I just bought a 69SS 350 (I’m assuming a clone because it does not have the original engine). After the engine warms up and is under load I get a knocking noise that comes in around 2000 RPMS. If I let off the gas the noise goes away. I have not been able to reproduce it at idle in the garage. The car has a 350, 4 speed,functional cowl hood, dual exhaust w/ headers. The car has been sitting a garage for several years, mostly undriven.The noise almost sounds like crank bearings, but it does not happen all of the time. Any ideas would be greatly appreciated.

 

First of all, congratulations on being smart enough to buy a '69!
Does it sound more like a solid knock sound, or could it be an octane knock you hear? If you had a rod knock, I would expect you to be able to hear something when revving it in the garage. What octane gas did you put in the tank, or is it still the old bad gas that was in the tank from sitting a number of years? And where is your timing set? Since your knock happens under load, I'm thinking you could be dealing with a tank of bad gas, or your timing could be too far advanced. If you have good gas, you can try backing the timing off a little (rotating the distributor clockwise) and see if that helps.

 

thanks for the ideas,I'll check the timing this weekend. If you are thinking timing could it also be related to the vacuum advance?I just put 92 octane gas in because it was empty, so that shouldn't be it.

 

How is the oil pressure? It could be a rod knock or a wrist pin or a lifterbut you should still be abile to hear it at idle. Detonation is more like a ping or rattle noise. My first guess would be a header gasket, I have a suburban with a 454 that has a manifold leak in one cylinder you dont hear anything at idle but get on the road and you can hear it. I can notice it in the drive if I rev it and can actually feel the exhaust leak with my hand. I need to fix it but the camaro needs line locks installed and plugs changed before Sunday so the Burb will wait till next weekend..

 

You didn't tell me if the noise is more like a rod knock klunk sound, or if it's an octane knock (which sounds more marbley). I'd know it if I heard it, but it's a little hard to tell from where I sit.
Do you have a timing light? Check your initial timing (with vacuum advance disconnected), and back it off a couple of degrees. Connect vacuum back up and take it for a test run. Backing off initial timing backs off the overall (full advance) timing as well. For best performance, getting the timing as far advanced as possible, without pinging, is where you want to be. If your engine has a lot of miles, you could also have some carbon build up inside the combustion chamber which can cause octane knock. A fuel additive (or even water injection) used over time can help to clean it out.

 

The oil pressure is good. I don't know what the guy put in for oil (what weight), but i checked it and it looked pretty new. I do have a timing light so i'll check that this weekend. I would say the noise is like a very loud lifter ticking, but again it seems to happen once the engine is warmed up and only under load. thanks again for the ideas and suggestions!

 

BTW - if it is a wrist pin what is danger of continuing to drive it? The guy i bought it from told me there was a noise, but said he didn't know what it was. He could not figure it out and he took it to a shop and they didn't know. They told him to just drive it.

 

If you can rule out the simple things like the timing or theheader gasket(inspect and change the gasket they are cheap)a very loud internal tick is not a good thing. It could be a bad lifter or a wiped out cam lobeor a whole bunch of other stuff? It makes me nervous if the garage couldnt find it and just drive it is not good advice. To start with I would pull the oil filter cut it open and inspect it for metal particals and I have also used one of those telescopic magnets to put into the oil pan drain hole to search for metal(it sounds stupid but it works). If there isnt anything significant then I would try and see if the rocker arms were in adjustment, one being way outmay siginal a problem. If they look good go to the timing and check it (a loud lifter tick just doesnt sound like detonation to me). If it still is there I would tear down the engine and inspect it.