HELP---Strange Engine Noise is very puzzling

[raythomas]

Checked the flywheel bolts and they are good. None loose at all. In your best opinion would I be better to put the trans back into the truck "before" I remove the front cross member and take the oil pan off the engine? Or take the pan off without the trans installed? Just curious if it would make any difference other than having the rear of the engine firmly mounted before crawling under the front side of the truck. Would seem safer to me. It is a mini truck and its sorta crowded under that thing 😁

Thx
Ray

[datzenmike]

I would put the transmission back in. Having moved everything and tightened everything start it up and see if noise is still there before dropping the pan. I've taken things out or off to fix, can't find anything, only to put back together and find the problem is gone.

 

If the pan does not easily slip out remove the idler arm bolts and let the steering linkage on the right side sag down.

[raythomas]

Just for giggles, what would you think "could" be wrong in the bottom half of the engine? Spun bearing? Loose bolt? I mean its just so weird that it only does it under load. Thats one reason I was thinking clutch. I'm telling you for real, this engine is smooth as a sewing machine when its idling or racing it up in neutral.

Thx

Ray

[datzenmike]

I can't really say as I'm not there to hear it. I only have your description. While under load the obvious difference to idle is the engine/transmission torques over to the right side. You are sure that the engine mounts isolaters are not torn. Nothing on the intake side rubbing or loose enough to vibrate? 

 

A spun bearing will not be quiet. Rod bearings* will hammer (mostly under load) louder and louder (till hammering all the time) till the shells are thin enough to slip under each other. If lucky and not driving hard enough the bearing friction welds the rod to the crank and engine stops. If flying down the highway the vehicle speed snaps the rod off and stuffs it through the block. Main bearings will screech. The oil will have silver particles in it or they will be trapped in the oil filter. Rotors on the oil pump will look like they were pumping sand. Oil pressure will be noticeably lower at idle than before.

 

Bolts don't come loose unless someone had then apart and didn't torque them properly. Then they usually come apart soon after, not years later.

 

* Possibly very early stages of a rod bearing turning bad but before the crankshaft is damaged. New bearings and a plastigauge to check the clearance should fix it.    

[Stoffregen Motorsports]

Yes, a rod bearing that has wear can make noise under load, but be silent otherwise. An old timer's trick is to use heavier weight oil. That's a really old trick and isn't viable with anything built since the 50s. But, you could try it and see if the noise goes away.

 

Really, I think it's time to pull the oil pan and remove a couple rod caps and inspect the bearings. Personally, I'd remove the pan before you put the trans back in. That way, if you find a problem, it is easier to get the motor out.

 

There is another possibility. The crank could be cracked. I've seen running Datsun L motors with broken cranks before and they make a clunking noise under load. It's pretty rare. I've only seen it twice before on a street engine.

 

Could it be the front bearings in the trans? I wouldn't think so, because the noise wouldn't change under load.

[datzenmike]

If it's early enough you can just put new ones in without taking the engine out. I would plasti-gauge it to look for gross wear damage. This assumes the crank is not scored and only the bearing is bad. 

[Stoffregen Motorsports]

You can replace them from underneath, but it's a lousy job fraught with dangers.

[paradime]

28 minutes ago, Stoffregen Motorsports said:

You can replace them from underneath, but it's a lousy job fraught with dangers.

 

Truly lousy job. I started hearing some ticking/knocking from an L20 I'd just built. I popped the pan to check my torque job on the rod brings, found nothing, put the pan back on, and no noise. Okay then, I dropped the hood, prayed it didn't come back, and it never did..

[datzenmike]

56 minutes ago, Stoffregen Motorsports said:

You can replace them from underneath, but it's a lousy job fraught with dangers.

 

If the engine is out and on a bench you can do it standing up, but other than that it's the same thing.

 

9 minutes ago, paradime said:

 

Truly lousy job. I started hearing some ticking/knocking from an L20 I'd just built. I popped the pan to check my torque job on the rod brings, found nothing, put the pan back on, and no noise. Okay then, I dropped the hood, prayed it didn't come back, and it never did..

