Engine knock

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Good day,
At idle there is no knocking, at high rpms there are none,
But say 4500 rpm there is a "knocking sound",
You all think engine the engine is bad, or am i lucky and its one of the pulley bearing?

And the knocking noise can only be heard for the split second as I let my food of the throttle.

Please tell me it could be a pulley. :-(
ONly recently this engine was installed and now this.
Oil was changed recently with a store brand 20w50.
I used valvoline maxlife before.
 
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I believe you posted something earier about this, and there was a recommendation given that you change out the store brand oil with a brand you've successfully used before. Valvoline Maxlife or the Royal Purple in your signature would be fine. Use a filter that you've used before as well. That will either solve your problem or we can remove those variables from the equation and start looking at other possibilities.
 
Sometimes theres a loud rattling noise from worn spring tension belt tensioners in between shifts, as you let off the gas, but its hard to say without hearing it.
 
Yes i posted before,
I will change out the oil and filter tomorrow. Hopefully this fixes it.
This is my main daily now as the other car got sold, and i have to pay for University. So money tight :-(
 
But question for mechanically incline people
If my engine had a mechanical failure, wouldn't it be knocking 24/7?
and my car has full power and no smoke.
 
"Letting off the throttle" knock does not sound like serious internal engine problems. Maybe a vibration from a pulley, bad engine or transmission mount, loose exhaust component etc.
 
What happens if you hold the throttle steady, in neutral, at a fairly high RPM (3500-4000)-do you hear any knocking then? Is it better when cold (just warmed up) & only loud when the oil is hot? Usually when I have had loose/worn rod bearings they're a LOT worse with hot oil. If it has a bad rod bearing(s), 20W50 may not be thick enough!
 
It could be a lot of things, tough to diagnose w/o seeing and hearing it. I had a noise in an old Ford van once, it sounded just a like an engine knock. I disconnected all the fan belts and ran the engine briefly and there was no knock. Then one accessory pulley at a time starting with the water pump I moved the pulleys from side to side to check for play and spun them to check for odd noises. I found the air pump was knocking. Years later I had the same noise in my 88 E-150, it was the air pump again. It could be an accessory or damper pulley in your case.
 
Originally Posted By: Nissan101

And the knocking noise can only be heard for the split second as I let my food of the throttle.


It is a broken piston skirt.
 
You can get a decent mechanics stethoscope at Autozone for $8 and a really good one amazon foe $20. Get one , it’ll open up a whole new world for you. Forget that long extension [censored] too. Once you have one you will use it again.
That will normally let you zero right in on where the noise is coming from by the process of elimination. As always while working on a running engine to tuck in long hair and long floppy clothes especially sleeves. Remember that fan comes on when it decides to so stay outa there always. Good luck
 
I cant even venture a guess but I would start by having someone operate the throttle while I listened under the hood to at least determine if it was an internal engine noise or external.
As you just put the engine in it could be a host of things from an exhaust hitting something, engine mount damage or a mounting bracket.
 
UPDATE
A mechanic said it sounding like the water pump,

Can a bad bearing on the water pump cause a knocking noise?
 
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