63 Mystery engine noise

[Steve D.]

327/340 setup LT1 cam

I realize that attemting to identify/diagnose an engine noise via written communication is difficult at best, but in the hope that someone may recognize a known situation, I will proceed.

After warm up (I have not noticed it at start up) I hear what I describe as a "bottom end" noise; a slight clunking sound. It is not very loud, but noticeable to me and to a club member that I enlisted to make sure my imagination was not in play. There is also a slight vibration in the floorboard. While stopped, I hear it with the transmission in neutral (clutch in or out, doesn't matter), or in any gear with the clutch in. I do not hear it or feel it while going through the gears or at cruise. I can hear it standing beside the car. The engine starts on half a crank, runs strong with no bogging and does not run hot. It has 2,500 miles on it since it was rebuilt.

I dropped the pan and did a visual inspection and did not see anthing unusual; i.e. nothing loose, broken, bent etc. I ran a magnet through the bottom of the pan and got nothing. I plan to check the torque on the bearing caps, but have not done that yet.

Any thoughts?

Steve

[Paul Y.]

Re: 63 Mystery engine noise

I would check for a loose harmonic balancer as that is what happened to me recently. It was the last thing that I would have been looking for but it did exhibit some vibration and some clunking noise that just kept escalating until snapping the bolt and allowing the dual fan pulley surfaces to grind against each other. It got quite loose but never came off and became airborne and for that I am grateful.

[Mike T.]

Re: 63 Mystery engine noise

Steve - You'd expect that any mechanical issue like loose bolts on the crank pulley, or fuel pump spring (under lever), would be present from start to finish and not only after it had warmed up. Any chance it's the heat riser flapper? Maybe the spring has given up the ghost?

[Steve D.]

Re: 63 Mystery engine noise

Paul

Thanks for the comment I have not inspected the balancer, but will put it on the list.

Seve

[Steve D.]

Re: 63 Mystery engine noise

Mike

I replaced the heat riser assembly with a spacer, but maybe its chindi is still hanging around haunting me. Thanks for the comment.


Steve

[Dan A.]

Re: 63 Mystery engine noise

Steve,

When you inspect the balancer make sure the outer ring hasn't separated from the hub. I had that happen once on my 69 350/350 and it made some strange noises like you describe.

[Joseph R.]

Re: 63 Mystery engine noise

Steve, it could be loose flywheel bolt or bolts. I know on some makes they are one-time-use. You mentioned the relatively recent rebuid - maybe one has worked itself loose. I had a similar noise once but with a GM torque converter connection. Joe

[Stuart F.]

Re: 63 Mystery engine noise

Hate to say this, but I knew of three 348s back in the day that broke their crankshafts in two right at a journal. This is highly unlikely in your situation, but recall this every time I hear complaints like this. They all sounded like some loose bolts in the clutch area with an intermittent rattle. The engines would still run, but a little rough due, I suppose, to a little timing issue.

Stu Fox

[Domenic T.]

Re: 63 Mystery engine noise

The vibration issue points to a rotables as Paul and others pointed out. Of all the things to come off, the flywheel scares me the most.
Back in 71 I was working at a Chevrolet dealership as a mechanic and was stuck doing warranty work had a engine crank noise repair that was the front pulley that was loose. Also had a cracked pulley once on a car. Hope it's a simple fix.

Dom