at idle the car has a small tapping sound to it. the tapping is only happening at random times and is not a constant tap. lets say, at idle, if the sound was constant if would make a tap every 0.5 secs but it actually taps at random times. sometimes it will make the noise in a fast pace and then stop for 2-3 secs and start again.

It started yesterday driving home from work. I was going over the bridge and decided to take 3rd gear as far as it will go. well when the car gets to about 3700rpms it makes a horrible loud clanking noise. I thought my car developed VTAK! This is the only thing that does happen consistently. the only time that the noise does not happen is when the car is in park or neutral.

this is the part that makes me think its not my engine. when in park or neutral i can redline and hear nothing wrong. when it idles down i hear the small inconsistent tapping. but if i just rev it up a little the tapping disappears. the small tapping noise does not raise with the engine.

last thing.. there is no performance failure. car is running strong still. no black smoke when reving. so park, neutral idles with small tap but goes away when rev'ed and does not make any odd noises no matter how far its rev'ed. in drive still small random tapping at idle but when rev'ed it goes away and at 3700rpms i hear a horrible clanking noise but performance and stability seems to still be there. no hesitation in throttle response or breaking up when it passes 3700rpms. just a lot more noise.

I've been told it could be push rod, spun bearing, and the one im hoping for is cracked flywheel. this is an auto if that makes a diff. its a 93 formula firebird. The tapping noise did get a little more noticable after driving and listening to it idle but is still not a steady tapping at all. Please give advice. Let me know what you think.

 

its ok... you can tell me its fucked... atleast something...

 

REBUILD FTW!!...ill just say it to say it to hope you rebuild it..your motor is FUCKED!

 

First instinct was a stuck lifter, but the ticking would increase with the rpms. Other things could be arcing from a plug wire, bad pulley, broken rocker arm/spring. I am a little puzzled. Almost all engine ticking sounds would increase with rpms. So that brings us to the tranny, and you said taking the car out of gear(ie putting it in N or P) stops the sound. Getter in the air and put it in gear, don't get under the car unless you have to, and listen. Let us know if you need help or if you solve.

 

thanks for the advice... yea the tapping sound does not increase with the engine... the tapping sound is there always... as long at its just idleing. as soon as i raise the engine just a little bit it goes away until it idles back down, then its back. the other loud clanking sound only happens when in gear and revs to about 3700rpms. as soon as it gets 3700rpms a loud noise "like rocks shaking around in a metal box" starts up. the clanking noise is the one that only happens in gear. while in N or P i can rev it to and pass 3700rpm and everything is good.

yesterday i put the floor jack under to look at converter and flywheel and im not sure if your suppose to be able to wiggle the converter and flywheel at all. but it does spin about 1/10 of a turn. is there really that much slack in the engine?? normal? i didnt have the tools to do anything yesterday but i will have them later today. hopefully i can find out what it is before monday and i hope its not to serious.

 

its hard to diagnose sounds from the internet, but if you wanna know if its knocking, put a scan tool on it.

personally, sounds like piston slap, but it could be alot of things. generally speaking, it sounds like something that goes away with increased oil pressure, so maybe dirt in a lifter or partially collapsed lifter.

 

The flexplate(auto flywheel) should be very hard to move. You would have to turn the motor over. The flexplate is not as sturdy as a flywheel so you may be able to bend/flex it a little. Time to drop the tranny is what it sounds like.

Sneakin,
Piston slap or lifter noise would inc with rpms, right?

 

not necessarily, in the LS1's it goes away and piston slap is a very common thing with factory LS1's. once the RPMs come up the increase in oil pressure quiets them from what i've seen.

and my last motor, you could hear the lifter tick at idle when it was warm (idled right at about 10psi) but once i got going around 1500rpm it went quiet.

 

dirt in lifter sounds likely... i got my car painted about 1 month ago and they had the hood up for most of the time. the whole engine compartment was very dusty and i never took a wrag to wipe it down.. it all soon turn to dirt. i dont think dirt got in my valve covers but im not sure. ill have it up in the air with tranny out tonight... let ya know my progress later. Thanks again!

 

...that'd have to be some bad ass dirt to make it into the valvecover somehow, through the head, down the pushrod, and into the lifter valley lol.