Diagnosing Valve Train Noise

[Sean240Z]

Desmond - In my case, I also thought I had a problem in the last two cylinders nearest the firewall. The hole in my header was at the very rear of the engine compartment and I could hear it distinctly on both sides of the car. I guess the sound bounced off the tranmission tunnel to the passenger side.

Good luck!

[Mixelplix]

Attached is the YouTube video.

260z valve rap: 260z valve rap - YouTube

[Jeff G 78]

Hmmm, yeah that is pretty loud. It sounds more mechanical than exhaust, but it's still possible it's an exhaust leak.

The gasket could be blown out and still leaking even though the nuts are tight. Hold a 2 foot long rubber hose to your ear and move the other end around the manifold. You will be able to hear the air rush if the manifold is leaking.

Just throwing ideas out... What about a dead valve spring??? It's quiet at idle, but gets louder at higher RPM. If a spring is weak it could be floating the valve.

[grannyknot]

Wow, that's jack hammer. Just throwing out ideas, take the tape off the header and see if there is a crack in the pipe.

It might be time to pull the head and have a look at things.

[Mark Maras]

It sounds like valve train to me. I'd pull the valve cover, start it up and use the prev. mentioned hose to find the source of the sound. I've used the hose for years. AmaZing tool. Works well for checking the carb. balance too.

[Mixelplix]

I assume I'd be able to feel a dead valve spring by applying pressure to them? Should it be obvious?

In my years if screwing with cars I've only ever seen broken valve springs... Do they have the ability yo just loose their tension?

[Mixelplix]

It sounds like valve train to me. I'd pull the valve cover, start it up and use the prev. mentioned hose to find the source of the sound. I've used the hose for years. AmaZing tool. Works well for checking the carb. balance too.

I'll do that tomorrow.

[Mixelplix]

As a follow up to this conversation (and hopefully help to anyone with a similar problem).

I ordered and replaced the exhaust manifold, and it did not correct the problem.

Grasping at straws, I decided to order two rocker arms, and lash pads. I removed and inspected the rockers and lash pads on cylinders 4, 5, and 6 and discovered that the lash pads on cylinder 6 were worn more than the others. I replaced the rockers and lash pads on cyl 6, and it's quiet as a mouse now.

I suspect my oiling bar was not properly lubricating cyl 6. I also suspect my cam has wear on cyl 6, but I'm going to leave it for the time being.

[madkaw]

There's a thread on Hybridz about rockers not being refinished or made square and they don't ride the lash pad square- which causes noise.

[FastWoman]

Mixel, that racket sounds like an exhaust leak at the exhaust manifold gasket. It is EXACTLY the same sort of tapping sound (yes, that sounds like knocking/rattling metal parts) as I had on a 318 in our boat. The exhaust risers were fussy to bolt down with the stainless studs, and they would develop leaks every 2 years or so, so I'm very familiar with this noise.

What I learned with that boat is that leaking exhaust gasses erode gaskets and even metal, so your having tightened the #6 bolts would likely not have fixed the leak. You've got to pull the intake/exhaust manifolds and replace the gasket.

Anyway, it's an exhaust leak. I'd bet money on it.

[Lazeum]

That's the thread we're talking about on hbz

Here are the changes we've made to quiet things down.

The rockers were not sitting straight on top of the lash pads. This solution could work obviously if you don't have stock valvetrain components.

Before:

During regrind with a dremel tool:

After polishing operation, still done with dremel tool:

Valve train is now quiet on my engine. Some small lash pad adjustments had to be made after the work. After 1000mi. every is now steady.

[Zdisease]

On 4/13/2014 at 2:40 PM, Mixelplix said:

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

I went all over the motor with a 1/2 hose pressed to my ear.  Narrowed noise down to exhaust port on header.