I have an 85 IROC with 350/5-speed. has an older sbc not sure on the year because i cannot find a serial number. So it all started one day as i was driving i started to get some lifter tap. so i adjusted my valve lash and worked fine for like 2 minutes then started tapping again. I pulled the lower intake and checked the lifters....the rear passenger one was pretty much chewed to all hell....i forgot to snap a pic but it isnt necessary....its not just worn....it looked like someone took a bite out of it.so trying to buy some time before i bought a new cam and had time to change everything i threw in a new hydraulic lifter and reassembled...worked fine with slight tapping for a week. Then tapping got worse so i readjusted the last on that one rear pushrod..worked a few minutes...then tapping again...so i got tired of messing with it and had to drive it to work the next day...on the way home pulling away from a stop light the engine started misfiring badly and i heard something snap and then a very loud mechanical knock started.it stalled and i drifted the rest of the way down a hill and into my driveway... fired it up again and still a loud knock...my question to everyone is what could be causing this knock? did i mess something else up by running it that way? i can change out a cam and lifters no problem....but i dont want to do that only to find a rod bearing went or a valve bent. I checked all the pushrods and none were bent. the knock sounds likes its coming from the cam in the rear passenger side where the bad lobe was...did i maybe mess up a bearing? any opinions on this would be very much appreciated. I have some video clips also http://www.youtube.com/watch?v=wqoarOnsyZk http://www.youtube.com/watch?v=gC0apt-1OHI

 

Sounds like it's time for a new block.

Your block has 70s Quality Control Problem #2 (#1 being, the starter bolt holes being drilled too far from the crank) which consists of the lifter bores not pointing straight at the cam. You can change the cam every day, and twice on Sundays even, and still NEVER EVER get one to last all the way around the block.

Sorry to be the bearer of bad news, but better to hear it now than to keep throwing money at a hopelessly messed up block that can't be fixed without spending more - ALOT more - than just getting another junk old block, and keep having it screw up, and never know why.

Just make sure that your "new" block doesn't have Problem #1 as described, or #2 like you have now, or #3 which is the bell housing dowel pins not being centered on the crank centerline, which makes it EAT torque converter bushings.

 

i figured as much....do you think that the cam is whats making the noise and not the cam bearings? If possible i want to just put in a new cam and sell the car cause its not really worth dropping an engine into....id rather get a nicer body and frame if im going to do all that. So it doesnt need to last forever...just till I get rid of it which wont take but a day or 2 after its fixed. Thanks for the advice though