Rod or lifter knock

[2bits]

Hey guys, when people talk about throwing a rod, they are typically talking
about the connecting rod correct? (not a pushrod) Usually it will be a situation where it connects at the top to the underside of the piston right?

I am just checking as my truck may have just done that very thing last night... Either that or a lifter went bad, hard to tell on a 6 cylinder, they
sound different than a V8. I am going to check it out more closely tonight.
It's real easy to get to the lifters on this engine so I am going to check that out first with fingers crossed. It still runs perfect and runs cool, and idles smooth at stop lights. Just knocks REAL LOUD. (I had to drive it home like that last night...)

[Burbinite]

Yes - Throwing a rod is the connecting rod, where it breaks doesn't really matter but... it is usually not going to "run smooth" and if it does run you're usually doing a TON of damage to the internals.

You may have spun a bearing which would allow it to run but make a distinct knock that is usually very loud.

I don't personally have experience with "lifter knock" most tick. You can bend a push rod if they sieze up. This makes a terrible noise as well.

Hope this helps.

[mrein3]

About 20 years ago my little brother was running a 1972 Chevelle with a stock 250. I needed to borrow it one day. I was tootling down a 30mph road, not speeding, when all of a sudden KNOCK-KNOCK-KNOCK!

Of course this always happens when you are borrowing something.

Lukily I was working at the local repair shop. We were closed weekends. The boss gave me the key the next Saturday and me and my little bro pulled the head off. A piece of carbon or something got in the cumbustion chamber and embeded in the top of one of the pistons. You can imagine the noise this made when it hit the valve above it. I carefully chisled the piece off, put a new gasket on it, and well-la! No more knock. He never had another issue with that engine.

Maybe you'll be as lucky.

[2bits]

Originally Posted by mrein3

About 20 years ago my little brother was running a 1972 Chevelle with a stock 250. I needed to borrow it one day. I was tootling down a 30mph road, not speeding, when all of a sudden KNOCK-KNOCK-KNOCK!

Of course this always happens when you are borrowing something.

Lukily I was working at the local repair shop. We were closed weekends. The boss gave me the key the next Saturday and me and my little bro pulled the head off. A piece of carbon or something got in the cumbustion chamber and embeded in the top of one of the pistons. You can imagine the noise this made when it hit the valve above it. I carefully chisled the piece off, put a new gasket on it, and well-la! No more knock. He never had another issue with that engine.

Maybe you'll be as lucky.

That happened to my friend when his son let a screw fall down carburator. It embeded itself in the top of the piston. they pulled the head and dug out the screw OK, but unfortunately, it had done more damage and it has to be rebuilt. I have that new engine in my garage, I really didn't expect to have to put it in so soon!

[Scott68-93-97]

If its a lifter or a pushrod youll know because the valve train rotates half the speed of the crank so after you let the gas off youll be able to tell if its direct with your rpm or half speed of that, its really hard to explain but you can tell, connecting rod knock usually go at the bearing but I have seen knocks come from the pin in the piston, and they get really loud under a load if its at the bearing and dont relly change if the piston pin is bad or a clip fell out of the side, I dont have much experience with the I6, Does anyone know if there pressed in pins or clipped on the sides?

[Scott68-93-97]

Originally Posted by mrein3

About 20 years ago my little brother was running a 1972 Chevelle with a stock 250. I needed to borrow it one day. I was tootling down a 30mph road, not speeding, when all of a sudden KNOCK-KNOCK-KNOCK!

Of course this always happens when you are borrowing something.

Lukily I was working at the local repair shop. We were closed weekends. The boss gave me the key the next Saturday and me and my little bro pulled the head off. A piece of carbon or something got in the cumbustion chamber and embeded in the top of one of the pistons. You can imagine the noise this made when it hit the valve above it. I carefully chisled the piece off, put a new gasket on it, and well-la! No more knock. He never had another issue with that engine.

Maybe you'll be as lucky.

Carbon knocks are common expecially if the vehicle was recently in an accident or something that jolted the car, sometimes it just falls off like in your case, hopefully he will be that lucky, I purchased a EFI toyota 22r from a truck that was in a wreck and he said after the accident it knocked I pulled the head off cleaned out all the carbon and she purrrrrred like a kitten with no problems and I only payed $100 for the motor, injection, and CPU

[cdowns]

sometimes a fuel pump going bad will knok// a loose harmonic balancer will knok

[CST*TEN in Katy]

My knock has stumped most that I let listen to it. A few of the lifters get noisy when it warms up. It's all nice and quiet when it's cold, but a 10 minute drive and they are tappin'.

I put in another cam and new lifters.
I adjusted them cold with 1/2 turn preload.
I adjusted them cold with 1/8 turn preload.
I adjusted them hot and running.
I replaced the fuel pump.

Now what? Throw away these Lunati lifters and try some new ones?

[2bits]

That's a great suggestion to try Scott, I will definitely listen for that tonight. I thought about the fuel pump too, I might try that afterwards, doesn't really sound like it is coming from there tho. Unfortunatly I have experience in the balancer too I'm headin toward lifters first, then maybe pulling the head (that's an interesting deal with the carbon) then putting my new engine in as option 3. I can pull the head and/or the pan once it is out. Thank alot for your help!

[Scott68-93-97]

Auto or Manual? PM sent

[mnunn454]

Originally Posted by Scott68-93-97

If its a lifter or a pushrod youll know because the valve train rotates half the speed of the crank so after you let the gas off youll be able to tell if its direct with your rpm or half speed of that

Hmmm. Hadn't ever thought of that, but you're right. Thanks! I'll file that away for future troubleshooting.

