Re: strange knock from Chevy 350
Other sources of knocking or clicking noises on a small block Chevy V8 are :
1. Fuel pump pushrod worn,or the rocker arm in the fuel pump has a busted spring,worn pivot points,etc..this sounds like a tappet ,but morphs into a knock at times,loudest at idle,goes away just above idle..you can run the engine briefly after removing the pump to see if its the cause of the noise,but usually the wear on the pushrod or pivot on the rocker arm is readily visible upon removal..
2. Timing chain!--many GM V8's used nylon coated aluminum cam sprockets,that shed the nylon teeth,and let the chain slop around!-I have owned a few that actually wore a hole in the timing cover and oil started leaking out!..be aware if you find this on your engine,you'd better be prepared to drop the oil pan and replace the oil pump,as well as the timing chain and gears,since every motor I had that "ate" the cam gear,had nylon gear teeth get past the oil pump screen and got crushed in the pump gears..a metal oil pump drive shaft coupler is a good idea to replace the cheesy nylon one used as OEM,and only costs 5 bucks..
3, Wrist pins,or collapsed piston skirts,and cracked pistons all sound very similar,but usually increase in volume as RPM's increase,sound more like a low pitched "Thock-Thock" noise at idle,like your tounge hitting the bottom of your mouth ,or a rapid clicking noise that seems to be half as fast as the crank is spinning..
5. Valve springs,rocker arms,or retainers can cause clicking noises--I have had more than one motor that the rocker arms hit the inside top of the valve cover too,had to massage the cover with a mallet to get rid of the worrysome knock!..valves ARE adjustable,and yes,Chevy's always had "soft" cam lobes,but mostly on their 307 and 305 V8's,not so much the 350's and other size small blocks..its easy to tell if one is worn,the rocker arm wont move much compared to its neighbors,if you start it up with the valve covers off--but be aware oil will sqirt everywhere!..I can "hear" a Chevy with a bad cam lobe a mile away--by taking off the air cleaner,and flooring the accelerator,you'll hear it "gargle" through the carb at high RPM's if a lobe is flat..90% of all the cams I replaced in Chevy V8's,had the #1 exhaust valve lose its lift--this causes pressure build up in the cylinder,and when the intake valve opens,the built up exhaust that couldn't get out escapes intead through the carb or intake!..and you can "hear" it..
I'd guess it's probably just stuck lifters or oil deprived parts from sitting so long,that is causing the noises in your case--oil probably got gummy,and parts may have had all the oil drain off and gotten a bit rusty as well..
I'd try adding a quart of Marvel Mystery oil to the crankcase,and run it for a week or two,then change the oil--the 15W-40 diesel oil will be good for it
,it has higher detergent content than regular oils,plus has more anti-wear additives..might not be good to use in a sludged up motor though,since it could loosen up heavy deposits--but ANY oil will,and I think an older engine will appreciate heavier oil than thinner oil...
Lucas makes good products too,I've seen them work when others did little or nothing..