G'day
only just became a member of this sight ,but have been gathering info of it for a while
i have a 1973 f350(Australian 73 is the same as american 72) which i have been doing a chassis up rebuild on for the last 5 years
the old truck is in the home stretch now and hopeing to put it on the road soon ,but i am haveing problems with a vibration at around 2k rpm
idles smooth and smooths out above these revs
The motor is a pre 79 internally balanced motor (thats what the block number works out to be)it has just been rebuilt and has only done about 5kilometers since as its not on the road yet
when i first put the motor together i made the mistake of fitting the externall balance weights (the hatchet weight and the weights flexplate)
i have since removed the weights and fitted a new neutrally balanced flex plate and the sleeve for the front of the crank and while i had it apart i fitted a new boss hoss convertor (2500 stall) transmission has only just been rebuild also
engine has a 2y crank so to my understanding this should have fixed the vibration problem , but unfortunatly no one told my engine that
So i am wondering if the harmonic balancer could cause this vibration if it was faulty or worn as i used a s/hand harmonic balancer of a later model 460 is this the cause of the vibration?
please help as i have run out of ideas

 

Using the later 460 balancer may be the problem with the front counter weight removed. My 79,original engine,has the added front counter weight. I really don't know what the problem could be.

 

Anytime you rebuild a big block you should get the crank balanced. New oversized aftermarket pistons just don't weigh close enough to the stock pistons to get away with it. I hate to be the one to say it, but to fix it you are going to have to tear it down again and get it balanced.

 

Thanks for the replies, I suspected that might be the case but didn't want it to be true, i will replace balancer first in the hope that might fix it ,and then if that doen't fix it , i'll pull it down and balance it, i guess while its apart i might as well get some alloy heads and a slighty more agressive cam etc(my moto is if its apart it goes back together faster)

 

From the sound of it you have a good understanding of the 460. I'm curious as to what block you have, as you say it's pre 79. That would make it a D1VE, a DOVE, or one of the C9/8 variations. If that is in fact the case, and you do have a 2Y crank, then you would be correct in running it without the hatchet spacer and with a neutral flex-plate. All 385 series Ford balancers(dampeners) are neutral balanced, 100%. The hatchet accounts for all the external weight on that end of the crank. I doubt very much that even an old unit with a deteriorating elastomer would be causing any perceivable vibration. Also, while performing a rebuild and changing pistons it is a good idea to check the balance. That being said, it would have to be off by a LOT for it to be noticeable to your senses. Say for instance you installed a set of heavy H-beam rods, and in doing so added 100+ grams to your bob weight. Your crank and bearings would know it, but it's unlikely you'd be able to "feel" it.

-Jared

 

Id still check (having it balanced would diagnose this anyway) that the outer portion of your stock balancer hasnt slipped in relation to the center hub. Its an occasional problem with 30yr old balancers -not extremely common but it does happen. Regardless, Mark and the others are correct...have your engine balanced.

 

^^FWIW, it wouldn't matter if the outer ring slipped, it is neutral balanced. It could slip 180 degrees, and it would not cause a vibration.

To the OP, you never stated any specifics of your rebuild.

-Jared

 

Hi again
The motor was purchased as a rebuilt short motor (standard rebuild)
and from there i upgraded camshaft ,lifters ,rockers etc
camshaft from is a mild street camshaft , i think from memory its about 268 degrees and 465 lift
motor has standard style pistons and rods ,crank is a 2y unit ,the block no. is D9-te
motor was built to be driveable but fun as i have a car carrier back for my truck and so i didn't want to wreck the low down torque of the motor,
motor was rebuild by a reputable machining workshop, but that doesn't mean they couldn't have stuffed up
unfortunaly for me , it took me to long to get the motor in and running so it is now out of warranty , Thanks for your replies

 

2y cranks don't fit into D9 blocks. Something's not right here. A 2Y can be made to fit, but it requires quite a bit of clearance grinding. Are you positive it's not a 3Y?

-Jared

 

Im not 100% sure its a 2y thats just what the paper work from the machine shop said, i put the sump on it myself and wish i had checked the crank numbers before i fitted the sump but i didn't
so is a 3y crank internal or external balanced ?

 

I'm more confused now
I checked the sight(ford forums) that i was looking at to see if it was internal or external in the past and this is what it said
(p.s. i tried it with the balancers first and now without and it's no better either way ,is there different type of weights???)

• [*]

Paul<!-- google_ad_section_end -->
<!-- / message --><!-- sig -->
__________________
<!-- google_ad_section_start(weight=ignore) -->

 

^^All that is correct. Your block is a D9, with the D standing for the number 7. D9 is the same as 1979, D1=1971,C9=1969,E7=1987, and so on and so forth. The external engines all share the same amount of imbalance, and I believe it to be in the neighborhood of 26 ounces and change. Omitting the hatchet and the counterweighted dampener could certainly create a noticeable vibration. I think you need to pull your oil pan to verify the crank before you go any further. Just my .02, good luck.

-Jared

 

Thanks heaps deluxtruck
That makes sense now, will take the pan off and check crank numbers and get back to you

 

I just read your second to the post, and there is one tiny little mistake that is probably causing all your confusion. It SHOULD read all EXTERNAL balance engines will have a cylinder block casting number of D9. The early blocks were internal, the later blocks were external. Hope that helps.

 

Hi again
I have checked the crank and it is a 3y crank after all
so now my questioned has changed to why did it vibrate when i had the hatchet weight fitted in the begining?
is it possible to fit the weighted flex plate in more than one position?
or could it be there is some sort of difference between the crank weights?
The flexplate and hatchet weight i fitted originally came from a 1991 fuel injected 460 if that makes any difference im not sure???
I'll put the hatchet weight on it again and see what happens