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Take educated guess?

ChrycoDUDE

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I'm trying to get a bead on this issue. I wonder if anyone would venture to take a guess at it.

So the other day I'm driving my 70' 383 down the highway, about 80mph when I start hearing a very light tapping sound. It was extremely light, but since I know my car very well, inside and out..I could hear it. Soon it got a bit louder, but not quite loud enough to where I could immediately identify what it was so I got off the highway and pulled into an Autozone parking lot and turned the car off. I thought at that point that maybe the fan shroud had come loose again and the fan blade was hitting it. So I started the car up again and the tapping sound had disappeared. I get in, drive off and get back on the highway. As I accelerate up to speed the tapping noise returns. Now I'm concerned. I decided to come back home. On the way home the noise continues until I have to get on an off ramp that makes a very sharp curve to the right. At that point the tapping stops all together and the engine begins to run extremely rough, as if it dropped a cylinder...like one cylinder has a dead plug. So the engine is firing on seven cylinders rather than eight. So It runs this way all the way back into my garage.

My guess is a lifter is collapsed...maybe more than one. This has happened before....two or so years ago. I had to take apart the top end and replace all the lifters...had one lifter with a concave head. I replaced with new lifters, fired it up, chatter went away. However that one noisy lifter never affected how the engine ran. It ran fine in fact.

So again I'm thinking another collapsed lifter...very damaged and I'm thinking that explains the rough (very rough) idle? I've got great compression in the cylinders..each is between 115 and 120psi when I checked yesterday. That was my main concern.

Comments? Am I on the right track? I've fiddled with Mopars for awhile now. I've got tools and stuff...but that doesn't make me a bonafide mechanic, lol.
 
First thing I would do is:
1. Open a cold Beer...
2. Pull the suspected plug (plugs) and check them out, inspect for oil or discoloration.

My question is:
Did noise increase in frequency with RPM rising or was the noise a steady "beat per minute"?
 
Id say you are in the right ballpark. My guess would be a punched out rocker or bent pushrod. Either way it shouldn't take you long to find.. good luck and please let us know what you find...
 
I had to take apart the top end and replace all the lifters...had one lifter with a concave head. I replaced with new lifters, fired it up, chatter went away.

you prolly should have changed the cam right then too..thats just my opinion.
i wouldnt be surprised to hear back that the bad lifter was again on same lobe.
but now,for sure,id change the cam,lifters,and check the timing chain out.
also give your harmonic balancer a eyeball too,hardly anyone does and ive seen them real bad.

My guess would be a punched out rocker or bent pushrod.
this happened on a 383 once,the pushrod kicked out sideways and Dropped into the camshaft....
at speed....04 seconds later,no more 383,trashed block and all.
saved the valve covers and the intake...thats about it

oyeah,if you have any doubt about the straightness of your pushrods,
lay them on a piece of Glass,and roll them one at a time as you take them out.
youll know right away if they are bent.
 
My first thought was an old rocker arm, too. Don't really know anything about your engine. I'd hope it was that or a pushrod, as stated above.
 
Okay,
Forget what I said...except the beer part...

The valve cover will be the best 2nd step in troubleshooting...

The cold beer being number 1

I remember now, this did happen to me in 1986 or so on a 400 CI GTO
 
easy enough to pull the valve covers off and inspect
Yep. I was thinking about that this afternoon also. Haha.

- - - Updated - - -

First thing I would do is:
1. Open a cold Beer...
2. Pull the suspected plug (plugs) and check them out, inspect for oil or discoloration.

My question is:
Did noise increase in frequency with RPM rising or was the noise a steady "beat per minute"?


Yeh, a brewski out the fridge. Lol

I pulled all the plugs, all looked good. I have the heads off and cleaned up a few months ago (reconditioned and hardened valve seats). Yes, the noise did increase in frequency with the RPMs. Most definitely.

- - - Updated - - -

Id say you are in the right ballpark. My guess would be a punched out rocker or bent pushrod. Either way it shouldn't take you long to find.. good luck and please let us know what you find...
Thx. Just wanted to hear it from other guys. Make sure I wasn't speaking out of my butt.

- - - Updated - - -

My first thought was an old rocker arm, too. Don't really know anything about your engine. I'd hope it was that or a pushrod, as stated above.
Its a 70' 383. Heads have been reconditioned. Typical modifications...aluminum intake, mopar performance cam, carb...yada yada. However the valve train is bone stock and has been apart twice.

