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Old 07-09-2008, 06:38 AM
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Broke flywheel?

I recently traded a volkswagon fox for an 80 model Z28. I've known about the car for seven years or so, it's been sitting up in a field. The story was a guy rebuilt the motor, cranked it up and it had a pretty loud knock. The guy being pretty disgusted with it loaded it up on a trailer and took it to my friends house to leave it until a later date. My friend that had the car hates chevrolets so he never did anything with it being a ford man....lol
He, my friend, said he listened to it when the guy showed up with it and he told the other guy it was a broke flywheel he was hearing, but the other guy said no, it's a rod knocking.
I finally got the car last week and wanted to hear it myself. I had to put a distributor, carb and fuel pump on it to get it started. I got it started today and was just wondering if a broke flywheel can sound like a rod knocking?
It sounds pretty severe but does sound like it's external. I listened all around on the block with a pipe but couldn't hear it. Any thoughts from someone with some experience??

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Old 07-09-2008, 06:52 AM
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Is there a windage tray in the engine. I have had one hit the crank and it sounded like a knock.
How is the oil psi?
I have had a flywheel crack but it only made noise in gear.
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Old 07-09-2008, 06:54 AM
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I have also had a converter come loose and it sounded like a rod knock. Some aftermarket converter bolts are longer then stock and if the bolts bottomed out without actually locking the converter down, then it will sound like a knocking.

Is it auto or manual?
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Old 07-09-2008, 07:10 AM
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Yeah I had a 81 chevy that a guy sold me for 100 bucks. Ran, drove, was lifted, had nice tires. So i figured "why not" it had an intermittant knock that sounded just like a rod rattling on the crank.

I pulled the transmission for another project and it turned out the flexplate was broken. It was cracked and as it spun it would flex and the pieces would grate across each other. I sold the motor for 500 bucks and the guy is still running it in his Monte.
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Old 07-09-2008, 09:19 AM
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x2. A cracked flywheel can sound exactly like a rod knock.
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Old 07-09-2008, 08:33 PM
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Thanks for the replies. I have no idea on the oil pressure, there's nothing hooked up to the sending unit. I cranked it again tonight and it ran a full two minutes before it ever started knocking. I guess I'll pull the transmission and check the flywheel.
Thanks again,
Mark
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Old 07-09-2008, 10:42 PM
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I too had a cracked flexplate on one car of mine (77 Nova) years ago, and it did sound much like a rod knock. I worked at a dealership back then (around 1985,86 or so) and it had come in on trade. Picked it up for $75 as wholesale special. Anyways, you MIGHT be able to see enough of backside of flexplate (between convertor and flexplate) by getting it up on a rack and pulling of the inspection cover and using a good strong narrow-beam flashlite, and looking up towards the boltcenters. They tend to crack around the bolt pattern and extend outward depending upon the severity. I took the one off the nova in 2 or 3 pieces!(Center section was still bolted).
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