around the head and block while engine is running and listen for the sound. This can also help lead you directly to the source of the noise. It is interesting to hear all the different things going on inside a running engine, and it is possible the sound you are hearing might not be from the head at all.

 

The question then becomes "WHY did it get bent?" Possibly will be evidence of an impact with the piston, though slight IF happened when running. Maybe while the head was off it was dropped onto a bench? Maybe the cam timing was out at some point, though that would more likely give you more than 1 bent valve...

[raythomas]

2 hours ago, EDM620 said:

Have you performed a compression test across all cylinders?

 

A "sticking" valve generally translates to a bent valve stem, and a slight bend could give an intermittent "stick". Use a compression tester and stick the release open, then watch as the engine is cranked over - if all is well, each compression stroke should peak about the same PSI, a "stick" would show as a low read. As the engine runs, the valves rotate a few degrees so the valve and valve seat don't land on the same spot every stroke. I can't recall how many degrees that is, but it will take many engine rotations for a valve to make a complete rotation, so expect to crank it over many times.

 

This test method would identify which cylinder but not which valve.

 

Once you know which cylinder, then the next step is to check both intake & exhaust valve. The sticking valve should show some blow-by on the valve edge grind opposite the side it is bent to, more evident on the intake than the exhaust valve.

This illustration is exaggerated but helpful.

 

Initially, use the solid stick against the ear method (or a mechanics stethoscope) and poke around the head and block while engine is running and listen for the sound. This can also help lead you directly to the source of the noise. It is interesting to hear all the different things going on inside a running engine, and it is possible the sound you are hearing might not be from the head at all.

 

The question then becomes "WHY did it get bent?" Possibly will be evidence of an impact with the piston, though slight IF happened when running. Maybe while the head was off it was dropped onto a bench? Maybe the cam timing was out at some point, though that would more likely give you more than 1 bent valve...

Wow, thanks for the advice. Now I have a new test to perform.

As far as the head being dropped or something. I don't really think so cause this engine hasn't been apart in years. And it's been running okay all that time.

So there's that.

Thx

Ray

Edited March 13, 2023 by raythomas

[Stoffregen Motorsports]

This noise could be everything, or it could be nothing. Meaning, there could be something really wrong with the truck and the engine will blow up tomorrow, or it could live for another ten years.

 

Back when 280Zs were new, my friend was working at a Nissan dealership and they had a 280Z that was still under warranty that made an engine knock, and they just could not diagnose the problem. Their solution was to help the engine blow up so they could warranty it for the customer. They tried and tried but could not get the engine to blow. They went as far as putting the car on the lift and smashing the throttle down with a brick and walked away. The car ran for hours on the lift at full throttle and still wouldn't blow.

 

I know you want your truck to be perfect, and you want to do your due diligence to find and fix the problem, but maybe you should just go enjoy it. If it's going to blow up, you'll know soon enough.

[Stoffregen Motorsports]

Thinking back, have you looked at the rockers? I know some of these Z motors had rocker issues. The rocker would wear into the shaft or even into the aluminum rocker stand, causing a noise.

[raythomas]

10 hours ago, Stoffregen Motorsports said:

This noise could be everything, or it could be nothing. Meaning, there could be something really wrong with the truck and the engine will blow up tomorrow, or it could live for another ten years.

 

Back when 280Zs were new, my friend was working at a Nissan dealership and they had a 280Z that was still under warranty that made an engine knock, and they just could not diagnose the problem. Their solution was to help the engine blow up so they could warranty it for the customer. They tried and tried but could not get the engine to blow. They went as far as putting the car on the lift and smashing the throttle down with a brick and walked away. The car ran for hours on the lift at full throttle and still wouldn't blow.

 

I know you want your truck to be perfect, and you want to do your due diligence to find and fix the problem, but maybe you should just go enjoy it. If it's going to blow up, you'll know soon enough.

Oh believe me, I've thought about doing just that. Just drive it until something blows or falls off it. At least then I will know what to fix.

Thx

Ray

Edited March 14, 2023 by raythomas

[raythomas]

10 hours ago, Stoffregen Motorsports said:

Thinking back, have you looked at the rockers? I know some of these Z motors had rocker issues. The rocker would wear into the shaft or even into the aluminum rocker stand, causing a noise.

Yes I have, but plan on checking them again when I do compression test but wouldn't that kind of noise be apparent all the time? And just get louder under load or acceleration?

 

Thx

Ray

Edited March 14, 2023 by raythomas

[datzenmike]

Sticking valve???? Is that even a thing today???? This isn't the 1950s.

 

Bent valve is practically impossible. What would be the mechanism for causing that outside of having taken the head off and laid it face down or revved it to valve float???

 

I wish I could hear what some of you all say you can hear but engines make noise. Owners sometimes fear the worst when in reality it's just normal 'noise'. 

 

What happened when the fan belt was removed?

[raythomas]

23 hours ago, datzenmike said:

Sticking valve???? Is that even a thing today???? This isn't the 1950s.

 

Bent valve is practically impossible. What would be the mechanism for causing that outside of having taken the head off and laid it face down or revved it to valve float???

 

I wish I could hear what some of you all say you can hear but engines make noise. Owners sometimes fear the worst when in reality it's just normal 'noise'. 

 

What happened when the fan belt was removed?

Alas, nothing different. Noise was still there with belt removed. I was really hoping it was the engine fan. But I guess not.

Thx

Ray

[EDM620]

Well if it ain't broke, don't fix it. it is just a noise after-all, it'll make itself more apparent in the future.

[raythomas]

2 hours ago, EDM620 said:

Well if it ain't broke, don't fix it. it is just a noise after-all, it'll make itself more apparent in the future.

I've honestly thought of that. I am so tired of trying to find and fix it. But then I get to thinking that finding it now might help me avoid a costly parts bill in the future. And with my luck it would entail a complete rebuild with new block, head and all 😞

Thx

Ray

[bilzbobaggins]

Sounds like water hitting a metal fan blade(im not saying thats what I think it is) or a couple rocks in the exhaust(once again, not a theory).

 

I for sure hear it.

[raythomas]

6 hours ago, bilzbobaggins said:

Sounds like water hitting a metal fan blade(im not saying thats what I think it is) or a couple rocks in the exhaust(once again, not a theory).

 

I for sure hear it.

Well the fan is all plastic except for the small clutch part in the middle and I've ran the engine with the fan disabled and not turning so there's that, and I've had the exhaust completely apart and its clean from header to tip.

Thx

Ray

[EDM620]

On 3/15/2023 at 9:39 PM, raythomas said:

I am so tired of trying to find and fix it.

If it is something more serious, and just a noise now, it will make itself more apparent (and easier to diagnose). 

If you still feel the need to find it, do the stethoscope/stick method and listen to the engine as it runs. If internal issue you'll know for certain.