Mystery ticking sound

[MaddieCycle]

Hello. I have a new mystery tick that began after I did all of the following repairs/maintenance at the same time:

 

Adjust valves
Retorque head bolts

Replaced all 3 drive belts, AC belt was very loose and squealing

 

The tick is mostly audible at idle and is present cold and warm. It for the most part gets lost in the engine sound at higher revs. Present with clutch in or out.  Engine is running great.

 

Does not appear to be coming from the valves.  Sounds like it is coming from the bottom. At first I was thinking AC compressor pulley bearing, since I had recently torqued that up.  But, I have to consider more sinister bottom end issues like rod knock or a main bearing.  It just does not sound as awful as I would expect a bottom end problem to sound.

 

I saw in a couple of forums people posted similar issues and in 2 cases it was a blown head gasket.  I have noticed quite a bit of condensation in the exhaust lately and am worried I may have blown the gasket.

 

Video of the sound is here: 

 

[datzenmike]

Unless that engine is cold that idle is way too high. Set at 700.

 

It's never 'rod tap' it's always 'rod knock' they never tap. When a rod bearing has too much clearance it's like hitting the block with a 6 pound hammer. It's a muffled knock. Low frequency. Rod knock is louder under load and quieter at steady speeds. Get the idle down and give a quick rev with the gas pedal. 

 

If this started after the valve adjustment, I would say one was mistakenly set wrong and that is very easily done. I only set on a thoroughly hot engine as this is what it runs at. Set to TDC on #1 cylinder compression stroke. Both #1 valves should be closed. Set intake and exhaust on #1, intake on #2 and exhaust on #3. Turn engine ONE turn and up to the TDC on the timing mark. Set exhaust on #2, intake on #3 and both valves on #4. done. This is fast and accurate and beats bumping the engine 50 times and the engine cooling off.

 

If still making the sound.... when was the last oil change? I've had 720 owner swear that their Z series engines get a tapping sound about the time it needs the oil changed. If you have changed the oil recently then don't worry about it. I recommend an oil with the proper ZDDP level in it like Shell (diesel) Rotella T4 10w30 is fine. I drive only in the summer and use 15w40. All gasoline oils have a severely reduced ZDDP content from what was available 35 years ago. Always change the filter. Anything but Fram, anything. NAPA gold or WIX are good.

 

It's winter and all exhaust is steamy and damp and readily condenses on the cold exhaust pipes. If you were loosing coolant your rad would constantly need topping up. Does it?

 

 

[MaddieCycle]

Thanks. Yeah I will pull the valve cover and check again.  I only adjusted 3 of the 8 valves and all were on the 2nd TDC cycle.  I can't hand-advance the engine on my truck because the AC and power steering components prevent access to the crank bolt, so I am stuck using the starter method.  Maybe I will jump the solenoid under the hood so I don't have to keep running back and forth.

 

It is due for an oil change by the calendar, only have put 250 miles on it since last December when I did the last change.  So I don't think that is the issue.  I did find it was down almost a quart of oil (I checked it when I heard the sound). I've used the truck for 1-5 mile trips only for the last year as I've been fixing it up, and many many start-stop cycles in the driveway. Assuming all of that oil blew by the cold rings.  All cylinders have good compression and the truck pulls like a mule.

 

This is a California emissions truck that passes smog no problem.  I have replaced all of the vacuum lines and full tune up.  I can't get it to idle at less than 1000, the idle just breaks up and it dies.  For my purposes, it works fine.  I don't mind the high idle.  Definitely hearing less, not more, of this noise at higher revs and under load, which is reassuring.  I'll bet it is a bad belt idler or pulley, or something else that won't cause problems for thousands of miles.

 

 

[datzenmike]

There is a solenoid at the rear passenger side of the carburetor with a Red wire to it. When the ignition is on, the red wire energies the solenoid allowing gas into the idle circuit. Without it you can't adjust the idle. It's called the 'idle cut' or 'anti dieseling' solenoid and cuts gas off with the ignition to prevent run on. You may have noticed that the engine tends to keep running when the ignition is turned off?

 

Seems excessive to be down a qt. in only 250 miles. Fill it up and see if it quiets. And check the valve lash.

[NC85ST]

Could that be a cracked exhaust manifold? Common problem on these. Crank it up cold and see if you feel the exhaust anywhere, especially the backside of the manifold (between the block and manifold). Just a thought.

[datzenmike]

Reach around the back side of the manifold quickly and feel for exhaust pumping out. On a cold manifold you will have 5-8 seconds to do this. It will also be louder under load.

 

Maybe the exhaust manifold gasket is blown. Are nuts tight?

[MaddieCycle]

Yes at first I thought it was an exhaust sound.  I need to pull the valve cover no matter what since this started after a valve adjustment. If that checks out I'll fish around the manifold.  I am going to get a mechanic's stethoscope too and see what that reveals.

[MaddieCycle]

Well I pulled the valve cover and 2 valves (#2 intake and #3 exhaust) were at 0.016 rather than factory 0.014. I don't know how I screwed this up but I quadruple checked before putting the cover back on this time. Also, one spark plug on the exhaust side had worked loose.  I took care of those issues and now the noise went away.  I think it was just a rough running engine with reverberations through the exhaust pipe and possibly #2 was misfiring since the plug was loose.  

 

For what it's worth, with a spark plug removed from each cylinder, it was easy to turn the engine with the cam bolt.  I can't reach the crank bolt due to A/C equipment in the way.