Wrong weight flexplate
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Cross-Country
Joined: Mar 2024
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I have a 85 flare side. I just bought it a couple weeks ago haven’t driven it. The dude put a crate motor and rebuilt trans in it. But I guess he put in the wrong (weight) flex plate. I believe he said 28oz so I bought the 50oz just haven’t put it in yet. Trucks vibrates pretty bad when I have it fired up and on idle in my driveway.
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Joined: Oct 2009
Posts: 16,188
Likes: 4,792
From: Burbank, WA
Part of the problem with crate motors is the potential for mis-matched parts, not knowing what's inside. The only engine that's affected is the 302, which changed the balance factor in 1981. If someone put a newer crank in an older block, or vice-versa, or mis-matched the rods, etc., going by date codes on the external parts, block and heads, no one would know until it's installed and running, which by then, as you've found, is too late. Did you get any paperwork with the truck and the alleged crate engine? Hopefully you got something that can help you make an informed decision. From your description it sounds like a reasonable place to start, but it's a lot of work to find out. If you think they may have messed up the flexplate, be sure to check the balancer, too.
https://www.motortrend.com/how-to/16...mpener/photos/
https://www.motortrend.com/how-to/16...mpener/photos/
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Hotshot
Joined: Oct 2009
Posts: 16,188
Likes: 4,792
From: Burbank, WA
The link in my post above has pictures. There's an article to go with them if you click on the back to article button, but it mostly says what I just said. The 50oz balancer goes with the later 302's and 50oz flexplate and internals, and is noticeably different. The whole rotating assembly must be a matched set.
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