d21 z24 carburated strange rattling noise

[ari falco]

I am sure that the noise comes from the engine itself, inside the engine and not from an external source.(sounds like valvenoise)

My thought is that the cam/crank/valve timing is not as it should , the chain and cam sprocket are at #2 hole , (factory setting) , I also tested with # 1 and # 3 on but with the same result .

 

I just mean that if you remove/shave between 0.050in / 0.078in in total from block/head must have some negative effect on crank/cam/valve timing,,, OR ???

 

The relationship between camshaft and crankshaft must be affected by the overshaved/milled head/block , (and logic says that the chain tensioner can not make up for the distance lost ).

 

ok...thats my theory...maybe i'm totally wrong

[datzenmike]

Internal parts cannot distinguish if you are accelerating under power or slowing down. All they do is turn or open and close. Things that do change are the engine torqueing over to the side when accelerating or leaning the opposite way when decelerating. This is even worse if one of the rubber isolators on the mounts is torn or broken. The engine and transmission may be leaning against the body or more likely the exhaust pipe is. Maybe the fan is rubbing the shroud?   

[nl320what]

The head and block milling past spec can be masked by 2 head gaskets, but lifespan would be questionable and not the way to go.  

 

Changing the head with an OE spec one would be next option, other would be new block with an OE spec head.

 

The timing not lined up on the chain links and the tensioner being past its extend would cause the chain slap rattle and pinging.

 

In the US, we only get the Z series with 8 spark plug heads for our emissions.

[datzenmike]

Again the engine does not know when you let off on the gas. The chain doesn't slap just because you let up. It might slap at high RPMs where the chain would naturally be spinning so fast it would try to form a circle, but the chain guides would take care of this. Now if the plastic coating on the chain guides was broken or worn off it might. But again it wouldn't do this only on deceleration.

[DIY 1985]

Is the spark plug heat range correct as to not cause pre-ignition? 

 

If the timing is off because of a milled head, it would result in valves off in relation to the crank, it would be more like manifold backfire?  The crank gear runs the oil pump and distributor.  Ping, or pre-ignition is because the flame front is working against the position of the crank.  How do the plugs look?  I have an inexpensive timing light that adjusts like 50 crank degrees so you can get a sense of distributor centrifugal and vacuum advance while you rev the motor beyond the limited marks on the factory indicator.

[captain720]

If you take the valve cover off you should be able to tell if tension-er is fully extended by looking down inside or putting a long screwdriver down there and feeling the tension-er. Until you personally get a timing light on there you won't know for sure, don't trust mechanics.