i have a 1990 iroc with a pieced together 383 in it im not sure what internal parts were replace or if it is a 383 or not. i do know the motor was out of the car because it is painted black. it also feels like it has alot more power than a 350. i am getting this diesel sound it sounds like it is coming from directly under the intake manifold. it does not sound like a simple lifter tick it is a rattle sound just like a diesel motor running.

 

a few things ive found may cause that sound are

severe overheating

incorrect valve lash

piston pin slap

improper timing

 

im sure by diesel sound, you mean that it has the noisy diesel rattle sound? Its most likely just the valves are a slight bit loose. Are you hearing a ticking noise?

 

Yes you are right its like a rattle sound, it basically sounds just like a diesel when you raise the hood. It does have a slight tick that i can only hear like when at a stop light and a car is next to me if you know what i mean. thanks for the replys guys

 

Im pretty sure your valves are getting extremely loose. Put the engine at Top dead center, remove the driver side valve cover, now wiggle the pushrods for #1 piston up and down. The pushrods should NOT go up and down, if they do, then the valves or loose. Its pretty simple to adjust them if they are.

 

Here are step by step instructions:

1. Remove the valve cover.
2. Identify the number one cylinder. Turn the engine over until you see the number one cylinder exhaust valve rocker arm JUST START to move from the closed position to open. You may need to turn the motor over a couple of times to reach this point, but do not turn any further.
3. Locate the intake valve.
4. Loosen the rocker arm adjustment nut until you feel some obvious lash or clearance in the adjustment.
5. Using the thumb and index finger of one hand, grasp the intake push rod below the rocker arm, and rotate it back and forth (clock-wise and counter clock-wise successively to be sure there is no remaining pressure on the push rod from the rocker arm as you loosen the rocker arm adjusting nut.
6. Using the other hand, while continuously performing step 5, with a 5/8 socket and ratchet, tighten the rocker arm adjustment nut slowly until you feel a resistance of motion on the push rod.
7. This will be the zero lash adjustment point. For hydraulic lifters, tighten the rocker arm adjustment nut 3/4 of a turn. For solid lifters, back off the rocker arm adjustment nut until your feeler gauge just fits under the contact point between the valve stem and the rocker arm. Fine tune the adjustment by checking it with a feeler gauge just slightly thicker than the preferred clearance to be sure the clearance is not greater than it should be. If the larger feeler gauge will fit, it needs to be re-adjusted. A lash tolerance of 1-2 thousandths of an inch in the valve adjustment for solid lifters would be acceptable since it may be difficult for someone who is in-experienced to be more precise than that.
8. Turn the engine over until the intake valve opens and then is almost closed.
9. On the exhaust valve, repeat steps 5 through 8 for the exhaust valve adjustment.
10. Repeat this procedure for each cylinder. Be sure to do each cylinder sequentially, either following the firing order, following the cylinders numerically, or in the case of a V8 doing one side of the engine at a time. I prefer to do one side of the engine at a time

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sorry so long for a response I did however do the valve lash adjstment and it did not make a difference it still sounds like cummins rattle box i dont know what direction to go now. should i start tearing into the top end and replacing push rods and rocker arms? if so how do i go about buying new ones and what size do i get?

 

Did it suddenly just start? Did you change anything to make it start? Did it get worse after you reset valve lash? Have you checked all your plugs for anomalous plug readings?

 

no it did not just start i bought it that way. should have known better but i really liked the car. P.O. said it needed valve lash adjusted. after valve lash adjustment it did not change anything. not sure what anomalous plug readings means. i did notice that i can hear it best when i put my ear close to the intake more to the center of engine. it sounds like it is coming from right under the intake.

 

May have one or more bad lifters.

Anomalous plug readings... pull the plugs, keep them organized, and see if any look bad, or if any look different from the others.

 

A/C is OFF right?

 

what do you mean off? the a/c.... unit is still on the car, but yes it is turned off

 

Just making sure, my compressor sounded like a diesel tractor when it kicked on. It was pretty comical.

 

ok guys i have found one more thing to add that may be linked to this problem. I took the passenger side valve cover off and the tunnel i guess u would call it, the hole the valve cover bolt travels through has a hole wore through it like the rocker is rubbing it or something else may be.... Anybody know what this maybe?

 

does it have a A.I.R. pump? there is a hose pumping air into manifold on some cars. if it comes off or has hole in it will sound funny.

 

no i dont think so... it sounds a little more aggressive than just a simple air leak anybody else

 

?

 

anybody please any input would help

 

bump!!

 

bump