502EFI Internal noise diagnosis...Listen
 

Ok, here's the deal......view video and send in your diagnosis. A few points to note......Motor has good push rods, bearings, rockerarms and all other mechanical parts except what's causing this noise.

*Final Note: Noise goes away when we remove the #6 spark plug wire........

H-E-L-P

http://www.youtube.com/watch?v=cTvA1...ature=youtu.be



Here it is running good without #6 plug wire.....

http://www.youtube.com/watch?v=6StcU...ature=youtu.be

Compression test? Does it idle smooth? It almost sound like it is popping back thru the throttle body.

Is this a quiz, or do you really need help?

Nope, not a quiz.....Need help

SOUNDS LIKE NO. 6 WIRE IS ARCING SOME WHERE!!! LOOK FOR ARCING FROM COIL TOWER TO POST ON CAP.....kEN

do a compression test... could be a bad valve

Probably not much of any help here, but interested. Agree on the bad plug wire but sounds loud for an arc. very hollow sheet metal like and rythmic not steady. (is it just following the slight lope of the idle?) Rocker hitting valve cover?

How would a valve sound like that? would think more back fire sound if it was bad. If it was sticking and smacking the rocker arm or something it wouldn't stop just because you pulled the plug wire.

Don't shoot me here, but how about a wrist pin?

Not that you'd run it like that under load, but when it started making the noise[GOOGLEVIDEO][/GOOGLEVIDEO] was there any lack of power or anything?

Just throwing some ideas out.

Exhaust manifold gasket leaking at the #6 cylinder would be my guess.

What were you doing when it started making the noise ?

Fixx
 

1) cyl 6 could be miss firing and causing the exhaust tio flap to bang away,,make sure theirs rubber on the flap or stichk your hand in the exhause when its running when the engineis stll cold(first starting the engine)

2) i have seen a misfire cause what they call a spark knock,,thats when the #6 cylinder is not firing on time and the cylinder prefires and causes a knocking noise...try changing the spark plug and start it,,if its still their try swapping the plug wire with the other engine..

3) broken valve spring and the valve is hitting the piston,,inspect #6 plug for color,,listen the that side of the exhaust,will sound different than the others..could be exhaust valve spring or even a bent push rod..

4) good luck!

Thanks for the replies!! Sorry, meant to update more information sooner.....

Motor started making this noise one day getting up on plane leaving the harbor.....

At the time of the video, which was last Friday. We had already broke the entire motor down (because we thought it was spun bearings), checked everything internal and all looked good except a bent push rod. Replaced that and reassembled with all new gaskets and plugs, etc etc.....Put the motor back in and the noise is still there......

Replaced the #6 spark plug wire, noise still there......

Swapped injectors, noise still there.....

No lack of power either......hope this helps

Thanks again for the ideas, hope one of them is it!

I would bet broken valve spring on #6.

yep,easy fix.

After listening again, I don't think the noise is consistent enough to be an exhaust leak. Valve train problems generally have a more consistent noise also.
I had a very similar noise on an SC'd SBC in a street rod. It ended up that the clearance was too tight on a wrist pin. There was no metal in the oil and no obvious damage until the wrist pin was removed.

fixx
 

when you say tore it down did you just pull the oil pan and look at the bearings?? its a sharp noise and sounds like either you broke a valve spring or one of the lifters may be slamming on the cam,,are all the dog bones for the lifters on correctly?
i remember on the gm trucks they had a distributor problem and would make a banging noise when the bushings wore out ..

Yes, took oil pan off.....everything looked good

thinking about basics,by removing plug wire while running, loading change is to wrist pin and rod bearing. also eliminates some exhaust pressure on that cycl. result from these changes.exhaust flapper,wrist pin,rod bearing. check and let us know,good luck

Would I be correct in assuming you did not remove the heads? That noise sounds to me like the piston is hitting the head. I suspect the piston is broken since it doesn't have a rod bearing piggybacked.

Heads came off, all checked out good unless we missed something? new head gaskets and reinstalled.........

Thanks to everyone for the replies!!

Sounds to me your exhaust valve is not opening all the way, and it is backfiring through the intake.

You mentioned a bent push rod, was it an exhaust valve rod? Chance that you siezed a valve and wiped a lobe off the cam?

Take the valve cover off and watch the rockers at idle.

fixx
 

ok i got a good night of sleep on this one,,what made the pushrod bend?? this is what i think is happening..the pushrod got bent obviously from the piston hitting the valve,,the stem on the valve could now be slightly bent and is sticking causing valve trane noise..most likely the rocker slamming into the pushrod..do a cylinder leak down test to see if you have any bent valves...i would start with the cylinder in ?

does not sound internal to me...not rymic enough...exhaust flapper of something in exhaust ?

my 496 is being rebuilt, corner of piston was floating around in cylinder. The compression test told the truth. It was #6.Caused a very odd sound.

That's why I was guessing exhaust valve not opening all the way, the backfire will not happen every rotation, not rythmic at all. The bent push rod says it all IMO.

I'm thinking like You. Artie

My exhaust flaps bang like that. Not steady, nor consistant. It sucks!
But odd that #6 removes the sound!
I would run it again in the dark, easiest to see arcing!

Also think what bent the rod to begin with?
Maybe the replaced rod is bent AGAIN?
Sounds like a piece of something floating around?

Hydraulic lifters?? Stuck? That would bend a rod, thus bend it again too.

On another note, looks like your running it in an enclosed garage? Overhead door was shut :(
Water running?? just my observation from the video

I would pull the valve cover an feel the rockers when spinning the motor. I really think its a valve. slapping a lifter back to the cam. You should be able to feel it if I'm right.

make sure your wearing your lifeline and the lanyards are attached!

Why would the noise disappear with the #6 wire removed if the rocker/valves/piston where contacting other parts or a broken spring? I'd think that those conditions would be there all the time regardless if #6 was powered or not???
The uneven noise is odd, in both sound and irregular clicking

I agree sounds like exhaust flappers. But the bent pushrod and the fact it goes away with #6 plug wire removed is odd.

Heat an combustion.

Hook your timing light to number 6 and see if the 'clank' coincides with the cylinder firing. Most likely it does, since it goes away with the plug wire removed...

Just thinking, since you had the motor out, assume you had the exhaust off, which rules out exaust gasket leak.

Whatever noise it is has to be related to number 6 firing since it goes away when you pull the plug wire off.

I still say...wrist pin.

Since the noise goes away when the #6 plug is removed, have you checked the distributor cap and rotor? Maybe something funky is going on in there.

muffler bearings aren't synchronizing

Thanks everyone!!!

good one Ben :lolhit:

Got a sound close to that now and I beleive it's y pipe exhaust flappers... At higher rpm it goes away.

I say the bent pushrod was on an exhaust valve and it is now bent again.
If it was a rotating part it would be rythmic - it isn't.
Had that happen before. Time to do a valve job and bronze wall the guides.

I agree that it does sound similar to the sound that counter weighted internal exhaust flappers make. Exhaust flapper noise also goes away around 1200rpms.
That does not explain the prior bent push rod or why the noise stops when the #6 wire is removed.