Help diagnosing an engine noise

[Locker537]

I've edited this post with a better video. You can hear the sound pretty distinctly when I place the camera near the transmission crossmember at the end of the following video:

https://youtu.be/iqjwFWcr0Vs

----

I think I'm hearing a new sound. The best example of the sound is in the video at 0.50 - 0.55 seconds.

https://www.youtube.com/watch?v=dRQr7JRD-xw

I apologize for the terrible camera work. :-)

For context, 3.0 engine with 40IDA Weber carbs. The coughing/sneezing out the carbs and exhaust pops aren't new. The engine runs great with lots of power at RPM and was setup for track use. Idle leaves something to be desired, but it's a DE car and I have not dug into tuning. It loves RPM.

I've used a long pry bar to listen to the intake valve covers, exhaust valve covers, and timing chain covers. Nothing stands out to me.

The irregular sound in the video concerns me. Any ideas? Thanks in advance.

[gomezoneill]

Valve train. Rockers to loose.

[Locker537]

Originally Posted by gomezoneill

Valve train. Rockers to loose.

I was planning to adjust them soon, so that would be good if that's it.

[proporsche]

ok 1st you should have you valves adjusted...2nd the clunk on 0,50 is possibly your flywheel is loose

Ivan

[Locker537]

Originally Posted by proporsche

ok 1st you should have you valves adjusted...2nd the clunk on 0,50 is possibly your flywheel is loose

Ivan

That thought crossed my mind based on reading other threads. Not from personal experience.

Is there a way to check the flywheel? I assume I'd be dropping the engine and transaxle.

I'll start with the valve adjustment.

[Locker537]

Update to this thread.

I've adjusted the valves and the noise is still present. I was able to capture it better in the following video. The noise is most pronounced from the transmission crossmember area.

https://youtu.be/iqjwFWcr0Vs

Any ideas?

[gomezoneill]

sounds like it's in the valve train to me. Collapsed tensioner?

[Locker537]

I can certainly double check the valves. I know it will be much easier the second time around!

Should I pull the tensioner covers and visually inspect?

I can really only discern the noise from under the car. It's most pronounced near the crossmember. I used a scope to pinpoint it and failed to do so.

[gomezoneill]

Sounds like chain rattle but it's hard to tell from listening to a audio clip. Wait for some members to respond. Did the noise change after the valve adjustment?

[Locker537]

Originally Posted by gomezoneill

Sounds like chain rattle but it's hard to tell from listening to a audio clip. Wait for some members to respond. Did the noise change after the valve adjustment?

Not in any noticeable way.

If I wasn't able to capture it on video, I'd say I was imagining it.

[proporsche]

the valve adjustment seems fine..but we are talking about the knock right? have you driven the car since?

Ivan

[Locker537]

Yes, the "knocking" sound that you can hear pretty clearly starting at the 25 second mark in the video until the end.

Yes, I drove it and it runs strong. Nothing appears wrong other than the noise.

[gomezoneill]

Wait for John Walkers advise.

[proporsche]

does it change when step on the clutch pedal?--i sounds like from the trans. main shaft

Ivan

[Locker537]

Originally Posted by proporsche

does it change when step on the clutch pedal?--i sounds like from the trans. main shaft

Ivan

I could not discern a difference while listening from inside the car, but will need to get a helper to step on the pedal while I am under the car. Good idea. Thank you!

[Locker537]

After adjusting the valves to eliminate that possibility, I replaced the spark plugs. I then went for a ~10 miles drive, a couple wide open throttle blasts, then pulled into the garage and let the car idle while hunting for the engine noise in the videos above.

My understanding is inspecting plugs after long idle won't indicate much, but I pulled the plugs to check them and was surprised by how sooty #4 and #5 are compared to the others.





Any thoughts? Could it be related to the engine sound?

[Walter_Middie]

When adjusting the valves, did you check for broken head studs? Especially around cylinders #4 and #5?

[Locker537]

Originally Posted by Walter_Middie

When adjusting the valves, did you check for broken head studs? Especially around cylinders #4 and #5?

No, but I will add it to the list. That would be very surprising given the history of the engine. It was rebuilt in 2006. I suppose that's longer ago than I realize typing it out...

[Locker537]

Thinking out loud...

Could it be the throttle linkage? I noticed there is a good amount of play in the part that pivots near the transaxle. I kinda doubt it...

[Locker537]

Ivan,

The noise does go away when I depress the clutch. I confirmed this over the weekend.