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rebuilt 318 knock noise around 2500

72RobCharger

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Hey everyone, Its been quite sometime since i've posted here. I did a little research before posting here so bare with me if its already been covered. Me and a friend rebuilt my 318 back in 2016. It was the second rebuild since id had the car. Its a 318.060 over. The reason for the second rebuild is while doing body work with the hood off the shelter i had the car under fell in on it and i wound up getting moisture in the number 2 combustion chamber and it actually cracked the top of the piston! :( I sent the block off to have it cleaned and everything checked. Made sure everything was still true. surprisingly it was ok. I weighed and ordered a new piston from Keith black (hyperpeutic pistons). new main bearings and connecting rod bearings, cam bearings too. When i first fired the motor and was breaking in the cam i noticed a strange almost knocking noise around 2,000-2500 rpm. It wasn't anything crazy so i continued the break in. I've had many people listen to the noise and can't figure it out. Now any sensible person would have probably pulled the motor back out and torn it back down but I was young and dumb. Fast forward to today and the motor still runs strong and the noise is still there. only around 2500 3000rpm. I've tried thicker oil 20w 50 and as of late i been running amsoil hot rod high zinc oil. It definitely likes the amsoil the best but the noise is still there. I know describing a engine knock in a forum is a long shot but i figured id give it my best. I've had people say it might be piston slap, that it could be a bad wristpin, the engine shop had to install the new piston to the rod so maybe they did something wrong but again ive drove this car like this and ive not been easy on it. Its my hobby and my toy to play with lol i do enjoy my car.. I've even swapped to the adjustable 273 rocker arms thinking it might be valve train related. I found an article once about the stamped steel rockers might be vibrating against the valvesprings :saying to not get them out of order because sometimes they might need to be clearanced. I've even added rocker pedestal shims to bring the rocker arms away from the springs. Hell, i drove the car to the machine shop that initially checked the block and let the engine guys listen to it and they said it was fine but this noise wasn't there before this rebuild. 318 .060 over, comp cam extreme energy 268, procomp aluminum heads, keith black flattop pistons with valve reliefs, block is zero decked too. There wasn't an oil pump gasket with the gasket kit and i read a lot of people dont use them. I've tried my timing everywhere to try an get the noise to go away too. The car runs strong and pulls hard. Its hard to tell if the noise continues after 2500/3000 or so because its got loud exhaust. It has like a desiel engine sound to it and only does it when u bring it up in a rev and then kinda float the throttle. I've had the intake off and checked all the cam lobes, they look good nothing out of the ordinary , nice wear pattern to the lifter. the only thing i can think of its maybe the rod bearings are wrong? but surely by now 8 years later it would have spun a bearing if they were that loose. They are CB481HX CLEVITE ROD BEARINGS. The description said they have .001 extra clearance. I almost wonder if that extra clearance is what im hearing? I figure one day soon imma drop the oil pan and check all the rods. I found a video of a guy with a chevy 350 small block who had similar noise and he wound up having a loose rod cap. Again i don't see how my engine hasn't blown if the rod bearins were loose. Oh, on oil changes the oil looks normal, no metallic or anything in the oil.Also oil pressure is good. 65psi on cold start. Oil pressure at idle is about 20. Hell, even after the cam break in the oil didn't look bad. Im stumped. My most recent suspicion is the rod bearings being just a tiny bit too loose. Thank you in advance for any and all input i'll be back in a couple days to see what everyone says
 
The description said they have .001 extra clearance. I almost wonder if that extra clearance is what im hearing? I figure one day soon imma drop the oil pan and check all the rods.

sounds like you do indeed have a loose rod bearing and you should probably check it before a rod drops itself.
im not comfortable with " i think the noise goes away but i cant tell because i have loud exhaust."

have you tried the old trick of using a piece of wood/dowel or handle to something,whatever
and then sticking it to various places on engine while running?
you can hear everything....good luck and let us know what it turns out to be.

ps,buy some Plastiguage to check your bearings and make sure that you have a Real name torque wrench.
 
To check for rod brg noise: engine idling, short out the spark plug on one cyl at a time. When it goes quiet, you have found the bad brg.
 
