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1970 360 flywheel in a 1970 390??

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SANCAPJJ View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SANCAPJJ Quote  Post ReplyReply Direct Link To This Post Topic: 1970 360 flywheel in a 1970 390??
    Posted: Mar/21/2014 at 8:10am
Hi all - I asked this once before - but want to be sure. I have a 1970 390 that I will be putting in my Javelin project. The project did not come w/ a flywheel. A parts car I purchased (also 1970) has a 360 w; flywheel. Can I use the flywheel from the 360 in the 390? The part numbers are the same - but I read somewhere that there may a difference in where the weights are placed. My ultimate question is - can I use the 360 flywheel "as is" in the 390. Thanks in advance for any help - John J
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Post Options Post Options   Thanks (0) Thanks(0)   Quote FuzzFace2 Quote  Post ReplyReply Direct Link To This Post Posted: Mar/21/2014 at 8:43am
No you can not use it "as is" with out issues if not right a way but will down the road.
 
Each flex plate (auto) or fly wheel is balanced for the size motor it is to be used on.
So even that the 360 fly wheel will bolt up you need to have it match balance to a 390 fly wheel or flex plate.
If you do not have either you will need to borrow one or take the motor apart to have the crank/pistons & rings/rods/front bal./flywheel assy. balance.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SANCAPJJ Quote  Post ReplyReply Direct Link To This Post Posted: Mar/21/2014 at 9:30am
That's what I thought was the case. I do not have a 390 flywheel to do a comparable balance from. Is my best bet to go with a new one? I am doing a complete restoration on this car. - JJ
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bigbadgreen Quote  Post ReplyReply Direct Link To This Post Posted: Mar/21/2014 at 10:08am
Part #s same...balance different. How about balancers?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote White70JavelinSST Quote  Post ReplyReply Direct Link To This Post Posted: Mar/21/2014 at 10:17am
The 1970 390 is a one year engine. Only a 1970 390 flywheel will be close enough to balance with the engine reciprocating assembly with a minimal of machining required. There is a chance that a 71 401 flywheel will be close enough to balance with the 390 parts.
Every so often a 1970 390 flywheel becomes available. Here's a new one from ebay
If that doesn't work, keep looking, you may get lucky and find a used one. As an option take the 360 flywheel to the machine shop and ask them how far out of whack everything is and if it's possible drill holes in the correct spot to rebalance or add Mallory metal in the correct spot to correct the balance.
 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 401MATCOUPE Quote  Post ReplyReply Direct Link To This Post Posted: Mar/21/2014 at 10:46am
A m71 401 Flywheel is not the same also.......................don't take chancs, get your rotating assembly balanced, once and for don't it will never haunt you.  I by alot of flywheels to use!!
 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 1970390amx Quote  Post ReplyReply Direct Link To This Post Posted: Mar/21/2014 at 12:53pm
I have been told that AMC  had a machine in there engine room to spin the rotating assembly of a short block then remove metal from flywheel and balancer to balance. If this was true no replacement flywheel is 100% correct without balancing the entire engine.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Class Guy Quote  Post ReplyReply Direct Link To This Post Posted: Mar/21/2014 at 1:08pm
Balance specifications for 1970 390 and 360 are the same. The flywheels will interchange.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote typhooner Quote  Post ReplyReply Direct Link To This Post Posted: Mar/21/2014 at 2:13pm
Iiiinteresting! I can't wait to see where this goes. I think there was something in the Harmonic balancer sticky about the '70 360 and 390 balancers having the same part number but weighted in a different clocking position. I don't recall if the different clocking position make them interchangeable or not. I imagine the same rules would apply to the flywheel factory balancing. Meaning the clocked position of balancing between 360 and 390 flywheels. It would be a Godsend to see a pic of both 360 and 390 '70 flywheels side by side.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote WARBED Quote  Post ReplyReply Direct Link To This Post Posted: Jul/24/2015 at 4:55pm
I have a 70 390 balancer and a 72 360 balancer. Tomorrow I must match them up. both are 3 bolt design, I am currious. yea and I know this is a old post. I should have the flexplate from the 70 390 engine laying around here also but it's the Borg Warner design.
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