Young Z Posted July 21, 2009 Share Posted July 21, 2009 Is this the dreaded sound of rod knock? I had rod knock in the last engine L28 that I replaced a few months ago but it didn't sound anything like this. So besides rod knock what could it be? I'm stumped and have replaced the water pump and checked for loose stuff that maybe tapping the engine to no avail. Fingers crossed that its not what I think it is or bye bye Zs until after I'm done with school. oh and the pulleys are hooked up on the front of the car because its a pain to put the e-fans back in with everything bolted down. L28et, bone stock with msa downpipe. Quote Link to comment Share on other sites More sharing options...
jt1 Posted July 21, 2009 Share Posted July 21, 2009 It's sort of hard to tell from the vid, but it doesn't sound metallic enough to be a rod. I would check all the spark plugs to be sure they're tight, check the exhaust manifold to be sure it's tight with no blown gaskets, then check the rockers. Something up in the timing chain area might also be a possibility. You could also cut open the oil filter to see if you have any metallic debris. If you can borrow a stethoscope , slow the motor down, and listen you might narrow down where it's coming from. jt Quote Link to comment Share on other sites More sharing options...
woldson Posted July 21, 2009 Share Posted July 21, 2009 Yea, sounding heavy, however it is so different to hear all sorts of cameras, "idea" of what sound is. Quote Link to comment Share on other sites More sharing options...
MAG58 Posted July 21, 2009 Share Posted July 21, 2009 Rod Knock should get a little quiter at higher RPMs as the oil pump tries to compensate for the happy new space that bearing shell vacated. That said it would be a really metallic sound, and that doesn't sound like it. I got a sound similar to that once, it was because the header blew a hole in the side of the #3 collector. Are you running the stock ex. mani? If so check the EGR valve, they can come loose which will cause high idle and make that sound. Quote Link to comment Share on other sites More sharing options...
MONGO510 Posted July 22, 2009 Share Posted July 22, 2009 Not a rod. Sounds to fast for a rod at idle. Something hitting fan? Fan bolt to long hitting WP? Bent Alt. cooling fan? Quote Link to comment Share on other sites More sharing options...
Xnke Posted July 22, 2009 Share Posted July 22, 2009 Timing chain tensioner worn out, down to the metal like mine was? Mine sounded similar, but more of a whirr than a hammering. What RPM is this? 750? That noise, if 750rpm is close, sounds like it could be at least 2x engine speed. Check the oil pump, dizzy, valve train, any fans/spinning things, ect. Quote Link to comment Share on other sites More sharing options...
Young Z Posted July 22, 2009 Author Share Posted July 22, 2009 Not a rod. Sounds to fast for a rod at idle. Something hitting fan? Fan bolt to long hitting WP? Bent Alt. cooling fan? the clutch fan wasn't on the motor during the 30 seconds of run time. Timing chain tensioner worn out, down to the metal like mine was? Mine sounded similar, but more of a whirr than a hammering. What RPM is this? 750? That noise, if 750rpm is close, sounds like it could be at least 2x engine speed. Check the oil pump, dizzy, valve train, any fans/spinning things, ect. I'm not really sure about what the rpm is since the tachometer isn't hooked up at the moment. Thanks for the suggestions guys! I'm going to tear into it for another day or two and if I cant the resolve the issue then I'm just gonna have a shop look at it. Quote Link to comment Share on other sites More sharing options...
DiscoPotatoe Posted July 22, 2009 Share Posted July 22, 2009 the clutch fan wasn't on the motor during the 30 seconds of run time. I'm not really sure about what the rpm is since the tachometer isn't hooked up at the moment. Thanks for the suggestions guys! I'm going to tear into it for another day or two and if I cant the resolve the issue then I'm just gonna have a shop look at it. ive blown many engines in my 240sx usually one about every 4-6 months ( i dog the SH** out of them) i've always gotten the difference between a rod knock but never really heard one at idle like that only under a little acceleration idk thas just me Quote Link to comment Share on other sites More sharing options...
