Explanation for connecting rod supporting needles & retainer assembly ...
Connecting rod supporting needles retainer assembly is applicable to the
medium and small size diesels.
The needle bearings, due to its special operational conditions, must bear
the shock force from the explosion in the cylinder,the inertia forces of the
piston, the connecting rod and the crank shaft. Therefore,needles and the
retainer must sustain the great centrifugal forces and acceleration forces.
Besides, it is responsible for the heat dissipation. So, the flow of lubricant
oils must be taken into account during the entity designing of the bearing
so that enough cooling area is increased,or coating copper, silver on the
surface to prevent the abnormal abrasion during the starting period.
To conclude,the Connecting rod supporting needle retainer assembly has
the following merits:
Light weight, lower inertial force, the use of highly anti-fatigue,highly rigid
and highly abrasion-resistant materials , low abrasion force in low speed
operation and high cooling capability.

KZK Crank pin supporting needle and retainer assembly
KBK Piston pin supporting needle and retainer assembly
KBK Piston pin supporting needle and retainer assembly(small end bearing)
Piston pin supporting needle and retainer assembly transmit the engine poser through the piston pin.To reduce the impact and
lower the noise, the inner diameter of the retainer is often close to the piston pin which means inner guiding method is used.
The retainer of piston pin supporting needle retainer assembly is generally made of 20 steel . The small end bearing retainer of
high torque force and high speed. is always made of 15CrMo steel.
KZK Crank pin supporting needle and retainer assembly(big end bearing)
The crank is driven by the big end of the connecting rod.Therefore,the outer diameter of the retainer should be as close as pos-
sible to the inner diameter of the big end of the connecting rod so that the impact can be reduced and the noise lowered . That
means out guiding method is used.
The big end of the bearing revolute around the center of the crank shaft and it the same time it rotates itself . When the speed
reaches very high(over 8000rpm),the centrifugal force will be very huge and thus extremely big load resulted on the retainer cr-
eating very poor conditions.The retainer of the crank pin supporting needle retainer assembly is generally made of suitably heat
treated 15DrMo steel , this greatly increase the strength and abrasion resistance . Meanwhile this will ensure the material the
same as the piston pin steel so that they have the same heat expansion factor under the same condition . When the working
speed exceeds 8000rpm or the temperature is very high,silver coating to the retainer is suggested.
Applicable materials
It is suggested that 15CrMo be used for connecting rod material.After carbonization quenching and tempering , its toughness
is increased . The tray surface hardness of the apertures of both small and big ends are no less than HV700 with effective ha-
rdened layer no less than 0.5mm.the surfaces of seat holes and the pin tray must be ground very precisely till its surface rou-
ghness doesn't exceed Ra0.2. the circularity,cylindricity will be controlled within 0.003mm.the parallelism of the two ends:for
high speed 0.02/100.For general purpose 0.03/100. For low speed,0.04/100.
If the above mentioned precision can not be reached , it is suggested to widen the radical combination gap . Or damage will
happen on the bearing due to the abnormal load resulted from over heat.
Big end guidance(lower guidance)and small end guidance(upper guidance)are constituted as shown in Fig 1.Big end guidance
is more commonly used . Lower end guidance is considered only in case of very high speed or the overheat resulted from big
end guidance.
Big end (lower guidance):
The big end of the connecting rod and the needle bearings are mounted between the two cranks.So when big end guidance is
used,the oil film lubrication among the crank,connecting rod big end and the bearings must be noticed.On the big ends of the
connecting rod,the end surfaces are always made into slit, hole or groove shapes so that the lubricating oil can enter the ne-
edle bearing smoothly and normal lubrication oil circulation can be maintained.
The width of the big end needle bearing is the same as the connecting big end.To ensure the effective guidance to the big end
bearings and to prevent the connecting from slanting, two washers made of phosphorus bronze are added by the two sides of
the big end and a gap of 0.2~0.5mm between cranks are ensured.
Big end (upper guidance)
The small end of the connecting rod and the needle bearings are mounted between the piston and the pin and are guided by
piston body.To reduce the axle gap,two hardened washers are added onto the end surface of the small end bearings to limit
the axial movement of the connecting small end.
Fiqure 1
Radical gap
The radical gap should be selected as per the engine type and the operational conditions. The speed, load, lubrication, temp-
erature, the material and machining precision of the engine must be specially noticed. The selection of smaller gap can be
used to increase the efficiency of the engine but all the parts must be guaranteed by the matched precision. Or the bearing
might be burnt. Suitable radical gap should take experience and the test values.
Recommended radical gap
Small end: 0.002 - 0.012mm
Double stroke big end: 0.015 - 0.030mm
4 stroke: 0.007 - 0.024mm (for high speed, 20-35% can be increased)