The 225 currently installed in my "Art Car" Dart has a valve or two hanging open when it gets up to operating temp. It's pretty random, but on average you can hear a slight "pop" sound maybe 1-2 times a second at idle. Doesn't make any noise when cold and runs beautifully otherwise. Not sure if it happens at higher RPM, but the sound doesn't seem noticeable if so.

This 1964 engine (with a drool-tube head) came out of the Valiant wagon I bought last year. It was in pretty rough shape and had been sitting for decades, but the cylinder bores were still barely within spec, so I rebuilt it in my garage without any machine work. Got to learn how to use a ridge reamer and cam bearing tool in the process. New rings, bearings, and seals all the way around. I cleaned up the block really well with heavy-duty oven cleaner and even experimented with opening up the oil passages in the block, since I figure it'll be a good thing to do next time I rebuild a race motor.

The reason I'm pretty sure the sound I hear is a hanging valve is because I never reamed the lifter bores. I really should have done this, considering that the old lifters were so crusty they had to be pounded out of the block with a screwdriver. What can I say, we were in a hurry. My friend Bob was actually the one who installed the new lifters in the block, and he said they went in fine but I have no personal reference for how good "fine" is. My suspicion is that the bores are just rough or tight enough to cause one or two of the lifters to stick once they get hot and expand a little. The engine is a thoroughly stock rebuild with no fancy parts, and it has about 50 miles on it since installation. I just drained the initial break-in oil today, and it honestly looked less metallic than I expected. There is oil coming out of the rockers when running, so that shouldn't be the problem.

Obviously I'd prefer to do this honing operation with the engine in the car. Ideally I'd like to do it without pulling the head, but that may be asking too much. I figure I'll pull the spark plugs and tubes, rocker assembly, pushrods, and lifters, then see if I can fit a wheel cylinder hone down in the lifter bores and ream the crap out of every one. Then flush the lifter gallery with oil and drain the pan again. Obviously I'll examine the lifters for signs of damage and replace any that don't look good. If there's not enough access I'll pull the head, probably with the manifolds attached to save time.

Anybody see problems with this plan? Any inputs or experiences to share?

_________________
Somehow I ended up owning three 1964 slant six A-bodies. I race one of them.
Escape Velocity Racing

I really doubt that you have a lifter sticking in the bore in the raised position, the pressure from the valve spring would be pressing it down on the cam,,,
It is not uncommon to have to work on lifters to get them out, after much run time they get a ridge of carbon at the ends of the travel area, they become trapped, but in thier normal movement zone they move fine,,, could be a valve hanging in a guide though. That can happen. Maybe take off the valve cover and watch the action at idle.

_________________
Doo Ron Ron and the Duke of Earl are friends of mine.....
https://www.youtube.com/watch?v=uX8Nj8ABEI8

What was done to the cylinder head? Valves stick a lot more often than lifters do.

_________________
Joshua

I'ma vote the same way: probably not sticking lifters. How do you know the misfiring is due to an engine hard-part problem and not something more likely such as…ignition issues? For the matter of that, what're you running for ignition and carburetion?

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.

It's a points distributor and a Holley 1920, but these same parts were used on a different engine in this same car without showing this symptom. It doesn't sound like a misfire, just a periodic mechanical "pop" or "thunk" that doesn't seem to follow a regular pattern.

The cylinder head is from a different engine; it's actually the original cylinder head from this car, not that it matters. I had it hot-tanked and magnafluxed a while back, then I used it to practice porting before going to work on my racecar head. All I really did was knock out the cast numbers in the runners and practice thinning out the bulges around the valve guides. When I put this engine together, I just lapped in the nicest set of used stock valves I had on hand. I'd expect the valve guides to have excessive clearance, if anything.

I guess I'll pop off the valve cover and watch it while idling again, but I don't recall seeing anything unusual last time when I set the valve lash.

_________________
Somehow I ended up owning three 1964 slant six A-bodies. I race one of them.
Escape Velocity Racing

and that is what can cause valves to stick,,

the valve stem gets cocked in the valve guide bore and momentarily hangs

_________________
Doo Ron Ron and the Duke of Earl are friends of mine.....
https://www.youtube.com/watch?v=uX8Nj8ABEI8

How 'bout some quality video so we can hear what you hear? Also, are you saying there's no misfire accompanying each pop/clunk?

