~FLATHEADS~
1. OVERVIEW & HISTORY                7. IGNITION
2. FUEL FLOW                                8. INDUCTION
3. HEADS                                       9. EXHAUST
4. CAMSHAFTS                             10. LUBRICATION    
5.
CRANKSHAFT
6. RODS & PISTONS
RODS & PISTONS
Every time I’ve looked at a Flathead Ford connecting
rod I’ve thought the same thing – how can something
that spindly be that strong? Truth is
that the flathead connecting rod is very strong as
Ford’s engineers were a heady lot. Forged from a
nickel/vanadium steel alloy, they were certainly
more than adequate for the horsepower and RPM
ratings they were designed for. Now, howz about we
start doubling (or tripling) horsepower and multiply
the RPM rating (3600) by one and half times? How
do they hold up at this point and beyond? The
answer I have found is quite well thank you. Having
used nothing but ‘stock’ rods myself in all
my race engines and, approached 6500 RPM at
times, I can honestly say that Ford Engineers knew
what they were doing when designing these
connecting rods. As in most engineering applications,
a ‘Factor of Safety’ is considered – bridges are usually
rated at a portion of their actual strength. I’m
assuming that Ford’s Flathead connecting rods
had a factor of safety somewhere’s around 1 ½ - 2 to
1, hence they will hold up under much heavier use
than they were rated for. Now, of course this is an
assumption and although I have found it to be true in
my experience, I’ll add the disclaimer here that this
assumption only holds true under the best of
conditions. In other words, things have gotta be
right. If they aren’t then you’ll have plenty of pieces
to pick up. In over 20 years of wringing out flatheads
on the race track, I’ve only lost two and both were
due to rod failure. It’s led me to this simple
formula: Fatigued rod + 6000 RPM = Schrapnel. Both
were well used engines and both were turned up to
their limit. The rod type did not matter as one had a
set of 8BA insert type rods while the other had 29A
floaters. Rods stretch. Barney Navarro told me that
they’re like rubber bands in the engine and can
stretch as much as 0.007 inch under duress.
This cyclic stretching and contracting causes fatigue;
after so many cycles and the material deteriorates
which is why many good racers of the flathead era
changed out their rods often. Ok, so what did many
racers do with them?
First of all, you have to start with a good rod. For
strokers the 21A and 91A floater rods are the only
two that will do, earlier floater rods fit but don’t have
the additional strengthening flange material so I
wouldn’t recommend them for anything but stock
applications. I’ve often read that the 21A was superior
in strength but in comparing the two, I can see only a
difference in the big end boss and have used both.
For the standard stroke Merc. and Ford cranks (2.139
rod throw) the 29A floater is preferred although the
8BA works fine on the later (two oil hole) cranks and
clevite inserts are still available which makes them
attractive. The rods must be perfect in alignment, pin
fit (they can be re-bushed) and large end fit as well.
Many of these rods came with additional material on
the small end (pin) boss – that wasn’t turned off –
these naturally are a bit heavier but again preferred
for additional strength in say a blower application.
My father recalls going out to B&M Speedshop in
Rochester where they had their assemblies balanced
and watching shop workers check rods for roundness
on the big end, often tossing them back until they
found (8) perfect ones. Cliff Kotary has told me the
same of his selection process. You have to start with a
good one, preferably new if you can find it, or at least
one that has been reconditioned as new. Racers of
the era started here, with good rods and then worked
with them. Some were cruder than others. Bob Cain
once told that he looked all day for a set of rods for
fellow racer Gordy Wood and finally came up with a
full set of new ones which he took over to Gordy’s one
day. Wood promptly took a piece of re-rod and welded
the chunks to the beam to ‘strengthen’ them. “If I
knew he was gonna do that I’d have gotten him a set
of used rods.” Bob related. Dick Nolte once showed
me a set of rods that had been gusseted with thin
plate on the beams, much in the same manner that
Ardun Guru Cotton Werksman had often done. My
first thought as I was bouncing them in my hand was
‘man, these are heavy’. They were, one of the few
advantages a flathead has (over say another
engine of that era) is their light rods and with this
procedure, that advantage is gone. Not to mention
the additional stresses induced to the metal from
welding, which now requires straightening and stress
relief, again another problem from the relief process
is that the rods bolt threads (which are integral with
the rod itself) may be weakened. I know
many used this procedure but I question just how
much they really gained, maybe someone with
experience can comment. Most of the guys I’ve
talked with simply had the rods properly sized and
magnafluxed to ensure integrity and then balanced
with the assembly. Bob Hayslett related a
‘poor mans’ magnfluxing trick to me once, using a
light (Mystery) oil on the rod, wiping them down and
then covering them with flour. The oil would seep out
of any cracks thereby exposing the rod as scrap. My
process in using rods includes magnafluxing first,
sizing and then polishing of the beams to remove any
edges or flashing that may cause a stress riser and
encourage cracking, then shotpeening to further
enhance surface tension and strength. Then (after
fitting) I send them for balancing with the assembly.
