balancing question

[Bill88Stang]

Here's a quick question for you. I'm about to put my 351W into my Mustang. The motor came from a truck with an automatic tranny. It was balanced with the auto flexplate on it. Now I'm putting the motor into my mustang with a stick.

My question is do I have to get my brand new Hays sfi certified flywheel match balanced to the old auto flexplate? I can't see how this would work since the difference in weight between the old flexplate and the new flywheel is a lot. Any info would be great. Thanks

 

[TIMMY2734]

going to need a 28oz flywheel. Though if its aftermarket, you can just change the counterweight on it.

 

[Bill88Stang]

It is a 28oz. flywheel.

What I'm asking is do I have to get my flywheel match balanced to the flexplate that was originally balanced on the motor?

 

[TIMMY2734]

You dont "have" to. Plenty of guys dont use their own balancers/flywheels when motors are balanced. You obviously know youd be better off, but if your not revving it to the moon, you should be fine.

 

[Bill88Stang]

It just doesn't make sence to me. If the flywheel is balanced.. how can it be match balanced to the former flexplate that was on the car? I mean if it's balanced, it's balanced.... if it's not its not. I don't think they're gonna match the weight of the old flexplate because thats a massive difference. What could they actually do to it?

 

[milner351]

balance questions

well there is balance and there is balance.

Fords are externally balanced, meaning, the crank itself must have a matched combination of the correct flywheel/flexplate and balancer to make the complete assembly "balanced".

We're speaking rotationally balanced here, not balanced in terms of two things being the same weight. A flywheel for a manual trans and a flexplate for an automatic will never weigh the same if you put them both on a scale, however, they both work properly with the crank and balancer if they are compatible, because they are balanced "rotationally" to match.

That is why 50oz and 28oz things don't work together.... you can't mix and match older flywheels / flexplates / balancers / cranks with newer ones.

When a set up is balanced at a machine shop, they are taking the factory matched rotational weights and making them match to much tighter tolerances.

As long as you make sure your balancer and crank and flywheel are all the same external balance be it all 50oz, or all 28oz, you will be fine.

If you want to match balance to great precision in order to sleep well at night and shift at 6500rpm ++ then, pull the engine apart, and bring the three components to your favorite machine shop. Here in the detroit area this service runs from $125 - $200 depending on where you go and how precise you want it.