73 240z engine rattle

[speedpenguin]

I have 2 videos of the noise, you can see the shorter one here:

I think you can see the other by looking at my videos (I only have Internet on my phone at the moment)

I bought this car 2 weeks ago, immediatly did an oil & filter change, and I replaced the plugs and wires with NGK ones. I didn't notice the engine rattle until after the oil change, but I then noticed it was present in a video I took the night I bought the car. I adjusted the valve lash 3 days ago while the engine was cold, most were close to the specs, but only 3 valves didn't need adjustment. I also did a cold engine compression test and all cylinders were between 145 and 152 psi. The front three spark plugs look pretty different from the last 3, I'm guessing the carbs are out of sync, they are the stock flat tops. The 4th plug is fouled wet and black, and I'm sure it's not firing because the engine doesn't bog when I remove the plug wire, but it is getting spark.

The rattle seems to be coming either from inside the engine, or around where the intake and exhaust manifolds are. It doesn't quite sound like the noise is coming from the valve cover, but I wouldn't rule it out. I haven't gotten a stethoscope or. Timing light yet, but I plan to tomorrow. I have Read several posts pointing to a worn timing chain tensioner, but wouldn't that sound come fronthr front of the engine rather than all the way down it? I can take more videos or pictures, just let me know.

Thank you,

Matt

[Pomorza]

I have 2 videos of the noise, you can see the shorter one here:

I think you can see the other by looking at my videos (I only have Internet on my phone at the moment)

I bought this car 2 weeks ago, immediatly did an oil & filter change, and I replaced the plugs and wires with NGK ones. I didn't notice the engine rattle until after the oil change, but I then noticed it was present in a video I took the night I bought the car. I adjusted the valve lash 3 days ago while the engine was cold, most were close to the specs, but only 3 valves didn't need adjustment. I also did a cold engine compression test and all cylinders were between 145 and 152 psi. The front three spark plugs look pretty different from the last 3, I'm guessing the carbs are out of sync, they are the stock flat tops. The 4th plug is fouled wet and black, and I'm sure it's not firing because the engine doesn't bog when I remove the plug wire, but it is getting spark.

The rattle seems to be coming either from inside the engine, or around where the intake and exhaust manifolds are. It doesn't quite sound like the noise is coming from the valve cover, but I wouldn't rule it out. I haven't gotten a stethoscope or. Timing light yet, but I plan to tomorrow. I have Read several posts pointing to a worn timing chain tensioner, but wouldn't that sound come fronthr front of the engine rather than all the way down it? I can take more videos or pictures, just let me know.

Thank you,

Matt

First off. What oil did you use and what oil was in there prior to the said oil change? How much did you put in? How does the sound act? Is it present at all RPM ranges, does it change pitch, noise level, area where it seems to be coming from?

To answer a number of your questions. Sounds tend to travel in metal objects so don't trust your ears. My advise would be to either pull the cover or the chain inspection cover and have a look at the chain. Pull it and see how much of stretch you have. If you have a remote starter hook it up and slowly crank the motor with the distributor off. See what the chain does where does it go, how does it act those kinds of things. Also look at what your valves do.

Now I'm not in any way a trained mechanic (I'm 22 and owned two cars in my life) but to me that sounds like an exhaust leak or air leak of sorts. I can't really tell you exactly as I've never owned a carbed car. Have a look at the exhaust and intake manifolds and see if there isn't any leaking air. Check the vac lines. The one thing I've learned on Z's is to go step by step and rule things out as you go. Just because the parts "looks" good doesn't actually mean it is.

Hope that helps and let me know what you find.

Jan

Edited March 19, 2010 by Pomorza

[JohnnyO]

Could it be the sound of the dead cylinder not firing?

[speedpenguin]

AH yes, I forgot to mention that the noise increases speed when I rev the engine. Someone asked if the rattle seemed to be at engine speed or half engin speed to help narrow down the source, that is why I am going to get the timing light. The noise increase in volume as I rev the engine, but seemingly because it's happenging faster. Apparent location of the sound doesn't change.

Although the rattling sound sounds like a physical object contacting another, I won't rule out the possibilty of the manifolds leaking air/exhaust.

[Pomorza]

AH yes, I forgot to mention that the noise increases speed when I rev the engine. Someone asked if the rattle seemed to be at engine speed or half engine speed to help narrow down the source, that is why I am going to get the timing light. The noise increase in volume as I rev the engine, but seemingly because it's happening faster. Apparent location of the sound doesn't change.

Although the rattling sound sounds like a physical object contacting another, I won't rule out the possibilty of the manifolds leaking air/exhaust.

Thanks for the info.

I would first determine the frequency of the sound (how often if occurs). Knowing this will give you a bit more information to work wit (duh) but it can also let you know what part of the motor is occurs on.

What engine RPM is that video at? It sounds to me a bit high 1500 or so?

Jan

[speedpenguin]

It is just warming up, so it is higher, but even after warming up, the Sound is present.

Is it safe to drive? At the least to a mechanic friend's place about 10 miles away? What are possible causes that would make it unsafe (to the engine) to drive?

[Pomorza]

It is just warming up, so it is higher, but even after warming up, the Sound is present.

Is it safe to drive? At the least to a mechanic friend's place about 10 miles away? What are possible causes that would make it unsafe (to the engine) to drive?

The only advise I'm going to give you is, if YOU don't feel safe driving your car for any reason don't. I can't tell you that it is safe or not. I'm not there and I don't know your driving style or the condition of the car. There are literally hundreds of things that could go wrong with a motor and all of them in one way or another can be unsafe. (A broken fan belt could in theory lead to a crash)

Hope that helps

Jan

[speedpenguin]

Thank you, I more meant safe for the engine. Like if the sound could be a piston hitting a valve, and that the car shouldn't be driven. What other cases that could be making a rattling noise could be severely detrimental to the engine.

Thank you.

[Pomorza]

There's a multitude of things that can make rattling noises in an engine. I know that's not the answer you're looking for but I can't really get really into detail. Remember that an engine is made out of hundreds of parts so it rather hard to answer your questions. Here's a try.

Hypothetically speaking let say that your chain is slapping the cover. This would indicate that the chain is stretched enough to slap around. Stretching can lead to the cam and crank to be off time a bit. If the chain is stretched enough it could in theory skip a tooth or more on the cam leading to issues. In the most extreme case it can snap completely and cause the piston to meet the valves.

After rereading your first post you said that "The 4th plug is fouled wet and black, and I'm sure it's not firing because the engine doesn't bog when I remove the plug wire, but it is getting spark." Now for what I remember if you remove the plug wire from a plug you should hear a difference in engine RPM as it is running on one less piston. So here's my concern. If the engine is running on 5 cylinders it is possible the noise you are hearing is a dead cylinder as suggested below by Johnny'O. This could be cause by either a weak spark or a fuel issue (too much or not enough fuel).

Hope that helps mate.

Jan