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Unread 01-03-2014, 11:36 PM   #1
cj7bullet
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Flexplate balance

I've got a amc 360 rebuilt. I put one new flexplate In and messed up the ring fear by not having the right mesh with the starter. I have orderd another and was just wondering the original that came with the motor has 2 extra weights on it. Do I need to match the new one to that or is it good to install from the store.

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Unread 01-03-2014, 11:55 PM   #2
only in a jeep cj
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IF when you bought it, they asked or specified what engine then it should be OK as the 6 cyl fllexplates and flywheels are neutrally balanced and the 304, 360, and 401 require a special balance flex plate or flywheel that matches that series of engine.

When they cast flywheels, the process isn't perfect and some will have holes drilled to remove or lighten an area the create the proper balance. Flexplates can have weights welded on to do the same thing. So while one may be slightly different from the very next, the end result is the same.....think of it like your tires getting balanced...same principle.
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1975 CJ-6 304 T15 Dana20 30/44 3.73
1983 CJ-8 258 T5 300 30/44 3.31 Looking for full or half hardtop buy or trade
1986 CJ-7 Laredo 4.6 stroker T5 300 30/44 3.31
1986 TJ-7 Trail Jeep project in the works
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Unread 01-04-2014, 07:32 AM   #3
cj7bullet
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Yes they asked what year make model it came out of etc. so I guess ill just put it on and go with it. The last one never did vibrate like it was out of balance but I never had it more than a idle eaither.
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Unread 01-04-2014, 07:58 AM   #4
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Guess what I'm getting at if I get one for the correct year and motor etc are they pre balanced for installation
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Unread 01-04-2014, 12:33 PM   #5
CSP
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Not necessarily. Some auto parts stores show the same part number for the 304, 360, and 401, which would be incorrect.

You may have the right one, you may not. There's not enough information given to tell.
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Unread 01-04-2014, 06:23 PM   #6
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Quote:
Originally Posted by CSP View Post
Not necessarily. Some auto parts stores show the same part number for the 304, 360, and 401, which would be incorrect.
Then I would NOT buy from a store/vendor like that, and try to find a place that knows that each is different.
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1975 CJ-6 304 T15 Dana20 30/44 3.73
1983 CJ-8 258 T5 300 30/44 3.31 Looking for full or half hardtop buy or trade
1986 CJ-7 Laredo 4.6 stroker T5 300 30/44 3.31
1986 TJ-7 Trail Jeep project in the works
2003 Inca Gold TJ Rubicon
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Unread 01-04-2014, 09:26 PM   #7
CSP
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Agreed, but the OP was asking about the flexplate already in hand.
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Unread 01-04-2014, 09:41 PM   #8
only in a jeep cj
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So the OP would need to go back and ask the seller if they have different part numbers for each flexplate of the AMC V8s in order to verify that they are not one of the generic one part fits all sellers? OR take to time and cash to take both flexplates to a good engine builder and get them to compare the two. IF they are both the same, them he's probably good, but if they are different, then what....roll the dice.
It sucks that to some degree we are at the mercy of the aftermarket suppliers and whether or not they give us quality or c r a p
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1975 CJ-6 304 T15 Dana20 30/44 3.73
1983 CJ-8 258 T5 300 30/44 3.31 Looking for full or half hardtop buy or trade
1986 CJ-7 Laredo 4.6 stroker T5 300 30/44 3.31
1986 TJ-7 Trail Jeep project in the works
2003 Inca Gold TJ Rubicon
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Unread 01-05-2014, 09:35 AM   #9
cj7bullet
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Everything comes back to the correct flexplate tooth count measurement everything. I have it back installed and put back together and the starter still doesn't look like its going to have the proper meshing to engage the flexplate. It looks like the gear on the starter needs to be bigger or something move closer but it can't move side to side any thing will help I rely don't want to shuck another flexplate. And this is all on a fresh motor only been started about 20 times
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Unread 01-05-2014, 10:32 AM   #10
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What bellhousing are you using ( or what transmission)??
Are you using the block spacer plate?
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1975 CJ-6 304 T15 Dana20 30/44 3.73
1983 CJ-8 258 T5 300 30/44 3.31 Looking for full or half hardtop buy or trade
1986 CJ-7 Laredo 4.6 stroker T5 300 30/44 3.31
1986 TJ-7 Trail Jeep project in the works
2003 Inca Gold TJ Rubicon
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Unread 01-05-2014, 11:39 AM   #11
cj7bullet
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It is a 78 amc 360 with a 79 amc style th400 that came from a quadratrac set up all compatible and no spacer housing straight to the block
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Unread 01-05-2014, 07:41 PM   #12
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Quote:
Originally Posted by cj7bullet
...I put one new flexplate In and messed up the ring fear by not having the right mesh with the starter. I have orderd another...
You ordered a new ring gear or the whole flex plate?
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Unread 01-06-2014, 09:53 PM   #13
Colt44
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The answer to the original query is that if you buy a new (whole, not just the ring) flex plate from any reputable parts store, it will come already balanced. As someone already said, there can be holes and/or weights involved, and no two will be exactly alike.
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