FlyingV5150

Hey guys, I was hearing something with my 72 cutlass 350 that had me concerned. At idle it is hard to tell, but I'm hearing a deep dull knocking noise. It becomes more noticeable the higher the rpm's go, though it still sounds deep. The sound is constant and doesn't seem to go away whether its warm or cold. The engine seems to run perfectly fine otherwise but that noise has me anxious. Could it be a rod bearing on its way out? I haven't pulled the plug wires out while the engine is running to check yet, should i do that first? Also, if a video would be helpful i can attempt to make one. Whats your guys opinions?

oldcutlass

Most often times if its not really a loud rod knock, it won't be discernible on a video because of all the other back round noise. I would pull the spark plug wires 1 by 1 and see if you can tell which cylinder. It may be time to start making plans for it's future.


How many miles are on the engine? What weight oil and brand of oil are you using?

FlyingV5150

About 94,000 miles on it, last oil change was probably only a couple hundred miles ago, after i had to have the oil pan swapped out. I put in Rotella T non-synthetic 15w40 as well as a zinc additive and some marvel mystery oil.

oldcutlass

Has it ever had the timing chain replaced? I would remove the spark plug wires and see what happens.

don71

The sounds you describe don't read good to me. Yea, it could be a bearing or something else. Videos and pics, all ways good.

Something happened between that oil change and pan swap. Anything else changed?

FlyingV5150

Timing chain was never replaced as far as i know.

The only other thing is that after the oil swap the engine was ticking really bad, the shop i had it in could not for the life the them figure it out. Eventually i got sick of them holding on to it so i took it back. I drove it around for about a day and a half with that ticking noise. Then i changed the spark plugs and one plug wire that came apart. It turned out that my distributor was coming out, probably happened at the shop from having to hoist the engine out to get to the oil pan. Anyways, i just pushed the distributor back down, adjusted the timing, and its been fine since. Could this somehow have messed things up?

jag1886

Pull the plug wires one at a time with the engine running like old cutlass said, if it's a bad rod bearing it will stop knocking as soon as you pull the wire on the bad cylinder. If that doesn't make it stop then move on to other things.
Does the car have an oil pressure gauge? Do you know what kind of pressure it is making?

FlyingV5150

I dont have an oil pressure gauge hooked up, but they had one hooked up to it at the shop after the pan swap, and it seemed like it was good, i think it was running around 50 psi cold. Not sure what its reading now though.

oldcutlass

The cold psi doesn't really mean anything, it's what does it read when it's hot. You can buy an inexpensive mechanical gauge.


http://www.summitracing.com/parts/sun-cp7977/overview/

edzolz

If the knock is that low and consistent, My bet is on a bad rear main bearing. Put the engine under a load (foot on brake) and see if it gets worse. If it goes away, it's probably not that. Do you know if they pulled the rear main cap to replace the rope seal when the pan was off?

Beob

I'm going through a knocking situation as well. After pulling plug wires the next step would be to drain oil into a pan and inspect for chunks of metal, especially brass. And cut open oil filter too.

FlyingV5150

I dont believe they did anything besides change the oil pan. I bought a cheap sunpro oil pressure gauge to hook up to see where its at, ill be doing that tomorrow. I will also pull the plug wires tomorrow. In the meantime i managed to take a video that hopefully highlights what i am hearing. Seems like if i am standing over the engine its low and deep like a bass drum, but underneath the car you can hear some kind of ticking which i am not exactly sure is normal or not. Let me know what you guys think.

Lars

sounds like a bent distributer shaft/housing, doesn't sound like a bearing.

MDchanic

Nobody has yet mentioned the possibility of loose converter bolts or a cracked flexplate.

These are real possibilities based on the sound you describe.

- Eric

nsnarsk65cutlass

I'm not hearing it,sounds like exh leak on the video.Nick

oldcutlass

I can't hear anything, but I'm deaf in one ear and can't hear out of the other.

FlyingV5150

It is pretty hard to hear in the video, once you are in the car or on the highway and at a higher rpm (not sure exactly what rpm's since i don't have a tach) its much easier to tell. I was gonna hook up the oil pressure gauge but its been pouring all day here, so i cant really do that. I'm just gonna pull the plug wires and hook up the gauge tomorrow. I will keep you all updated.

FlyingV5150

Ok, so today I crawled under the car and checked out the torque converter to flexplate bolts and they all seemed tight. The flexplate didn't seem cracked or damaged at all either. I also pulled the plug wires one at a time while it was running and the noise was still present, only difference was a change in idle. I wasn't able to hook up the oil pressure gauge because i did not have the right tools to remove the factory sender unit. I'll continue to work on getting that done.

Lars

"It turned out that my distributor was coming out"


loosen the distributer and start it up, see if it wobbles. put your hand on it when its running see if you can feel it

redoldsman

Take a long screwdriver and put it to the engine in different places and put the other end to your ear. You may be able to pinpoint it. Harbor Freight actually has a cheap stethoscope. I have one and it is great.

oldcutlass

If the distributor isn't making the noise as Lars suggested, loosen your accessories and remove your belts and run the engine to see if its something up front. See if you can get an oil pressure reading, Both cold and with engine warmed up.

classicmuscle442

X2 two on taking belts off, appears a/c is on with frost on suction line. With belts off and fan noise gone lower RPM's and you should be able to tell if its rod knock or piston slap, not good after just changing pan, did they forget to put oil in it when they re-started it?

deadeyejedi

just food for thought but i had a similar knock in my 350 rocket years ago .since we were rebuilding i wasn't too concerned.when we pulled the oil pan noticed the oil pick up on the pump had worked its way down a bit and was getting hit just slightly by a rod bearing . this was why the guy sold it to me for a 100 bucks cause his mechanic told him he had a bad bearing .