Symptoms of Connecting Rod Failure

[Stuart F.]

Re: Symptoms of Connecting Rod Failure

Clem;

My fuel pump spring failures were due to a porosity crack in a 305 block, circa late 1986. GM had a bunch of bad blocks that cracked completely down the valley from front to back. The mix of Antifreeze into the oil would some how bring about a chemical reaction on the fuel pump springs. Other symptoms were greasy like substance under oil cap and in pump cavity. I ran Mobil1 which led me to go through two pumps before it finally wiped out a cam bearing causing all kinds of valve clatter. One doesn't do too much troubleshooting when it's -10 degrees outside in an Illinois winter. My friends at the local Chevy dealer gave me a new 350 engine under warranty) paid to work for GM back then. The was one hot Caprice Broughm after that.

[Jerry G.]

Re: Symptoms of Connecting Rod Failure

I have expirenced on more than one ocasion a broken rod. (see black death posting) If you have any question pull the engine and make sure what you are dealing with. Why take the risk? It's just not that hard to pull a motor. Jerry

[Paul J.]

Re: Symptoms of Connecting Rod Failure

Joel,

There's not much I can add to what's been said, other than to reiterate the previous commentsand say that I've always heard a heavy knock with bad bearings. I've also been able to to run an engine with a loud knock for over 5000 hard miles before it got so loud that I could'nt stand it any longer.

However, the goal is not have any of these.

Paul

[Joel T.]

Re: Symptoms of Connecting Rod Failure

Guys;

My thanks to all of you for all your thoughts and advice. I should be able to get my hands on this car this coming weekend.. and I will let you know what I find.

Regards to all;

Joel

[Steven B.]

Re: Symptoms of Connecting Rod Failure

One outside possibility is that of a broken crank at a main journal. When they break, they often have a third piece (sort of like a wedge) in between the two sections. The engine will remain relatively close to "in time", but the clearances between the pieces will increase causing some loss (lowering) of oil pressure and enough effect on timing to get slightly late or pre-ignition in several cyliders causing the rattling sounds. I've seen three back in the late 50's, early 60's.

Stu Fox

I had the same thing as Stu describes with a forged 350 crank in 1980. All sounded and ran good on a 10 mile ride at 65 mph then a rattle for no more than 3 seconds before I shut it down. Tore it down and I had a very clean and straight break under a bearing cap.

Steve

[Loren L.]

Re: Symptoms of Connecting Rod Failure

Loreen, I have seen a few of the fuel pump springs break on the fuel pumps over the years, it is rare, When they do break the sound almost like a lifter that out of adjustment or a bad lifter. connecting rod bearing failures are alittle more of a heavy knock.

The sound to the neighbor was loud enough that it was shut down after three heavy bangs.

[Clem Z.]

Re: Symptoms of Connecting Rod Failure

remember valve train noise will be at 1/2 engine speed where rotating assy noise will be at engine speed

[Tim S.]

Re: Symptoms of Connecting Rod Failure

remember valve train noise will be at 1/2 engine speed where rotating assy noise will be at engine speed

You then can take a timing light to determine if the noise is at crank speed or cam speed. If you determine it to be crank speed (light flashes half as often as the noise, you then can move around to different cylinders to determine which one.

The only other thing I will add.........if the noise proves to be in the bottom end, I would not waste a lot of time. You are going to have to pull it apart no matter what. Just get busy.

Just sucks (unless you are looking for a reason to dive into a project)