[DeTomaso] Vedr. what crankshaft to get?

[Daniel C Jones]

> I asked if possible to use my old flywheel and that was ok as long as it
> was a 28oz? What will that men? Internal balance ore just piston and con.
> rod all the same wt?

There are two ways to balance the reciprocating assembly.  The first is known
as internal (also known as neutral) balancing where all the balancing is done
internal to the crankshaft (within the crank counterweights).  The second is
known as external (also known as Detroit) balancing in which some of the
balancing is done in the crank counterweights and some is done external to the
crank in the harmonic damper and the flywheel or flexplate.

OEM balance for a 351C was 28.2 oz-in (Boss 351C's were slightly different).
Internally balanced flywheels are available as are flywheels with a 50 oz-in
balance factor (as used by 5.0L Ford V8's) that will bolt to a Cleveland
crankshaft.  Note the balance factor is a product of mass and distance so the
units are oz-in.

IIRC, you are looking at 4" stroke kit that SCAT designed for 28.2 oz-in.
The assembly could be internally balanced but that would require drilling
the crank and filling the holes with several slugs of dense Mallory metal
(tungsten) which would cost more than simply drilling ot grinding on the
crank to balance to 28.2 oz-in.

There are production tolerances and it is common to do small adjustments to
the flywheel and damper if those are provided.  However, if you have to replace
those components in the future, the replacement parts would not have the same
balance factor.  Dave McLain does the machine work on my engines and uses spec
flywheels (neutral and 28.2 oz-in) and does all the balancing within the
reciprocating assembly, leaving the flywheel and balancer alone.  That way, if
you ever have a problem where the flywheel or balancer has to be replaced, you
can simply bolt up a new one.

FWIW, I've switched between flexplates and flywheels (of the same nominal
balance factor) and never had a problem.

Dan Jones