Low end knock after rebuild - Chevy235

I could use some advice. Just finished rebuilding the bottom end of my '53 235 (with Powerglide) and I've developed a knock at low RPM which I can't pinpoint.

With an tube to my ear the sound is strongest at the oil pan. When I removed the oil pan everything looks fine. No metal in the oil. I also removed the plug wires one-by-one trying to isolate the issue on the power stroke of each rod, but the sound remained regardless.



Please listen to the videos below and voice your thoughts.

Engine at high idle (do to auto choke), in park. NO KNOCK! (note, after shooting this I realized the #2 plug is off - as seen in video - but I assure you it has no effect in the knock)

Engine at low idle in park here you can hear the knock.

Any advice would be greatly appreciated.

Carl

 

Check the oil supply line from the pump to the block... #3 or 4 rod may just be grazing the top where you can't see...
I say that after a dozen 'pan drops' looking for a similar knock.

 

WHOAH! ...that's interesting. Thanks for the tip.

~ Carl

 

I had the same problem with a rebuilt sbc , it was the oil pickup touching the bottom of the oilpan.

Sigge!

 

check for small dents at the front of the oil pan.Press your finger in the dent & you will feel the crank/rods hitting and the noise will change

 

Helpful advice guys -thx!

 

Is this one of the 235 that you have to shim the bearing caps to set the bearing clearance ?

 

Yes, the motor originally had shims, but after machining they weren't necessary. The new bearings were within spec without.

 

Six cylinder Chevys will sometines develope a wristpin knock after an engine refresh don't know why but they just do.

 

Wife,s 235 had a knock after a rebuild, sounded real bad, turned out to be a small dent in the oil pan where it had been resting on a piece of wood, easy fix for me hope yours is too.

 

Lot's to look for when I get that pan off this weekend. Thanks for the input guys.

~ Carl

 

its there on the high speed just as not pronounced I can hear it , also check your torque converter bolts to make sure they are tight ( and not bottomed out against the convertor ) and fit tight in the hole as that will make this sound also , but it can disapear when a load is place on the driveline when the rpm goes up because of the firing impulses are closer together .

 

The three torque converter to flex plate bolts?

 

I had one making a knocking noise after assembly. Turned out to be the crank counterweight kissing the pan baffle.....I don't know about your engine's knock, sounds deep and follows the idle as it rolls a bit..A defect in the timing gear may make noise.......When the pan is off do pull the bearing caps and check them out ...Hopefully I'm full of shit and it's a hammer fix.

 

Thanks for the input - I'll be checking the bearings. ...and everything else too.