347 Flexplate/flywheel Help

James Herbert said:

Hi all,

I have a 1969 Mustang convertible with a T5z 5 speed transmission; and am replacing the tired old 302 with a 347 stroker I had built from an 87' block and 91' GT40 heads.

I just received the engine from the builder. He provided a flex plate and said the engine was externally balanced to it. But I have a manual transmission that needs a flywheel. Can I install the flywheel as is or do I need to have it balanced to the engine?

Sorry if this is a no-brainer dilemma but this is the first time for me doing an engine swap

Thanks!

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The flywheel must use the same imbalance as the motor was built for. That was basically determined by the aftermarket crankshaft used in the rebuild. Both the balancer and the flywheel must match what the crankshaft was meant to be balanced to.

If it was me, I'd first contact the builder and explain the situation. The info could also be found on the build sheet if one was provided. Typical ford imbalance would be 50, 28 or even 0 oz. Flywheels for these imbalances can typically be bought off the shelf and installed--as long as you know the what the motor was balanced for. If the motor was balanced to any other spec (rare but unfortunately possible with poor builders) you are basically screwed. Do not install your manual flywheel without knowing first that it is the same imbalance.

If you post a photo of both the front and rear of the automatic flywheel you received (and maybe a part # if one was included), it is possible that it can be ID'd by an astute poster as there are typically visual differences that can help.

The simplest way is to contact the builder-he should know.

If they are both 28oz imbalance, they you should be golden.

That said I try to have the flywheel also checked for balance when the crank is being balanced, but I am being extra cautious in that regard as I am spinning a big motor at higher than normal RPM's in a race environment.

(The pics don't depict the side that the weight is on.)