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Shotgun Diagnosis: 85 BII, 302 C4 4WD, Engine Wobble?


Bampity

Well-Known Member
Joined
Sep 7, 2014
Messages
51
City
Near a Great Lake
Vehicle Year
1985
Transmission
Automatic
My credo
Credo?
Hoping to do some spitballin on what might be the issue with this Bronco II I recently bought. Maybe to come up with a plan of attack once the weather breaks.

I never drove it.
I didn't build it.
I wish I did.

A few months ago, it sheared the flexplate from the crankshaft.
Full ring right around the bolts, I'm sure some of you have seen it before.
I took it to a shop, ordered both, 50oz and 28(?)oz.
Shop said it was the 50 and put the new 50 on.
Reinstalled everything, transmission, torque convertor, etc BUT now it seems the original problem is now showing itself.

The starter struggles to start, it cranks...cranks...cranks...but doesn't spin consistently.
Very slowly, like maybe a 1/4 rotation until it finally catches and fires up.
Brand new battery, starter condition unknown but looks new.

When it runs at high idle, ~3,000rpm on the tach, the big problem isn't noticeable.
When it drops to around 1,000rpm, very noticeable front to back wobble on the entire engine.
From underneath, you can see the engine and bellhousing kind of 'clamshell' or clap each other. They are mounted together but the way the C4 is with the bottom half nonexistent you can see the whole unit rise and fall. When you look under the hood is when you notice the front to back motion that's going on.

Kind of hard to explain but if you can imagine, the engine rocks back and forth not side to side. Also, hard to put in gear without giving it some gas otherwise it will stall.
And it shifts quite erratically, first second first second, at stop lights it will run high then shift down...kind of strange. Like its staying in the gear and rpm I was driving and takes a few seconds before it decides to 'chill out.'

So, taking the best description I can give, What would you do?
What do you think?
Where would you look?
Where would you start?


Thanks in advance for any help you can provide.
 
WAG; could the crank have been dropped and bent the flexplate bolt on area?
 
WAG; could the crank have been dropped and bent the flexplate bolt on area?

That could be one possibility. Definitely one of, if not the most extreme potential problems.

Is that typical of a 302 crankshaft to get bent? Its not a super high performance motor as far as I can tell. Just a few aftermarket mods, intake, coil, etc.

Wouldn't a bent crankshaft in that area cause a rear main seal leak?
 
If I were you I would get the casting numbers of the block to see the year and confirm it needs 50oz rather then 28oz
 
If I were you I would get the casting numbers of the block to see the year and confirm it needs 50oz rather then 28oz

My understanding I would need to pull the intake or oil pan.
IIRC, its an E6, anything else to verify I'd have to check it.
Was told its an 86 TBird engine. So the E6 matched that much.
 
That could be one possibility. Definitely one of, if not the most extreme potential problems.

Is that typical of a 302 crankshaft to get bent? I don't know enough to say Its not a super high performance motor as far as I can tell. Just a few aftermarket mods, intake, coil, etc.

Wouldn't a bent crankshaft in that area cause a rear main seal leak?

A leak would make sense. Sorry, I'm no help.
 
On my old 429/460 motors, the casting number is just above and behind the starter.
 
bab58c0e2308083cbf2b7a4077897c58.jpg

I think in the "other" articles on trs they have a explanation of what the numbers mean, I pulled my motor out of a 76 f100 it is actually a 69 fairlane engine,
 
bab58c0e2308083cbf2b7a4077897c58.jpg

I think in the "other" articles on trs they have a explanation of what the numbers mean, I pulled my motor out of a 76 f100 it is actually a 69 fairlane engine,

I'll check out the tech pages and get under there for a look.

We'll see what comes of it...
 
bab58c0e2308083cbf2b7a4077897c58.jpg

I think in the "other" articles on trs they have a explanation of what the numbers mean, I pulled my motor out of a 76 f100 it is actually a 69 fairlane engine,

F1SE BB 7 cast into the drivers side.
The little clock thing under the starter I can't read.

Looks to me, the shop actually installed the 28oz flexplate because the 50oz I still have.

I'm thinking they should've installed the 50...
 
Yeah you have a 91 Thunderbird block witch is a 50oz I would take it back and complain, anything 81 or newer is 50
 
Yeah you have a 91 Thunderbird block witch is a 50oz I would take it back and complain, anything 81 or newer is 50

I already have it taken apart and about to install the 50oz.

Just looking over if there is an orientation to this thing.
Weight up, weight down...TDC crank?

I guess it goes on one way and that's it.
My 400 Cleveland was easy as two of the bolts were obviously out of symmetry...
 
It only fits one way. All of the older external balanced engines were that way.
 
Yeah like adsm08 said one way but it'll fit 5 other ways really close as in all the bolts but one, I put a mark on my flywheel and then just rotated it till it worked
 

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