Help! Wiped cam lobes? - Video inside

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perko

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Hello!
I would like to draw on the collective expertise of this great community. I have been trying to diagnose a carb backfire and Its really starting to stress me out.

It is pretty consistent and very noticeable under throttle. Sounds like a machine gun at higher RPMs. People have suggested that it is the cam shaft, but I would like to be a little more confident about that before I tear the whole engine apart. It is a 1973 plymouth duster with a 318. I have pulled the valve covers to observe the lifter movement, but I'm just not well versed enough to convince myself that it is a cam problem. A few of the lifters were a little loose and there was some play in a few of the push rods, but noting appears to be bent, and the springs seem to be fine. Some lifters do not move as much as others, but they all move. Also, some pushrods spin consistently, is that a problem?

I uploaded two videos of the lifters moving as I turned the engine over. Can anyone draw an opinion about the condition of the camshaft from these videos? Picture quality and angle sucks I know, but it was the best I could do.

Right bank
[ame="https://www.youtube.com/watch?v=HWz91fRITdM&feature=youtu.be"]wiped cam shaft? - YouTube[/ame]

Left Bank
[ame="https://www.youtube.com/watch?v=a8D88u8SZ4k&feature=youtu.be"]017 - YouTube[/ame]

Thank you for your time! I could really use a hand here.
 
with nonadjustable rockers, should be no slack in valve train. pushrods should spin as does the lifters. all rockers should move same amount , when running. need to run with covers off for few seconds and listen to rockers and observe movements. also, can run a cranking compression test. hook up a vacuum gauge , and see if vacuum holds steady. if cam is bad, it will move. just have to test.
 
Compression and leak down testing is your friend.
 
Oh yeah we can tell a lot from a 7 and 10 second video with the camera panning. Come on man. If you want some help, you gotta do better than that.
 
Rotor phasing,pick-up polarity, bad plugs, or a combination of these.

A)The cheapest fix is the rotor phasing. Do you need help with that?
B)Disable the vacuum advance, and retest. Put the timing lite on it,and observe the advance pattern.If the pattern is solid and progressive, polarity is good. If the lite comes and goes,or jumps around all wierd like, check no 6.If its goofy too, then check them all, until you find one that has a consistant firing pattern.Cant find one?
C) Reverse the pick-up polarity and reset the base timing.Still not cured?
D)Replace the plugs. Check the base timing. Cured? Whoopie!
E)Still goofy?Put the polarity back.
Cured? Whoopie. Still not right? IDK

I watched the vids 4 times each. Unable to tell anything. Except didnt hear any rocker lash.
 
Backfiring is not going to happen over wiped lobes.

When the cam lobes flatten, the valves have exactly the opposite problem. They don't open enough and stay closed for a longer duration. Backfiring through the carburetor is caused from the ignition firing when the intake valve is open. It could be hung open from a stuck lifter, or it could be doing exactly what it should be doing and the spark could be igniting when it is not supposed to be.

Is it backfiring through the carburetor or exhaust?

If it is coming from the exhaust, you could also have a burnt valve seat.

A leakdown check will tell you if it is valve related.

If you don't want to rent/borrow/buy a leakdown kit, AJ's advice is sound on the ignition end.

The first thing I would check is the ignition timing on a light, followed by a leakdown test.
 
Dave, I love you man, and you're a super genius. I really mean that, but you are incorrect on this. Anything that keeps an exhaust valve closed will indeed cause a backfire through the intake and carburetor.

With the exhaust valve closed, the cylinder still fires. Where else is the exhaust going to go? It will follow the path of least resistance back up through the intake and right out the carburetor. Seen it happen literally hundreds of times on different type valve train failures, mostly wiped camshaft lobes.

While it does not cause a miss or a dead cylinder, as that cylinder still builds compression and fires, it certainly disrupts the engine and makes it run rough and lose power.

