76 Eldorado - Mechanical Clacking

[SlowCredit]

Obviously something very wrong - Valve?  Starts rough - obvious misfire.  Can't find my compression gauge, so going to borrow one this weekend before I take the valve covers off to have a look.  Took a video - any guesses/advice?

https://youtu.be/x5G1D3hyKdU

Thanks!

Slow

[79 Eldorado]

I don't know what it is. It almost doesn't sound like an engine noise. I would find a spark plug tester and take turns removing a wire from each cylinder to see if deactivating a particular cylinder changes the sound. Use the tester so the spark has someplace to go on the removed wire each time.

Edit: To clarify I meant it doesn't sound like an internal engine noise to me.

Scott

[V63]

Might check the exhaust EFE valve? Next I would run it without any fan belts

[The Tassie Devil(le)]

I agree with Scott, doesn't sound like any engine noise to me.

Bruce.

[Cadman-iac]

  To me it sounds like a spark misfire, like a wire is not connected correctly with either one of the plugs or to the cap.
My initial thought was that it sounded like a misfire from a bad exhaust cam lobe, but it's not really misfiring through the carburetor enough for that, unless the lobe is just beginning to wear off.
Did you just replace the plug wires? And if so, have you double checked that each one is going to the correct plug, and in the correct sequence?
But I agree with Scott, V63, and Bruce that it's definitely not a mechanical sound, to me it sounds like a spark misfire.

  Rick

Edit: looking at your video again, I can see that you have a slight backfire through the carburetor, and there's only a few things that could cause that. One is miss-wired plug wires, ignition timing that's too far advanced, or a camshaft exhaust lobe that is worn down. The lobe doesn't open the exhaust valve enough for all the gases to leave the cylinder, so you have a build up of pressure as the intake valve is opening, causing a reversal of airflow into the manifold, and if the engine is hot enough, it will cause a big backfire through the carburetor because it actually ignites the incoming fuel before the intake valve is even closed. But this type of a misfire is much more dramatic than what you have in the video, and it is worse when the engine is running while under a load too, and not as noticeable when the engine is just idling.
What was the reason for why you replaced the wires? Were you having a misfire before this?
Also, how hot was your engine when you made the video?

[TJ Hopland]

Note that this engine layout is flipped from most of the other American engines from the era.  Driver/left is the even numbers and passenger/right is the odd bank.   That gets a lot of people that are not looking at an original service manual.  Since previous and later engines were more traditional the internet and universal manuals can often confuse or flat out be wrong.

Also don't get hung up on where the wires are on the cap.  Since it mostly runs they are likely pretty close so just check the order.  Rotor turns clockwise looking down from the top.  1-5-6-3-4-2-7-8

Another thing that could be happening is the plastic fell off an original timing cam sprocket so the timing chain is loose.  Quick check to see if that is possibly problem is to take the distributor cap off (no need to disconnect the wires just swing it out of the way) so you can watch the rotor while you by hand turn the crank back and fourth.  Turn the crank one direction so the rotor starts to turn then turn the crank in the other direction and see how much crank rotation it takes before the rotor starts turning the other direction.  If you are not sure how much that was you can put a chalk or tape mark by the timing indicator where you stop turning the one direction then turn the other and mark it again when it starts again.  It should only be maybe be 1/2"-1" of rotation before it catches up.   

 

[V63]

It's hard to tell with a video but do I see the choke plate flapping?

[signart]

Sounds like backfire through carb to me. Could mean worn cam. Rev it up, should have a more severe backfire if that is the case.

[The Tassie Devil(le)]

It's hard to tell with a video but do I see the choke plate flapping?

Only moving on actual starting, then still the rest of the time.

Bruce.

[Cadman-iac]

Only moving on actual starting, then still the rest of the time.

Bruce.

This can be explained easily. During the cranking, the choke pulloff isn't getting any vacuum to open the choke, but once it's running, it keeps the choke plate steady.

[Cadman-iac]

Note that this engine layout is flipped from most of the other American engines from the era.  Driver/left is the even numbers and passenger/right is the odd bank.   That gets a lot of people that are not looking at an original service manual.  Since previous and later engines were more traditional the internet and universal manuals can often confuse or flat out be wrong.

Also don't get hung up on where the wires are on the cap.  Since it mostly runs they are likely pretty close so just check the order.  Rotor turns clockwise looking down from the top.  1-5-6-3-4-2-7-8

Another thing that could be happening is the plastic fell off an original timing cam sprocket so the timing chain is loose.  Quick check to see if that is possibly problem is to take the distributor cap off (no need to disconnect the wires just swing it out of the way) so you can watch the rotor while you by hand turn the crank back and fourth.  Turn the crank one direction so the rotor starts to turn then turn the crank in the other direction and see how much crank rotation it takes before the rotor starts turning the other direction.  If you are not sure how much that was you can put a chalk or tape mark by the timing indicator where you stop turning the one direction then turn the other and mark it again when it starts again.  It should only be maybe be 1/2"-1" of rotation before it catches up.   

 

You are right, it could be a cam gear, I hadn't thought of that.
A timing light would show that up though normally, as it would be jumping around, would it not?

 Rick

[79 Eldorado]

When I first heard it I thought maybe it's a sound an air pump is making but I don't see an air pump. I then though maybe an exhaust leak but it doesn't seem quite right for that either. The strange thing is, even when the RPM is relatively constant, it seems like the cadence changes.

Even in the video it sounded a little louder in one area unless it was just the orientation of the phone (passenger side I think). Maybe a follow-up with a walk around, trying to maintain the phone orientation with respect to the engine, or try using an automotive stethoscope.

Scott

[TJ Hopland]

If things are loose in the timing chain area I would expect it to jump around which would change the engine speed which would make it wander around even worse.   I don't know that it would be worth trying to check with a timing light at this point. 

Since he was planning on a compression test he will have the plugs out so that would make it easy to turn over by hand and watch the rotor.   If it sloppy I suppose you could still do a compression test just to see how even they are but I would not worry if the overall number is low because if the cam timing is off that would effect the overall compression.

Pulling the plugs for the compression test will also give you a look at the plugs and look to see if they are all looking the same.  Mark so you know which cylinder they came out of so if one looks different than the rest you can see if that one is also one with a different compression reading.