Hello,
First time in this forum.
I have an odd noise coming from the number 1 cylinder of the 360/390 engine of my '75 F250. This truck has had a hard life as a ranch truck and I know the engine was gone through at one time, perhaps in 'auto shop' so I am unsure if it was changed from a 360 which I am almost positive was the original CID. The sound is similar in rhythm as a single lifter noise but does not sound like it at all. As opposed to a TIC or a TAP it sounds more like a (forgive me) THWOC or a THWOC-DOC. Kinda reminds me of an engine knock. The sound does not present much at idle, mostly on acceleration especially when cold but not so much at high speeds. Tends to get quieter when the engine is running at temp. I pulled the valve cover and found that some if the unloaded push rods have a slight bend when I rotate them. I guess my question is could this sound be what a valve coming int contact with a piston sounds like? I know I need to do more research, so this is a preliminary query that I may be on the right track. When I originally got the truck the right exhaust manifold gasket was blown, and I replaced it. That is when I started noticing the noise. It sure does not sound like a leaking exhaust gasket to me, the manifold was not distorted, and I double checked the bolt tightness. Temp and oil pressure are good on a new sender. Any thoughts would be much appreciated!
Thank you, John

 

Most of the time that's either the gasket or a cracked manifold.

If you have bent pushrods they need replaced, seems odd to have multiple ones with a slight bend. pull one out and roll it on glass to be sure. very doubtful you're smacking a piston that would not make much noise but you'd have other symptoms.

 

Thanks 440, will look into both.

 

It sounds like you can replicate the sound in your driveway by revving the engine from under the hood?
If so, what happens when you disconnect that cylinder’s plug wire?
Does the sound change, remain the same, or go away completely?

 

I disconnected/connected each sparkplug wire and the noise is still present.

 

Well, do one more thing to help eliminate extraneous noises being transmitted through the metal. Remove the fan belt(s) just to see, again, if the noise changes or goes away.
The only reason I'm thinking of this is because a knocking sound that was certainly coming from inside a 302 one time, turned out to be something completely different and removing the belts completely eliminated the noise!
I don't know what the problem eventually turned out to be (not my engine) but that sure put the owner's mind at ease!

If the noise is still present, and because it started (or you only just started noticing it) after the exhaust manifold was replaced, I would keep checking there.
Maybe when you first start it up, before the manifold becomes super hot, spray water around all parts of it, even underneath if you can get a hose or sprayer under there, to see if you can find a leak.
It would not be the first time a new manifold install leaked. Gaskets or not...
And speaking of which, did your engine use gaskets or just iron to iron on the exhaust? Many of them did not use gaskets from the factory, but many have put gaskets in upon replacement.
Curious which way yours went.

Paul

 

Could you post a video with good audio quality to help us help you?

 

I ran the engine with the valve cover off, could not see any issues, and I checked each rocker with a sound sensor, the sound does not appear to be coming from the valve train at all.
I could pull the exhaust manifold off, and double check it. Could any other issues with this type of engine be making this kind of noise, like a loose wrist pin or piston slap? I do not think it is a rod knock, oil pressure is good, and it has been noisy for over a year now, figure a rod knock would have ended in catastrophe long ago.

 

I don’t think FE’s typically have an issue with piston slap. Piston slap usually happens on engines with forged pistons. I agree that rod knock would have taken out your block a long time ago if you let it go for that long. Video would help.

 

Paul,
One of the first things I did was to remove the accessory belts and run the engine, no change.
I replaced the right bank gasket because it was blown through with the same type, I used a FelPro aluminum laminate with perforations.
Interestingly, the exposed portions of the gasket seem to have deteriorated more than I would have expected, Is that normal?

-John

 

Viper,
I will try to get a good vid after the motor has cooled, the noise is much more pronounced when cold.
-John

 

It's typical for exhaust leaks to be worse cold, heat expands the casting and closes the gap. stock FE manifolds are known for cracking.

 

Here are some photos of the right bank exhaust, they are pretty large unfortunately. I cannot see and cracks or carbon buildup on or around the manifold.

 

They could be under your heat shields on the back side.

Or it could be something else. when you rev it up is it worse on the way up or down?

Does it smoke and burn oil?

 

The noise is much more present on engine rev especially when cold, and higher RPM, not so much on the way down.
Truck is not an oil user, no blue smoke.
I tried to take a video of the engine running, the engine is still too warm to get a good read, just barely hear the noise above everything else.
Cannot seem to be able to upload it to the site, will try to get better audio later when stone cold.
Another idea, could a fuel pump not making proper contact with the cam excessive or perhaps a poorly shimmed cam that is drifting cause a noise similar to the one I am trying to describe?
I had a wagoneer once that I thought had sticking lifters, apparently turned out to be a drifting cam, according to the guy who worked on it.