Can rod knock come and go?

89whitepkg

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#1
So, I thought that I may be getting rod knock. However, the nosie seems to come and go....can rod knock do this? It is best heard at idle and smooths out as you speed up. However, some days you can hear nothing.....it's just as smooth as can be. I know it is comming from the engine, but I'm wondering if it could be in the valve train.....lifter or shim. It is not a really sound like a valve ticking...more of a thump. I was wondering if it could be the spark plugs, the plugs are from the last owner and I think they are bosh platinum. It doesn't sound like a miss, it's not that random.

Also, I'm planning on pulling the engine this summer. If it had rod knock will it be visable on the bearings?

let me know what you guys think
 

7MGTEsup

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#2
Rod knock can't come and go. Once enough damage has been done that you can hear the rod rattling there is no way back.

Common noises that get confused with rod knock

Loose Cam wheel/s
loose drive plate (auto's)
loose TV damper
 

GrimJack

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#4
And yes, the bearings are an extremely easy indicator. :)

Very early stages of RK can come and go, but they will be easy to reproduce on demand - park the car in neutral, let it idle, then blip the throttle so that the RPMs bounce up to about 3k, you'll hear the knock as the RPMs peak and start to drop.
 

Mk3runner

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#5
time to yank to bottom end out and catch it before it gets worse. either that or be ghetto and change to a thicker oil.
 

89whitepkg

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#6
so as long as there no damage to the crank I can just change the bearings right?
If it's damaged i need to get it cut right.

I'm building a diffrent engine right now to swap in....but my little brother just bought his first supra this week and he was going to use this engine.
 

Mk3runner

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#7
pretty much, I'd still mic the crank tho. be pretty pissed if you went standard size bearings and ended up with the same problem.
 

89whitepkg

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#8
so, i just ran the car up to 3k like suggested ....nothing at all. Early this morning on the way to school I heard it....but not the rest of the day. CAN"T DUPLICATE???
 

Nick M

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#12
Yes it can come and go. Depending on the cause of the noise. The bearing is filling up with oil. That often shuts it up.
 

IJ.

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#13
^ Yep lightly loaded at high enough rpm so there is enough Oil volume to fill the increased clearence the knock will go, load the motor slightly and it'll displace the Oil wedge and knock some more.

There is also a point in the rpm band unloaded where it'll cancel out and be quiet free revving the motor.
 

gaboonviper85

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#15
I have a feeling that if this car is a five speed then he is just letting the clutch out too fast too soon while going from a dead stop...when you do that you can usually hear the motor start lugging and its at its almost stall point...you say its not constant so are you actually paying attention to rpm when it happens?

If its makeing that chatter/diesel engine sound then my guess is that you kind let off the clutch a little to soon.
 

89whitepkg

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#16
I have a feeling that if this car is a five speed then he is just letting the clutch out too fast too soon while going from a dead stop...when you do that you can usually hear the motor start lugging and its at its almost stall point...you say its not constant so are you actually paying attention to rpm when it happens?

If its makeing that chatter/diesel engine sound then my guess is that you kind let off the clutch a little to soon.
i know what your talking about and it's not that.
 

starscream5000

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#17
so as long as there no damage to the crank I can just change the bearings right?
If it's damaged i need to get it cut right.

I'm building a diffrent engine right now to swap in....but my little brother just bought his first supra this week and he was going to use this engine.
ALWAYS, check the clearances of something important such as rod and main bearings. Don't assume the size of them being standard, if you do that, you could very well be back in this same boat or worse, seize the motor.

"When you assume you make an ass out of you and me" ;)
 

ATL88Supra

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#18
Do you have a automatic trani ? i had this same thing turned out that it was my crank bolts holding on my flywheel/drive plate i ended up shearing them all off at the drag strip but it was knocking for along while
 

Rennat

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#20
do you get it on cold start-ups in the morning? but not when its hot outside? if its that, i use to have that... but its gone now thats its warmer. and i run 5w30