Horrible rattle at 2000 rpm

[oldiron]

This just happened on the way home today. Stock '68 302 rebuilt about 8-10K ago, stock intake and 2bbl. Engine has never given any sign of trouble and runs perfect....until today. It idles perfect but starts to "rattle" LOUDLY at around 2K rpm. I kept the rpm down below 2 and nursed it home. It does this in neutral, sitting in the driveway, throttling it by hand. I pulled the valve covers thinking that it was probably a loose rocker, those check out fine, no bent pushrods, pulled all the plugs and they all look like new (only have around 1200 miles on them). Oil pressure is 45 psi at hot idle. Oil has no "sparkles" in it. Could a lifter fail in this manner? i.e. idle fine but rattle at 2K?
Any thoughts are certainly appreciated.
Greg

 

[AC932]

Couple questions.

Can you tell where abouts it's coming from? Like, one side or the other, closer to front or back?

Is it just a noise, vibration, or both?

Manual or Automatic?

Put a vacuum gauge on it?

 

[oldiron]

Couple questions.

Can you tell where abouts it's coming from? Like, one side or the other, closer to front or back?

Is it just a noise, vibration, or both?

Manual or Automatic?

Put a vacuum gauge on it?

To answer your questions.
Sounds like dead center of engine under the intake, hard to tell exactly though.
No vibration, just noise.
Manual trans.
Havent put a vacuum gauge on it.

Looking at youtube videos for the last few hours it appears that a spun rod bearing may be the culprit. The fluttering sound off idle is identical.
Thanks
Greg

 

[jckkys]

People often describe the sound of pre-ignition as a rattle. Pre-ignition can be the result of overly advanced timing or over heating. Have you looked into this?
The '68 Broncos were built with 170s and 289s. Was your stock '68 302 from another vehicle?

 

[spap]

What trans

 

[DirtDonk]

And you can't dig any deeper until you remove the fan belt(s) as a test of the accessories and, most importantly, the damper.
The damper can make some really scary noises under the right conditions.

Paul

 

[oldiron]

People often describe the sound of pre-ignition as a rattle. Pre-ignition can be the result of overly advanced timing or over heating. Have you looked into this?
The '68 Broncos were built with 170s and 289s. Was your stock '68 302 from another vehicle?

Not 100% sure that it isn't pre-ign, but seems unlikely at this stage. In the interest of thoroughness I'll pull all the timing out and see what happens.
The engine is from ( I believe) a '68 fairlane.
Greg

 

[oldiron]

And you can't dig any deeper until you remove the fan belt(s) as a test of the accessories and, most importantly, the damper.
The damper can make some really scary noises under the right conditions.

Paul

Those were eliminated last night.
I'm getting started again this morning. I believe at this point its narrowed down to spun rod bearing or loose flywheel bolts. I will certainly keep you posted on findings.
Thanks
Greg

 

[B RON CO]

Hi, I would think if there was a spun bearing it would clatter all the time and there would be little or no oil pressure.
How does the clutch pedal feel just pushing down and letting it go in neutral?
A very wild guess is maybe the timing chain is rubbing on something. You can check for slack by watching the rotor and turning the bolt on the balancer back and forth.
you can try a mechanics stethoscope or a long screwdriver or extension to zero in on the noise.
Good luck

 

[Speedrdr]

The only experience I've had with a spun bearing, there was no rattle, just a high pitched 'scream' as the oil pressure dropped. No noise at all until the temp gauge showed 170 degrees and then the noise began. Never a knock or a rattle. Just my experience.
Randy

 

[oldiron]

Here's the autopsy report. Pulled the engine out and found that the new clutch I had installed was done "poorly". Two of the pressure plate bolts were loose, one was broken off in the flywheel and one had backed completely out and cut a groove in the bell housing and was laying in the bottom, one was missing completely (no marks on PP, never installed). While it was out I dropped the pan and found "glitter". A complete disassembly followed. Rod and Main bearings were fine (near perfect) but the front cam bearing is toast and most likely the source of the glitter. Also found the #2 cylinder has been burning oil, not a lot but enough to leave signs on the piston crown.
That answers the question of "will I get to drive it to Townsend".
Re-build starts monday.
Thanks for the replies and advice.
Greg