Method of obtaining a longer stroke on an existing engine

Engines are needed to perform a variety of functions in a variety of horsepowers. The subject method of obtaining a longer stroke on an existing engine makes it possible to increase the horsepower capabilities without replacing or modifying the cylinder block or cylinder head. The method includes replacing the existing crankshaft with a crankshaft having a larger throw "T" to increase the stroke length of the engine. In order to compensate for the increased stroke length, a spacer is provided. In addition, the existing connecting rod with the outer swing path "S" is replaced with a connecting rod having an outer swing path "S". In order to avoid interference with the block the existing connecting rod bolts are replaced with connecting rod bolts having reduced diameter shanks and angularly disposing the bolts in relation to a connecting rod axis. The compression ratio os the long stroke engine is maintained substantially equivalent to that of the existing engine by increasing the clearance volume at top dead center within the bore in relation to the increased combustion volume created by the crankshaft having a larger throw "T".

TECHNICAL FIELD 
This invention relates generally to engines and more particularly to 
obtaining a longer stroke on an existing engine. 
BACKGROUND ART 
Engines are designed to perform a variety of functions and may be used, for 
example, as power plants for vehicles and generator sets in a variety of 
output horsepowers. 
U.S. Pat. No. 4,638,769 issued to Benny Ballheimer on Jan. 27, 1987 relates 
to the design and construction of present multipiece block and 
midsupported liner engines. The patent discloses an engine which includes 
a multipiece block having a top and bottom portion, a cylinder head, and a 
midsupported liner. The top block portion and cylinder liner form an 
annular space therebetween for cooling the combustion area. The top block 
portion is structurally designed to have a simple profile which is easy to 
cast, core, and machine, thereby reducing overall costs. In addition, the 
patent states that a variety of engine sizes can be manufactured on a 
common machining center with a minimum of component changes through use of 
this design. By varying the height of the top block portion, the annular 
space, and the stroke, the horsepower output of the engine can be varied 
while using the same bottom portion and cylinder head. However, the patent 
does not disclose the componentry changes which are essential to varying 
the horsepower output of the engine. 
DISCLOSURE OF THE INVENTION 
In one aspect of the present invention, a method of obtaining a longer 
stroke on an existing engine is disclosed. The existing engine has a block 
defining at least one cylinder bore which has an axis, a cylinder head 
mounted to the block, a crankshaft rotatably mounted in the block, a 
cylinder liner disposed within the cylinder bore and having a liner bore, 
and a piston which reciprocates in the cylinder liner along the axis of 
the cylinder bore. The piston has a combustion crater and defines a stroke 
between a top dead center position and a bottom dead center position of 
the crankshaft. A combustion volume and a clearance volume is provided 
within the liner bore. A connecting rod is removably attached to the 
crankshaft and the piston. The steps for obtaining a longer stroke 
includes replacing the existing crankshaft with a crankshaft having a 
larger throw "T" and increasing the clearance volume at the top dead 
center position within the liner bore in proportion to the increased 
displacement created by the crankshaft having the larger throw "T" in 
order to maintain a substantially equivalent compression ratio as the 
existing engine. 
In another aspect of the present invention, a method of obtaining a longer 
stroke on an existing engine is disclosed. The existing engine has a block 
defining at least one cylinder bore which has an axis, a cylinder head 
mounted to the block, a crankshaft rotatably mounted in the block, a 
cylinder liner disposed within the cylinder bore and having a liner bore, 
and a piston which reciprocates in the cylinder liner along the axis of 
the cylinder bore. The piston has a combustion crater and defines a stroke 
between a top dead center position and a bottom dead center position of 
the crankshaft. A combustion volume and a clearance volume is provided 
within the liner bore. A connecting rod having an axis and a pair of 
connecting bolts is removably attached to the crankshaft and the piston. 
The steps for obtaining a longer stroke includes providing a spacer having 
a predetermined height between the block and the cylinder head, replacing 
the existing crankshaft with a crankshaft having a larger throw "T" 
corresponding to the predetermined height and increasing the clearance 
volume at the top dead center position within the liner bore in proportion 
to the increased displacement created by the crankshaft having the larger 
throw "T" in order to maintain a substantially equivalent compression 
ratio as the existing engine. 