You are correct that ignition problems can and certainly do cause pops back through the carburetor, but physical valve train problems can and do as well.


DaveBonds said:
Backfiring is not going to happen over wiped lobes.

When the cam lobes flatten, the valves have exactly the opposite problem. They don't open enough and stay closed for a longer duration. Backfiring through the carburetor is caused from the ignition firing when the intake valve is open. It could be hung open from a stuck lifter, or it could be doing exactly what it should be doing and the spark could be igniting when it is not supposed to be.

Is it backfiring through the carburetor or exhaust?

If it is coming from the exhaust, you could also have a burnt valve seat.

A leakdown check will tell you if it is valve related.

If you don't want to rent/borrow/buy a leakdown kit, AJ's advice is sound on the ignition end.

The first thing I would check is the ignition timing on a light, followed by a leakdown test.
Click to expand...
 
Funny. Worked on a buddy's car on the weekend.
idled not bad, start to accelerate and back fire.

He had 2 wires wrong in the cap position.
It actually idled not bad so we thought uh oh not good and were thinking all kinds of
catastrophic problems. We clamed down went back to basics and bang...2 wires in the cap
in the wrong spot.
 
RustyRatRod said:
Dave, I love you man, and you're a super genius. I really mean that, but you are incorrect on this. Anything that keeps an exhaust valve closed will indeed cause a backfire through the intake and carburetor.

With the exhaust valve closed, the cylinder still fires. Where else is the exhaust going to go? It will follow the path of least resistance back up through the intake and right out the carburetor. Seen it happen literally hundreds of times on different type valve train failures, mostly wiped camshaft lobes.

While it does not cause a miss or a dead cylinder, as that cylinder still builds compression and fires, it certainly disrupts the engine and makes it run rough and lose power.

You are correct that ignition problems can and certainly do cause pops back through the carburetor, but physical valve train problems can and do as well.
Click to expand...

I concur my dear Rob! First think I thought when I read Daves post, Wrong!
 
Fire it up with the valve covers off,yes it will be a little messy but with it running you will notice any rocker arms not moving as much as the others. If it has wiped a lobe bad enough the back fire it will be noticeable with it running with the covers off.
 
67DARTGTCONV said:
Funny. Worked on a buddy's car on the weekend.
idled not bad, start to accelerate and back fire.

He had 2 wires wrong in the cap position.
It actually idled not bad so we thought uh oh not good and were thinking all kinds of
catastrophic problems. We clamed down went back to basics and bang...2 wires in the cap
in the wrong spot.
Click to expand...
talk about back to basics and cheap fix?!
Aaaaaa, ya! This is exactly where I would start! like I think everyone of us have had that happen?
 
RustyRatRod said:
Anything that keeps an exhaust valve closed will indeed cause a backfire through the intake and carburetor.

With the exhaust valve closed, the cylinder still fires. Where else is the exhaust going to go? It will follow the path of least resistance back up through the intake and right out the carburetor. Seen it happen literally hundreds of times on different type valve train failures, mostly wiped camshaft lobes.

While it does not cause a miss or a dead cylinder, as that cylinder still builds compression and fires, it certainly disrupts the engine and makes it run rough and lose power.

You are correct that ignition problems can and certainly do cause pops back through the carburetor, but physical valve train problems can and do as well.
Click to expand...

Xs3

The 5th rocker back, on the passenger side hardly moves,, and it's an exhaust valve.. see if the pushrod's bent,, (roll it across a flat surface/floor).. if bent replace it,, if not bent better see if the lifters moving up and down,, that could be a big part of the problem,, other rockers seem to have limited movement also.. jmo
 
Also you named the right bank and left bank wrong. Left= drivers side, Right = passenger side. It is always from the drivers seat.
 
RustyRatRod said:
Dave, I love you man, and you're a super genius. I really mean that, but you are incorrect on this. Anything that keeps an exhaust valve closed will indeed cause a backfire through the intake and carburetor.