 

I'd rather be lucky than good.

[raythomas]

23 hours ago, datzenmike said:

I can't really say as I'm not there to hear it. I only have your description. While under load the obvious difference to idle is the engine/transmission torques over to the right side. You are sure that the engine mounts isolaters are not torn. Nothing on the intake side rubbing or loose enough to vibrate? 

 

A spun bearing will not be quiet. Rod bearings* will hammer (mostly under load) louder and louder (till hammering all the time) till the shells are thin enough to slip under each other. If lucky and not driving hard enough the bearing friction welds the rod to the crank and engine stops. If flying down the highway the vehicle speed snaps the rod off and stuffs it through the block. Main bearings will screech. The oil will have silver particles in it or they will be trapped in the oil filter. Rotors on the oil pump will look like they were pumping sand. Oil pressure will be noticeably lower at idle than before.

 

Bolts don't come loose unless someone had then apart and didn't torque them properly. Then they usually come apart soon after, not years later.

 

* Possibly very early stages of a rod bearing turning bad but before the crankshaft is damaged. New bearings and a plastigauge to check the clearance should fix it.    

Motor mounts are good. The engine moves very little if any from torque. And no sir, nothing on the intake side or exhaust side rubbing anything. I knew we spoke about putting the trans back in before removing the oil pan, but was wondering if it might be better to leave it out in case I need to remove the crank. Pulling the oil pan is next on my list.

Thx

Ray

[raythomas]

9 hours ago, Stoffregen Motorsports said:

Yes, a rod bearing that has wear can make noise under load, but be silent otherwise. An old timer's trick is to use heavier weight oil. That's a really old trick and isn't viable with anything built since the 50s. But, you could try it and see if the noise goes away.

 

Really, I think it's time to pull the oil pan and remove a couple rod caps and inspect the bearings. Personally, I'd remove the pan before you put the trans back in. That way, if you find a problem, it is easier to get the motor out.

 

There is another possibility. The crank could be cracked. I've seen running Datsun L motors with broken cranks before and they make a clunking noise under load. It's pretty rare. I've only seen it twice before on a street engine.

 

Could it be the front bearings in the trans? I wouldn't think so, because the noise wouldn't change under load.

Can you explain "cracked crank" a little more in detail? What would I be looking for if that turned out to be my problem?

Thx

Ray

[raythomas]

8 hours ago, datzenmike said:

If it's early enough you can just put new ones in without taking the engine out. I would plasti-gauge it to look for gross wear damage. This assumes the crank is not scored and only the bearing is bad. 

If I don't have a spun bearing and they are all in the correct place. And the crank has no noticeable wear or gouges. The plasti-gauge would tell me what "over size" bearing to put back into the engine I'm assuming?

Thx

Ray

[datzenmike]

The plasti-gauge is a good enough method to determine your bearing clearance. Do this with the new bearing and as long as within spec (I forget now) but around 1-2 thousands of an inch and away yo go. If too much clearance then you know that the crank or rod is worn or damaged.

[Stoffregen Motorsports]

Acceptable rod bearing clearance is between .001" and .002" and .0025" can be ok, but that's really pushing the limits for rod bearing clearance.

 

A broken crank is not usually detectable by visual inspection. It usually sounds like a frequent clunk, and is not very loud. It can often sound like a piston knock, but the frequency would be less. Instead of four pistons making noise, there is one crack making a noise. Make sense?

 

When I say broken, I mean cracked. The crack can be so large that there is flex between the two halves of the crank, causing the clunk. I've seen plenty of L series race motors and a few street L motors with broken cranks and they tend to crack at the fourth or fifth main bearing, though they can also crack at the snout and the rod throws of the crank too.

 

The only way to check for a broken crank is to have the crank magnafluxed.

