timewr The videos are greatly helpful. I watched both several times. After hearing it, I believe it is in the valve train. It seems to be to slow to be in time with the rotating assembly. It sounds like there is one or maybe two valves set much too loosely. Cut a slot down the top of a set of old valve covers...maybe you already have a set like this. Put them on to allow valve lash to be set with engine running. They'll keep the oil from flying all over and making a big mess as long as you don't get silly with the rpm. If it is in the valve train, you will find it. Worken2much ps: There is a 65 or 66 Elcamino on youtube with what I am sure is a rattle caused by 0 rod angle at top dead center. Far different than yours. Search youtube for 383 stroker noise.
I did listen to the vid and it's not real plain. I can say you have a slow single beat knock and not the rythmatic beat of 8 pistons. So now the connecting rod clearance. On a 3.750 stroke engine with 5.7 rods #2 & #6 will hit the camshaft unless they are clearanced. And yes I have had engines brought into my shop that had ran quite awhile with these rods pounding on the cam with an unknown nock >>>>.
Here's a list of things to check: 1): It's a 383, which means a 350 block with a 400 crank. YOU MUST HAVE A COUNTERBALANCED FLEXPLATE IF YOU HAVE A 383. Check to see if the flexplate has a welded or riveted counterbalance. If not, that's your problem. 2): Many of the GM 383 crate engines like the ZZ383, with the factory-style roller cams use small base circle cams. The reason is, GM uses the 5.7 rod in the crate engine, not the 5.56 rod that's in the 400. The main difference (besides the end-to-end length) between the two rods is that the 5.56 rod has severely radiused rod bolts for clearance. There is a remote possiblility that you might have a rod bolt banging the camshaft. Check #2 and #6 rods for any signs of interference. Usually, it'll leave metal flakes in the oil, so check that, too. 3): Usually, when a knocking sound goes away when you advance the timing, it's a wrist pin. From the first post, this is my speculation of what's wrong with the engine. I hope not, but it has the tell-tale sign. I'm at work, so I can't listen to the youtube video. I'll check it out when I get home.
Might seem overly simple, but I had a 383 in a forty I built that "developed" a knock in the bottom end. Wasn't there for the first couple of thousand miles, then it appeared one day. A little Sherlock Holmes on it and we suspected the pan was getting tapped. Dropped the pan, could see anything. Put it back on loose and pushed it around and the knock went away. It was so damn close that it had shifted a tiny bit over time and was getting hit by a rod cap, yet NO SIGNS of it! Moved it around and carefully re tightened and all was fine.
a friend of mine had a similar problem with a 383 crate engine. turned out to be a clearance issue with the windage tray in the oil pan, like hotroddon said.
the windage tray is to obvious !! That's why I never brought it up before, but I have had the stroker 383s come in with the stock pan and tray set up on them and the rods are hitting. I guess when you have so many variables it's just like opening a big can of worms !!! >>>>.
Thanks for the replies everybody. As part of the investigation work already done by the shop, they have checked all the rod clearances to the block, cam and pan. They have also pulled out all the push rods, rockers etc, checked them for any damage, odd wear etc and set it all back up. The flexplate has been confirmed to be correct. The shop has had a fairly good look through the engine. Their vote is still for piston slap, on one particular cylinder. If you wind off one of the rockers to imitate a loose valve setting, you get a light tap at the top of the engine. However the problem we have seems to be coming from "deeper" in the block. I noticed on the weekend that the knock is a lot clearer and still loud when heard at the other end of the shop (10 yards away) so I will try to do another video from there to try to better indicate the deeper clunk.
Try using an automotive stethoscope. They really help pin point the sound location. BTW, it sounds like 1/2 engine speed to me, so valve train / dist Remove either the #5 or #7 plug wire to see if the noise goes away. Be sure to ground out the pulg wire
New video loaded onto UTube showing how loud it is : http://youtu.be/PZjdVwxV2xo We have tried isolating it by removing spark plug leads, without success.
you might wanna see if someone can hook you up with a set of 'chassis ears'. its a set of 6 pickups that you can place around the engine to isolate vibration (caused by the knock). we use it to look for chassis rattles in the suspension and such, but it might be of use here.
Whoooha guess after you beat the pistons in they make a racket. I know you meant .040 bore and .030 pistons.
Sounds a lot like piston slap. Pull the plug wires and ground them one by one till it goes away or changes. If it does not go away or change it is likely an interfearance issue. I do hear 2 distinct rythmic noises with the same sound. Could be a 2/6 cam/rod interferance problem.
So did we find the problem with this engine yet ?? I listened to the video and I just can't hear it very plain. Just wondering ??? >>>>.
Sounds just like the 350 or 5.7 Vortec I put in my coupe. I also went with a carb. It sounded like valve lash to me, so I went through the settings a couple times warm. Still there. I have 500 miles on it now and still sounds like a gear drive or ??? Runs great but have had several pro mechanics tell me to forget it and just drive it.
The engine manufacturer is adamant that it is the valve gear but that has all been taken out, checked and reinstalled and, anyway, the knock seems much deeper than a valve gear rattle. Loosening off a rocker gives a totally different sound. We recently visited a local engine shop and the guy had a set of these pistons under his bench that he had taken out of a customer's new engine because they caused a knock, just like ours. They now refuse to build engines for customers that want to use those pistons. So we have ordered a set of pistons with offset pins and different skirt. We will also recheck everything again when the motor is stripped down for the new pistons. I will let you know the result but it is probably a month away as we have to wait for the pistons. Thanks for all your help guys.
I wish I could make out the noise plainer on the video. I can say when I discovered this problem with the wrist pins it sent me on a scramble for the pistons and Probe is the manufacture I used. It seems they were the only pistons I could find at the time with 4 valve reliefs and the off-set pins. Good Luck on the rebuild and keep us updated >>>>.
Interesting that one would have to have off set P-pins in a 383. Never had that issue my self but have seen off set P-pin pistons installed the wrong way round. That'll rattle. I agree with the offset pin reducing a system's propensity to rattle though I mean that is one major reason to use them. Either way, hope you ca fix it.
The new Probe pistons with offset pins fixed the knock. It is now a quiet, smooth running 383. It is also interesting to note that the probe piston skirts are twice the thickness of the KBs. Thanks to everybody that provided suggestions. Steven
i had the same problem with a 350. it was a piece of rubber hanging out of the balancer and knocking on the timing cover.
Steven, thanks for sticking with it - if I run across a customer with a similar problem it'll sure shorten the learning curve. I pretty much learn something new every day here - little stuff to tuck away in the "hot rod" box in the brain.
Great to hear you fixed the problem,have been following this thread and it is nice to hear that the solution worked.
So are whores. Ya know I have probably already posted on this thread so what I am going to say is probably not worth much or already said but there is one sure cure for a crate motor that knocks, that is to build your own engine. I know that one may have to learn something to do that but it doesn't hurt a thing to learn how to do something.
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