- - - Updated - - -

...And so it begins. The rocker arm covers...I appreciate the prompt replies. I just wanted to make sure I wasn't going off on some crazy ill informed path...thanks guys
 
I rebuilt a small block years ago that within a week developed a noise that was one chewed out exhaust valve guide. Head off and had guide replaced. Some time later it developed same symptoms you describe that was pushrod punched through an exhaust valve rocker. Good luck.
 
If you had a lifter with a concave surface i got bad news for you. The cam lobe that wore the lifter out it worn out too.
 
I you can find a lifter removing tool the intake can stay on the lifters will feed threw the head. You been using modern oils with low zinc levels? The old lifts need the zinc to lub properly and prevent early failure.
 
Is it possible that the Sparkplug wire is arcing to ground
Negative. That was the very first thing I looked at..hoping it would be something silly and simple lie that. No such luck : (

- - - Updated - - -

If you had a lifter with a concave surface i got bad news for you. The cam lobe that wore the lifter out it worn out too.
Or maybe not....That event was over two years ago. The cam was still fairly new. So I pulled the old lifters, replaced with new ones, lubed everything up properly and preceded to go to shows, a few interstate top end shots, and cruises with not so much as a squeal. The motor ran great and ran strong. I don't know what has cause it this time around... maybe it is that...but I won't know for sure until I lay my own eyeballs on it.

- - - Updated - - -

I you can find a lifter removing tool the intake can stay on the lifters will feed threw the head. You been using modern oils with low zinc levels? The old lifts need the zinc to lub properly and prevent early failure.
Ya...but I prefer to take it all apart. I can see what shape everything else is in, maybe catch potential problems before the get bigger. Yep, I know about the zinc additive...been doing that for awhile now...since buying this car (five or so years).
 
Ok. So looks like I've discovered the problem. One of the rocker arms on cylinder no8 can be moved (by hand) up and down just slightly. It should not be possible to do that by hand. I'm not sure if it is on the exhaust or intake side...Look straight at the front of the engine with the even numbers on the left...as I'm sure you all know no.8 is last one in the rear on left side of the engine..the "flippy" rocker arm is the first one on the cylinder (I forgot if its intake or exhaust..intake?). Anyways I'm sure that lifter is collapsed. Gonna take it all apart, inspect everything...hopefully I did not bend a push rod...or worse. If I have to dig into though then I'm gonna get some better stuff to go back in...been thinking about getting a new cam...I might like a little more ummph downstairs. Any suggestions?
 
Time for a new cam and lifter and to be honest you probably want to look at a few things closer if you keep having flat cam issues with proper break in and lubrication zddp levels etc..such as coil bind, retainer to valve stem clearance etc etc. The valvetrain can drive you nuts if you arent careful.
 
First one at the rear passenger side is exhaust, not that it matters at this point. If you look at the valve train, the exhaust rockers are inline with the exhaust ports. Hope it's just a worn rocker arm cup or bent pushrod. Good luck...
 
I agree with some of the others, one my cars had a ticking at rpm above 2500 turned out to be a collapsed lifter. Replaced it 200 miles later same problem, this time it was the lobe on the cam. Time to upgrade your cam and lifter set up. If nothing else a good excuse
 
Ok. So I've removed the rocker arms and shaft from the pass side of the engine. The first thing I notice is the one push rod (where I could move the rocker arm by hand slightly) was out of place. In other words the bottom end of the rod was not sitting directly down into the lift plunger..it was off center, sort of sitting on the left side lip of the lifter. I don't think it could have moved into that position, by accident while I was removing the shaft. I also pulled both push rods (for intake & exhaust). I ran both across and absolutely flat glass table top. Both rods were completely flat and rolled easily on their own across the surface with little effort.

Visually I can't see anything wrong with the suspect lifter. Here's a pic....its the lifter on the right. Its been my experience that no problems is this easy to fix..meaning I don't think the rod just "popped" out of place. However, I would rather not go in and distrub anything if there is nothing wrong either.

I dunno, whadday think? Any eagle eye see something I missing with that lifter? Should I pull them all out now that I'm in there anyways? I'd hate to do that if this is just a stupid little problem. Everything else looks fine to me.
 

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Pull the lifter out of the bore and take a high resolution picture of hit and the cam lobe....
 
Pull the lifter out of the bore and take a high resolution picture of hit and the cam lobe....
I know this may be a stupid question but here it is anyways....if I pull one lifter out, and there's nothing wrong with it, can it go back in? I mean I KNOW it can go back in, but do I want to disturb it when I can see the plunger is not damaged? Last time I replaced them I could clearly see that the noisy lifter was collapsed..the plunger was crushed down.
 
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