[DeTomaso] Ford flywheel size and weight????

Wed Jun 11 14:40:33 EDT 2014

Thanks for the easy-to-understand explanation Dan!

-----Original Message-----
From: DeTomaso [mailto:detomaso-bounces at poca.com] On Behalf Of Daniel C Jones
Sent: miércoles, 11 de junio de 2014 18:52
Cc: De Tomaso List
Subject: Re: [DeTomaso] Ford flywheel size and weight????

> Why are not each component balanced to zero. Then when assembled it could
be balanced to a small amount to refine it.

A V-8 has an unbalanced couple that rotates the same direction and
frequency as the crankshaft.  If you hang the engine from a chain and run
it with no balance weights on the crank, it will wobble.  A point on the
front of the engine will travel in a circle, as will a point on the rear of
the engine, but the middle won't move.  Like holding a broom handle in the
middle and moving one end in a circle.  The other end moves the same but is
opposite.

To balance this, offset weights are needed at the front and rear of the
crankshaft.  The farther away from the center of the engine and from the
center of the crankshaft these weights are, the smaller they need to be.
If this weight is inside the block, it is considered to be internally
balanced, if these weights are on the flywheel and front pulley, it is
externally
balanced.

External weights apply their force through the first and last main bearing.
Moving the weights inside more, means more force is needed, but it
distributed over more main bearings.  In addition to these weights, other
weights are placed on the crank to minimize main bearing loads.

Sometimes you will see it claimed that internal balancing is best but
that's not strictly true.  Splitting the "bob weight" portion of the
counter-weights between internal and external, both front and rear will
generally give the lowest crank bending stress.  The "bob" weight is best
centered about the #1 and #5 bearings. Note that all of this applies only
to V-8's with 90° cranks.

A 90° crank V-8 needs a bob weight at each end to balance out the motion of
the reciprocating masses (pistons, pins, rings, and small end weight of the
rods).

The internal/external thing is little more than a question of WHERE these
two bob weight masses are located.   Internal takes more weight than
external and puts out-of-balance couples across the front and rear main.
This is most noticed on the front, since the flywheel or convertor tend to
damp the rear.

Some external is good but too much is bad.  Ford saved a few lbs of mass
when they went from 28.2 oz-in to 50 oz-in but it came at a price.  With 50
oz-in, the couple across the #1 main on the 5.0L is larger than at 28.2
oz-in; in SCCA A Sedan racing, it was common for 5.0L cranks to fail at the
cheek of the rod throw. While many jump straight to internally balanced,
28.2 oz-in seems to be fine for most applications, though it is likely
dependent upon the RPM being turned.

Sometimes there isn't enough room to make the throws large enough in a
casting or forging to internally balance without adding slugs of a heavy
metal like tungsten.  An example of this is the Ford 428 SCJ that required
an external hatchet balance weight to offset the heavier rods.

Dan Jones

On Wed, Jun 11, 2014 at 11:13 AM, Larry - Ohio Time <Larry at ohiotimecorp.com>
wrote:

> Please file this in the stupid questions folder.
>
> Why are not each component balanced to zero. Then when assembled it could
> be
> balanced to a small amount to refine it.
>
> Do not understand the principle behind this way of doing balancing.
>
> Thanks,
>
> Larry - Cleveland
>
>
>
> -----Original Message-----
> From: DeTomaso [mailto:detomaso-bounces at poca.com] On Behalf Of Daniel C
> Jones
> Sent: Wednesday, June 11, 2014 11:14 AM
> Cc: De Tomaso List
> Subject: Re: [DeTomaso] Ford flywheel size and weight????
>
> > He ordered a 347 stroker kit for the 302 and they wanted to know how many
> teeth on the flywheel.
>
> Presumably, they are making an assumption on the imbalance.  All
> 289/302/351W/351C 164 teeth flywheels were 28.2 oz-in, though the same
> flywheel on a 300 I6 was neutral balance.  Later 5.0L's used a 157 teeth
> flywheel with a 50 oz-in balance factor.  Be aware that some people use
> flexplate and flywheel interchangeably.  Though the 5.0L HO used a 157
> teeth flywheel with a T-5 5 speed manual transmission, the same engine used
> a 164 teeth flexplate when mated to an AOD automatic overdrive
> transmission.
>
> > The crank/rods/pistons are the same, regardless of the flywheel.
>
> Some manufacturers make different kits for different balance factors (and
> assumed rod length). The raw forgings are the same but the cranks are
> finish machined to be easily balanced to a particular imbalance and
> bob-weight.  Some of the Scat kits, for instance, are designed to need only
> drilling (no Mallory metal) to balance.  Trying to internally balance a kit
> designed for 50 oz-in can cost more in Mallory metal and machining than the
> crank cost so it pays to know what you are getting.  The manufacturer
> should be able to tell him you imbalance (and even bob-weight) the kit was
> designed for.  You want to avoid 50 oz-in unless you plan on keeping the
> revs down and need to re-use an existing balancer.  Depending upon the kit,
> internal balancing may require a fair bit of mallory metal. 28.2 oz-in is
> fine for most uses.
>
> Be aware that most balancers for 28.2 oz-in require a spacer to work with
> the OEM 5.0L HO serpentine belt accessory drive.
>
> Dan Jones
>
>
> On Mon, Jun 9, 2014 at 8:57 PM, Jerry Knotts <knottsj at galstar.com> wrote:
>
> > There are many questions that I can't answer but this one is vexing.
> >
> > A Chrysler motor builder friend of mine is working on a Ford 302 and
> asked
> > me a question about flywheel tooth counts.  He ordered a 347 stroker kit
> > for the 302 and they wanted to know how many teeth on the flywheel.  He
> > asked me why they needed that information?
> > I fumbled through all my extraneous explanations.  There are 2 major
> tooth
> > configurations 157 and 164 lesser used 148 teeth.  There and 2 major
> > imbalance configurations 28oz and 50oz lesser used 0oz.  Both balances
> take
> > a particular harmonic balance that is compatible with the imbalance of
> the
> > flywheel.  Backing plate sizes and starter ends vary by diameter and
> depth
> > for standard and auto trans and flywheel teeth.
> > I finally figured out I have no idea.
> >
> > Is there a concise explanation.  If so what is it.
> >
> > Thanks in advance,
> > jerry knotts
> >
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