Annoying intermittent chirping noise from back of SBC. Help!

Ok, here's the deal...
I had the original 283 in my wife's 58' rebuilt. When I put it back in, I also swapped out the original cast iron PG for a TH350. I got the transmission from my Dad, who got it in a trade. It was supposedly rebuilt. Before I put it in, I replaced the front & rear seals. I also pulled the pan and replaced the filter just in case. I used a new converter as well. It looked very clean inside so I decided to run it.

I've got most of the bugs worked out, but there's an intermittent chirping sound coming from the back if the engine. At first I thought it was the linkage jingling on the transmission but it's not. It happens in park, neutral, or in gear. But not all the time. It increases with RPMs. Sometimes it doesn't make the noise at all.

This afternoon I put the car on ramps and let it run for a while. When the noise started, it seemed like it was coming from the crankshaft near the rear seal or maybe near the torque converter. I sprayed a shot of WD-40 on the crank at the seal and it seemed like it stopped but I'm not sure. It started again again a few minutes later then went away on it's own.

The flex plate and bolts are new. Everything is tight and I used loctite.

Any ideas?


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I forgot, the transmission works fine. No problems or leaks so far...


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first disconnect the convertor and pull it back from the flywheel to rule out the transmission ( yes you can run the engine with it unconnected just make sure its pulled away from the flex plate so it don't touch and chock the wheels !! ) . I never heard a tight rope seal chirp just rubber ones that were not fitted right . also look at the teeth on the flexplate and starter and see if the bendix is out of reach of the flex plate ( sometimes they will stick out and touch and the flex plate will machine the bendix with the gear teeth and as the motor revs the flex plate flattens out and the cutting stops . also I would check the back of the heads to make sure you do not have a improperly torqued head gasket as that will make a chirp noise and come and go too ( disapears as the motor gets warmer and revs up ) . have seen several rebuilt motors where someone forgot to put the final torque on 1 bolt or didn't do a retorque after break in on steel shim head gaskets .

 

Are you running a flywheel cover maybe its rubbing double check the converter bolts and flex plate bolts.

 

Check the distributor for a dry bush. If it still has points put a dab of grease on the cam. JW

 

Sometimes the SBC's have rocker ball squeak, GM came out with an oil lubricity additive for this. GM part # 992961, not sure if that's what is happening to your engine though.

 

I have encountered the exact same thing. HRP

 

Did you have to re-route the trans cooler pipes? Maybe you need to re-route them again or they need to be clipped back together into a bracket or a retainer somewhere?

 

You said the linkage was not jingling but is it lubricated at all pivot points?

 

Does it make noise when you rev the engine? I wonder if the flex plate is flexing, moving the crank...and you are hearing the rear main.

 

Flexplate to crank bolts.

 

Flex plate is suspect. Can you see if there's any marks where it may be contacting something when flexing ???

 

Thanks for the ideas guys. I'm gonna try to make some time after work to get underneath it. Might have to wait till the weekend though.

I don't have a dust cover on yet so it's not that. I'm positive it's not the linkage or rattling tranny lines. The rope seal leaked bad when we broke in the cam, so I replaced it with one from Paragon Corvette. The crank bolts and converter bolts are all new and tight, with loctite. I'll check for starter/ flexplate contact and I'll disconnect the converter to isolate it to the motor or tranny.

Thanks again. I'll let you know what I find.


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Flex plate cracked between holes ?

 

I had one do that and it turned out a cracked trans case. Some one must have pulled the trans in with the bolts instead of sliding it. Good luck

 

Sounds like a loose bolt somewhere. Check the trans-to-engine bolts. Are they good and tight? Tranny mount-to-cross member bolts good and tight? Header collector bolts? Check em all. Start with the easy stuff.

 

I know this sounds dumb, but check the PCV valve. I had one do this weird noise that sounded like the convertor, but all that was ok. Swapped it out and the noise was gone

 

I wonder if the flex plate is flexing, moving the crank...and you are hearing the rear main.

 

please post what you find when it's fixed.

 

I've had exhaust manifold gaskets squeak that were slightly loose. Each exhaust pulse on that port would make the gasket squeak as it leaked past.

 

Sounds like a crack in the flexplate. Or something in the flexplate.

 

Does the engine have to be warm for the noise to be present? Does it change with load (throttling up versus down)?

 

^ Check for a vacuum leak.....crankcase not vented good enough.

 

A couple guys have mentioned. ... cracked flex plate is my bet. Might be hard to spot the crack.

 

Any news?

 

My father in law just went through something similar. He found the problem when the hub on the 1 year old convertor broke off and puked ATF all over the side of the road. Seems as if it wasn't welded properly. It broke right at the hub where it enters the trans.

 

Get out the ol stephoscope. Sounds like flexplate bolts to me to or distributor.

 

Patiently awaiting the news. HRP

 

was gonna say the same thing -

 

Have dealt with this many times. If you run a PCV valve and don't have a fresh air vent in the opposite valve cover, it will suck a vacuum on the crankcase and pull air past the rear main seal. Usually either a constant whistle or an intermittent chirp. Easy try is open the crankcase somehow while the noise is occurring (i.e. remove oil cap, loosen valve cover, pull pcv hose off, etc..) and the noise will stop. If you have an adequate pcv fresh air vent, then this is not it. I would then agree with the others on flexplate noise...