383 Knock between cylindar 5 and 7

[larrysupersport]

I have rebuilt my 383 from the ground up motor has been bored decked and the crank was balanced. New camshaft bearings where installed as well as main bearings. New pistons and wrist pins were put on the stock connecting rods. New heads, valves, lifters, cam, push rods, etc.

The issue is that I haven't run the car too much but I took it to a mechanic for a final tune and he has discovered a knock between the 5th and 7th cylindar. It's not really loud but if you know what to listen for you can hear it. The valve clearances were rechecked and they are good. Although when I checked the valves I noticed that there was a very fine aluminum dust in the top of the head. Not a ton but enough to notice if you run your finger accross a rocker arm.

Any ideas? My mechanic has suggested pulling the motor back out and going in from the bottom to check.

 

[RustyRatRod]

First thing I would do is check all of the pushrods to make sure they are not hitting the heads where they go through. Most notably, 5 and 7 since that's where the noise seems to be coming from. It's a common problem to have to elongate the pushrod holes in aluminum heads for Mopar applications. That is where I would start. It could explain both the aluminum in the oil and the noise. Nice looking engine, btw.

 

[larrysupersport]

Thanks I will check that especially since I did go to thicker push rods..

Dam right it's a good looking engine it's a Mopar 383!

 

[RustyRatRod]

If that's what it ends up being, I would not mess around with it trying to elongate the holes on the engine. I would remove the heads. I know....ain't what you wanna hear, but that's the best way. I would also do them ALL because if one or two are hitting so you can hear it, you can bet more are too. Good luck. I hope that's it because that would be a relatively easy fix.

 

[Meep-Meep]

Depends on the sound. Most valve train sounds are more like ticks. Rod knocks have a bit more bass to them - more of a thump. If you can hold the RPM while it's knocking and pull plug wires one by one until you find a cylinder where the sound changes or goes away, it's probably a rod. "Aluminum dust" on the rockers sounds like you are pumping metal particulate through the engine. I'd be doing some investigation. Since it's a big block pull the oil pump and see if it's full of metal.

 

[Roadbird]

Might be sucking in air from top and causing a too lean air fuel mix ratio into the cylinders, thus causing the knocking in that particular cylinder or maybe both 5 and 7. Try listening for a exterior sucking sound in the intake or possibly a bad head gasket or cracked head.