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Banging Noise

3536 Views 37 Replies 16 Participants Last post by  71350SS
Well I fired up my 383 for the first time the other day and was able to keep it running for the break in time. Thats the good news. Bad news is there is this banging noise that sounds like its coming from the rear of the engine and I have no idea what it could be. At first it sounded like maybe a rod hitting the pan but I can feel any banging on the oil pan when I put my hand on it. So Im thinking it might be more somewhere in the bell housing area.

Anyone got any suggestions what could make a banging noise in there? I heard it when we fired up the engine for the first time as well but then it seemed to quiet down after a while. Now its back and I really dont want to run the engine much more until I figure out what it could be.

If there are any details I can provide that you think might help let me know.
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Is it a bang or a tick. I had that and it was the flywheel bolt ends tapping the dust shield.

Can you rotate the motor by a socket/wrench and listen for a noise while looking at the flywheel area? With the dist shield off or through the rear block plate on a scattersheild I can see these bolts.
It sounds more like a banging noise then a ticking noise. Your the second person to mention try removing the dust sheild. Thats a pretty easy thing to troubleshoot, just need to take the starter out to do that.

If thats the case will those bolt be sticking out like a sore thumb and be obvious its to long? And it is to long did you just file then down or did you pull the tranny and replace the bolts with shorter ones?
Bowtie, I'm in your area and would be willing to take a peek if you wish. LMK.

Banging noise, Sounds like either the Flexplate to crank bolts are loose or the Torque Converter bolts are loose. When you get the flexplate cover off you can either turn the crank by hand(socket/ratchet) and the converter should move in unison.
had this happen on a 406 small block I built. Problem noise was the big 400sb crankshaft counterwieghts hitting the windage tray. The pan was not original to the engine/crank.
I was able to trim the dust shield. The bolts (ARP) stick out the back by about two threads. Unless you have a heavily resurfaced flywheel or are using unknown bolts this may not be the issue but I don't think they would cause a banging. That sounds more solid. Try rotating the engine and listen for anything. Maybe with someone listening by the pan/bellhousing. Is this a stick? Is the clutch fork installed correctly?
Many years ago when assembling a 383, we had a rod bolt hitting the pan. Not sure what it would have sounded like when running because we (my son's engine) caught the problem when assembling it. A grinder solved the problem. The interference was at the gasket flange. That means the block would have prevented much of the noise from being felt in the pan sheetmetal. Hope this helps,,,,,
I had the experience of a rod nut hitting the oil pan, but it was either #3 & or #4 hitting. Helluva of sound, worst rod knock I've ever heard.

No dents in oil pan from the outside or inside, just a scrape. Engine needed rebuilding anyway, so continued on.

Place your hand on the oil pan to feel it if you think its hitting the pan. Listen from underneath and try to locate the sound.
Thanks for all the good tips guys. I wasnt able to work on the car this weekend put I will see what I can find next weekend.

Vince, I'll keep you in mind if I need some extra help finding this problem. Thanks for willing to help out!
Got an update on the engine noise. Looks like those of you who suspected the flywheel bolts are correct. I took the dust plate of the bell housing and sure enough atleast one of the flywheel bolts are longer then the other and are poking the rear main seal. So this would explain the oil leak in the rear of the engine in a brand new engine as well. I feel bad not checking this clearence when I put the fly wheel on, just figured the guy who built my engine, sold me the new flywheel and the bolts to go with it would have sold me the correct stuff.

So looks like Im going to pull the engine and tranny again to replace this bolts as well as replace the rear main seal and inspect the oil plan to make sure nothing else is damaged. I took a pic from under neath the car, its hard to tell in the pic but the bolt on the right of the screen is clearly larger then the other two that you can see.

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I wonder - do those bolts use washers and the one bolt doesn't have one? I used the ARP bolts. Good luck. We get good at doing some of these jobs more than once!
FLywheel bolts are "special", big thin heads and no washers. (automatic trans flexplate bolts have star washers I think, been quite a few years) Factory bolts have a glob of red threadlocker on them so they don't come loose. Get a new set form your dealer.
Well, I got the engine out and did find the problem at hand. It wasnt the flywheel bolts after all, they were fine and same with the rear main seal. Turns out the bell housing I bought, a brand new GM -621 repo bell housing, wasnt shaved down to proper length in the inside and the fly wheel was doing the shaving itself. There is no damage to the flywheel and I have gone ahead and shaved down the bell housing where there signs of it being hit.

Next weekend I'll paint the inside of the bell housing and put the fly wheel and bellhousing back on and crank the motor by hand then inspect. If no more scratches then I put the clutch back on, cover it up and drop the engine back in. If it does scratch I sand some more and repeat.

As for the oil leak, turns out Im to blame for that. I guess I didnt have the oil sending unit in deep enough so after all that PSI was sent to it, it looks like it trickeled out and dripped down the back of the block.
put some pipe tape on that pressure guage threads
Make sure the pressureplate cover is not hitting also.
Make sure the pressureplate cover is not hitting also.
Im doing some extra grinding to the bell housing to ensure I have the clearence I need all the way around due to the fact I really dont want to have to pull this engine or tranny again any time soon.
Im doing some extra grinding to the bell housing to ensure I have the clearence I need all the way around due to the fact I really dont want to have to pull this engine or tranny again any time soon.
While clearancing the bellhousing, be sure to allow for crankshaft movement fore & aft, as in crankshaft endplay plus another 1/8 inch.
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While clearancing the bellhousing, be sure to allow for crankshaft movement fore & aft, as in crankshaft endplay plus another 1/8 inch.
When you are talking about crank movement are you talking about the entire flywheel moving back and forth a bit?

I have probally shaved at least 1/8" off the 3 main areas the flywheel showed signs of hitting and then about 1/16" on the rest of the bottom part of the bell housing for good faith.
Also you might want to double check your flywheel bolts,from the photo it looks like they stick out about a 1/4 in., thats longer than I've ever seen.
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