The prior art does not disclose the component changes necessary to produce 
a longer stroke, higher horsepower engine from an existing engine. The 
present invention details the method of producing a longer stroke engine 
and the necessary component alterations. The present invention increases 
the horsepower capabilities of an existing engine while eliminating the 
need to replace or modify the cylinder head or block.

BEST MODE FOR CARRYING OUT THE INVENTION 
An existing internal combustion engine 10 is illustrated in FIG. 1. Only a 
single cylinder has been illustrated and will be described. It should be 
understood, however, that the invention is capable of use in engines 
having multiple cylinders and various cylinder configurations. 
The engine 10 has a cylinder block 12 rotatably mounting a crankshaft 14 
having a throw "T". The cylinder block defines a cylinder bore 16 having 
an axis 18. A removably connected cylinder head 20 is mounted at the upper 
end of the cylinder block 12 in a conventional manner. A camshaft 22 is 
rotatably mounted in the block 12 and is operatively associated with a 
pushrod 24, a rocker arm 26, and a bridge 28 to operate a plurality of 
engine valves 30. A cylinder liner 32 having a liner bore 33 is disposed 
within the cylinder bore 16. A piston 34 having a combustion crater "C" 
reciprocates in the cylinder liner 32 along the axis 18. 
A connecting rod 35 having an axis 36 is removably attached to the piston 
34 and the crankshaft 14 in a conventional manner. The connecting rod 35 
has a cap portion 38 and a rod portion 40. A pair of connecting bolts 42 
removably attach the cap 38 and rod 40 together. The connecting rod 35 
traces an outer swing path, illustrated by broken line "S", as it 
oscillates through a complete revolution of the crankshaft 14. 
An embodiment of an internal combustion engine 10' for the present 
invention is shown in FIG. 2. It should be noted that the same reference 
numerals of the existing engine 10 in FIG. 1 are used to designate 
similarly constructed counterpart elements for the embodiment of FIG. 2 
and that primed reference numerals designate that a modification has been 
made to the counterpart element. 
In this embodiment, the crankshaft 14 has been replaced by a crankshaft 14, 
having a larger throw "T". A spacer 50 having a predetermined height is 
positioned between the cylinder head 20 and the cylinder block 12 to 
partially compensate for the longer stroke produced by the crankshaft 14'. 
The piston 34 has been replaced with a piston 34' having a modified 
combustion crater volume. The connecting rod 35 has been replaced by a 
connecting rod 35' having a cap portion 38' and a rod portion 40' modified 
to accommodate the longer stroke produced by the crankshaft 14'. The pair 
of connecting bolts 42 have been replaced by a pair of connecting bolts 52 
to removably attach the cap 38' and the rod 40' together. The connecting 
bolts 52 have reduced diameter shanks 54 and are angularly disposed in 
relation to the connecting rod axis 36. This permits the outer profile of 
the cap 38' to be decreased in size in order to decrease the outer swing 
path "S". 
In addition to the component modifications mentioned, it should be 
understood that other component modifications may be necessary depending 
upon the existing engine configuration. For example, the length of the 
pushrod 24, cylinder liner 32, fuel lines (not shown), etc. may also be 
increased to compensate for the longer stroke of the engine 10'. 
Another embodiment of the present invention is shown in FIG. 3. It should 
be noted that the same reference numerals for the first embodiment of the 
present invention, shown in FIG. 2, are used to designate similarly 
constructed counterpart elements for the embodiment of FIG. 3. 
In this embodiment, the camshaft 22 is rotatably mounted within the 
cylinder head 20 instead of the cylinder block 12. The rocker arm 26 is 
conventionally driven by the camshaft 22 to operate a plurality of valves 
(not shown). The spacer 50 having the predetermined height is positioned 
as in FIG. 2 between the cylinder head 20 and the cylinder block 12 in 
order to partially compensate for the longer stroke produced by the 
crankshaft 14'. A gear train, not shown, drives the camshaft 22 and 
crankshaft 14' in a conventional manner. 
It should be noted that the replacement of the piston 34 and the connecting 
rod 35 could occur jointly or separately depending on the existing engine 
configuration. 
