About hit the limit on troubleshooting this...I got a loud knocking noise at idle when the engine is warmed up (everything expanded I suppose) But when the rpms get above around 1500+ it goes away. Timed it anywhere from 30-40 total timing, ported/manifold vacumn, no difference at all. I pulled plug wires to isolate and hooked up an electric stethescope and got it down to the #2 cylinder bottom end. The knock/tap doubles in frequency when I pull the plug wire on that cylinder. Also, when you run it up (goes away) and let it spin down it comes on loud intermittently, then has the knock at idle (pattern). I already changed the fuel pump and pushrod, tightened all exhaust manifold bolts, etc. Any thing else before I pull the pan? The car runs great and pulls hard from 2000-6500 rpm with no oil pressure problems or hesitations.

I'm fed up with this noise: BTW I just ordered a custom 355 to drop in, since my car is NOM anyway. Still would like to find out what is wrong with this 327, rebuilt 2yrs ago from what I know of it.
Thanks, EZ sends

 

If it was 'piston slap' it should lessen as it warms up. The skirts would expand with heat and decrease the noise. REAL common with forged pistons. The fact that the frequency doubles with th plug wire off, sounds like rod bearing clearance to me.

 

Take off the valve cover and see if the rocker fell off the pushrod. I had a pushrod bend because I have a matching set of heavy springs with my big cam. The rocker fell off and it created a funky noise like that-- the pushrod was hitting the valve cover!

It's not necessarily likely, but it is something to check out. You may find something else under there.

 

d1_bradley,
Yeah I thought piston slap lessened at temp also, but trying to get a sanity check here after taking it to a couple of shops to diagnose. One shop thought the piston was walking. I had the valve covers off last week and adjusted the valvetrain to see if it made a difference...none really. If it was rod bearing clearance, wouldn't I hear the noise at high rpms also? I might try to loosen up the rockers on that cylinder again, maybe it is too tight? Gotta friend with a borescope so if I can track him down, maybe I can try to peek at the cylinder...Wadda ya'll think.... Thanks, EZ sends

 

I had a 240 ci 6 cyl ford van years ago that did the same thing. No probs other than a constant rapping, and it went away at hi rpms also. Finally got too irritated with it and took it apart. The only thing I found was one piston with too much clearance. Put a new piston in the hole and the noise was gone. Probably woulda went forever with no probs, but ya just never know. So I'm going for a piston skirt with too much clearance. Our old forged piston 2 stroke dirt bikes used to rattle like mad but ran fine. Don't think it's a rod, those would get noisier with revs and get worse with time. Hope this helps ya some. :cheers:

 

I agree. It sure sounds like it could be a rod bearing to me. The fact that it stops at a certain rpm has me confused as I think about this however. If it is a loud solid rap like a knuckle hitting a real solid desk top or a solid wood door I gotta stick with the rod bearing theory even though it stops at a certain speed.

Better shut that baby down and don't drive far from home till you figure this out.. When rods "go away" they go away big. If you have it down to that one cyl. and the valve gear is ok it has to be in the rotating parts. You can pull the oil pan down in a very short time on these cars. Just unhook the center link and one tie rod. Then you know one way or the other for sure what is happening.

I am back again after signing of this thread a second time. Could this be a wrist pin? Does this engine have floating pins in it? If one of the locks has found its way outta the piston... Well you would know that real soon. If the engine has pressed pins perhaps that cyl has a piston that cannot rock back and forth correctly on the pin? The fact that this motor pulls strongly to higher RPM and the oil pressure is OK points away from the rod bearing and the change in frequency when you pull the plug off says the problem is below the plug. If the bearing were ruled out it has to be the piston or the pin.


[Modified by TheOman, 8:28 AM 4/20/2002]


[Modified by TheOman, 8:34 AM 4/20/2002]

 

I'd call it a wrist pin, especially because it doubles in frequency when you pull the plug wire :(

 

I'm thinking wrist pin also. My neighbors old truck with a 350 was knocking and he was certain it was a rod. He was waiting for his budget to allow a new engine and put off doing anything about it for over 20,000 miles. When it started guzzling oil (rings) he took it to a friend for a complete rebuild. After tearing it down he found that the "rod knock" had been a loose wrist pin. I suspect whatever it is may seem quiet at higher rpm due the increase frequency blending the individual knocks and the increase in sounds from the rest of the engine. In any case, good luck!

 

Thanks for all the responses...definitely thinking wrist pin. Well only a week til the new engine comes in...Hopefully have it installed by mid may, time permitting. Man, don't want to garage it that far into spring but oh well. Will let you all know what I find when I tear it apart... EZ sends

 

I had a wrist pin walk on a "rebuilt" ( hate that term) motor some years ago. It was doing exactly the same thing. Only at certain speeds. Dropped the pan and there it was. Had to resleave the motor as it was the original and I wanted to save it. Turned out the pin was a press fit ( low hp ) and was overheated by the rebuilder.......he redid for zero $, but the labor was on me.
Let us know.
Jim