I think I can here ya KNOCKING!

-
Valkman

Valkman

Well-Known Member
Joined
Sep 13, 2012
Messages
954
Reaction score
292
Location
NC
So I've been working on getting my 65 Barracuda up and running and of course I've run into several issue along the way, and the people on this great forum have really help me out so far.

Now I have another one.

What I have is a recently reworked over '73 340 with solid lift cam that I got with the car, it's connected 904 Trans with a high stall conerter. I've been having trouble getting to idle right, but other than that it's been running really strong. That is until the other day. I took it out for test drive and it was running great, but it then started to have a mild rapid knocking noise! I tried pulling the spark plug wire test on each cylinder one at a time to see if the knock went away but it didn't. I went ahead and pulled the valve covers and even the intake and the valve train and cam and lifters all look good. Is there some other tricks I can use to try and determine if it is indeed a rod knocking or maybe something else without tearing the engine apart 1st? I think I can rule out "piston slap" because the knock is still there even after the engine gets good and warmed up.
 
Flex plate or converter snout. I broke half of a converter snout off once on a 904 and it sounded like a valve train knock. It stayed in place and didn't leak but the noise was bothering the heck out of me....
 
Oil pressure stay the same? Also like mentioned above, check converter/flexplate.
 
OK, a few questions: original trans? IF so, look at your flex plate. I bet its cracked if its the original trans and no 1/8 thick bushing was used on snout. Mine broke 3 ears and kept working until I threw a piece out on the freeway, bounced up and hit the floor with a loud clack and bounced down the road behind me. Remove 1 convertor bolt at a time and see if any ears fall out. Running headers? Check for heat pulses around exhaust flange while running. 3rd, just drop the pan and start jiggling rod caps. Itll be quite obvious if there is a bad bearing.
 
on my old 440 with 727, the torque converter bolts kept backing out, sounded like a rod knock.
 
You may be able to use a broom handle or some solid wood rod to more closely ID where the noise is coming from; place one end firmly on the block or where ever while running, and put the other end up to your ear and listen. Move the rod around to locate. If the flex plate, it will show up at the back of the block or on the trans bell housing the loudest. A rod could be anywhere.
 
So if it's the flex plate or the converter, could pull the cover off and see this?
 
yes, pull plate and undo a bolt at a time to see if the ear is cracked. If it is, it will fall out when the bolt is removed.
 
pishta said:
OK, a few questions: original trans? IF so, look at your flex plate. I bet its cracked if its the original trans and no 1/8 thick bushing was used on snout. Mine broke 3 ears and kept working until I threw a piece out on the freeway, bounced up and hit the floor with a loud clack and bounced down the road behind me. Remove 1 convertor bolt at a time and see if any ears fall out. Running headers? Check for heat pulses around exhaust flange while running. 3rd, just drop the pan and start jiggling rod caps. Itll be quite obvious if there is a bad bearing.
Click to expand...

I believe the transmission in an AutoZone special, and came with the motor.
 
Valkman said:
Yes it is, would that rule out a spun bearing?
Click to expand...

When I spun a rod the oil pressure actually dropped a bit before going up when revving it, presumably because the rod moved away from the crank and allowed somewhat of a leak, so to speak
 
Distibuter cap on..flex plate will wobble.hit stone quard.
 
I'd try re-adjusting the valves first.

You sure it's not a header leak at the head?

Try all the simple cheap stuff first, it's not always doom and gloom
 
Did you get your idle issue resolved?

The broomstick idea works pretty good, but I switched to using a long steel rod, like a 3/8 drive extension; it fits better into my ear, and doesn't seem to be affected by my holding on to it. Run it along every intake runner and every exhaust port; Perhaps it's just a lifter or valve lash.
But then, it's hard to confuse valve-train noise with a rod-knock.
Every time I've had a rod go down, I had a dickens of a time proving which one it was, using a sounding-rod.I mean I knew it was a rod,cuz I recognized the sound, but which one? The noise was not easy to pin-point. Valve noises are easy to pinpoint,so, if it ain't in the valve-train or the fuel pump, or crank end-play, well then;Off with the Pan!
Took-a ,took-a, took-a, took-a................somewhere deep inside.
 
No l haven't fixed the idle problem yet, but this seems like a bigger fish to fry right now.

I'm using magnum manifolds, and I don’t think it's the valve train, this noise is pretty pronounced. I'll take a look at the flex plate tommorrow and post an update on what I find.

All your input has been great, thanks so much you all!!!
 
distributer ...roter... cap will hit if not on correct.same sound. flex plate or bolts backing off u can still drive...metalic sound. next is a clapsed lifter.. u can still drive around. hope not that.....good luck. bent push rod ...back firing out of carb...I'm still running it lol...u runnin nitros?
 
Also check your bottom pulley bolts to damper. Makes a nasty sound when they are loose also.

Could try and see if damper will move fore and aft. Would be thrust bearing.

Rapid knocking at idle? Rod wouldn't be rapid at idle, but then again, don't know your definition of rapid compared to mine. I'd check for starters teeth to flexplate, flex plate teeth to something else or, and this happened on a new motor (sickened me till figured it out ), crank throw hitting dipstick. Sounds like a rod knock.
 
A trick I sometimes use is to slowly rev it up a little to about 1200 and then gently back off; all in one motion or doing. On the way up to that rpm, if it's a rod the knock-volume will increase just a little bit. Then,just as the engine transitions to no load the volume will decrease. Then as it returns, the volume will increase again. As soon as you have proved this, shut it off and don't restart it. Every second it runs is damaging the crank. The rod is probably already lost.No other noise generated by the engine does this.
 
FWIW

this is the number 7 or 8 rod with a spun bearing

[ame="https://www.youtube.com/watch?v=HAPH8xQPzCY"]20150706 181443 - YouTube[/ame]
 
There ya go! Excellent demo.
45 seconds of pure torture to the crank.
If you catch it real early,I have gotten away with just a bearing replacement.And a crush adjustment. But this is well beyond "early". This is the final stages of mass destruction........lol. That's like "I drove it home from nowhere-ville like that. I didn't even notice it 'til I stopped for gas. Good thing I was just a block from home!". heehee
 
A transmission funnel makes a good listening tool.
When the fault is cracked flex plate/flywheel, or converter snout, or just loose bolts in the back area, I can feet it in the floor under my feet.
I have removed all the spark plugs and got the knock with starter operation. This would often produce a extra knock the instant the engine stopped turning.
 
You must log in or register to reply here.
-

Back
Top