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Re: 408C damper and flywheel question

May 2 2012 at 11:28 AM
Dan Jones  (Login 74Pantera)
from IP address

Response to 408C damper and flywheel question

> I bought a rotating assembly from K1 technologies to bump my cubes up to 408
> and had them balance it at the factory.

Did you buy this directly from K1 (or perhaps from a vendor who supplied the
pistons to go along with the K1 crank and rods)? I wasn't aware that K1 did
a complete kit for Cleveland engines and don't see anything listed in their
current catalog. Do the pistons have valve reliefs for canted valve heads or

> Will it mess up balancing?

I spoke with Tom Molnar of K1 about their Cleveland cranks. This was in 2008.
At the time they only made 3.5, 3.75 and 3.9 inch stroke Cleveland main journal
crankshafts but they have since added a 4" stroke version. Tom indicated all
of their SVO cranks were internal balanced. I asked about skirt clearance
with the shorter 6" rod required for a reasonable pin height in a 9.2" deck
351C block and he said I was the first one to ask about it. He confirmed the
3.9" stroke crank that I was interested in was designed for a 9.5" deck blocks
and 6.2" rods but was unable to say if there would be an issue or not with a
6" rod lengths. Understand that the K1 cranks are "SVO" type. They are
essentially a Windsor design with the main journals turned down to fit SVO
and other race blocks. For use in a 351C block, it will need a Ford Motorsport
snout spacer (part number M-19009-A341C, required with 351 SVO crankshaft when
used in production 351C engine). This part number is no longer available but
I have the dimensions to make one or there are timing sets with the spacer
built into the gear. The latter can be pricey and check to make sure a good
quality chain is used (not the inferior Rolon chain from India).

Subsequently, a European Cleveland drag racer order a 408C stroker kit which
used a 4" stroke K1 crank, 6.2" H-beam K1 rods and Wiseco pistons. When he
assembled it, the pistons stuck about 0.200" above the deck indicating the
pistons were designed for 6" rods. When he tried 6" rods, the piston skirts
hit the crank. It was my understanding that the kit was put together by

> It is probably clear by now that I know nothing about engine balancing, or
> how its done, or what parts balance it.

A 90 degree 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). Internal/external balancing is a matter of where the two bob weight
masses are located or distributed. Internal (also referred to as neutral) and
external (more rarely referred to as Detroit balance). Neutral or internal is
where all of the balancing is done within the crankshaft (once the weights of
the rods are equalized) and the flywheel and balancer are symmetric (no balance
weights). With external balancing, some of the the balance mass is moved to
the damper and the flywheel. A V-8 has an unbalanced couple that rotates the
same direction and frequency as the crankshaft. 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 or damper, it is externally balanced. External
weights apply their force through the first and last main bearing. Moving the
weights inside 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. From the factory, most 351C engines are
externally balanced and use a 28.2 Oz-In balance factor (HO and Boss 351C
were slightly different). Notice the units are ounce-inches. It's the product
of the mass (ounces) and the distance (inches) that is important. With
external balancing, both the flywheel and damper will have this imbalance and
not be symmetric. It's common for racers to internally balance but that
requires a matching flywheel and damper with zero balance factor.

Brent supplied the stroker kit for my 403C and internally balanced it. I used
a new old stock Schiefer neutral balance aluminum flywheel originally meant
for a Ford 300 truck inline six cylinder engine which shares the 351C's bolt
pattern and 164 teeth ring gear but is neutrally balanced.

Dan Jones

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