Because of this (Brain kicking in here ) use a timing light in conjunction with your search. If the tap occurs once every flash of the light, the problem is related to the valve train. If it knocks twice for every flash of the light then the problem's in the rotating assembly. (Is this where I should put the "Opportunity only knocks once" joke?)

Mechanic's stethescope should help you locate the noise as well. Slapping lifters sound more like a surface tap, where a knocking rod sounds a little more like you're rapping on the block with a hammer.

Good luck.

[BCOWANWHEELS]

250 I-6 engines are bad about pushing a rocker arm stud up. put a straight edge across the tops of the rocker arm studs and see if ones higher that the other, if it is take a hammer and gently drive it back down. if it comes back up you,ll have to install a over size stud or screw in stud. you can take a wood broom handle and put the tip at different places on the engine and hold other end up to your ear and locate the sould also. probably not a wrist pin going bad unless you run it low on oil or high RPM,ED IT. those bottom ends are mostly trouble free. i,ve run 250,s for 30 yrs up and including today.
bob

[Scott68-93-97]

Originally Posted by mnunn454

Hmmm. Hadn't ever thought of that, but you're right. Thanks! I'll file that away for future troubleshooting.

Because of this (Brain kicking in here ) use a timing light in conjunction with your search. If the tap occurs once every flash of the light, the problem is related to the valve train. If it knocks twice for every flash of the light then the problem's in the rotating assembly. (Is this where I should put the "Opportunity only knocks once" joke?)

Mechanic's stethescope should help you locate the noise as well. Slapping lifters sound more like a surface tap, where a knocking rod sounds a little more like you're rapping on the block with a hammer.

Good luck.

Wheels are turning I like

Good bit on the timing light, and yes the opportunity only knocks once joke could apply here

[Scott68-93-97]

Well 2bits hasn't responded on the tranny but the reason for my asking was I have had torque converter bolts come loose and it sounds just like a rod knock so anybody with an auto check there first

[raceman29]

break out the garden hose and play doctor see where u hear the sound

[2bits]

Sorry guys I am at work. I just lost a huge reply too argh... firewalls... It is a turbo 400 trany though. It was much louder with the valve cover off too, it is definitely the engine IMO, but I will check everything easy first for sure! Great suggestions guys!

[2bits]

OK, you won't believe this... I started the engine up and the noise was alot quieter. I listened with my scope and it seemed to be coming from the #5 cylinder but I revved it up and it was just like a mild lifter tap, nothing like the banging that you could hear loudly from across a busy street last night! So before I dug into it, I decided to make the noise come back so I can diagnose properly. I take it out and by the time I get out of the driveway the noise is gone. I take it down my street, fine... I take it up the city street, fine... On the way back I nail it pretty good (I could care less if this bastard blows at this point) I get up to 60 and almost get a 2nd gear scratch, and it is totally silent. I get back to the garage and rev it six ways from Sunday and it is solid... I don't understand it! ! ! This doesn't solve my problem it only means I can't trust it, but I can't fix something that ain't broke! After thinking about all the posts, I blew off picking up the new set of lifters tonight because I decided that if it was a lifter, it would run rough. Gonna replace them and the rods now! Rolling the dice again though and I am so sick of that... I am going to put my new engine in it anyway... that's the problem, I have too much of a lead foot to drive anything but a new engine and tranny, I guess I will now!

You're right Kelly! You said my truck kept looking at that new engine in my garage and it just DECIDED that it wanted it! Freakin' christine I bought man! ! ! Damn Canadian Chevy's haha

[2bits]

The fact that it runs good again now, and even when it was knocking, makes me think less about mechanical failure but toward lack of oil flow either from a lifter or stopped up rod, so I am going to just replace those. It wasn't all the cylinders knocking so I don't *think* it would be an oil pump.

Any other possibilities?

[68gmsee]

It's great that it stopped, but I'm like you. Now you have to worry if it will come back when you least expect it and with more drastic results.

First thing that comes to mine is what someone mentioned about a piece of carbon jamming something up. Or as you mentioned, lack of lubrication.

I believe I'd try some way of cleaning the engine out with additives or the transmission oil in the crankase trick. Change the oil and filter a couple of times and hope for the best.

Good luck...

[2bits]

I took it out again tonight and drove it to the post office then to the store, then out on the freeway for about 10 min and everything was fine, and then it came
back like gangbusters... Still runs fine, good temp, good oil pres. Coming from the lower rear. I checked the torque converter bolts and they are tight.

I just uploaded a video clip of it for "fun"

http://www.youtube.com/watch?v=-kjXdQQC_eU

I am not touching it tonight, I am reserving tomorrow for that but I thought you might be interested in seeing/hearing it

[Longhorn Man]

that sounds like upper end to me... it was tickin faster than it was running, and it is more of a loud click than a knock.

[Cyclone44]

Hey 2bits that sounds like lifter clatter to me, I had a inline doing the same thing and replaced the lifters and pushrods, And put another 200k on that motor, Good luck George

[68gmsee]

I agree with above assesment. Sounds like the lifters when you first install new ones and before you adjust them.

Something I noticed on the video that makes me wonder though. Did I hear you rev the engine up towards the end and the clatter didn't speed up with it? Maybe it was a delayed reaction....

Now, you have to wonder what's causing this in the first place... Several lifters don't all of a sudden go bad unless there's something else causing it. I wonder if your oil pump is gone or clogged up... ???

[68gmsee]

Listened at the video again. Earlier, my computer was doing it's morning scan and there must have been an audio delay or something. But now I can hear the lifter clatter speed up when the throttle is moved.

[Scott68-93-97]

Im going to say upper end, put your new motor in you know you want to anyways