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Discussion Starter #1
Okay, okay... I'm the guy with the sickness... (see post by C Schu's wife) fortunately, I think it is contagious.

I am the proud owner of a '70 Chevelle, but have been looking for a daily driver. I found an '86 Z28 for $600. It needs some work, but there is no rust on the body (although the paint has seen better days) and the AC needs to be replaced. The only problem that I heard was a knock in the motor. It was barely audible at idle, but as the car revved, it naturally got louder. As the idle lowered, so did the knock, until it was once again barely audible.

Could this be a spun bearing? That would be an easy fix, IF that is all that is wrong. Any suggestions? What else could be making this noise.

The motor is a rebuilt 350 with Edelbrock intake, heads, and carb. Stock distributor, 3/4 racing cam, stock manifolds, 2-1/2 Flowmaster, and rebuilt 700-R4. The interior needs a little work, mostly elbow grease, and the paint needs buffing badly, and eventually it will have to be shot again.

??
 

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A spun bearing? An Easy fix? I could think of a few things I'd rather fix. The knock could be a number of things. Could very well be a bearing, most likely a rod bearing if it is, Doubt that is is spun yet since you say the knock is barely audible, probably excessive clearance which would need immediate attention........GT
 

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Spun bearing in SB chevy= Bad Rod,Crank, oil pump has probably picked up enough metal to wipe out the rest of the bearings. But for what you paid for the car (the heads are worth that) so what if you have to put a bottom end in it. Personally I prefer buying used cars with bad motors as they are cheap and after the rebuild I know what I got.
just don't keep running it until it puts a rod into one of those alum heads.
Note: once (out if many) knocking SBs the knock turned out to be a bent cam.

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Harley
69 461 El Camino Nitrous Model
69 Chevelle coupe
71 SS Camaro
75 L-82 Corvette
71 Gremlin X
Kerrville,Tx.



[This message has been edited by Harley (edited 08-25-99).]
 

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It could also be a loose or cracked flywheel. You said it had a rebuilt tranny I'd look at this first. We always look for the worst case, it's usually not. For $600 I don't think you'll lose money, even if you rebuild the motor. When diagnosing always KISS (keep it simple stupid). My .02.

BillsSS
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Discussion Starter #5
First off, thanks for all of the replies. The information one can receive here is unbelievable.

One more question. I've never had the pleasure of hearing an engine with a spun bearing. The thing that seemed odd to me was that while the engine was at idle, you really had to concentrate to hear the knock. But, once the idle rose, the knock became VERY clear. Is this a common symptom of a spun bearing? I would think it would knock pretty loud all of the time.

I know that in the end, I'm the one who has to make the call, and I am a little apprehensive about these things. I just want to make sure that I make an informed decision.

Thanks again.
Chuck
 

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Sounds like a bad rod bearing to me. For some reason I have heard a lot of late models with that same syndrome. The knock gets the loudest when letting off the gas. Are the newer motors more prone to bearing problems, I have heard lots of 80's 305's and some 350's like this. or am I wrong??

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Frank W
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hometown.aol.com/folingo/myhomepage/auto.html
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Two things you can try, listen down low through the wheel well. Also turn the idle up a bit 1000 rpm or so and pull the plug wires one at a time ( I recommend a well insulated tool for this or an adult diaper) if the knock stops on any cylender then the motor is going to have to come apart whether it's a rod bearing or not.

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Harley
69 461 El Camino Nitrous Model
69 Chevelle coupe
71 SS Camaro
75 L-82 Corvette
71 Gremlin X
Kerrville,Tx.
 
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