flywheel diameter for 1966 170 Bronco

[edgewood bronco]

I took my soon-to-be-new 200 block to the machine shop today and when we were talking about the rotating assembly, he said I'd either need to pull the flywheel out of the vehicle it's going in, or get a new flywheel that can be balanced with the crank, harmonic balancer, and clutch/pressure plate. I'd like to keep my bronco on the road until I'm ready to do the swap, so I'm hoping to find a spare flywheel and get it balanced and ready to install as a unit.
That brings me to my question: What flywheel do I need? I am beginning to understand that there apparently are both an 8.5 and 9"flywheels by searching the forums. Which one might I have? Is there an easy way to check this?
Anything else I should be careful of?
Thanks!

 

[CoupeBoy]

I'm not terribly proficient in Early Broncos, so hopefully this doesn't lead you astray..
From what I've read the 170's of that age in Broncos only came with the 3.03 3 speed manual transmissions. Which use the 9" clutch and flat flywheel.

quick way to tell is to answer this easy question.
Is 1st gear on your current transmission synchronized?
(same question, asked a different way)
Can you downshift from 2nd gear to 1st gear while still in motion?

I must say, I am a little surprised that they need a flywheel to balance the motor. What if you were putting it in front of an automatic? What if the flywheel you have cannot be used for some reason? Do they have to rebalance?

The other way to tell would be to look at your current bellhousing and determine if you are using a small pattern bellhousing or a larger patterned one. Small bell = 8.5" flywheel/clutch and bigger bell = 9".

this is a 1970 170 that I have sitting in my shop.

You can see that the automatic (C4) that came with the motor uses the inner/smaller bolt pattern. This is the same pattern a 2.77/8.5" flywheel bellhousing would use.

The outer/larger pattern is the one that is used by 3.03/9"

good luck
-ron

 

[edgewood bronco]

Thanks, Ron.
You'd think that you'd want the engine balanced independently of the flywheel so that you could put any balanced flywheel on there and everything would be good, but maybe things don't work that way. The Falcon Six handbook says to balance everything from the flywheel to the balancer...

You forgot an important part of the diagnosis: If first is synchronized, what does that mean? 8.5 or 9 inch?
Thanks.
Andy

 

[CoupeBoy]

Means 9"

However if it is not synchronized. It could be either still. A friend of mine had a 1966 Mustang (200/2.77) that had the 9" flywheel.

 

[edgewood bronco]

Cool. Thanks.
Mine's synchronized... anybody have a 9" flywheel I can take off their hands?