clacking noise under acceleration - (solved)

[Falco]

Howdy,

Since my rebuild this winter (new L35 heads, rockers, springs, pushrods, 50's, PT52, Innovative WG) I can hear a clacking noise when I'm on the trottle. I can't hear the noise when the turck idles, or when I rev it up in P or N or when the truck decelerates. It seems to be RPM related. I thought this over several times, here comes my "mental path":

*Since I can't hear it at idle it's not a valvetrain noise, even if it's sounds like it

*I thought it's an injector tick, so I moved up the fuel rail and all the injectors to the highest position. The noise is still there...

*Exhaust leak? Can an exhaust leak sound like clacking!? I'm using copper SCE header gaskets, which fits like sh*t so there could be leak(s) there and I've a definitive leak at the end of the downpipe. Any experience with the SCE gaskets or with sounds caused by exhaust leaks are appreciated...

*The truck idles great and performs acceptable beside it has serious spark retard, I guess, because the knock sensor is picking up the same noise (I've no real knocks according to the spark plugs, no lean conditions etc)

*The noise seems to be there only when the engine (drivetrain?) under some load or from an other viewpoint when the timing is not so advanced (is this a good though?), but I'm running out of ideas, so pls HELP if you can!

TIA,

 

[Buster]

This exact noise has been haunting me for two years. When I had the poly mounts it was very noticeable, now with the stocker it's less noticeable, but still there.

My only guess is the poly mounts put the tranny a little closer to the cab floor boards, maybe the fuel lines are touching giving off a clicking like pulse.

My next attempt will be to replace the cab mounts maybe giving me a little more clearance under the cab.

 

[Dealboy]

i have a wierd noise only under hard accelaration also and i know my motor mounts are shot. Maybe that is it.

 

[Falco]

Thanks guys. I'd say my motor mounts are in good order, at least the usual symptoms of broken mounts are not there.

The fuel lines is a good bet, I'll check the clearence around them. However I've not removed the tranny or the engine, so I don't see how could anything changed down there. The only thing somewhere around this area, which I changed is the downpipe. It's really close to the frame, but if it's rubbing it would give a different noise IMO.

Anyway. if I can't eliminate it, I'll have to relocate the knock sensor. You have already done this, righ Mark?

Later,

 

[Buster]

Yeah I already relocated it. I'm sure it's not perfectly calibrated, but seems to work fine.

 

[Falco]

Mark,

Do you have a picture of the sensor on the new place. That seems to be my favorite question Today. :-?

BTW, I've spent a significant amount of time under the truck Today and now I'm quite positive the noise is comming from the downpipe rubbing against the TC cover and frame. Will be a pita to correct this...

Later,

 

[rarebit]

i had a noise like that before. it was the crank hitting the oil pan. i found out what is was real quick though.

 

[Falco]

Since I found this thread searching and I've made some progress in the meantime, I though I update it.

The clanking noise was an exhaust leak between the heads and manifolds. Removed the SCE copper gaskets and it went away at once. So far so good. Did a couple of hundreds miles on it since then, no leaking at all.

I've also corrected my downpipe rubbing against several things (heat shield-removed, frame-DP modified, tranny house- grinded down), but my falso knock problem is still there...

Peace,

 

[Pittman]

That SCE header gasket is gonna leak unless you re-torque after about 5 heat cycles. I personaly like the lead mesh style, but use sce most of the time.