Diagnosing Valve Train Noise

[Mixelplix]

While slowly reconditioning my early 74 260z, I decided to do a valve lash adjustment.

After I was done I was able to notice a significant valve train noise somewhere around cylinder 5 or 6. The noise is sharp and follows the RPM. It's the same hot or cold. With a stethoscope it appears to be more loud on the passenger side. It makes the noise regardless if the spark plug wire is plugged in or not.

I've triple checked the lash both hot and cold. And they're extremely close to perfect at .008 intake / .010 (cold) and .10 intake / .012 (hot).

My oiling bar is recently cleaned and silver soldered by me, and I visually verified that it is working (what a mess).

I believe it did make the noise prior to the lash adjustment, but it's definitely louder now.

The cam looks fine, the wipe pattern between the cam and rocker seems fine, the springs and retainers are all there and not obviously broken.

I'm not a novice mechanic, but nearly all of my experience is from much newer cars.

What procedure should I follow to figure out what the problem is exactly?

Desmond

[Mixelplix]

Just a little more info: It runs and idles excellent. The compression is terrific and equal across all six cylinders.

I do lose a little oil from valve stem seals (slightly at first start up, and under heavy throttle).

[Zed Head]

I have a noise from my #1 cylinder. It's been there for about 20,000 miles, no change. I also adjusted lash, and double-checked. And have excellent compression numbers, a smooth idle and otherwise great performance. I've kind of come to the conclusion that some rocker arms and their associated parts just move differently than others and are noisier. Or I have a loose part somewhere that is just noisy, but okay. I decided that noise is not a problem.

I've also noticed that I hear odd noises more after I work on the engine.

[grannyknot]

I know the 2 aren't related but when there is a crack in the seal of the exhaust manifold or header flange it is easy to hear the exhaust valve slap against the valve seat. #1 and #6 are the first break a stud or have the nut back off.

Chris

[Mixelplix]

On your suggestion I retightened the exhaust studs.

Number 6 was loose, but it didn't effect the noise.

Zed Head, I know how you feel. My Land Cruiser is the same way. However, this noise is so loud that it's literally a spectacle. I had one of my non mechanic friends say 'There's something broken in your motor'.

[Diseazd]

One at a time, after you adjust each valve while the lobe is up, try to rock the rocker back and forth......if you find one that feels loose, take a little out of the adjustment. You can usually feel the play in a noisy rocker. Some Z engines just have more valve train noise than others.....but you can usually isolate a loud rocker by doing this procedure. IMO

[Zed Head]

Different scene then. Before and after seems like where you're at. If it didn't make the noise before, but it does now, then you must have altered something when you were adjusting lash. Did you knock one of the anti-rattle (mouse-trap) springs off or bend it? Easy to do since they're right next to the locknuts. Their purpose is to keep the rocker arm tight on the pivot. So it doesn't make noise.

[Mixelplix]

One at a time, after you adjust each valve while the lobe is up, try to rock the rocker back and forth......if you find one that feels loose, take a little out of the adjustment. You can usually feel the play in a noisy rocker. Some Z engines just have more valve train noise than others.....but you can usually isolate a loud rocker by doing this procedure. IMO

When you say rock the rocker, do you mean front to rear, or drivers side to passenger side?

Both my 5 & 6 exhaust rockers seem to move a tiny bit more in the front to rear direction than the other ten. And I mean such a tiny amount that it might be placebo effect.

And do you mean loosen the lash when you say 'take some out'?

Different scene then. Before and after seems like where you're at. If it didn't make the noise before, but it does now, then you must have altered something when you were adjusting lash. Did you knock one of the anti-rattle (mouse-trap) springs off or bend it? Easy to do since they're right next to the locknuts. Their purpose is to keep the rocker arm tight on the pivot. So it doesn't make noise.

My mouse trap springs are ok. It did make the noise before... but it's more pronounced now (both because the valvetrain is overall less noisy, and the rapping noise became louder.

[Diseazd]

Shake em side to side.......if one or two feel loser than others, tighten the gap from .010 to .008 inches. Sometimes when you torque the lock nuts down, you'll change the lash clearance on that final lock down. Your noise is almost certainly in the valve train....loose is noisy...right?

Edited April 14, 2014 by Diseazd

[Mixelplix]

As an update, I got a chance to jump on this a little last night.

I adjusted the valves in question both much tighter, and way more loose and the noise still persists.

I'm convinced it's valvetrain noise - but I'm at a loss as to why it's so much noisier all of a sudden.

I'm going to try to take a video and post it tonight.

[Sean240Z]

I was chasing a similar noise over the last month, trying to get my 240Z on the road (L28, SUs, Schneider cam with springs and lash pads, MSA 6-1 header).

I inspected the valve train (including camshaft, rocker arms, lash pads, springs) and adjusted valve lash. Everything looked good. Started the engine and the noise was still there.

I next checked all the manifold nuts and they all seemed tight. I inspected the intake and header (MSA 6-1 coated) and could not notice any obvious leaks. I installed the header in ~2005 and noticed some discolouration of the coating where two pipes come close together. Though when I held my hand nearby, I could not feel or see any obvious leaks.

Finally, I removed the header to properly inspect it. I clamped a piece of wood over the manifold section of the header, covered it in soapy water and inserted a funnel and my wife's hairdryer in the exhaust end. Bubbles!! Turns out that the header has a leak where the 6 pipes come together, on the inner side, so the hole was not visable as the pipes are very close together. New MSA 6-1 header will be here Thursday, so now I'm cleaning up and painting the driver side of the engine compartment and polising my intake.

Not sure if you have a manifold or header, but take a really close look for a leak at the manifold (could be warped) or a hole or crack in one of the pipes. If I had not fould the leak in my header, the next step would have been to pull the head, thinking that I must have damaged a valve.

NOTE: I've had my Z since '91 and replaced a warped exhaust manifold with an uncoated header. I made the mistake of wrapping the header and it only lasted four years before it developed a hole under the wrap (held moisture against the pipes and increased the heat, increasing rate of deterioration). This last coated header has done well, lasting nine years.

As an aside, now that I have the manifolds off, I can really see gunk / carbon build-up on the valves. Once it's back together, I plan to complete a careful water mist decarbonization through the SUs (been researching this since I noticed the state of my valves). Interestingly the rear valves are cleaner than the front valves. I have a 280Z vented hood and suspect that water dripping through the driver's side vent, has been dripping into the K&N filter on the rear SU and helped to decarbonize those valves.

Good luck.

[Mixelplix]

Thanks for the heads up Sean!

While I'm running the OEM cast manifold, I'll definitely take more time to inspect the head to manifold bolts for tightness.

I couldn't see any logical reason why my cast manifold would warp overnight, so I think that's ruled out. From the manifold down is headder wrapped however, so I'll take a close look at that too.