The Stationary Engine List

By Staff
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The Stationary Engine List is an internet mailing list which
specializes in worldwide computer ‘conversations’ about
engines. It was decided sometime last year that the GEM readership
would enjoy some of the discussions which take place, so I pick one
of the many topics covered over the past month to pass on. This
month starts with a query from New Zealand:

I’ve got a question for all you welding experts out
there. I’ve had a 3 HP National for some time now, complete but
with three broken spokes, so it’s sat at the back of the shed.
Just yesterday I was given a flywheel with one cracked spoke.
I’ve tried for a long time to find a good one, but they all
seem to be connected to complete engines. What’s the best way
to weld the spoke?

When I collected all the responses together, I had around 6,000
words to deal with, so I have disregarded all the tales of havoc
wreaked by broken fly wheels on cars and tractors (this is, after
all, an ENGINE magazine!) and tried to stick to the subject.

Clean up the flywheel real good. Vee out the crack real good,
heat the fly wheel on a forge or in an oven and get it good and hot
(around 600 degrees will work), braze it, put it back in the oven
and cool it down slowly. Grind and file the braze job and put it to
work. I have had a great deal of success so far with this

The other option is to use the best one as a pattern and get a
new one cast. The reason for the preheat and cool down is sometimes
if you localize the heat and just braze it you can make matters
worse. The preheat dries out the iron and helps to prevent too much
stress building up in the braze area.

If there is only a crack in one spoke, I would do nothing.
Trying to weld it could stress other areas and actually you could
end up with more than one crack. At 150 to 175 rpm, one cracked
spoke shouldn’t present a problem. Now, if you are planning on
running this thing like a Maytag (5000 rpm!! Maybe not quite this
fast but when the smoke’s rolling they seem so) at a high rpm
(400-450), I would possibly have second thoughts. For
‘play’ purposes, you should be fine. (This from a guy who
has personally watched two single cylinders

Seriously, I’d look that flywheel over REALLY REALLY GOOD
(one crack could mean two, depending on what caused the crack you
can see!) and if it is indeed only one cracked spoke, I’d do
nothing. Run it slow and fun. My JD E 1.5 has had a cracked spoke
(just one) since 1979 and has made a show nearly each year, often
running a pump or something. Do look it over, however, as a crack
can exist that you won’t see easily.

Just a word of caution to everyone. You never know what these
old engines did or how they were treated by their owners 80-90
years ago. Give them careful inspection, especially in the
cylinder/base/flywheel area, to assure that the 100-year-old iron
can handle the stress.

The subject of welding flywheels gives me a headache. I’m
taking an aspirin and going to bed!

The wheel in question has six curved spokes with a rather heavy
rim; the crack is near the rim. The engine should be happy below
150 rpm. Being 88 years old, I think she deserves a rest.

I have had flywheel spokes repaired using a stitching method.
The method uses no heat. A slot is milled perpendicular to the
crack then a specially shaped wedge is inserted. Then overlapping
holes are drilled along the line where the wedge was inserted.
These holes are tapped and plugs screwed in. The plugs are then
flushed off.

In the end after a coat of paint you will not be able to tell
there was a crack. This process is widely used for heavy press and
shear repairs.

Metal spraying torches are for buildup work only. They should
never be used for this type of repair. They have been used for
decades for motor shaft build-up, etc.

To weld something like a cracked cast iron spoke you need to
heavily grind the broken ends to about 45 degrees to allow the weld
rod to get down into the break and build up a good thick weld.
It’s not done like soldering.

It does help to preheat the part but it’s not as critical as
the old ways.

Metal spraying is not the best for welding broken flywheels. It
is great for building up shafts or bores or filling in holes. It
bonds pretty well to the part but doesn’t have the same tensile
or tear strength. It can be ground to size and if done right there
are no pin holes or separation. It’s hard to even pick the

Aren’t you supposed to NOT grind cast iron with a normal
disc? I was told the carbon is deposited from the disc which
results in a crack point after welding. Vee out using rotary burrs
instead, or use gouging rods instead- lotsa neat big sparks..

A machinist friend of mine repaired a flywheel with two cracked
spokes by drilling down from the outside rim, through the center of
the spoke, past the crack. He then counter bored the hole down to
the crack. The top of the hole was also enlarged.

What he wound up with was a hole down through the spoke with
three steps. The bottom diameter was the correct size for a
3/8 tap, the mid-section was for clearance
for a 3/8 bolt, the top opening formed the
shoulder for a special bolt that he made on a lathe.

Can you see where this is going? After all this machine work, he
coated the long threaded bolt with some kind of epoxy, stuck it
down through the spoke, cranked it in tight and, presto, the crack
disappeared. The top of the bolt was cut off flush with the rim and
the outside face was then machined smooth to get rid of the rust
pits. When the repair was done the only evidence of it was two
round spots on the rim, where you can see the difference in color
between the steel bolt and the cast iron.

When finished, the machinist’s only comment was, if he
thought about it a little more, he would have made the top counter
bore deeper and installed a cast iron plug above the pin, so that
nothing would have shown on the flywheel rim.

This repair was done after considering all kinds of ideas, from
metal stitching to welding. It was a lot of work to align the wheel
correctly for the drilling process. But the end result was better
then expected and I would guess that the repaired spokes are now
stronger then the other four.

? The only fix I’d consider is no heat, no heat stress!
Ottawa log saws are bad about getting over on their side and
busting flywheels. I’ve seen two different saws with repaired
flywheels and a steel ring shrunk around the outside.

As is common with the Mailing List, the direct responses to the
questions caused a great many discussions to go off at tangents,
the safety aspects of running an engine with such a repair being a
primary one. This in turn led to complicated mathematical equations
(many impossible to reproduce with a normal 102-key computer
keyboard!) to calculate the speed at which a flywheel runs, and the
force with which it could burst apart. One calculation compared the
rotational inertia of one 66 lb., 2 ft. diameter flywheel at 500
rpm to the muzzle energy of a 6.5x55mm Swedish Mauser bullet.

From what I can gather, all that pounding on ancient cast iron
could cause fractures and the resulting blow ups discussed on the
list. The presence of a broken flywheel is forbidden at my club
here because of obvious liability concerns. I just wouldn’t do
it to me it is like bringing a bomb to class.

If you heat a flywheel to repair it, out of fairness to the
public and the people that run the shows you should keep the engine
at home and run it at your own discretion.

I agree with you, 100%. Perhaps the person making the repair
will be aware, but what about the next generations of unsuspecting
collectors? I feel that a welded spoke is a time bomb due to
stresses that will invariably be imposed with heat.

Imagine the forces on a shaft that has been built up by metal
spray, or a cylinder bore-it’s not too bad and they are
supported and contained. The forces are in shear. But consider the
centrifugal force on the spokes of a flywheel where the force is a
direct tensile pull on the two parts of the spoke. Metal spraying
is a bit doubtful in that application.

In the light of these comments, one would certainly think twice
about a fly wheel repair. So, with that thought in mind, I’d
like to wish you all a very happy and SAFE show season.

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