440 engine making a noise that sounds like an exhaust leak, but no leak is found

[DC118us]

Hi all,

It's been a long time since I've been on here. My 1975 T&C wagon, stock 440 is giving me trouble.

I've spent the last 1.5 years (not a typo) working on a holley efi install. Finally got all my issues resolved and it was finally running right. I took the family on a trip to the pumpkin patch and it drove great, coming back it developed what sounds like an exhaust leak, pfft, pfft, pfft, sound, not a ticking or something weird. Trying to figure it out has me stumped.

I pressurized the exhaust looking for leaks up to the head, none found
pulled #4 plug wire and noise stopped, so that cylinder is the issue.
swapped plugs with #6, no change, #4 still the problem
swapped wires with #6, still no change, #4 still the problem
pulled valve cover, loosened the rocker shaft and put air into the cylinder (via plug hole) I hear pressure escaping, but it's not coming from the intake or exhaust valves. It's a very slow escape of pressure, like it might be creeping past the rings.

I'm wondering if a lifter may not be compressing and holding the valve slightly open when it should be closed, but I don't know how to verify this, any ideas?

Anything else I should be looking for to diagnose this issue?

Any help will be appreciated.

 

[CBODY67]

Is it a "miss" or just the sound?

 

[DC118us]

Is it a "miss" or just the sound?

It's just the sound, no miss at all

 

[sprice]

Does it occur when engine is hot or cold? Does it go away at any time? Is it all through all the rpm range?

 

[DC118us]

All the time, hot, cold, idle, driving rpms. Doesn't seem to change at all (other than quicker/slower per rpm)

 

[Just Carbs]

Pull the valve cover and press on the side of the valve spring while the engine is idling.

 

[DC118us]

I'll give that a shot, what should I be looking for? The springs don't appear broken.

 

[Just Carbs]

Valve guide or stem wear.

 

[Justin Plant]

roll the rockers shut on #4. pull the plug, insert your compression gage hose and apply air pressure from your compressor. Listen for the escaping air. Find and fix, of coarse that may be easier said than done.

 

[DC118us]

Ok, so I pushed on the springs while idling (not easy) but the sound didn't change. I couldn't see any movement either.

 

[DC118us]

roll the rockers shut on #4. pull the plug, insert your compression gage hose and apply air pressure from your compressor. Listen for the escaping air. Find and fix, of coarse that may be easier said than done.

I did something like this. I loosened the rocker shaft to unload the valve springs. pushed air in and it wasn't coming through the intake or exhaust. I assume the slowness was air bypassing the rings

 

[DC118us]

as a test I repeated my cylinder pressurizing test on #2 cylinder. The air escape was almost inaudible. So #4 is definitely dropping pressure really quickly. I just can't tell from where, not intake, not exhaust, not radiator and not crankcase (that I'm able to discern)

Any thoughts before I decide to pull the head?

 

[CBODY67]

Might need to get a "Critter Cam" or borescope attachment for your smartphone to look inside the cyl itself. Via the spark plug hole.

If the compression is going into the crankcase, the amount of "blow-by" should be much greater. Remove the pcv valve and also the breather on the rh valve cover and see what happens when the engine is running. Puffing or just drifting vapors?

CBODY67

 

[DC118us]

Might need to get a "Critter Cam" or borescope attachment for your smartphone to look inside the cyl itself. Via the spark plug hole.

If the compression is going into the crankcase, the amount of "blow-by" should be much greater. Remove the pcv valve and also the breather on the rh valve cover and see what happens when the engine is running. Puffing or just drifting vapors?

CBODY67

I actually do have a small cam and looked into the cylinder, but didn't see anything crazy. Piston did appear to have 2 bevels or something along the front edge of the piston (towards front of engine) But they seemed more like they were made that way vs damage. I'm not sure what stock 440 pistons normally look like, but I didn't see anything that appeared to be damage (hard to control the end of the unit though).

the air is pretty audible on #4, but almost non-existent on #2. I'll give that a shot if I can get the breather out of the cover. Currently I have the valve cover off

 

[DC118us]

I actually do have a small cam and looked into the cylinder, but didn't see anything crazy. Piston did appear to have 2 bevels or something along the front edge of the piston (towards front of engine) But they seemed more like they were made that way vs damage. I'm not sure what stock 440 pistons normally look like, but I didn't see anything that appeared to be damage (hard to control the end of the unit though).

the air is pretty audible on #4, but almost non-existent on #2. I'll give that a shot if I can get the breather out of the cover. Currently I have the valve cover off

Oh, also of note, it doesn't smoke either.

Also, could a diluted oil cause these symptoms? I believe the oil is diluted with gas (this happened before trying to work the bugs out of the efi system).

 

[volksworld]

idk if it runs fine and just has a noise I'd be looking for a cracked exhaust manifold or gasket leak...even up into the heat riser on the intake...I'd at least give it a compression test and/or leakdown test before I started pulling the head

 

[413]

Air is leaking by the rings, normal. Don't remove the valve cover, it's a waste of time.

Remove the exhaust manifold, you will see the black soot at the leak, or a blown out manifold gasket.

 

[Jayarr]

Before any disassembly, get a long metal rod or screwdriver put it to your ear and go about trying to find EXACTLY the area from which the sound is coming from. Valve cover, timing cover, exhaust manifold...you get the idea. If nothing else, it's fun to hear what the inside of your motor sounds like!

 

[Just Carbs]

Cracked/broken compression ring?

 

[413]

Before any disassembly, get a long metal rod or screwdriver put it to your ear and go about trying to find EXACTLY the area from which the sound is coming from. Valve cover, timing cover, exhaust manifold...you get the idea. If nothing else, it's fun to hear what the inside of your motor sounds like!

Engine, a motor doesn't have exhaust leaks.

Also try this listening with a piece of heater hose to your ear. You can hear metal tapping with a metal rod, but not so good for exhaust leaks.

Also with the engine cold have a helper start it and you feel around for exhaust leaks for the first minute until the manifold gets too warm to touch.