Popping from exhaust when starting warm

[Los_Control]

Just now, Noah H said:

The exhaust Is about a year old, but the gasket between the manifold and the pipe looks pretty chewed up, I will try tightening it up more. 

That reminds me of another truck. Early 60's chebby 6cyl. I was a carpenter on a project, the older gentleman was the Finish carpenter and was his truck.

The truck was cherry, ran perfect well taken care of. It was quiet. Every now and then when running it, would pop so loud it sounded like a hunting rifle going off.

I heard it a couple times, was always in the parking lot. Either going to lunch or going home ... so not really when warm. I was just a dumb kid with no clue, he was puzzled by it.

Eventually he did find it was the gasket between the exhaust manifold and the tail pipe. A new gasket cured it. Something about cold air and hot air colliding.

 

Just throwing ideas out there of past experience. If the gasket is questionable, it may be worth the time to just change it or at least inspect it  ... if it is actually loose, maybe tighten it would be enough. If not physically loose I would inspect it.

[Noah H]

5 minutes ago, Los_Control said:

That reminds me of another truck. Early 60's chebby 6cyl. I was a carpenter on a project, the older gentleman was the Finish carpenter and was his truck.

The truck was cherry, ran perfect well taken care of. It was quiet. Every now and then when running it, would pop so loud it sounded like a hunting rifle going off.

I heard it a couple times, was always in the parking lot. Either going to lunch or going home ... so not really when warm. I was just a dumb kid with no clue, he was puzzled by it.

Eventually he did find it was the gasket between the exhaust manifold and the tail pipe. A new gasket cured it. Something about cold air and hot air colliding.

 

Just throwing ideas out there of past experience. If the gasket is questionable, it may be worth the time to just change it or at least inspect it  ... if it is actually loose, maybe tighten it would be enough. If not physically loose I would inspect it.

Thank you, I will snap a picture of it and upload it here for a second opinion.

[Los_Control]

This would be a very rare issue. I am 59 years old ... think I have seen 2 cars do this. The truck talked about above. Then there was a old beater impala with a V8 did same thing.

 

Would take certain circumstances to recreate it. Normally if you have a leak there you will hear it, and fix it or not. Will just leak and not randomly go KAPOW!

Seems when you have one that kinda sorta leaks but not always so you can hear it while running.  Almost like hunting unicorns.

 

Possibly the gasket has some damage, maybe a warped tail pipe flange, it is normally sealed but enough back pressure at the right time, the route opens up and  cold air is sucked in meets the hot air and KAPOW!

 

Just not convinced a photo of the installed gasket will help.

Not even convinced this is your problem.

Both times I have seen it in 50 years, were not my cars and I never fixed them. Has others seen this and fixed it?

 

 

[Noah H]

16 minutes ago, Los_Control said:

This would be a very rare issue. I am 59 years old ... think I have seen 2 cars do this. The truck talked about above. Then there was a old beater impala with a V8 did same thing.

 

Would take certain circumstances to recreate it. Normally if you have a leak there you will hear it, and fix it or not. Will just leak and not randomly go KAPOW!

Seems when you have one that kinda sorta leaks but not always so you can hear it while running.  Almost like hunting unicorns.

 

Possibly the gasket has some damage, maybe a warped tail pipe flange, it is normally sealed but enough back pressure at the right time, the route opens up and  cold air is sucked in meets the hot air and KAPOW!

 

Just not convinced a photo of the installed gasket will help.

Not even convinced this is your problem.

Both times I have seen it in 50 years, were not my cars and I never fixed them. Has others seen this and fixed it?

 

 

tighted up the bolts and still continues to pop. I’m also getting a clicking when idling. This has now got me stumped. I’ve had the valve covers off twice now and have the clearances set per book .008 intake and .010 exhaust. I have a stethoscope and when placed over each cylinder, they have a slight clicking, but not the sound I am hearing. I’ve put the scope over the fuel pump as well and there is no clack there.  The timing is directly on top dead center on the harmonic balancer.  Or “0” or is it better if I rotate the distributer and time the car via a vacuum gauge? 
 

thanks 

[Sniper]

Water pump bearings?  Generator bearings?  Might actually be hearing the spark jumping to something other than the plug gap.  Have you looked under the hood with the engine running when it's dark for any evidence of sparking?

[Noah H]

24 minutes ago, Sniper said:

Water pump bearings?  Generator bearings?  Might actually be hearing the spark jumping to something other than the plug gap.  Have you looked under the hood with the engine running when it's dark for any evidence of sparking?

Yes. I have looked under the hood at dark no sparks, I have also checked the bearings no clicking. 

[Sniper]

well, dang.  there go all the easy options.  Only other thing I can think of is the plug wire connections?  Are they tight on both the plug and the cap ends? 

[Los_Control]

How about a youtube video of it happening?

[keithb7]

Not s solution but a related story. I had a chirping at idle in my 1938 Plymouth engine. I could not find it. I gave up looking as there seemed to be no harm. Later when I tore the engine down, I found it. Inside the exhaust manifold. The exhaust diverter valve had removed itself from the shaft. It was floating around, bouncing about inside the exhaust manifold. Pretty hard to find that and solve it by searching around & listening.

Edited September 18, 2021 by keithb7

[squirebill]

Do you still believe the popping noise is coming from the drivers side of the engine?  Maybe in order to eliminate the situation I had in the late 60s:  you could get the car to the warm start condition that makes it pop, but before you start it, release the bale clips that hold the distributor cap and lift the distributor cap off the distributor enough that you could blow some compressed air or wave a piece of cardboard at the distributor to try to blow away any oil vapors that may have collected under the cap.  Replace the cap and fasten the bale clips.  Now start the engine and see if it still "POPs".  If it does it is probably not a result of oil vapors in the distributor.  If it doesn't pop maybe it is time to get a distributor cap with a hole in the side and or eliminate the oil leak between the distributor base and block. 

[Noah H]

On 9/17/2021 at 4:34 PM, Los_Control said:

How about a youtube video of it happening?

https://youtube.com/shorts/zrQceFeTwKY?feature=share 

[squirebill]

Having looked at the youtube video: I hear a "Pop" about 6 seconds into the video and then it seems like I hear a rpm surge a second or two after the "pop".  Is this correct or is it because of a change in the microphone position during the video?  This does not seem to be the situation I had in the 60s I previously reported.  In my situation the "pop" occurred immediately after I turned the key to start the engine (like within the first crank) and not as the engine was running. Interesting problem.  Please keep us advised if you determine a solution. Good luck and best regards.

[Noah H]

2 hours ago, squirebill said:

Having looked at the youtube video: I hear a "Pop" about 6 seconds into the video and then it seems like I hear a rpm surge a second or two after the "pop".  Is this correct or is it because of a change in the microphone position during the video?  This does not seem to be the situation I had in the 60s I previously reported.  In my situation the "pop" occurred immediately after I turned the key to start the engine (like within the first crank) and not as the engine was running. Interesting problem.  Please keep us advised if you determine a solution. Good luck and best regards.

 
yes you heard correct. After a hot start it’s either immediately after turn the key, or about 3 seconds after it’s running, it then surges and runs rough until I give it gas then idles fine. 

[Sniper]

What is your hot restart procedure?  I almost wonder if your choke is setting properly?

[Noah H]

51 minutes ago, Sniper said:

What is your hot restart procedure?  I almost wonder if your choke is setting properly?

Sisson automatic choke is completely open and works properly. 1/4-1/2 open on the gas when I got hot start