Loud Engine Knocking?

[DopeStar 156]

Went to start up my '76 today and while it was idling I was revving the engine since it sounded like it was bogging a little. After a few revs I now hear this loud knocking coming from the engine when it runs. Car has oil in it and no fluids are pouring out of the car or anything like that, the engine just knocks really bad. What happened and how can I fix this?

[Stingroo]

Plugs and wires maybe?

[csbuckn]

If it sounds like a metal knock or tic that gets faster as you rev the engine......
I know how mad you get when the cars arent going right so I dont want to tell you any bad news. If its just a lifter, you may be able to get away with some fresh oil and some additive. Another thing you can look at is the flywheel, when it comes loose or cracks it makes a simular sound. The flywheel is a long shot but it happened to me on a caprice. An automotive stethoscope would be a big help.

[DopeStar 156]

Originally Posted by csbuckn

If it sounds like a metal knock or tic that gets faster as you rev the engine......
I know how mad you get when the cars arent going right so I dont want to tell you any bad news. If its just a lifter, you may be able to get away with some fresh oil and some additive. Another thing you can look at is the flywheel, when it comes loose or cracks it makes a simular sound. The flywheel is a long shot but it happened to me on a caprice. An automotive stethoscope would be a big help.

It's a knocking sound that matches the speed of the engine, I guess it sounds like metal. Whatever it is I just wanna know. I wasn't even revving it that hard, just a few shots of the accelerator to stretch it's limbs so to speak.....

[csbuckn]

Worst case scenerio, its a bearings or a lifter. Either way the motor will have to be opened up. Lifters are not that hard but a bearing is a decent amount of work.

[tateos]

I did that once to an engine once - the ticking got worse and worse - ended up I had spun a connecting rod bearing

[greencadillacmatt]

If it was a bearing that's on it's way out, wouldn't he have low oil pressure? Might that be a way to identify what it is? I hope it's nothing too serious, I really like that '76 of yours.

[csbuckn]

He'd still have oil pressure unless maybe the bearing material spun down into a main oil passage and clogged it but I've never seen that before.

[thefleetwoodguy]

racing a cold engine can and does cause lifter "hangup"
Im not sure id call that a knock, more of a clacking sound
which will normally go away after a mile or so of driving

if its a loud wrapping noise, that would make me think connecting rod big end

[flux1414]

racing a cold engine can and does cause lifter "hangup"
Im not sure id call that a knock, more of a clacking sound
which will normally go away after a mile or so of driving

I've been wondering what that damn clicking noise is for the first minute or two after a cold start...Thanks

Is that something I should worry about?

[Angry Matt]

My 472 was tapping really bad after a recent unrelated issue. It sat for a week or two prior to me starting it and the tap worked itself out after about 5 minutes or so of idling. How long did you have it running for? Chances are, if you haven't been driving it and you didn't do anything to harm it, it's probably nothing. Try some tranny fluid down the primaries when it's idling high, that should cure a carbon knock.

I've been wondering what that damn clicking noise is for the first minute or two after a cold start...Thanks

Is that something I should worry about?

No, mine does that, the oil just hasn't worked its way everywhere yet.

[jayoldschool]

Lifter tick is a lot different than rod knock. No possible way to confuse the two.

[DopeStar 156]

Thanks everyone. Car's been sitting since this afternoon so what I'll do is do an oil change this weekend and start it up again. The car does do a lot of sitting so it might just be something that's stuck or hung up. For the time being I'll leave it alone and maybe it'll free itself up, if not it looks like I may be taking an engine apart at some point....

[I~LUV~Caddys8792]

Dope, before you do an oil change on the old beast, go to BGfindashop.com, type in your zip code, and when you find the nearest retailer, have them sell you a can of 105 (BG Quick Clean For Engines) and add that to the old oil and run it for 15 minutes and change the oil. What 105 does is eat away at the deposits that build up on lifters & rocker arms and washes it away with the oil. If you do this and the noise goes away, then it's just a noisy lifter or rocker arm. If not, then it's something more serious. Either way, a can of 105 runs about $7.00, so it's cheap insurance.

105 is described in further detail here:
http://www.bgprod.com/products/engineoil.html

Here's BG find-a-shop.
http://www.bgfindashop.com/locator/index.php


Let us know what happens!

[sven914]

Engine noises can be the hardest to diagnose, mainly because there are some many things that make similar sounds, but also because people have different way of describing the sound.

Rod Knock: Occurs when either the wrist pin bearing or the rod main bearing deteriorates to a point that it allows the piston to move in the cylinder bore (small end knock: commonly referred to as piston slap) or the end of the connecting rod to bang around on the crank shaft journal (big end knock: most common and is terminal). Rod Knock is most noticeable over 2500 RPM, but feathering the gas will cause a distinctive back rattle between 2500-3500 RPM.

http://www.youtube.com/watch?v=x9LJP1mw0es

Valve Train Noise: Gets louder with an increase in RPM, and is caused by Low Oil Pressure, Excessive Valve Lash, or Damaged Parts. If the noise goes away after the engine warms up, it could suggest a sticking lifter.

http://www.youtube.com/watch?v=48KGzC9RS5U