There are other options of course. Back in the day
Howard Johannsen reportedly offered aluminum
rods, I’ve never seen a set but I’d lay a bet that they
were race only and considered expendable. Today
there are many options as Cunningham, Crower,
Scat and Eagle all make an H beam severe duty rod
for the flathead. I contacted both Cunningham and
Crower years ago to inquire about their rods as many
‘Left Coast’ drag racers I had talked with
recommended them for their high quality which I
don’t doubt. The prices at that time were $1800.00
and $1500.00 respectively which is why I’ve stuck
with the stockers. The Scat and Eagle rods are a
cheaper alternative pricing in at around $300.00 now
(they’ve come down) and offer some advantages in
that they use a Buick insert bearing which is readily
available, and they are rugged. They’re also heavy
and may require extra work at the balancer. I only
know of one fellow who has used them and his
experience at Bonneville left them picking up pieces
so I can’t really say from experience how they
compare. My latest thought is to continue to use
what Henry’s boys created and work with them,
maybe even check out freezing (cryogenics) them to
make them even tougher than they already are.
OK, just a little on fitting them and we’ll move on.
Insert 8BA’s are a breeze (so long as they are sized
properly), snap in the bearings and check clearances,
0.002 – 0.0025 is good for a race engine. Floaters, as
discussed briefly in the crankshaft page, are a bit
trickier as you have to check for clearances with a
good micrometer to be accurate, measure the rod end
ID, then subtract out the crankshaft rod throw
diameter, then subtract the bearing thickness (X2)
and then divide by two (remember, they’re floaters)
and that’s the clearance. Again, 0.002-0.0025 is good
but in practice, you’re just guessing to be truthful.
Bearing adjustments on floaters is still done
employing the tried and true hammer whacking
method. I use a rubber mallet and a good piece of oak
wood to make the adjustments, place the rod on the
bearing with plenty of Permatex Super Slick (STP
works good too), torque to spec. (43FtLbs) and then I
want to see that rod be able to drop to the bench. It
takes time and a lot of scotchbrite to make it
work but in the end, that is the way it has to be. You
also want your rod to have free play on the crank
journal in the horizontal plane, again as with the
bearing, 0.015 end play is necessary. This can be
achieved by placing a piece of sandpaper on a flat
plate and scuffing the rod surface until you get the
required clearance between two of them, as they both
ride on the same journal. You can see why it’s
important to fit them up before you send them to
balance as many things can change if you don’t.
Lastly, replace the rod nuts with some good
hardened (ARP) nuts and I loctite them in place when
assembling.
Pistons for the racing flathead were available from
many different companies in the day and still are.
Most racers I know, and most engines I have seen
used the sand cast 3-ring racing piston either from
Jahn’s or JE, both excellent choices. This is a rugged
design that not only held up well but also gave the
balancer plenty to work with. The skirt is of a solid
design which offered greater strength than their stock
counterpart, (which often was slotted to allow for
expansion and hence offered better sealing
characteristics) but also meant that allowances          
had to be made when honing cylinder walls for
clearance. Bob Hayslett always set his clearance at
0.0065 which again supports the ‘loose is
fast’ theory I’ve always maintained. Three rings
offered less friction than four which were found on
the OEM pistons and the racing pistons
skirt was shorter too, again reducing friction. There
were other, lighter pistons available as well. Art
Sparks developed his ForgedTrue pistons for
Offenhausers but soon offered them up for the
flatheads as well and Silvolite also developed a lighter
piston for racing use. Both were excellent choices but
as I’ve said, most racers I know used the
sand cast versions, or modified stock pistons. Bob
Hayslett often experimented in his second car, the
B28, with the aforementioned self done cutdown
crank that nearly shook the fenders off and also with
stock pistons in which he shortened the skirt to
remove the 4th ring land. He didn’t tell his driver Bill
Maxon what he was up to in the engine compartment
and Bill drove the car hard, sometimes besting his
teammate Dick May in the B29, which had the ‘good’
stuff.