DREW RBZ Posted July 22, 2009 Share Posted July 22, 2009 Hmmm...I would have to agree that it doesnt sound like rod knock...I would go with the previous suggestion that it is timing tensioner/chain related...good luck and let us know!! Quote Link to comment Share on other sites More sharing options...
frank280zx Posted July 22, 2009 Share Posted July 22, 2009 look for shaft play on your waterpump.. i had one knocking like this before .. though camarera sounds dont really tell detail Quote Link to comment Share on other sites More sharing options...
jhm Posted July 22, 2009 Share Posted July 22, 2009 Like jt1 suggested, quickest route to solving problem is to narrow down location of noise source. If you don't have access to a stethoscope, any long steel bar will work as an alternative (e.g. long screwdrive, extension drive for ratchet wrench, etc) -- place one end of the bar on the engine and your ear on the other end. It's amazing how well it works! Move the bar around until you've located the source of your noise. Just as a crazy thought, have you recently hit anything that might have dented your oil pan? If it's dinged sufficiently hard, it will impinge inward and interfere with the normal rotation of the crank/rods, causing a very disturbing (but easily fixed) knocking noise. Good luck and let us know how it goes! Quote Link to comment Share on other sites More sharing options...
SHO-Z Posted July 22, 2009 Share Posted July 22, 2009 Old School Method, At idle remove one spark plug wire at a time. If the noise goes way or changes it is a rod. Quote Link to comment Share on other sites More sharing options...
m4xwellmurd3r Posted July 22, 2009 Share Posted July 22, 2009 Old School Method, At idle remove one spark plug wire at a time. If the noise goes way or changes it is a rod. lmao that's how I knew which rod spun a bearing in my old VW bug. It doesn't really sound like rod knock though. then again, I spun the bearing in my bug pretty bad when I did it (sounded more like a thrown rod) it could just be the audio quality, but it just doens't sound...metallic enough i suppose. have you tried probing the engine with a long screwdriver or something? Quote Link to comment Share on other sites More sharing options...
rinn240z Posted July 22, 2009 Share Posted July 22, 2009 I just had a similar sound in my 240. I dropped a valve due to bad machine work, they had ground the tips of the valves causing interference between the lash pads and retainers and the locks fell out. Anyway, my suggestion is to pull the valve cover and inspect it before you cause more damage. Remember the cam is spinning twice the speed of the crank which would explain the "fast" knock. Hope this helps Quote Link to comment Share on other sites More sharing options...
SHO-Z Posted July 23, 2009 Share Posted July 23, 2009 Remember the cam is spinning twice the speed of the crank which would explain the "fast" knock. Hope this helps The cam spins at half the speed of the crank. Quote Link to comment Share on other sites More sharing options...
rinn240z Posted July 23, 2009 Share Posted July 23, 2009 sorry, for the bad info. I'm dyslexic! regardless, i think you should check the valvetrain. Quote Link to comment Share on other sites More sharing options...
Young Z Posted July 24, 2009 Author Share Posted July 24, 2009 Turns out it was rod knock according to Ray @ Garage Autohero. We pulled the valve cover to check things over and the head looks fine. He thought it was really wierd that it just started knocking in at a more noticeable volume but said it was rod knock none the less. 2nd motor in 6 months and I'm starting to lose the motivation to get this car running again. I'm going to start looking into places that I can store it while I amass some money for a rebuild but this car has been very troublesome from the get go and I'm tempted to just sell it and never look back. Quote Link to comment Share on other sites More sharing options...
luckygerman Posted July 25, 2009 Share Posted July 25, 2009 It sounds like something is out of balance, like your harmonic balancer or something near your bellhousing.I would take a Stethoscope, pull the metal piece off so that all you have is a hose and listen to the Oil Pan, valve train ect. Quote Link to comment Share on other sites More sharing options...
HowlerMonkey Posted July 26, 2009 Share Posted July 26, 2009 I've heard loose torque convertor bolts make that exact same sound but that is rare. That sounds like a lot more than 750rpms in that video....more like 1,100. For rod knock diagnosis you cannot use a constant rpm....just tip into it a couple of times slightly and see if the character changes. Quote Link to comment Share on other sites More sharing options...
DiscoPotatoe Posted July 26, 2009 Share Posted July 26, 2009 sorry about the engine man hope you manage to get it going again Quote Link to comment Share on other sites More sharing options...
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