Thread: 390 noise

Tweet

I have a 390 with a recent rebuild - less than 500 miles. Immediately after first oil change it started making a ticking noise . Sounded like a bad exhaust lifter at #7 cylinder. Replaced both lifters for #7 but noise is still there. Loud at idle but gets more quiet as RPMs go up. When I pull the #7 plug wire when the engine is running the noise stops. I understand it might be a rod bearing but the noise is a metalic tick, not a lower end knock. Any idea's before I pull it apart?

Head gasket maybe? Or possible exaust header/manifold gasket or seal. I've had these and they sound like a tick. These would be the most obvious. Just a thought......G.

Thanx for the reply. It's not an exhaust manifold leak. The noise is coming from the valley area - below the intake. Heads have not been re-torqued so I'll give that a try first.

Silly question but if you have hyd lifters did you soak or compress them in oil before installing? How did the lifters look that you replaced? I'm assuming everything was new or fresh being it's a rebuild. And last are you using the stock rockers and are they adjustable or not?

All new hydraulic lifters, push rods, valves ,springs etc. I was instructed by the machine shop not to prime the lifters prior to install, only prep with assembly lube. He told me to let the lifters pump themselves up during start up.
The lifters I replaced still appear new and hold pressure very good.

Stock cast iron exhaust manifolds with no leaks manifold to block. Slight leak on passenger side around doughnut at manifold to pipe. Stock rocker assemblies with new shafts and re-conditioned rocker arms.

Are the rocker arms the adjustable kind or non adjustable? Most stock hyd cam had the non adjustable but some like to upgrade to tweek a bit if needed. Does it sound like a sticking valve that kind of tick or deeper? And does it sound solid or tinny? G.

The fact that it stops when you disconnect the spark plug wire really makes me lean towards an exhaust leak. Even a bad rod bearing would keep making noise after you disconnected the plug because there is still compression and vacuum creating loads on the bearing. Valves, lifters and such are all still moving up and down even if the cylinder isn't firing, so that leads me away from lifters and such. However, on any of my engines, when I pull a plug they start running rough and making all kinds of noises. These noises can drown out a quiet ticking, so it may still be there and you just can't hear it.

First of all , thanks for all the replies.
Rocker arms are non-adjustable. I'm leaning away from a sticking valve because I ran a vacuum test. Gauge at idle reads 13in/Hg and is fairly steady with only a very minor needle vibration. I'm running a mild Torque Cam and our elevation here is 7000ft, so vacuum is pretty good. This is leading me to believe more toward a bad head gasket but I'm still open for all suggestions. Ticking is more tinny than solid. Sounds like a BIC pen when slapped on your knee, only much louder.

ok this is not neccisarily the problem but i've had it before, try putting a different plug wire on #7 or wait til its dark and run it and watch plug 7, sometimes its the plug or plug wire grounding to the exhaust manifold or head, I've had it happen before and it does make a ticking noise... just a thought

And plug wire number 7 & 8 should be well seperated from each other to prevent induced firing. I'm sure your aware of this but I've had it happen. Sometimes the most obvious things are the culprit. From the sound you describe it does sound like spark or something arcing. Thesals had a good suggestion about running in the dark and looking for a spark. That and the fact when you remove the wire the noise stops. I've had new wires cook being to close to the headers and cause this. The arc sounded like a bic pen being tapped on your knee...Or the head gasket but I'm more swayed towards the spark thing. G.

Hello,
Most the time it never happens, but have you checked the pushrod length on the cylinder (s)? I learned that the FE made a change in the length of it's pushrods in about 1968. The earlier ones are .060" longer.. Also the valves are set at a certain height, by the machinist,for the pushrod length to be correct on installation.
I would compress the lifters on that cylinder, and check the rocker to valve tip. It should be between .100" and .200". This will center the lifter. To make sure that you are correct in adjusting them properly. Turn the engine over till the cylinder you want to check, Exhaust valve just starts to open, check the Intake. Then turn the engine over till the Intake is fully open, and then just starts to close.. Check the Exhaust.. If they are more than .200" the pushrod is short.. If it's under .100" the pushrod is to long.
May not help, but it's good info, Ray
Anybody else out there do it this way? or any other way that's better?!

Had a '68 Mach 1 428 that sounded like that. We rebuilt it twice over 4 years and it still ticked. 80K miles, it never skipped a beat. Never did find that tick!

you have probably already found the noise since your question was posted about a month ago...but if not:

I had the same problem with a 390 and found a bad wrist pin. The higher pitch of the noise fooled me for a while. But the fact that it goes away when you disconnect the plug wire hints at either a bearing and/or wrist pin.

Please let me know what it turned out to be.

I have the same thing. Thought is was many things, but still haven't found it. I broke my engine down to the block to refresh the heads and replace cam/lifter/pushrods/timing chain. Basically a new K kit from Comp along with the heads and new dynomax headers. Hoping that damn tick is gone for good! Still ran like a scalded dog though!