I HAVE done research on this. I HAVE had other gear heads listen to the noise. Nobody has been able to diagnos it. I even took it to a mechanic - to no avail.
I have an AMX with a 401 in it. Large cam, well say .550 lift for simplicity sake and about 11 to one compression. The motor was rebuilt about 1500 miles ago. The sound didnt start untill about 600 miles into the break-in.
I have this annoying loud tick that wont go away. It occurs at all rpms except at idle. It gets slightly louder at higher rpms but not much.
It is not an exhaust leak. Replaced the headers and several sets of gaskets already.
It is not coming from the valve train. Take off valve covers and noise does not get louder. I have also replaced the hydraulic lifters and the push rods and inspected the rocker arms and springs. Rocker travel appears to be the same on all valves. I have adjusted the lash hot and cold and even with the engine running. The sound of a loose rocker is not the same as this tick.
Also, cam lobes were all good.
Feul pump and all external parts are quiet.
Can this be piston slap?
Internet sites tend to say no, that slap would not be consistent through the rpm ranges.
What the hell else can make a loud tick?
If it was something mechanical it would have quieted down by now(like a bolt on the fly wheel(that was checked too)).
If I really hammer it and then let off the gas, it seems to be a little quieter for a brief period.
It is not louder or quieter during ecceleration or decceleration.
Can you tell if the noise is coming from the top side or bottom side of the engine? Also, have you tried the broomstick handle trick to help pinpoint where the noise is coming from?
Sounds llike its coming from the sparkplug area on the drivers side. Plugs do not leak. I have not put a steth. or broomstick handle up to the engine yet. What would that tell me? Piston or wrist pin? do they tick? or knock? This does not sound like rod knock. Plus its always there(except at idle (warm or cold idle)).
A shop rebuilt it - A reputable one at that. That guy listen to it too and said in his opinion it was valvetrain. It`s not.
Anything else?
Sounds like Ill have to yank the motor but Im afraid its not going to be a piston. How can one diagnose a piston slap before yanking the motor? Is there possibly something Im overlooking?
(if you hold the motor at a certain rpm shouldnt slap be quieted?,this isnt the case here).
I remember reading that article online now. I couldn`t find it again when I wanted to reference it tho. I was in a flurry at the time to fix the sound.
I will try that and repost if it does not do a damn thing.
If anyone else has any comments or input, feel free to continue to add suggestions.
I was hoping someone else may have had these exact symptoms and found the problem not to be piston related.
Well, I suppose the easiest answer to this whole scenario is that since it was a reputable shop that rebuilt it for you they should be the one diagnosing it as long as they stand behind their work.
I think it is a possibility, but even if it isn’t once you pull the engine it can be gone over with a fine tooth comb and you should be able to discover it.
The piston slap idea is a good one unless you used the hypereutectic type pistons during the rebuild - these don’t expand like standard or even forged pistons.
To check for slop in the wrist pin/rod assy try unplugging one spark plug and running the engine, attach the plug wire and move to the next cylinder until the noise goes away.
Without the load of the fuel being fired, the noise should go away if the noise is caused by slop in that area of the rotating assy.
I have the hypereutectic type pistons. So they will not slap?
Also, I have tried the one spark plug at a time trick with no discernable difference in the noise. The sound comes in at about 1200 rpm even if the gas is just feathered with no load. Or mashed to the floor boards with a load. Always consistent always there and always pissing me off.
Its not a tick like a lifter or a fwip like an exhaust leak. Its a tack tack tack but a little louder.
I had an old ford with a 351 that did something very much like what you describe. Turned out to be the water pump. The front bushng was going out. R&R’d the pump and all was quiet again.
And how about the oil pump? A couple of times I’ve seen the intake screen slip and start causing a noise.
Both long shots, and I don’t know if they apply to your engine, but maybe worth thinking about.
Exhaust leak, but from nonexhaust area- IE, a cracked casting that allows a leak, but won’t be sealed with any header, manifold or gasket.
Rod bearing. If the clearance is out, or you spun a bearing, you’ll have a definite knock. But in these cases, it usually goes quiet when you lift off the throttle and you’d hear it at all RPM ranges including idle.
The 401 has the distributor in the front… timing chain slapping the cover? Loose oil slinger on the cam gear? How about the fuel pump, pump cam or pushrod?
Eleven to one compression is pretty high, likely necessitating "pop up pistons (domes that protrude above deck height.) The shop is reputable, but did they check valve-to-piston clearances? Also, I’m not entirely sure I recall correctly, but didn’t the old AMC engines have free-floating wrist pins? Or am I thinking old Dodge?
Anyway, if the pins are free-floating, a bad setup could allow the pins to knock the locking rings. After enough time the rings pop out and all sorts of havoc ensues.
I replaced the headers - I have eliminated exhaust leak. Even from the heads or the heat exchange in the manifold. Dont see or smell exhaust in the engine bay or telltale signs of carbon on any surface. Its not the oil pump screen. And it does not sound like a rod knock or bearing issue. Iv`e changed fuel pumps to no avail. The water pump is also out of the equation. I have thought about the oil slinger, and that is quite a project to replace, with everything on the front of the motor. It MAY be the oil slinger. The fly wheel is perfect ( 4 speed ).
I think piston to deck clearance it ok or I would have had a piston in my lap by now. I routinely take the rpm`s up to 7000. And this has been going on for about 1000 miles now with no increase in sound level(same noise all the time).
What I will do is fog the cylinders one at a time to check for piston slap, whilst going over the engine with a steth.
Thanks for the tips, I`ll post the findings.
Blown and Injected? Cool username
Are you a Heroin addict and a Cocaine user?
You are obviously referring to your current usage of intake delivery on your automobile…Right?
(wonder how many users know that?)