Auto mechanics - listen to my Caprice engine

[cone9]

'83 Caprice 305ci 102,000 started knocking a week ago. There is a rythmic knock that follow the RPMs and a louder random knock that sounds like a heavy wooden ball being tossed about inside the engine. I check the flex plate and it look fine.
I put a broom handle to the bottom of the engine (oil pan, exhaust manifold) and the sound is very loud - not so from the top of the engine.

Any diagnosic suggestions?

Caprice engine knock2

Caprice engine knock3

[dwd5813]

unlock the vids, says they are "protected"

[cone9]

Originally posted by dwd5813
unlock the vids, says they are "protected"

done - i didn't notice that settings

[dwd5813]

kinda sounds like my old car when the valve train was on the way out. i had a bent valve stem that i didn't have the cash to fix and it started making all kinds of funky sounds that got reeeal loud right before the engine siezed. i'm no expert though, so i recommend waiting till later on when some serious car people show up. good luck!

[Hoggn]

Getting ready to throw a rod. Main bearing is about to goooo.

[BigSkyBart]

sounds like a rod knock
most likely a connecting rod bearing, but could well be a main bearing

if the car's a keeper, think about a crate motor, small block chevy engines are plentiful & relatively inexpensive

[t-bone2]

ive actualy have heard broken flywheels make the same kind of noise like the knocking and skweeking sound in the vid never over look the obvious it does sound bad

[juststartingout]

I agree with BSB, it sounds like a connecting rod bearing. If so you should be able to disconnect the sparkplug wires (one at a time) to isolate the problem cylinder.

If its a con rod, it would be better to replace the engine with a rebuilt/crate motor. Its silly to take the time to pull the engine and replace the crank and a con rod on an engine that has that many miles on it. I can assure you that the cylinder walls probably have some issues (taper/out of round)

Like t-bone 2 said never overlook the obvious, cracked flexplates can make a simular sound. GM's are real easy to disconnect the torque converter from the flexplate (3 bolts) this will change the sound if it is a flexplate, as there is no "load" on the flexplate, plus by sliding the converter away some it provides you with a little extra room for inspection. Look very closely at the crankshaft bolt area.
Now since you are there, pry the crankshaft fore and aft in the block (front to back) this will indicate the condition of the thrust bearing. The noise is not consistant with a thrust noise, but you should check it while you are there. Spec on the thrust will be about .005-.007", always refer to the specs in the book though.

Good Luck

[dwd5813]

i claim total credit for this diagnosis!!! you never would have heard the motor if i didnt tell him to unlock the video!!

*hangs head in shame and slinks off*

[Satori]

The good thing about small block Chevys is that they're cheap and easy to work on. I replaced the connecting rod bearings on my old Chevy van with a 350 just by pulling the oil pan. The bearings are 2 piece, so you just take off the bottom of the rod, rotate the top half into the gap, put the lower half in the cap, and re-bolt. Sure, it would be much better to pull the motor, rebuild it, get everything in spec. But that's not an immediate option for everyone. I drove that van for another ~40,000 miles without a problem before selling it.

[heyfredyourhat]

i would also say main bearing or rod bearing. did you try and take the belt off, i have heard wierder things come from accesories sometimes

[MandM]

Originally posted by juststartingout
I agree with BSB, it sounds like a connecting rod bearing. If so you should be able to disconnect the sparkplug wires (one at a time) to isolate the problem cylinder.

I'm not a mechanic but with a family full of them I know more than your average girl. I'm not saying you don't know cars but you lost me this recommendation. If the noise is from a rod, how would preventing the cylinder from firing help isolate? The crank still pushes the rod up so wouldn't it make the same sound even if it didn't fire?

I agree with the crate motor or a rebuild if you wanted to keep to original running gear.

[Scuba_Dave]

The hoss says......It's the carbeurator.....

[der_wille_zur_macht]

Originally posted by MandM
I'm not a mechanic but with a family full of them I know more than your average girl. I'm not saying you don't know cars but you lost me this recommendation. If the noise is from a rod, how would preventing the cylinder from firing help isolate? The crank still pushes the rod up so wouldn't it make the same sound even if it didn't fire?

The combustion event puts a ton of stress on the rod bearings, hence it causes the noises. Removing the stress of the combustion event reduces the stress on the bearing, so it won't be noisy enough to hear over the sound of the other cylinders running.

Though, it's probably arguable that the noise an engine makes running 1 cylinder down is probably really weird to most people, regardless of rod bearing knock.

If that is a rod bearing, it sounds REALLY bad. I've never heard one that loud before, but I really don't have much experience with domestic engines. Are you sure the noise is coming from the bottom of the engine and not the top? Like someone else mentioned above, I've heard valvetrain problems make noises like that.

[MandM]

Cool. Thanks.

[BigSkyBart]

sawdust&90wt
willquietthingsinthecrankcase

[Satori]

Originally posted by BigSkyBart
sawdust&90wt
willquietthingsinthecrankcase

I worked at a Ford dealer through High School. I know this trick!

[needlepimp]

sell the car to a deaf man

[BigSkyBart]

Originally posted by Satori
I worked at a Ford dealer through High School. I know this trick!

iboughtacarfromyourboss

[Satori]

Lol, we didn't do it but from time to time we found sawdust in the trade-ins. Mainly just manual trannys and rear-ends though.

[juststartingout]

Although you stated that the noise is more pronounced from the bottom, those small block chevy's in the early 80's had soft camshafts.
Does the engine misfire? I think a soft camshaft would have gone south on you a long time ago. Hook up a vacuum gauge to the engine, it should be smooth and steady 18-20 in'mg

[chainsaw5vent]

sounds fatal.

[Hoggn]

go on the highway and keep the pedal floored for 30 miles or so and see what gives way and report back...

[BigSkyBart]

Originally posted by Hoggn
go on the highway and keep the pedal floored for 30 miles or so and see what gives way and report back...

if I had a dollar for every time I've followed that advice....
I'd have 8 or 10 bucks by now

[The Grim Reefer]

"There is a rythmic knock that follow the RPMs and a louder random knock that sounds like a heavy wooden ball being tossed about inside the engine"

Sounds like a broken flex plate or maybe even the cam that drives the fuel pump would be a maybe. Sounds like something might have broken causing the RPM related tapping and the loose piece is banging around making the wooden ball sound. I had a torque converter bolt fall off a old Chev and that made a hell of a racket until it finally blew threw the inspection plate