Going out on a limb here. IF you have a automatic transmission.You may have loose converter to flexplate bolts OR a cracked flexplate. This can cause a knocking sound when changing rpm's. Just a thought.
 
Hi I went through the same business after I finished rebuilding the Poly in my wagon very slight knocking sound in around 2000 rpm . It was the mechanical fuel pump! The spring between the arm and the pump body was missing so the pump arm would not follow the eccentric on the camshaft at higher rpm!!
I replaced the whole pump ....knocking gone! Just a suggestion
 
Hey everyone, Its been quite sometime since i've posted here. I did a little research before posting here so bare with me if its already been covered. Me and a friend rebuilt my 318 back in 2016. It was the second rebuild since id had the car. Its a 318.060 over. The reason for the second rebuild is while doing body work with the hood off the shelter i had the car under fell in on it and i wound up getting moisture in the number 2 combustion chamber and it actually cracked the top of the piston! :( I sent the block off to have it cleaned and everything checked. Made sure everything was still true. surprisingly it was ok. I weighed and ordered a new piston from Keith black (hyperpeutic pistons). new main bearings and connecting rod bearings, cam bearings too. When i first fired the motor and was breaking in the cam i noticed a strange almost knocking noise around 2,000-2500 rpm. It wasn't anything crazy so i continued the break in. I've had many people listen to the noise and can't figure it out. Now any sensible person would have probably pulled the motor back out and torn it back down but I was young and dumb. Fast forward to today and the motor still runs strong and the noise is still there. only around 2500 3000rpm. I've tried thicker oil 20w 50 and as of late i been running amsoil hot rod high zinc oil. It definitely likes the amsoil the best but the noise is still there. I know describing a engine knock in a forum is a long shot but i figured id give it my best. I've had people say it might be piston slap, that it could be a bad wristpin, the engine shop had to install the new piston to the rod so maybe they did something wrong but again ive drove this car like this and ive not been easy on it. Its my hobby and my toy to play with lol i do enjoy my car.. I've even swapped to the adjustable 273 rocker arms thinking it might be valve train related. I found an article once about the stamped steel rockers might be vibrating against the valvesprings :saying to not get them out of order because sometimes they might need to be clearanced. I've even added rocker pedestal shims to bring the rocker arms away from the springs. Hell, i drove the car to the machine shop that initially checked the block and let the engine guys listen to it and they said it was fine but this noise wasn't there before this rebuild. 318 .060 over, comp cam extreme energy 268, procomp aluminum heads, keith black flattop pistons with valve reliefs, block is zero decked too. There wasn't an oil pump gasket with the gasket kit and i read a lot of people dont use them. I've tried my timing everywhere to try an get the noise to go away too. The car runs strong and pulls hard. Its hard to tell if the noise continues after 2500/3000 or so because its got loud exhaust. It has like a desiel engine sound to it and only does it when u bring it up in a rev and then kinda float the throttle. I've had the intake off and checked all the cam lobes, they look good nothing out of the ordinary , nice wear pattern to the lifter. the only thing i can think of its maybe the rod bearings are wrong? but surely by now 8 years later it would have spun a bearing if they were that loose. They are CB481HX CLEVITE ROD BEARINGS. The description said they have .001 extra clearance. I almost wonder if that extra clearance is what im hearing? I figure one day soon imma drop the oil pan and check all the rods. I found a video of a guy with a chevy 350 small block who had similar noise and he wound up having a loose rod cap. Again i don't see how my engine hasn't blown if the rod bearins were loose. Oh, on oil changes the oil looks normal, no metallic or anything in the oil.Also oil pressure is good. 65psi on cold start. Oil pressure at idle is about 20. Hell, even after the cam break in the oil didn't look bad. Im stumped. My most recent suspicion is the rod bearings being just a tiny bit too loose. Thank you in advance for any and all input i'll be back in a couple days to see what everyone says
Check the crank seat... basically, how far forward and aft does it move when not running. Some engines, if built a little lose, will have a crank knock at around 2500-3000 due to thrust bearing clearance. Will sound like a rod knock. HTH
 
Don't worry, all noises from under the hood will end soon....Just kidding.
No way to figure out your problem really.
Here is a way to determine if it is a rod bearing. Disconnect the ignition wire on each cylinder while runnung one at a time. And then plug it back in.
If the noise stops or is reeduced greatly, you have found the problem cylinder.
Otherwise only a complete teardown is the answer. Only so many external things you can do.
 