Industrial Applicability 
In order to better understand the invention, it is relevant to present some 
commonly known engine definitions including stroke, combustion volume, 
clearance volume, and compression ratio. The stroke is defined as the 
distance traveled by the piston from a top dead center (TDC) crankshaft 
position to a bottom dead center (BDC) crankshaft position. The combustion 
volume is established by multiplying the stroke times the area of the 
liner bore. The clearance volume is the minimum combustion volume produced 
when the piston is at the TDC position of the crankshaft. The compression 
ratio is defined by dividing the combustion volume by the clearance 
volume. 
To achieve greater horsepower capabilities, the stroke of the engine is 
increased to gain greater power during normal engine cycles. The throw "T" 
of the crankshaft generally determines the stroke of the engine. 
Therefore, to achieve a longer stroke, the crankshaft throw "T" is 
increased. 
Once the larger throw "T" crankshaft 14' is rotatably mounted within the 
cylinder block 12, the spacer 50 is positioned between the cylinder head 
20 and the cylinder block 12. The height of the spacer is preselected to 
partially compensate for the longer stroke length established by the 
crankshaft 14'. 
During operation of the engine 10, there can be no interference between the 
connecting rod 35 and surrounding components. Due to the larger throw "T" 
of the crankshaft 14', the outer swing path "S" would normally increase 
and interference may occur with the bottom of the cylinder liner 32 or the 
cylinder block 12 when using the longer stroke engine 10'. However, the 
connecting rod 35' can be modified in order to decrease the outer swing 
path "S". This is partially accomplished by replacing the existing 
connecting rod bolts 42 with connecting rod bolts 52 having reduced 
diameter shanks 54. In addition, the outer swing path "S" is decreased 
even further by angularly disposing the connecting bolts 52 in relation to 
the connecting rod axis 36, generally within the range of 5 to 10 degrees. 
The angular disposition of the smaller shanked bolts 52 allow the 
connecting rod 35 to be manufactured with less material on the cap 38" and 
rod 40' which decreases the outer swing path "S". 
It is important for the longer stroke engine 10' to maintain a 
substantially equivalent compression ratio of that of the existing engine 
10 in order for the longer stroke engine 10' to operate as efficiently as 
the existing engine 10. In order to maintain the compression ratio of the 
existing engine 10, the clearance volume within the liner bore 33 of the 
longer stroke engine 10' must be increased in proportion to the increased 
combustion volume created by the crankshaft 14'. The increase in the 
clearance volume is determined by applying the relationships mentioned 
above between stroke, combustion volume, clearance volume, and compression 
ratio. In order to achieve the increased clearance volume, some component 
modifications may be necessary. For example, the increased clearance 
volume can be achieved by decreasing the length of the piston 34 or the 
connecting rod 35 or modifying the combustion crater volume in the piston 
34. 
Thus, as described above a method is provided for obtaining a longer stroke 
of an existing engine having a cylinder block defining at least one 
cylinder bore which has an axis, a cylinder head mounted to the block, a 
crankshaft rotatably mounted in the block, a cylinder liner disposed 
within the cylinder bore and having a liner bore, a piston which 
reciprocates in the cylinder liner along the axis of the cylinder bore, 
the piston having a combustion crater and defining a stroke between a top 
dead center position and a bottom dead center position of the crankshaft, 
a combustion volume within the liner bore, a clearance volume within the 
liner bore, and a connecting rod tracing an outer swing path "S", an axis, 
a plurality of connecting bolts, and being removably attached to the 
crankshaft and the piston. The method comprises the steps of replacing the 
existing crankshaft with a crankshaft having a larger throw "T", 
positioning a spacer having a predetermined height between the block and 
the cylinder head, and increasing the clearance volume at the top dead 
center position within the liner bore in proportion to the increased 
combustion volume created by the crankshaft having a larger throw "T" in 
order to maintain a substantially equivalent compression ratio as the 
existing engine. The step of obtaining a longer stroke includes the step 
of replacing the existing connecting rod with a connecting rod tracing a 
decreased outer swing path "S". The step of increasing the clearance 
volume includes the step of replacing the existing piston with a piston 
having a modified combustion crater volume. 
In view of the above, it is apparent that the present invention provides a 
method for increasing the stroke of an existing engine, thereby, 
increasing horsepower capabilities, without replacing or modifying the 
cylinder block or head. 
Other aspects, objects, and advantages of this invention can be obtained 
from a study of the illustrations, the disclosure, and the appended claims 
.