Piston’s often didn’t vary too much in design from
one another although there were a few options which
related to compression. The ‘LC’ designation related
to ‘low crown’ or ‘low compression’ and these pistons
were designed with a pin placement that put the
outer edge of the piston dome approx. 0.030 (it varies
based on the crank and block) from the top of the
cylinder bore. Many racers corrected for this by
planing the block and heads to get more
compression. The ‘HC’ designation related to ‘high
crown’ or ‘high compression’ pistons and these had a
pronounced amount of additional material over the
top ring land which would often push the outer edge
of the piston dome beyond the block deck height. The
set of JE’s I used actually were 0.090 beyond the
block deck and required the heads to be bored to fit,
quite a job but WOW what compression. Pin heights
to the top ring land don’t vary between these
two designations of the same stroke, the difference
only lies in the amount of material over the top ring
land. There are other ways to pop up pistons, for
instance you can stroke your crankshaft 1/16 of an
inch (that’s 1/32 up and 1/32 down) to get the edge
of the piston dome at the block deck and pick up
some cubes as well as lighten the assembly – a
very successful and clever racer did this in the 60’s
and his engines were often compared to the
overheads of that time (guess who). You can go a step
further by placing 4” Mercury pistons on a 4 1/8
stroker crank, so long as your top ring land works
with what ever relief you’re employing. You want at
least 0.020 of bore over the top ring to be safe I’d say
as a SWAG, remember, rods stretch and the rings
move in the piston lands, you don’t want to catch
that top ring on the relief. Some guys even tried Ford
pistons on a Merc. crank but as my Dad told me, they
had to use two head gaskets to clear the dome and
kept blowing them out so it wasn’t successful (at least
in their case). The pop up idea is a good one as it
makes the builder create a deeper combustion
camber in the head, which is where the intake
charge wants to go in the first place, and then fills
the chamber with the piston creating terrific
compression. The problem with the early design,
according to Barney Navarro, was that the end gases
tended to blow head gaskets (although I’ve not had
this problem) and his solution was to build a head
with a hemispherical chamber and then combine it
with a corresponding piston (made by Arias) that has
only the piston dome out of the deck surface at TDC
while the edge of the piston dome sits flush with the
deck surface. Good idea and I’m sure it’s a good set
up, they’re still available if you have the flow, in other
words, they are more expensive than the
conventional equipment. Baron also makes set-ups
such as these with the additional forethought of
scalloping a bit of the leading edge of the piston
which corresponds to the relief or transfer
area, further enhancing flow. Pretty neat stuff.
My last commentary is on stroker pistons. These vary
from the stock stroke pistons only in pin placement
and, as you get to the bigger
strokes, skirt length, or lack of it I should say. The
longer the stroke, the shorter the skirt and more
pronounced the scallop is in the piston skirt in order
to clear the crankshaft counterbalances. What this
does to the piston in the bore is makes it less stable,
more susceptible to scuffing and more likely to get
sideways, especially as it wears. Couple this with the
increased angle of the rod in relation to the bore
and piston and you can see why you not only can’t
turn one of these engines as hard, but usually not as
long either. Still, properly built, there’s nothing that
sounds or goes like a stroker and a 4 1/8 setup is
really one of the best flathead engine combinations
available. OK – to finish up here with pistons you
have to check several things such as ring land width
(they vary from manufacturer, do this before you
order your Grant or Total Seal rings), pin fit and of
course, locks. If you’re buying an old set of pistons,
check to ensure they aren’t too scuffed up, that ring
lands are in good shape (hopefully without the need
for the steel spacers or ones that haven’t been
knurled) and most importantly that they aren’t
cracked. You’ll also need the pins which can vary in
weight, I use the lightest I can get my hands on but
hopefully you’re set come with the ones from Jahn’s.
And you’ll need the locks too, the Jahn’s and JE
pistons used a heavier gauge wire when making their
C-clips than OEM which means the groove is wider as
well. You can’t use a stock OEM clip in these pistons
and stock pins are heavy as well, get a complete set.
Or, buy some nice new Ross pistons which come with
nice pins and spyrolocks – these are copies of Art
Sparks ForgeTrue’s; very nice pistons and will hold
up to that 4-71 you’re dreaming about dumping on
top of your flattie. Lastly, check the rings in the
bore before assembly for sizing, you want 0.003
clearance on the ends per 1 inch of bore, or 0.011 –
0.012 for the 3 3/8 bore (give or take), who cares if it
uses a little oil? At least the mosquitoes won’t bother
you and it’s a good indicator that there’s still oil in
the thing right?! Just keep repeating ‘Loose is Fast,
Loose is Fast….
Pictured above is one tough
connecting rod. This is a
29A that went through
catastrophic failure, you
can see that these will take
a lot of abuse.
Early floater on left, NG for
racing; 91A rod center, AOK;
21A with sturdier big end
boss right ~ the best stroker
rod.
For heavy duty (blower or
Ardun) applications, the rod
on the right with a sturdier
small end boss is preferred.
Polishing the beam reduces
stress risers, toughening the
rod as well as lightening.
Cunningham and Crower
rods (left) represent the
pinnacle of new technology
available. Boxed stock rod
(right) was the answer for
decades before.
Floater rods and bearings,
the best set up for racing
flatheads of the 50's and 60's
Jahn's racing pistons
offered a variety of bore and
stroke combinations in a
rugged design.
Stock OEM 4-ring piston,
Jahns racing 3 ring and new
Ross forged racing pistons.
Here we see the differences
in casting design, Ford
'Stock' on left, Jahns 'waffle'
strengthening ribs center
and Ross forged on right.
Illustrated here are the
differences in pin height
and skirt length. 4&1/4
stroker on left, 4&1/8 next,
then 4 inch and Ford 3&3/4
stroke on right.
A lighter pin (left) equals a
lighter assembly and
quicker engine.
Depicted here is the outer
limit of flathead stroking
and lightening. The 21A rod
on left has been whittled to
the extreme, the piston above
is scalloped to clear the
crank counterbalance, as
required with a 4& 1/2 inch
stroke. On right is a
conventional 4 inch set-up.
You need the heavier gauge
retaining clips with your
earlier design Jahns or JE
pistons, replace the stock
rod nuts with ARP hardened
units.
8BA Rod with insert bearing
and well used ForgedTrue
Piston, a reliable set-up.