[paradime]

It should be noted that although it happens on rare occasion with a hopped up street engine, it's much more rare for a stoke Z24 to crack a crankshaft. Finding the noise is a process of elimination and magna flexing the crank is last step.

 

Is it possible a rod bolt to backed out? I've seen this happen on V10 Ford engines, but not L or Z 4 cylinders.

 

 

[raythomas]

3 hours ago, paradime said:

It should be noted that although it happens on rare occasion with a hopped up street engine, it's much more rare for a stoke Z24 to crack a crankshaft. Finding the noise is a process of elimination and magna flexing the crank is last step.

 

Is it possible a rod bolt to backed out? I've seen this happen on V10 Ford engines, but not L or Z 4 cylinders.

 

 

At this point I'm not ruling out anything because I have yet to pinpoint anything down. I was sure hoping it was the clutch. It's not a fast noise its more slow and methodical if that makes any sense. What is still got me stumped is why the engine sounds so good at idle and racing it up in neutral, I can't stress enough how well it runs and sounds. Its only when its loaded it down. And I thought I mentioned it but may haven't, when it starts the sound you can increase throttle or load the engine harder and the noise will almost completely go away.

Thx
Ray

[Stoffregen Motorsports]

I think we need to go back to square one.

 

How many miles on the motor? Lots? Little?

Has anything else happened, close to the time this noise started?

Did you do any major or minor maintenance prior to this noise?

What's your history with the vehicle? New to you? Owned it for many years?

Are there any nasty oil leaks or, conversely, rust spots on the engine block? Or transmission?

Visual inspection of the motor mounts revealed what?

Any part of the powertrain close to frame or suspension?

This noise, it is engine related right? Meaning, it makes the noise based on engine load or RPM, not based on road speed or what gear you're in.

 

[Stoffregen Motorsports]

Back to the motor mounts. Visually, they can appear normal, but if you pry on them with a pry bar, sometimes they can show to be broken. Same goes for the trans mount.

 

I just re-read your opening statements and one question came to mind. Did the engine ping or make noise during hard acceleration before the noise appeared? Pining can create enough force to crack a piston. Not at the top, but along the areas that hold the rings. This is what you call a broken ring land and this can make the noise you describe.

 

A loose wrist pin can also make this noise, but usually goes away after the engine warms up, and the pistons expand a bit.

Edited January 5, 2023 by Stoffregen Motorsports

[paradime]

2 hours ago, raythomas said:

At this point I'm not ruling out anything because I have yet to pinpoint anything down. I was sure hoping it was the clutch. It's not a fast noise its more slow and methodical if that makes any sense. What is still got me stumped is why the engine sounds so good at idle and racing it up in neutral, I can't stress enough how well it runs and sounds. Its only when its loaded it down. And I thought I mentioned it but may haven't, when it starts the sound you can increase throttle or load the engine harder and the noise will almost completely go away.

Thx
Ray

If it's only at specific RPM and throttle position, that sounds more like a harmonic vibration of some sort. Stoffregen's point is that under partial load the engine may tilt a bit on the rubber engine mounts that are worn. It's possible what you're hearing is some bit of metal contact at just the right combo of stressors. This may have been asked already, but do you have any oil leaks from the front or rear seals?

[raythomas]

Let me see If I can answer all this:

No, I didn't buy the truck new, It's been in the family since 1990,  I got it 2nd hand. My father-in-law gave it to me after he got a newer truck.

There is only a little oil leaking from the valve cover gasket that needs replacing, no oil coming from front or rear main seals.

As far as changing anything before this happened, that's a no. Other than usual oil changes and greasing nothing out of the ordinary.

And also, no nothing "major" happened as far as the way it was driven or wrecked or anything else that would differ from my normal driving.

The noise first started just slightly and grew over time. At first it sounded like pinging coming from bad gas.

