Thread: Help Identify Knock Sound Chevy 350

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Passenger side rear ----------thats where the distributor sets in its boss/hole-------IFFFFFFFFFFFFF------the dist is not exactly straight into hole( manifold at top not centered perfectly in line) lower housing undersized, oil rings ( if used) bulged out into oil galley, and/or a few other conditions-----------at low speeds the flow of oil to those rear tappet bosses can bleed off enough that there isn't flow/pressure enough to do the job of filling the tappets at a rate that beats the collapse rate of the lifter-at higher speeds the lifter isn't in that part of the cycle for it to collapse far enough to bottom out. but-------at some certain rpm rates the lifters spend more time ( mili,mili micro sec) that total collapse is possible where at high rpm ( compare 600 rpm to 6000 rpm---10x ???) and add in the oil flow rates etc etc---------

Also-being an used older block that has been rebuilt-which brings up countless areas where clearances have been disregarded ( mainly $$$$$$$$$) in the rebuild process-------if a flat top piston is put on the rod backwrds, it will double the amount of normal wrist pin offset-----some HP forged pistons won't have any offset and are noisy at some idle range rpm with lighter oils---I'll try to look up the specs on the wrist pin offset so I can maybe explain this line of thought----

Be sure to remove the rockers on the suspect cylinders and check those rockers too. Eliminate those possibilities before performing the screw driver test. You just might find some broken ones.

40FordDeluxe.

Will do. I am really starting to suspect the lifters now. I drove it around a bit and although it ran pretty smooth with good power, it started running rough like it had a sticky lifter or something. Like 7 1/2 cylinders.

I then changed the spark plugs, new fuel filter, rotor and cap and it stayed rough.

Do you have pic of the spark plugs??????

And are you ignoring my posts or are they above your level of experience????

Hi Jerry,

No, not ignoring your post. I am waiting to get the rocker clips in so I can run the engine with valve covers off while avoiding too much oil spill mess. I will get a picture of the plugs. They were fairly white with some black down low on the insulator.

Regarding the engine rebuild, have no idea. Was just told it was a performance rebuild. Not sure the rest.

My level of car experience is pretty good. Been around big blocks and small block Chevys for about 40 years. Built a few engines from ground up. Changed some cams, heads, etc. however, troubleshooting like this one, not sure of.

Just watched/listened to your vid----------noticed that the starter ring gear appears to have some wobble----are there any shiny spots on the flywheel that you can see------like maybe the teeth runout maybe hitting starter????????

Also---some rockers hit baffles and vents in aftermarket valve covers-noticed the breather at rear right side about where sound is coming from??????

Jerry and Denny,

I did find earlier in the week a few shiny spots on the valve covers hoping it was the issue. However, after grinding the spots down and rechecking to see if there was any more abrasion, the was not more marking and the sound persisted.

On the flywheel, I looked as close as possible for wear but did not see any. The flywheel has a slight wobble, but not sure as to why. The flywheel bolts are tight.

Tomorrow I will put the clips on.

Hi,

It is not yet fixed. We drove it a bit and runs strong. I changed oil again to 10w30 brand name oil with some Lucus oil stabilizer hoping maybe it would help but stayed the same.

Sound does not get worst when rpms raise or when driving around. It remains prominent at high idle mostly.

At this point, I am thinking the next and cheapest step to rule out the lifters, is to put new ones in.

Look at each of them very carefully as you take them out----also keek them in order for later referance-----and if any come up a littlle bit and then get harder to pull it will probably be because of a wiped out bottom leaving bad edge------and look at each and every cam lobe for wear patterns