I would start with a visual inspection of all the rod journals. Look for any filings around them. If you spun a bearing and shut the motor right down you probably won't see anything. You could try to wiggle the rod to check for excessive play,but again you probably won't find anything. I think your going to start pulling off rod caps one at a time to find the "knocker". You will have to turn the motor over to get a socket on the nuts(coil wire off and spark plugs out)and you should get your answer. Make sure to put the caps back on exactly as they came off with plenty of oil and retorque to factory specs. If the rods are all good the next step is the main journals the same way.
BTW did you pull the valve covers to check for a bent pushrod or valvetrain problem? Just a thought? Let us know what you find.
You should have done as much trouble shooting as possible before tearing it down. Sometimes a fuel pump can make a knock. If an object fell down into the engine and imbeded itself into the top of a piston, that would do it too.
Many times when a bearing spins, the piston can strike the cylinder head. There is only .030" clearance between the piston and cyl head.
Sometimes you can pull a plug wire one by one and determine which cyl is knocking, the knock will change.
Since you have it out. look at the front weight on the crank. sometimes the thrust bearing wears out and the crank can contact the block there.
Driving up a hill can cause the knock to go quiet with that problem, downhill will cause it to get louder.
If I had to guess, I'd start at the front and take off rod caps until I found it.
For some reason # 5 and 7 have more than their share of troubles. Could be the firing order.
Good luck, David
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Hey Guys, I spent the weekend checking each rod and the main bearings of the crank. Everything looked good. Then pulled the valve covers off to see if any pushrods were bent and everything looked good. I pulled a few spark plugs out and they had carbon built up on them. Then I removed the heads and the valves were totally coated with carbon. Can it be pre-ignition causing what I thought was rod knock? At this point if the heads are the problem I think I would like to up grade the heads and the cam. The motor is a 1980 350 standard bore, rebuilt to stock 5k miles ago, I think 8.5:1 compression. The heads I was thinking of were Edelbrook Performaer RPM 64cc 2.02/1.60 valves and the cam with a lift .487/.490" or .477/.480". The car is a 4spd with 3:42 gears. Sorry for all the all the questions. Any advice on this set up or if you could recomend a better one would be appreciated.
Rob, any idea of what cc your heads are now?? If you dont mind running 93/94 octane you could go to 10:1 compression. this would also allow you to run a bit more cam. But I would stay in the 230 duration area with your gears. A nice small solid lifter maybe!
Yeah, crudded up heads could cause knock. The carbon builds up hot spots and can act as your second "spark plug" causing preignition.
I dont know where you stand financially, but if it all looks good down below, invest in some new bearings/Plastiguage and an oil pump, and button it up. Or, since you'r so quick to yank the mill out anyway, just button it up. You could spnd the $$ to get a rehone and new rings fitted. Then its fresh.
You have to get an idea of what the 64cc chambers will do to the compression. Sicne the motor is apart, you should take some time to measure everything and calculate your own CR, instead of relying on heresay (unless they have run exactly the same combo).
If you got up to 10:1 I would seriously consider a cam upgrade. High lift, relatively short duration, SOLID LIFTER
yes carbon build up can cause a motor to knock but it wont sound like a rod or main bearing knock it will be a diff.kind of sound if u checked ur rods and mains and they r good the only other thing it could be is a wrist pin and u dont want to put a hydraulic or soild lift cam in ur motor u want to go with a roller cam the other two types will eat ur horse power up fast if any of this helps let us know and i have a little project going on a s-10 so belive me ive dealt with chevys for a long time and know them like the back of my hand friend
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