720 Z24 ticking sound a few minutes after startup

[dimitrisprophet]

Hello all,

 

I have owned this 720 for a little over a year. When I first purchased, it was neglected and in a non-running condition. Once I got it running again, I noticed that the stock carb was trash, and the exhaust was rusted completely through at the lowest section of the header, so it was obnoxiously loud. A 32/36 Weber and a custom exhaust with a Mangaflow later, and things are much more manageable, although now I can actually hear the engine.

 

I am hearing a persistent ticking sound coming from the head (maybe towards the back), that is based on RPM. This is not a knocking sound, and the only thing I could compare it to would be hydraulic lifter tick, which is not possible for a Z24. Upon start up (with or without choke), there is no tick, but after 2 minutes the ticking will slowly develop and get louder until resting at a certain volume until the engine is turned off. While driving, the ticking is honestly not loud enough to be concerning, but definitely loud enough to be audible, and you can hear it better while in lower gears.

 

I have adjusted the valve lash while the engine was hot, this did not impact the ticking at all. I changed the oil, and that seemed to make the ticking a little less raspy, but it's still there. I have not done a compression test yet to check for a head gasket leak, but the oil and water are not mixing. I know the Z24 is notorious for blowing the gasket in between the 3rd and 4th cylinder, so could that cause a ticking sound like I'm describing? The ticking has zero impact on how the truck accelerates, and I do not feel a loss of compression or missing while driving.

 

What else could this possibly be? The timing chain looks fine, and does not have excess play, and I have not replaced the chain, so to my knowledge the tensioner is still locked in place. I did notice that there may be an exhaust leak coming from the exhaust manifold or gasket, could that cause what I'm describing? The sound is getting to be annoying, and I'm starting to get concerned that there is a deeper issue I need to address, but I don't want to pull the head without reason.

 

Anyways, I appreciate all of your wisdom in advance, here is a video I took where you can hear the ticking: 

 

[datzenmike]

A crack in the manifold or the down pipe that widens as the metal expands from the heat. Possibly the gasket between the manifold and the down pipe.

 

Going out on a limb here... but it could be a leak in the connecting pipe between the exhaust manifold and the EGR valve on the intake. This pipe goes around behind the head. At idle there should be no flow of exhaust to the EGR so the pipe should be cold. Try running your fingers along and around the EGR tube and see if you can find a leak. If hot try a wet rag and hold it on the pipe and move it along the length. If it gets quiet you have your leak.

[dimitrisprophet]

Thank you king rat 🙂

 

As always, you're awesome. I'll check the EGR crossover pipe for a leak. Based on the hours and hours of time you've spent listening to running Z24s, how does the one in the video sounds to you?

[datzenmike]

Sounds like a valve lash. Factory says 0.012" on both when hot. Warm the engine for at least 15 minutes first.

 

What I do to find the loud one is push down on the valve adjustment end of the rocker arm with a wooden hammer handle or something similar while idling. This removes the valve clearance and transfers it to the cam lobe. The lobe meets the rocker much more gently than the rocker suddenly hitting the valve top. It's jumping around so hang on and push down hard enough. If the tick goes away but returns when you let go that's the one. They all make some clatter but the loudest one becomes obvious when it goes quiet. You can probably try 0.011" or 0.010" clearance.

[DwayneOxford]

3 hours ago, datzenmike said:

Sounds like a valve lash. Factory says 0.012" on both when hot. Warm the engine for at least 15 minutes first.

 

What I do to find the loud one is push down on the valve adjustment end of the rocker arm with a wooden hammer handle or something similar while idling. This removes the valve clearance and transfers it to the cam lobe. The lobe meets the rocker much more gently than the rocker suddenly hitting the valve top. It's jumping around so hang on and push down hard enough. If the tick goes away but returns when you let go that's the one. They all make some clatter but the loudest one becomes obvious when it goes quiet. You can probably try 0.011" or 0.010" clearance.

I use a short piece of garden hose to listen through. You can pinpoint most any noise.

[dimitrisprophet]

Update: setting the valve lash to .010 hot made a large difference. Still a slight tick, but it is miles better than what it was before.

 

Thanks!!

[datzenmike]

This is a little tighter than what the factory recommends so check this clearance regularly.