Knocking sound at idle

TurboSupra7

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#1
I just recently (about two months ago) purchased my 1990 Supra Turbo w/ manual tranny. I absolutely love this car and it runs great, it boosts strong and pulls hard until redline. Lately though I've noticed a kind of clunking sound at idle. Once I start accelerating the noise disappears, either that or I can't hear it over the exhaust and engine noise. The strange thing is that it doesn't always make the sound, but over the past week or so it has been doing it pretty much every time I drive the car. Sometimes the sound is very quiet and the radio must be turned down to hear it, and sometimes it's fairly loud, and I can feel the vibration through the shifter. Klunk, klunk, klunk, and a quick rev makes it disappear. Please help, I don't want my new car going to the shitter!
-Nathan-
 

scottiedawg66

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#2
whats ur oil pressure. change out your oil and run 20-50, if this cures the clunk cluck as you describe, you have rod knock. My car clicks at idle due to vavles, not rod knock.

~scott
 

lagged

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#3
scottiedawg66 said:
whats ur oil pressure. change out your oil and run 20-50, if this cures the clunk cluck as you describe, you have rod knock. My car clicks at idle due to vavles, not rod knock.

~scott

the heavier oil wont "cure" anything. all it MIGHT do is quiet the sound for a little while. itll come back, rest assured.
 

TurboSupra7

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#5
are you guys confident that this is rod knock? Would a bad throwout bearing or old gear oil in tranny cause this at all? I really don't want to have to get rid of this car
 

TurboSupra7

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#8
Well I guess that isn't the problem then, because the noise continues whether the clutch is pushed in or not.
Damnit this is fucking bullshit. I blew all my money on some piece of shit, how long is this thing gonna last? If that is the deal then I guess I'll restart my search for an AE86 corolla.
One last thing, why can't I hear this noise any other time that idle, shouldn't it get progressively louder with RPM?
 

IJ.

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#9
With the increase in revs the oil pressure comes up fills the gap between the bearing and crank and the noise goes away.

Eventually the bearing wears enough that the oil can't achieve this anymore and you get the knock all the time.
 

americanjebus

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#10
what if you have an auto. i put mine in drive and i get this weird sound as if the tranny wasnt alligned with engine right i put it in neutral and its gone but it does this seldomly. almost as if i hadnt harnessed exhaust and i know i did.
 

GrimJack

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#11
Many things can cause a knock sound at idle. Most of them are loose or broken parts. See if you can figure out where the sound is coming from in general - is it louder on one side of the engine or the other? Could your engine mounts be broken? What RPM does your idle sit at? How far up do you have to rev it for this noise to go away? (Get someone to report the RPM from the driver's seat while you rev it manually from under the hood.)

Rod knock usually starts at about 2500rpm, and gets more noticable across a wider RPM range as it gets worse. The easy check for rodknock is this:
- Shut off the car
- Unplug a spark plug lead
- Start the car. Noise still there? If yes, go to step 1. If no, you have rod knock on the cylinder you just unplugged.

The only time this doesn't really work is when you have rod knock on two cylinders or more. :)
 

VanSupra

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#12
TurboSupra7 said:
are you guys confident that this is rod knock? Would a bad throwout bearing or old gear oil in tranny cause this at all? I really don't want to have to get rid of this car
Check to see if your pressure plate is tight on the flywheel. Also a loose harmonic balancer that was incorrectly installed can also simulate the sound of rod knock at the back of the engine..hth
 

TurboSupra7

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#13
Actually, the noise only happens at idle, even the slightest rev makes the sound disappear until it returns back to a steady idle and the noise comes back. My idle tends to sit at an even 650 RPMs, however sometimes it will sit at around 1000-1100 RPMs which I don't understand either.
Also the sound seemed to be emanating from the rear of the motor, but I can't be sure about that until I double check, which I will do on wednesday, and I'll also do the spark plug check on wednesday as well, but wouldn't I get rod knock whether the cylinder was getting spark or not?? Because isn't the piston still going to be moving in the same way with or without the spark?? Thanks for the help guys!
 

