noise arising at 4,400 RMP

[takebackthepower]

I have owned my 1976 280z for about a month and after getting it smogged and insured was finally able today to take it out and see how the engine preformed at higher RPM. I noticed that when the RMP's pass 3k in 2nd gear, the entire engine seems to vibrate more than it should ( at least in my perspective) and when it reaches 4-4.5 RMP's (because of this i haven't raised it further than 5k) there is a slight noise of almost something loose and vibrating, similar to the noise the clutch fan would make on the plastic shroud but with metal. I asked my friend and he suggested my engine was pinging, but with the slight knowledge i have i was leaning against it.

If anyones knows about this or has had a similar experience i would loves some insight.

 

Johnny B

[josh817]

I would guess pinging myself. Check your timing, should be simple enough... if you have the equipment. Try running higher octane gas and see if it goes away, play with the mixture. Those seem like common ways to diagnose pinging.

[HowlerMonkey]

I've recently replaced my water pump because of suspected runout because of a similar noise.

 

When watching the fan (careful)....with the fan at low rpms (cold clutch) and engine at high rpms, I could see the fan running out enough to touch the front pulley (power steering extra pulley).

 

I can also feel more vibration..........but....it only happens when fan is in slippage mode and not when it's tightening up.

 

I'll be trying a variety of clutches to see if that's the problem or whether this problem is runout of the crank pulley being transmitted through the belts to the less robust water pump rotating mass.