Conrods AND PISTONS
Part two in a five-part series: Restoring an Amanco 2-1/4 HP Hired Man
By Peter Rooke
February 2006
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All the sheet metal came from an old fire truck...
The connecting rod presented a major problem as
it was badly twisted and there was also a crack in the casting,
which ruled out heating and straightening. I searched for a
replacement but had no luck so after six months I decided to try
and make a new one.
To simplify the process and work within the capabilities of my
workshop I decided to fabricate a new connecting rod from steel in
three parts, rather than from solid. The connecting rod itself is
generally under compression, so I expected pegged, braised joints
to hold, as my engine had a poor bore and would not be working
under heavy load. Some were of the opinion that this was a
dangerous step, but to date, after 50 hours of running, there are
no signs of any problems.
Measurements were taken from the original, making allowances for
the kinks. The small end was turned from 1-3/4-inch round stock,
with an undersized hole of 3/4-inch bored in it to be finished off
later.
The big end was fashioned from a 3-1/2-inch length of 2-1/2-inch
by 3-1/2-inch steel, roughly shaped on the mill and finished by
filing. Again, an undersized hole was bored in the block for the
big end bearing and 7/16-inch holes were drilled for the clamping
bolts, which were then turned on the lathe. The two nuts and their
jam nuts were made earlier. The partially finished big end block
was then cut in half on the milling table with a slitting saw and a
center punch was used to mark both blocks at one end for correct
re-assembly.
The central section of the connecting rod was made from 10-1/2
inches of 1-inch-by-1-1/4-inch steel and was again rough-shaped on
the milling machine to provide the taper and create the "H" profile
with two 1/2-inch round pegs machined at each end on the lathe.
These two pegs were to locate in two similar sized holes drilled in
the big and little ends with flats machined on these end pieces to
provide a close-mating surface. These holes were dual purpose: to
provide a positive location point and also increase the surface
area for brazing.
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