With the exhaust valve closed, the cylinder still fires. Where else is the exhaust going to go? It will follow the path of least resistance back up through the intake and right out the carburetor. Seen it happen literally hundreds of times on different type valve train failures, mostly wiped camshaft lobes.

While it does not cause a miss or a dead cylinder, as that cylinder still builds compression and fires, it certainly disrupts the engine and makes it run rough and lose power.

You are correct that ignition problems can and certainly do cause pops back through the carburetor, but physical valve train problems can and do as well.
Click to expand...


Polite and true.
 
Hi everyone, thank you very much for your input. sorry I wasn't able to respond quickly.

Yeah, the rockers seem to have limited movement. I haven't taken any push rods out to check them yet because It needs to leave the garage for a party this weekend, but there's nothing that's obviously bent or broken. Wires are in the correct firing order, I suppose the wires could still be arcing though. It seems to me that if there is a problem with one of the lifters it probably damaged the cam lobe associated with it? I know the first videos sucked so I made these better ones. well, one of them is better. My battery died making the second one. I'm wary of driving it like if is if I'm going to be moving a bunch of metal through the engine.

[ame="https://www.youtube.com/watch?v=ib-l-UJqbMY&feature=youtu.be"]IMG 0707 - YouTube[/ame]
[ame="https://www.youtube.com/watch?v=ac08wzrPCwU&feature=youtu.be"]IMG 0708 - YouTube[/ame]

I just wanted a second opinion because I'm not sure how much movement is acceptable or not. Also, people have suggested that If the rods are not spinning, this is also a sign of a bad cam or lifter because tapit cams are slightly angled to spin the lifters and reduce wear. Is this true?

Its not looking so good for me. Thanks for the help.
 
Exhaust rocker on #6 is your culprit. It's not moving at all.
 
Yup I agree, on your second video, 5th rocker back from the front #6 exhaust is barely moving. And yes camshaft lobes are ground so the as to promote lifter rotation.
 
yes the #6 exhaust lobe looks wiped and rrr is right it will back fire up through the carb when the gas cant exit out the port. very common problem with brand x
 
No 6ex alright. But I wonder if the lifter is defective, and not pumping up. There doesnt seem to be the rocker clatter I would expect if the lobe is that far gone.Perhaps the lifter is acting to maintain zero lash, but not actually transferring lobe lift to the arm.
Longshot I know, but easy to prove.
 
Thanks guys,
AJ/FormS i'm new at this, how would I prove to myself that the lifter is maintaining zero lash? Also, wouldn't I expect a faulty lifter to damage the cam anyway? Its a little hard to tell whats going on for cylinders 2,4,6, and 8 because the battery died on me. Its at O'Reillys getting charged now.
 
Yeah, we could hear the battery dying in the vid.I think that starter might be lazy too. Guess we will see in a bit.
Well, since Inertia, and Rusty spotted that right off, leaving me in the dust, I think Iought to hang back and let one of them help you out. Those guys know their stuff.
 
With the intake valve open on that cylinder, the exhaust valve is on the heel of the lobe. If there is not a lot of slop and play on that rocker, then the hydraulic plunger in the lifter has taken up all the slack or all that it can. If the rocker is in fact not opening and closing as much as the others and that looks to be the case by your videos, your going to have to pull the intake so you can inspect that lobe. You may find others with some wear on them also. That lifter is more than likely mushroom and will be a PITA to remove. A faulty lifter will not necessarily damage the cam.
 
AJ/FormS said:
Yeah, we could hear the battery dying in the vid.I think that starter might be lazy too. Guess we will see in a bit.
Well, since Inertia, and Rusty spotted that right off, leaving me in the dust, I think Iought to hang back and let one of them help you out. Those guys know there stuff.
Click to expand...

And you don't? Man you're crazy. You're one of the sharpest guys on here. Gimmie a break.
 
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