i have a 71 grabber and ive been getting some strange rotational vibrations comming from my motor ever since ive owned it so i finally took it in to my buddy/good mechanic and after discovering that the engine block is from a later model ford suggested strongly that the flexplate is probably the incorrect balance for the year and the the motor was probably frakenstiened together with various original and newer 302 pieces. does anybody know how to tell if its the proper flexplate or not? is there some numberes or way to tell? or if anybody just knows the proper plate that needs to be there? i mean the motor runs, timing and firing is right, motor mounts and tranny mounts are good, we ruled out the drive shaft being out of whack. does this even make sense or sound right to anybody? and does any body have other suggestions/ideas? all input is welcome, thanks!
If it vibrates when revving the engine, then it's likely out of balance... Cranks changed in '81 to a 50oz imbalance and then again in '82 to the one piece rear seal... Sooo if it's a newer than '82, it uses the one piece rear seal and is defiantly a 50oz imbalance engine... very possible to have a 28oz flex plate installed vs 50(see link posted)... If it only vibrates while driving, you have other issues...
Thanks for the link Dave, that should help with identifying the parts. And yeah it's definitely RPM based vibration, and yes the engine block is from the early 80's, 81 I believe. But my question is which one do I need? I mean yeah it's probably not the one that's in there so it has to be the other but with an early 80's block does that mean I need the early 80's flex plate? Or should it be the lighter one?
You could quite possibly have the wrong imbalance harmonic balancer on it too. Both the balancer and the flywheel/flexplate have to be the correct pieces to match the crank. Look at the casting numbers on the block, that will give you an idea as to what might be there. It is also possible to use a 28 oz/in crank in a 1 pc rear main seal block, it's not likely to be this combo, but it is a possibility. My 331 has a 28 oz/in crank in an 89 block. You can pull the balancer and check the casting numbers on it to verify what the balance is on it (E2 and later will be a 50 oz/in unit)
How can I tell if its the right balancer? Because the way I look at it it's probably an 81 block with 81 parts but just the 28oz flex plate. Is it possible to have an 81 block with the 71 balancer and a 50oz plate? I just need to figure out the right combination here.
It can be any combination. The only sure way to know, besides pulling the flexplate and replacing it with the opposite imbalance unit is to pull the oilpan and check the crank. I know this is asking a lot, and you'll have to know what you're looking for, but this is the only sure way to know. It's also possible that you've got the right pieces there, but the balancer's outer ring has slipped, thereby throwing it out of balance. Where are you located ? It's possible there's a member close by that can help.
Hmmmm, I'll have to have my guy take a look at both. I mean the vibrations tolerable, but definitely noticeable and I'd kinda like to get it straightened out. It can't be good to just let it be.
there is a big difference in the flexplates...I think side by side you can see the diff. in the balancers...
The balancers are easy to ID, just look at the casting numbers. Flexpates, you have to compare it to a "known" part, or know what it is you're looking at.
from the "stock" AOD flexplates I've seen they have a big hole in it refereed to as a..."suitcase handle"... http://www.rowand.net/Shop/Tech/images/FordFlexplates01.jpg
