mwalls54 Posted April 29, 2008 Report Share Posted April 29, 2008 this is a fresh rebuilt 408 from LME with about 15 miles on it. at idle there is a very bad knock noise coming from the bottom of the motor, but as soon as i give it any gas it goes completely away. its idling around 800rpm and if i keep it around 1000rpm its gone. its not exhaust hitting on anything, oil pressure at idle is around 50psi and goes up to 80ish with the throttle. I have a couple of suggestions but i want to hear what other people think. VIDEO Quote Link to comment Share on other sites More sharing options...
zeake Posted April 29, 2008 Report Share Posted April 29, 2008 this is a fresh rebuilt 408 from LME with about 15 miles on it. at idle there is a very bad knock noise coming from the bottom of the motor, but as soon as i give it any gas it goes completely away. its idling around 800rpm and if i keep it around 1000rpm its gone. its not exhaust hitting on anything, oil pressure at idle is around 50psi and goes up to 80ish with the throttle. I have a couple of suggestions but i want to hear what other people think. VIDEO I'd contact LME. Quote Link to comment Share on other sites More sharing options...
misterp Posted April 29, 2008 Report Share Posted April 29, 2008 (edited) Something's busted in the rotating assembly of the motor for sure, it's frequency/rhythm is too slow to be valvetrain IMO. I'd call it rod knock; you might try listening to the intake and exhaust manifolds with a mechanic's stethescope (probe) to pinpoint which cylinder it is but that sounds like it's hammering so lound you'll never figure out which one it is because of the echo inside the crankcase. I'd pull the oil pan but you better contact the manufacturer and ask how they want you to proceede. Mr. P. Another way to figure out which cylinder it is, do a cylinder ignition/injector kill test, the knock will be far less pronounced when the cylinder is "coasting" vs. making power. Edited April 29, 2008 by Mr. P. (see edit history) Quote Link to comment Share on other sites More sharing options...
Tzer Posted April 29, 2008 Report Share Posted April 29, 2008 As above mentioned. get ahold of LME and I'd try to recoupe some $ for install labor x2 as well. Quote Link to comment Share on other sites More sharing options...
mwalls54 Posted April 29, 2008 Author Report Share Posted April 29, 2008 it runs on the street too good and has too good of oil pressure for something to be busted in the rotating assembly. I have ran it up to 6000 rpm driving it. Quote Link to comment Share on other sites More sharing options...
misterp Posted April 29, 2008 Report Share Posted April 29, 2008 it runs on the street too good and has too good of oil pressure for something to be busted in the rotating assembly. I have ran it up to 6000 rpm driving it. Then I'm stumped! Maybe it's something in the bellhousing? Loose flexplate bolt? Converter issue? I dunno... Mr. P. Quote Link to comment Share on other sites More sharing options...
sprayed99 Posted April 29, 2008 Report Share Posted April 29, 2008 (edited) it runs on the street too good and has too good of oil pressure for something to be busted in the rotating assembly. I have ran it up to 6000 rpm driving it. Call LME right away....did they do the install or was it a DIY install?.....was the windage tray clearanced for the longer stroke (could be wrong this may only apply to F-Bodies)? Edited April 29, 2008 by sprayed99 (see edit history) Quote Link to comment Share on other sites More sharing options...
dozer Posted April 29, 2008 Report Share Posted April 29, 2008 Call LME right away....did they do the install or was it a DIY install?.....was the windage tray clearanced for the longer stroke (could be wrong this may only apply to F-Bodies)? I bet its the windage tray also. I had to space mine for clerance for the added stroke with my 408. So did you put it on or them? Quote Link to comment Share on other sites More sharing options...
wody Posted April 29, 2008 Report Share Posted April 29, 2008 does have the kind of sheet metal sound like the windage tray was being slapped. could always pull the pan yourself, but thats what a warranty is for too. Quote Link to comment Share on other sites More sharing options...
Fireman31 Posted April 29, 2008 Report Share Posted April 29, 2008 It has 15 miles on it and you had it to 6000rpm already?? I sure hope LME ran it on a dyno to seat the rings........ Quote Link to comment Share on other sites More sharing options...
mwalls54 Posted April 29, 2008 Author Report Share Posted April 29, 2008 I have been running this 408 for a little over 3 years now so the windage tray is fine, With the last rebuild the motor has ran for a few hours while i was tuning the idle and letting every thing get set. it has about 100 miles on it now and i still have never gone over half throttle. the noise started after it had only 15 miles on it. Quote Link to comment Share on other sites More sharing options...
SS_bnoon_SS Posted April 29, 2008 Report Share Posted April 29, 2008 I just went through this SAME EXACT NOISE on my recent trans installation. On mine, I crawled under with it running and found that the noise seemed to be coming from the converter/starter area behind the bell housing. I pulled the starter to find slight nick marks on the edge of the aluminum area near the gear teeth. It seemed to be cocked just enough to touch the converter bolts as they came by, and/or the edge of some of the teeth, or maybe a balance weight on the flywheel?. I simply reinstalled the starter while making sure the starter stayed "straight" as it was tightened. Noise hasn't come back... Quote Link to comment Share on other sites More sharing options...
wkeil Posted April 30, 2008 Report Share Posted April 30, 2008 Drop the oil pan and starter first. i would contact lme and present that video to them. Quote Link to comment Share on other sites More sharing options...
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