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Wrist Pin Knock

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Old 04-02-2011, 08:57 AM
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projectresto83
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Default Wrist Pin Knock

I just picked up a motor (for free) that the owner said he thought it had a wrist pin knock. How can you visually tell a bad wrist pin? There isn't any obvious damage to the cylinder walls or pistons from what I have seen so far. It just looks like a high milage motor that needs to be reworked.
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Old 04-02-2011, 09:43 AM
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TrimDrip
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may just be wore out. I have seen rebuilt motors have the knock when not being bored and honed.
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Old 04-02-2011, 10:38 AM
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projectresto83
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Oo Its definitely worn out. The rod bearings are all showing copper and a couple of the mains are showing copper. There is no crank walk that I can see (didn't throw the dial on it). The number 5 piston has a broken skirt but it looks like it was broke after the engine got pulled out since the broke area is clean and not discolored. The edge piston looks like it started comming apart slowly below the bottom ring and started embedding itself into the skirts of the piston as well thus causing the vertical wear marks in the cylinder itself. The crank does look like its in pretty good shape. Just in need of a slight polish to remove the burnt on oil. I bet the sounds he was hearing was more piston slap and rod noise than wrist pin.
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Old 04-02-2011, 10:59 AM
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Now that you've gotten a better look at it and said the piston was cracked or coming apart, do you think it was due to high mileage or maybe forced induction caused it? How old was the block and does it have the forged or hyper pistons?
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Old 04-02-2011, 11:19 AM
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I doubt it had anything extra ran on it. Its a stock 78 motor. Not sure what came from the factory with them. I haven't decoded the block/head numbers yet.
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Old 04-02-2011, 12:20 PM
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like you said earlier it was probably piston slap or something. i havent heard of wrist pin knock before.
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Old 04-03-2011, 12:34 AM
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I believe it was piston slap too from just being worn out. For all we know, it could have just been a collapsed lifter and the guy just didn't know the difference.lol
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Old 04-03-2011, 12:44 AM
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The lifter is kinda what I was thinking too until I seen the condition of the pistons. It just sucks that I never heard it run but then again it doesn't matter because the only thing I can use from this anytime soon is the crank.
So with this I might end up using the crank in my motor to fix my vibration issues. I need to pull out the dial indicator and make sure this crank is within spec.
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Old 04-03-2011, 12:50 AM
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One thing I would look at is the 93 motor in the car know may have a hyper piston in it and the motor you bought could be forged. Which could throw the balance off even more I guess since cause of the different piston weights and crank balance.
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Old 04-03-2011, 09:14 AM
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projectresto83
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Originally Posted by TrimDrip View Post
One thing I would look at is the 93 motor in the car know may have a hyper piston in it and the motor you bought could be forged. Which could throw the balance off even more I guess since cause of the different piston weights and crank balance.

Nope, my motor is a 80 block with a 79 crank and speedpro hyper pistons. The crank is what determines the balance....so long as all the rods and pistons are within a certain tolerance of each other. Both motors are 28oz motors. Again, the pistons in the new motor are trashed. If I didn't have to pay to get the pistons swapped to the other rods I would swap in the crank and rods into my block and use my pistons.
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