L24 Nasty engine noise. What is this? (video attached)

[Zed Head]

I have a minor exhaust leak on my engine but it seals up and goes away once the engine warms up. It might even be a crack, I won't know until next time I take things apart. But it sounds pretty bad when the engine is cold.

You might let the engine run for a while, and listen to see if things get worse or better as it warms up. Also, if you hold your hand close to the manifold-head pipe connection you might be able to feel the pulse of the exhaust leak, if it's there. And, if you have the old manifold gasket take a look to see if it was leaking. If ti wasn't and the noise is the same as before you can discount a leak at the head. If ti was leaking before then it should be quieter now if the leak is fixed.

[Tomzern]

Silly question, but are you using a metric feeler gauge.?

Yes, I am using a metric feeler gauge and the metric specs from the FSM

[Tomzern]

Does the noise change when you push on the clutch pedal?

Mark in Portland

I have not tried that yet, but when I listen closely to the engine it really sounds like it is coming from somewhere in or around the head. I will try it though, but I have the wrong type of clutch slave cylinder for my clutch fork so I have to find a solution..

Actually I have a nice stethoscope intended for use on engines, so I will try to locate the sound more precisely later today

I have a minor exhaust leak on my engine but it seals up and goes away once the engine warms up. It might even be a crack, I won't know until next time I take things apart. But it sounds pretty bad when the engine is cold.

You might let the engine run for a while, and listen to see if things get worse or better as it warms up. Also, if you hold your hand close to the manifold-head pipe connection you might be able to feel the pulse of the exhaust leak, if it's there. And, if you have the old manifold gasket take a look to see if it was leaking. If ti wasn't and the noise is the same as before you can discount a leak at the head. If ti was leaking before then it should be quieter now if the leak is fixed.

OK, I have just let it run for about 5 minutes in total because I have not filled the cooling system yet. The old gasket is gone unfortunately, but I can check for signs of a leak on the old head!

I'll get back to you later today

Thanks

[z boy mn]

I'm not sure if this helps or not, but I had that exact noise (from what I heard on the video) last summer. I have antivibration mounts on my triple webers, and during a backfire through the carbs, one of the o-rings was blown partially out, creating an intake manifold leak in cylinder 4. It was that same chugging with each stroke of the motor. I listened and listened for days and when I had my head stuck in there I finally spotted the rubber o-ring. It sounded very mechanical at first, but once I replaced the o-ring it went away completely. So, my (very amateur) vote is for some kind of in-take or exhaust leak. Good luck!

[tlorber]

I'm in with exhaust group too, especially at idle. You can also sniff around the motor while its running. There should be no exhaust smell up front.

[Tomzern]

I'm in with exhaust group too, especially at idle. You can also sniff around the motor while its running. There should be no exhaust smell up front.

There is no exhaust smell up front, and I can't find any signs of a leak around the manifold gasket.

I also tried pulling the plug wires one by one, but none of them got the noise away. If it had been an exhaust leak the sound would have at least changed when I pulled the wire for the cylinder with a leak...

I removed the valve cover and took of the oil spray bar. It actually had warped quite a bit but did not hit any of the lobes. I changed it with the bar from the other engine, which was nice and straight. Before i mounted it back again, I tested it with compressed air to make sure all the holes were open.

Tried to start and had it running for a little while, but no change =/

Then I used the stethoscope to search for the noise and found out that it most likely comes from intake valve no. 5 or 6. I can hear a loud "dinging" sound in the stethoscope when in that area.

Can it be a worn out valveseat or valveguide causing this?

[z boy mn]

I'm definitely new at diagnosing problems, but I listened to the video a few more times and it really sounds exactly like the sound I had last summer. The leak for me was right between the carb and the intake manifold...the sound came for the piston sucking in air on the intake stroke and had a very mechanical tenor to it...but it was just distinct puffs of air. I didn't have any smells anywhere...probably because it was on the intake side. I did notice that my idle dropped some, but that was probably because that cylinder was running a little lean. I looked for the video I made of my sound so I could post it and you could hear how similar the sounds are, but I must have deleted it. :-(

[Costjo]

Here is a video of my header/intake gasket leak. I replaced gasket and all is good now no tapping sound noise. I will try and post update video with it replaced when I get a chance.

http://www.youtube.com/watch?v=4OmdCuJLYtc&feature=youtu.be

[Costjo]

Here is video with new header/intake gasket cold start choke on

http://youtu.be/vwzoQit6C3s

[Tomzern]

I agree that the sound is similar, but I don't think it is exactly the same sound. I found a video of another Z that has the exact same sound as mine:

Is it possible that a leak can sound completely mechanical even through a stethoscope?!

[Jeff G 78]

Pull the diaphragm and metal rod off the stethoscope and use just the hose to listen to the sounds. Many times, leaks can be detected better that way. Any airflow around the open hose will be magnified and the location can be pinpointed.

[Tomzern]

Thanks Jeff! I forgot to try it today, but I will do it during the weekend!

Today I noticed something. When I coldstarted the engine, it ran smoothly with almost no noise at all for the first few minutes, and then as it heated up the noise got louder and louder.

I don't think it was like this before, but I am not sure.

Can this mean that there is one valve that needs adjustment when engine is hot?