Hello fellow Thirdgeners. I am having an issue I just haven't been able to solve. 305 TPI has been making a really irritating sound for the past 6 years. I have never been able to pin point where it is coming from. Car runs great but everyday once it is warmed up it makes a rattle/grinding noise. It is intermittent and makes the noise at around 1000 rpms. So I can hear the noise when the car is in park or at any other time the engine is in the rev range of 1000 rpms. I have replaced the water pump, smog pump, I have even taken the serpentine belt off and ran it a second and the noise is always there. Sounds louder from underneath the car. Almost sounds like it is coming from the crankshaft/timing chain/balancer area. I would think if it was something really bad it would have progressively gotten worse over the years but it has not. The sound is very annoying and embarrassing when driving through a parking lot. I saw a members post on here and you tube named foofighters92 but I have not been able to get in contact with him. His engine was making the same exact noise. If anyone knows what it could be or have any thoughts I would really appreciate it. I have put a link to my engine running while it was making the sound at the top of this post. Thanks.

 

it could really be your timing chain rattling or grinding against the cover! Or, depending on the year of the block it could be the retainer cap has come loose and your camshaft is moving a little bit forward which will make the chain grind on your cover or if an older block the cam button, pushing against the cam and cover is doing the noise. I would propose to use a hearing aid (is it also called Shethoskop in english? I'm from Switzerland so I don't know :-) ) and track down the issue.

 

If you haven't done the timing chain, you should. That is the most likely source of such a noise after ruling out the accessories by removing the belt.

GD

 

If it was the timing chain would the noise get louder the higher the engine revs? It is only at around 1000 rpms, any lower or higher the sound stops. It is the original motor in my 1989 IROC. Thank you for the advice. I will look into the timing chain.

 

It's a resonance at that rpm. May be that the timing chain is slapping at that speed because it happens to be at a natural frequency of the chain slack. Lower is not the right frequency. Higher may be at some point but drowned out by other noises.

This is merely speculation. But the SBC is known to develop chain slack and ideally wants serviced about every 60k miles or so for best performance and stability of timing, etc.

GD

 

If that is your original timing chain, that is likely it. Mine did that. It also sounds a bit like it could be a broken cat.

Here's my OEM chain after 120,000 miles, stock LB9

 

I removed the cat

 

Thank you all for the advice. I appreciate it. I will look into the timing and post an update.