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.

If lifters were sticking you probably would have knocked lobes off the cam by now. Sticking lifters won't spin.

_________________
Official Cookie and Mater Tormentor.

Loosen your valve lash a couple thousandths. See if it goes away.

CJ

_________________
Part of Tyrde-Browne Racing

I pulled the valve cover and ran it for a while again after changing the initial break-in oil. Just like before, I didn't notice anything unusual when the engine was cold (aside from running a little rough since it doesn't have a functioning choke yet). After it started to get warm, the noise showed up again. I had the idle set a bit too high, so after dialing that back down I noticed the noise didn't actually show up until just above proper idle speed. Seems to be most prevalent just off idle, and after that it might become less common but more likely just can't be heard over the rest of the engine noise.

This first video was recorded after the thermostat opened, but the oil was probably not up to operating temperature yet. Popping sound comes in after I throttle up, around 0:16-0:17. When I put the camera closer to the valve train it actually becomes harder to hear over the valve clatter.
https://youtu.be/YktiZm4MCAU

This second video was recorded after another ~20 minutes of fast idling, so the oil was probably a lot closer to operating temp, if it makes a difference. Again, you can hear it sporadically starting around 0:15-0:16 when I open the throttle a bit. When I run it at higher RPM and then release the throttle again, you can usually hear it a few/several times in a row as it drops down to idle, like a bbbbbbp sound. When I hold it at a high idle from about 1:15 to 1:50, you can definitely hear it in sporadic groups of a few at a time. Then I think you can still hear it periodically after I drop it down to idle at the end of the video.
https://youtu.be/1j02gXiYTfE

The noise is no louder than before with the valve cover off, so Dan might be right about this not being a pure mechanical issue. One thing that might not come through in the videos is that the "pop" always seems to be accompanied by a very faint metallic ringing. Also, you can feel a slight shudder in the body of the car whenever it happens.

After recording these videos, I went ahead and checked the hot valve lash again just to be sure. A few of them needed a little adjustment, but none were off any more than a couple thousandths. Also, not sure if this is relevant, but I take back what I said about top-end oiling. The rocker shaft is getting plenty of oil, but very little is actually coming out of the rockers tips. I think I'll be pulling these off again and cleaning them individually. (Like I said before, I was in a hurry during final assembly.)

_________________
Somehow I ended up owning three 1964 slant six A-bodies. I race one of them.
Escape Velocity Racing

Don't forget to check the orientation of the oiling holes on the rocker arm shaft. The holes in the shaft should be pointed down at the head to provide oil to the rockers.

I went ahead and added more detailed descriptions of what I heard in those two videos I linked, now that I've had a chance to sit down and listen to them again.

I'll check on the oiling holes when I pull the rocker shaft, but for now the notch on the end of the shaft is pointing forward and up, per the FSM. Based on the appearance of the rockers, I think it's more likely the internal passages of the rockers are just gummed up. I'll probably soak them in carb cleaner (as many as I can fit in the jug at a time with them hung on a coat hanger to keep them in order), then poke through all the oil passages with a wire.

Any ideas on that popping sound heard in the videos? It's unfortunately a little harder to hear in the recordings than it is in person. When I get some more time later this week, I might run through the ignition system with a fine tooth comb. Maybe hook up a timing light to each plug wire in turn and see if I notice anything screwy to go along with the noise.

_________________
Somehow I ended up owning three 1964 slant six A-bodies. I race one of them.
Escape Velocity Racing

Can you hear the noise out the tailpipe?
What does a vacuum gauge show in the intake while it's happening?
If you do have a sticking valve situation, that air is going somewhere.

To me, it sounds more like a lean misfire than an ignition breakdown but it's hard to tell in a recording.
It has a jazz rhythm instead of a march

_________________
O==\=/==O

"A mechanic is Somebody."
- Jim Preston

Going on the lean misfire theory....

What spark plugs are you using and what's the gap?

_________________
Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Yup…I hear a great deal of misfiring in those videos. Could be fuel/air related, could be ignition related, could be both. The non-oiling lifters suggest there's other stuff overdue for attention. Like, those breaker points are overdue to be ejected in favour of something not from the stone age.

Pull all six spark plugs. Show 'em to us so we can clearly see the firing ends.

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.