rlang

Fresh 68' 350 with top end knock starting 5 minutes into startup...only on one side though! Prelubed engine and checked that good oil supply making it to valve train..new oil pump...60# pressure. Didn't do the machine shop work myself...just putting it back together. Checked everything out before assembly and looked good...at least from a shade tree mechanics standpoint. There is a larger than stock cam installed (JM 18/20H 488/260) with stock pushrods/rockers etc....so was wondering if noise could be from valve job tolerances not quite what they should be. Although the noise being only on one side seems kinda strange.

Basic insights appreciated on diagnosis, what I could check to reach reasonable cause and effect, etc. ....open to any info to aid in next step. This is only my 3rd motor assembly adventure so still pretty much rookie status...other two were pontiac 400's as well. Somewhere I read that Olds top ends took alittle more quality assurance than most.

Thanks

MDchanic

Knock how often?

Every rev? 1/2 rev? 2 revs?

First thought - loose rocker pivot bolt.

- Eric

rlang

Very regular knock...I'd say every revolution. Checked rocker pivot bolts and they were torqued down. Thanks Eric for the comment. Sure hate to crank it up again but may have to in order to see if I can isolate further.
Russ

70 cutlass s

It could be a exhaust leak. I would try to listen to see if the noise is from under the valve cover or from the alternator, something external.

MDchanic

Listening through a mechanic's stethoscope or a length of pipe may help isolate the location of the sound.

rlang

Will check out on both counts....thanks

thorpedo91

I had something similar happen to my car. Tapping like noise every rev. Except mine starts as soon as the car starts.intake valve in a cylinder ended up breaking, there fore cracking the piston. heard the tapping noise for about 150 miles off a fresh build before piston cracked. Put in new piston, had head worked by shop, and now exact same noise and same place. I'd just be careful running it to long and I hope some one here can help figure out the problem