I once had a car with what I thought was a rod knock. It turned out it was a bolt backing out behind a windowed power steering pump pulley. It sure had me convinced.
 
Hi I went through the same business after I finished rebuilding the Poly in my wagon very slight knocking sound in around 2000 rpm . It was the mechanical fuel pump! The spring between the arm and the pump body was missing so the pump arm would not follow the eccentric on the camshaft at higher rpm!!
I replaced the whole pump ....knocking gone! Just a suggestion
Thats interesting! I'll try the cheapest things first before pulling the motor! here is a good question for your situation. did you have any issues with fuel since the spring was missing? I've literally ran this car like this since 2016 and been chasing the issue around ever since. I've been hard it it. many burn outs and pulling mountains on the interstate and the motor lives.
 
I once had a car with what I thought was a rod knock. It turned out it was a bolt backing out behind a windowed power steering pump pulley. It sure had me convinced.
I will give this a look also! I may even upload a video of the noise so you all can here it.
 
Don't worry, all noises from under the hood will end soon....Just kidding.
No way to figure out your problem really.
Here is a way to determine if it is a rod bearing. Disconnect the ignition wire on each cylinder while runnung one at a time. And then plug it back in.
If the noise stops or is reeduced greatly, you have found the problem cylinder.
Otherwise only a complete teardown is the answer. Only so many external things you can do.
It would be so strange if it was a rod bearing because i've ran it like this since 2016 and ran it hard. Doesn't knock at idle really. Only when you bring the rpm up and feather the throttle. I plan to do that test tho
 
Check the crank seat... basically, how far forward and aft does it move when not running. Some engines, if built a little lose, will have a crank knock at around 2500-3000 due to thrust bearing clearance. Will sound like a rod knock. HTH
If it was this would it hurt the motor? Again i've ran this like this since 2016 chasing the noise around with different things and the motor lives. Puzzles me. once i was across the river from a buddys house and did a burn out and he heard me. Before he saw it was me he thought there was a diesel over there doing a burn out. It sounds somewhat like a diesel when you hear the noise at the motor
 
Possibly detonation, caused by excessive vacuum advance
 
Hey thank you all for you replies. Imma definitely do some checks and tests as you all recommended.
Possibly detonation, caused by excessive vacuum advance
Ive tried the timing many different ways. With vacuum advance plugged and unplugged
 
What model KB piston did you use some of them come up out of the bore .018 at zero deck it doesn't leave much clearance
 
What model KB piston did you use some of them come up out of the bore .018 at zero deck it doesn't leave much clearance
If i remember correctly the 167's. Funny thing tho, the first time the motor was built was a long block build by a machine shop. When me and my friend rebuilit it the second time the only thing we changed was the cam. We stepped up from the 256xe to the 268 xe comp cam. Same head gaskets and everything. Keith Black KB Performance Pistons those are it. Something i'd forgot to add was I'd read some people thought the extreme energy cams by Comp Cam were noisy cams with the aggresive ramps on the cam lobes. Oh to add, I swapped out heads back in 2020 for aluminum heads. There was no evidence of the valves hitting the piston tops. When i installed the new heads i even made sure with some clay on the piston to check the clearance and there was still plenty
 
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Wouldn't you think after all these years if say it was a rod bearing being a touch loose that over time ( the course of 8 years ) that my oil pressure would gradually being going down? To this day the OIL pressure on cold start at idle is 60-65 psi and then once warm it goes down to 20 at idle. When im driving the car it definitely good oil pressure.
 
Thats interesting! I'll try the cheapest things first before pulling the motor! here is a good question for your situation. did you have any issues with fuel since the spring was missing? I've literally ran this car like this since 2016 and been chasing the issue around ever since. I've been hard it it. many burn outs and pulling mountains on the interstate and the motor lives.
ok so i took the fuel pump off is this normal for the arm to move vertically a lil bit by hand? also note the wear mark
 
Run it up to 2,000 rpm without the fuel pump installed and see if the noise is still there. Should be enough gas in the carb to do this.
im gonna try that. I may go to the parts store and see if a new pump has this amount of vertical play as well.
 
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