Any idea on what this knocking is 72 C20 350

[toolboxchev]

Or you can use a paint pen on the pushrods after a slight clean with degreaser to ensure you lifters are working.

With each move of the lifter you should see the pushrod spin.

[Chilly178]

I took off the cover for the flex plate and it looked fine. No loose bolts or cracks that I could see. Ran the truck and it still was knocking. Only thing that the flex plate was touching was part of the starter. I assume this is normal??
https://i.imgur.com/1CO957f.jpg
https://i.imgur.com/tMO0RRv.jpg
https://i.imgur.com/sx5OkaX.jpg
https://www.youtube.com/watch?v=Oqi1iJYcvMk
I also took your advice toolboxchev and tried the paint marker trick. Seems to be moving alright. https://www.youtube.com/watch?v=iw-abCBXKQU
I'm starting to think that this is a more major internal issue.

[geezer#99]

Originally Posted by Chilly178

I took off the cover for the flex plate and it looked fine. No loose bolts or cracks that I could see. Ran the truck and it still was knocking. Only thing that the flex plate was touching was part of the starter. I assume this is normal??
https://i.imgur.com/1CO957f.jpg
https://i.imgur.com/tMO0RRv.jpg
https://i.imgur.com/sx5OkaX.jpg
https://www.youtube.com/watch?v=Oqi1iJYcvMk

No. Flex plate doesn't touch the starter.

[Chilly178]

Hmm. You think its possible that its grazing the starter a little bit and making the sound? Look at the last two images. I can't tell if the fly wheel is actually touching that little roller on the starter when it spins. Are they lined up fine and it just sits that close or does mine look different/closer than what it should be?

[AussieinNC]

The video appears to show a manual flywheel, not a flexplate...

Is this a stick truck...4 speed?

The video of the rockers with the push rod spinning still shows the rear rocker has way less lift than it should have...

Still looks like a bad cam lobe of a bad lifter...

[Chilly178]

Sorry yes it's a SM 465. Well I took the last two rocker arms off like you said earlier to compare them and they both look identical. No issues there. https://i.imgur.com/f7AEbHl.jpg
Not sure what else to really do. I guess the engine is gonna have to get pulled.

[AussieinNC]

Ok...those rockers look a little galled...but have seen worse....

Re starter clearance...I would shim it down about a 1/16"...shims are available from large online parts houses...

Before you pull the engine...I would be removing the intake manifold and pull those last two lifters...then inspect the cam lobes...look at the bottom of each lifter for pitting and damage...post pics...

Maybe a lifter has collapsed internally...or worse...cam lobe has died...

In reality, if the cam lobe has been damaged, that engine will need a full overhaul...

It might be time to invest in a nice Vortec 350 SB...gets rids of the two biggest gremlins in a small block chevy...flat tappet cam design and oil leaks from rear main oil seal, which I can yours has...350 Vortecs use a one piece rear main oil seal and a roller cam design...

[Chilly178]

Yeah I know the rear main seal leaked probably long before I got it I just kept dumping oil in it.
I'll either get this engine rebuilt or get a built 350 that I know someone has in a Chevelle for 3,000. I'll look into those shims and post back eventually with the lifters out. I might even take the oil pan off if that isn't too hard and check if everything is tight underneath. If anyone else has anymore ideas I would be willing to try them.

[AussieinNC]

If its gone, suggest you look at something like this...


http://www.jegs.com/p/Chevrolet-Perf...AaApp4EALw_wcB

Take your time and have fun...

[Chilly178]

Hello I'm back with an update. So I drained the oil out and I also cut open the oil filter with a pair of tin snips. The filter and oil had quite a bit of metal shavings. I put a magnet in the oil and picked up a ton of metal shavings. So my guess is one of the cam lobes is worn flat. I'll take off the manifold and dig deeper when I get some more time. So right now the plan is to buy a GM performance crate engine, either the L31-R or the HT 383 depending on how much I have to spend. Only thing I don't like about the L31-R is the electronic fuel pump, but then the 383 is over double the price. I wish there was a good middle ground by GM that had a one piece rear main seal, hydraulic roller cam, vortec heads, and uses a mechanical fuel pump.

[jocko]

Originally Posted by Chilly178

I wish there was a good middle ground by GM that had a one piece rear main seal, hydraulic roller cam, vortec heads, and uses a mechanical fuel pump.

you and me both. I think the HO 350 has a mech pump - about $2800.