I just completely rebuilt my magnum 360. All new bearings, pistons, etc. Well it makes a small knock at idle. Can hear it louder from under the truck. Almost can't even hear it from above. It's a rhythmic noise that will raise with rpms. Doesn't get louder, just goes up. Can't even hear it driving. Any simple things it could be? Oil pressure is good. Almost sounds like rod knock even though I replaced those and they all measured great. Any help is welcome. I'm at a loss right now

 

Perhaps piston slap, but the magnums generally have pretty good bores even after high mileage. Sometimes elimination is good to do, pull the belt and see what changes. Maybe check to see if the flex plate is loose or cracked.

 

I did replace the pistons and used the standard bore. The machine shop said it was not worn too bad. They did hone it. They also checked over the crank. That was good to go. Idk what it could be. I thought I did this all right... maybe I will check the flex plate but bolts but I just put those on today...

 

Flex plate is a great place to check. Hopefully, its just a loose flexplate bolt that might be hitting the block and not a cracked flex plate. I typically use locktite on my flexplate bolts to ensure they don't loosen up.

 

Maybe you missed torque on a cap bolt or main? I wouldn't run it too much with it making noise. Can you get to everything and pull the pan from underneath? Would suck to have to pull the engine out to verify the bottom end.

 

ok well I have an update. Started it up today and ran it for a bit. Noise is barely there now. If I didn't hear it yesterday, I wouldn't have heard it today because u have to be right under the oil pan to hear it. Had a retired mechanic come and listen with a stethoscope. It is coming from the front right of the oil pan area. That's the only place he could hear it. Not the block or anywhere near the top of the engine. Not even on the underside or left side of the oil pan. It's so quiet he said to run it and keep a close ear on it. Worse case scenario I pull the pan and replace the front 4 cylinder rod bearings. I can do that easily. For now I'm going to drive it and if it gets to the point I can actually hear it when walking around the truck, I'll drop the pan. Also going to do an oil analysis after the second oil change. We basically came to the conclusion the only thing it could possibly be is one of the front rod bearings didn't get enough oil on yhe first startup and maybe wore a little bit. Will update this thread if something changes.

 

Yep... (sorry I'm going half glass empty here) but worser case scenario, the journal gets buggered while you delay, and you end up having to pull the crank to grind it. I'd pull the pan and find out, but I'm neurotic, lack patience, and never rely on hope as a plan :-) Good Luck !

 

oh trust me. I am the same way. New rod bearings are already on the way. The noise is so quiet though that if it wasn't louder yesterday, then I would have never heard it at all and never known it was making a noise. Going to keep a very close ear on it and if it persists after the first 500 or so miles, the pan will most likely be coming down and the front 4 cylinders will be getting new rod bearings. Also the second it gets a tiny bit louder, I will have new bearings ready to go in. The crank was polished and all bearings were plastigaged so our guess is on the first startup the front bearings didn't get oil as quickly and may have caused this. Either way, it's goijg to get fixed if it persists or worsens.

 

You should have primed it before starting it. Did you at least use assembly lube on them? Where any of the wrist pin bushings worn?

 

all pistons and wrist pins were replaced and the pins well oiled before install. All bearings were coated in tons of assembly lube. Completely filled the oil filter before startup and ran the engine over without plugs and injectors disconnected to get at least some oil moving. Really don't understand how the noise came about as I was careful with everything but crap happens I guess. Rod bearings are on the way.