I put in higher octane gas with octane booster and that changed nothing. Also, at first the noise only seemed to happen if the truck was lugging or loaded like going up a hill in high gear. You could downshift or increase throttle and the noise would go away. It did not "PING" under hard acceleration. Over time the noise grew, or got louder. The last time I drove it down the road it would make the noise on flat level ground if you lugged the motor in any way. And just like before, you downshift or increase throttle and the noise would all but stop. Its a manual 5 speed so it makes the noise in gear and pulling. I can clutch the truck and the noise will stop. At this point I can rev the engine and its just as smooth and quiet as can be. There is no part of the engine or trans or exhaust rubbing or touching any part of the body or frame. I have double checked all that with as many times as I've been around and under this crazy thing. I'm triple sure it's not the exhaust, I have beat, pulled and banged on every inch of it from header to tailpipe. That's why I was thinking it was something in the clutch or transmission maybe.
The truck doesn't "burn" or use any oil between changes. And it doesn't smoke any.

I'm hard pressed to think that a bolt has worked loose now, given all the years of trouble free service its had so far.

I did not know the motor mounts could look good but be bad. Never heard that. These look fine just looking at them. I will try to pry on them with a crowbar or something tomorrow night and see what happens. That being said, I did think maybe the cooling fan was rubbing the shroud or radiator. But I've poured all over that thing and can find no spot where rubbing or hitting might be happening. No scratches, scored marks, nothing.

From my best judgement from listening while driving and laying under the truck and looking under the hood. The sound seems to be coming from the rear of the engine. I could "feel" the tapping, ie noise in the bellhousing is the whole reason I took out the transmission to check the clutch.

UPDATE: I just figured out I can now upload files to this forum. I took a 30+ second clip from a video and extracted just the audio. I had mounted a gopro under the hood to try and catch some sound. There is some fan noise but if you listen you can distinctly hear the ping or clatter as the engine is run through the gears from a dead stop.

Hope this helps. If you have more questions, please ask. I don't mind trying to answer them best I can.

Thx

Ray

 

 

Edited January 5, 2023 by raythomas
added .mp3 file

[raythomas]

Made another sound file. This one is from underneath the truck beside the transmission on the right side, opposite of the exhaust. The other sound file above was with the camera mounted under the hood beside the exhaust side of the engine.

Thx

Ray

Edited January 5, 2023 by raythomas

[thisismatt]

Is this while driving? Wonder if you have a bearing that partially let go in the transmission and a shaft is bouncing around a bit, but will "take a set" when loaded down.

 

You said the noise goes away if you disengage the clutch. Does the noise occur if you leave the e-brake engaged and load the engine down with the clutch, or only when you get moving?

[paradime]

Also, can you feel the knock through the stick shift while it's happening? 

[raythomas]

6 hours ago, thisismatt said:

Is this while driving? Wonder if you have a bearing that partially let go in the transmission and a shaft is bouncing around a bit, but will "take a set" when loaded down.

 

You said the noise goes away if you disengage the clutch. Does the noise occur if you leave the e-brake engaged and load the engine down with the clutch, or only when you get moving?

Yes, we tried that by using the E-brake a few weeks ago. and yes it makes the racket sitting still with the E=brake applied and trying to take off. that's how i was able to feel the bell housing and I could "feel" the knocking through the side of the bell housing. That's what led me down the road to removing the transmission to check the clutch.

Thx

Ray

[raythomas]

5 hours ago, paradime said:

Also, can you feel the knock through the stick shift while it's happening? 

No sir, Can't feel a thing through the shifter. Only "hear" the sound from inside the cab.

Could maybe excess play in the pilot bushing cause this?Reason I ask is its the only thing I can't really pull out and inspect. Its still in the end of the crankshaft. All I can do is basically look at it. Don't know if I could get a set of dial calipers in there to measure ID. I'll upload pics of the clutch I took out. It looks amazing for the miles on it. And actually I should say "years" on it instead of miles. My father-in-law didn't drive this truck a lot. It was his backup work truck in case something happened to his other truck.

 

Thx

Ray

Edited January 5, 2023 by raythomas