First let me give a rundown. My freshly rebuilt Magnum 318 is cursed. Standard rebuild parts replaced, rings, bearings, oil pump, timing set. When I first fired it up, there was a coolant leak at the rear of the intake that was contaminating the oil. Fixed that. Next, the oil pump locked up. Replaced it with a standard volume pump. Then I lost two lobes on the flat tappet cam that was in there, so I put the stock roller back in it. Now I have what sounds to be a bottom end knock at idle only. When built, I measured bearing clearance at .0015" on the rods, and .0015 on the mains. The original bearings looked great when removed. I'm running the same trans, converter and flexplate as the before. It only knocks under 1,000rpm. It has a little knock that's more pronounced at startup, but as it warms up, there's a steady "thump thump thump" that has the repetition of an exhaust leak, which leads me to believe its on one cylinder only. But 90% of the time its there, with no noise on decel, and no noise revving it up or at steady cruise. There is also a vibration above 3,500 or so. I'm am running a neutral balance converter though. Is it possible to have a rod bearing on its way out as a result of the oil pump locking up? When it happened, I had to idle for roughly 1/2 mile or so to get it out if harms way. But it runs great other than that. Any ideas??? It's not a big deal to drop the pan, but I figured I'd get some input from the masters first

It's probably as a result of the oil pump locking up. I assume you had zero oil pressure for that 1/2 mile drive? If so I would say you're SOL. That and the rod and main bearings clearances (escpecially the main) seem a little on the tight side, shouldn't they be closer to .0015-.002?

that and any metal from the cam going out... could have helped take the bearings out while the filter was in bypass...

does not sound good. Might be a good idea to pull the pan and check for any looseness and fix it before you are turning a crank

That's what I was thinking. I'll drop the pan before I run it any longer and hopefully the crank isn't beat up. It's just a driver and track time for this car is no more. I'm becoming a pro at dropping a small block pan with the engine and headers still in the car though!

As said pull the pan & go from there & hopefully R&R the bearings will restore it but I'm not optomistic on this one

I had a chunk of casting flash break loose and get sucked up into the pump of my 360. Lost oil pressure and drove it home for probably 3 miles. New pump and pick up and I was good to go. I don't think a 1/2 mile drive would have wiped the bearings. Maybe some junk from the wiped cam made it past the pump and wiped the bearings?

With the motor running, pull and replace the plug wires one at a time. If it is a rod bearing you will know by the sound...

Before you pull it apart, try cranking it up and pull one plugwire off at a time. The knock should get a lot worse on the dead cyl. At least you'll know where to start. If they're tough to get at and get off the plug, do it when the engine's cold and one start at a time, until you find it. Chances are you wiped a rod bearing, but maybe a main too. Best of luck guy.

maybe it a crack piston skirt?

have you cut open the oil filter yet ?

I haven't cut the filter open but the pan is coming off tonight. The knock is barely audible. You actually have to try to listen for it. It's not something that is just banging away. I just happen to notice it. Hopefully as said, there is no damage to the crank/rod

Wrist pin. Had a sbc do the same thing. For a long time I could only hear it while idling, but as time went on it got worse. But try the plug wire thing, if no change in sound, its either a pin or a crack somewhere. Probably you do need a complete teardown and re-check everything, but what a drag!

Well I'm going to pull the pan first. It didn't start making the noise until the oil pump incident

Take no chances and pull it apart (again!), you will find something wrong for sure.......

If you remove the pan AND oil pump, take the pump apart to see if chunks might have gone trough it, there will be visible marks inside

.015 is too tight, shoot for .020-.025
Dan

Well I got the pan down and checked all the bearings. The main bearings and all looked great. The rod bearings were a little scored and #4 had the slightest little bit of movement. As mentioned above, it looks like some foreign material got in there (from the cam I'm sure), and wiped the bearing. The bearing shells pretty much fell out of the rod and cap when I loosened the nuts. The journals look great with no scoring or grooves. I put a used standard bearing in there for checking purposes and plastigauged it and its at about .0015". I also turned the motor over by hand and there is no abnormal binding or dragging. My new bearings will be arriving tomorrow and hopefully it all stays together ok. I don't see any metallic material in the oil, but then again, there has been two oil changes since the cam went flat and the roller cam went in. Fingers crossed!

Before you pull anything off the engine, check to make sure the flex plate bolts are still tight. I had this happen a few times on a 440 and swore it was a rod knocking or something. Same as with you, it was more profound at idle and seemed to "go away" when reved.

Well I guess I should read these things the whole way through before I post. Nevermind then if you already found the problem.

One has to ask, how did it get past the filter? I hope you are changing that too.

Absolutely. Oil and filter every time. I'm just surprised the crank looks unscathed. I'm just glad I caught it when I did.

I don't know exactly how, but the debris from a wiped cam seems capable of getting in a lot of places it shouldn't. Perhaps the filter was so plugged after the debris it burped its bypass valve and let some unfiltered oil through. It should be cleared out by now.