TurboSupra7

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#14
well i drove home from work today (about a half hour drive) and didnt get the sound until i was about two minutes away from home, and i noticed that the lower the idle is the louder the knocking is, for example when I have my foot on the brake or am rolling the windows up the sound gets noticably louder. I don't know if this means anything at all but I figured it may be worth mentioning. I also noticed the sound gets progressively quieter up until about 1000 rpms and then disappears, would rod knock be loud enough to hear over my 3 inch exhaust and the sound of the motor? THanks
 

GrimJack

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#15
Rod knock will get louder as the bearing wears more, until it's so loud you can hear it over your stereo / engine / mac truck using the engine brakes beside you on the freeway.
 

rakkasan

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#16
VanSupra said:
..... Also a loose harmonic balancer that was incorrectly installed can also simulate the sound of rod knock at the back of the engine.....
Get a 3/4" socket & a long breaker bar & tighten the shit out of your HB. To stop the motor from turning, take of the tranny cover & have a friend hold a flat tip in the teeth of the flywheel. I had to do this after repairing a BHG, I had the same type of knocking sound.
 

Boostedstr8six

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#17
rakkasan said:
Get a 3/4" socket & a long breaker bar & tighten the shit out of your HB. To stop the motor from turning, take of the tranny cover & have a friend hold a flat tip in the teeth of the flywheel. I had to do this after repairing a BHG, I had the same type of knocking sound.
Or just put it in 5th gear and apply the parking brake.
 

IJ.

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#19
GrimJack said:
Rod knock will get louder as the bearing wears more, until it's so loud you can hear it over your stereo / engine / mac truck using the engine brakes beside you on the freeway.
Shortly followed by the little man with the hammer smashing a hole in the side of the block so he can escape! ;)
 

huntin5L

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#21
i get that noise also, everything seems to be ok, but mine sounds like woody wood pecker as they use to describe it in the last forum. Its annoying, but i don't think its a rod knock.
 

americanjebus

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#23
mine sounds exactly like a f250 turbo diesel. cept not as loud. its like i can hear the cams spinning like in the f250 thats best way i can describe mine
 

Shawndude

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#24
The sound could be anything. From an exhaust leak, to loud alternator bearings or a blown engine.

Buy a mechanics stethoscope for about 10 bucks, and track it down. The crystal ball of sound analysis, doesn't work too well over the internet.
 

TurboSupra7

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#25
Where exactly can I find the bolt to tighten the harmonic balancer? It seems pretty tight back behind the engine, doesn't look like I could fit anything back there. Thanks
 

Blue87T(Dan)

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#31
Is this something that you hear when you inside the car with the windows up at idle but can't hear if your outside the car with the hood either up or down?

Have any fuel mods been done to the car?

Dan
 

huntin5L

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#32
for me, i hear it inside my car at idle with the windows up and when you lower the windows you can't hear it pretty much at all
 

Bigdough666

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#36
Make sure everything is tight.

When I 1st started my car after my rebuild, everything was cool, then all of a sudden I got this SUPER LOUD NASTY KNOCK, and I was like WTF?? Took the front cam cover off, and turns out the cam gears werent tight, so they were hittin the cover.

Does it sound like popcorn? OR marbles in a can? If so, it could be detonation, which is also bad. Using 93 octane? Hope its not rod-knock, good luck with it.
 

TurboSupra7

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#39
well in my situation, as previously stated it sounds like a woodpecker peckin on an ol' oak tree or somethin. I can't hear it inside the car with the windows up only when the windows are down, and when I put stress on the engine (i.e. windows being rolled up or down, or putting my foot on the break) it becomes twice as loud. I assume this is due to the drop in RPMs under stress, for the most part I can't hear the sound at all until stress is put on. Sometimes however it will do it without any added stress, but as i said it gets much louder with the stress. I think i overused the word stress, hehe.
Still haven't had a chance to tighten up that HB as I dont have proper tools at my current residence, but do ya'll think it may be worth checking those cam gears? Thanks.