Piston features include: high swirl combustion bowl cast aluminum body and 3 ring grooves. The piston for turbo
charged, turbocharged/aftercooled engines includes a ni-resist insert with a keystone profile for the top piston ring. Always check the part number to be sure the correct configuration is used during piston replacement.
In addition to the ni-resist insert, automotive turbocharged engines also feature pistons with a hard-anodized combustion surface.
The piston ring sets are also different. While both sets consist of three rings, the top ring of the turbocharged/
aftercooled set has a keystone profile which operates in a ni-resist insert cast into the piston. The naturally aspirated top ring is square cut and operates in a groove machined into the aluminum piston.
The 1994 automotive pistons utilize different top ring locations. The 160 hp to 175 hp ratings use 8 mm crown to
ring land pistons and 190 hp, 210 hp and 230 hp use 10mm. The 1994 industrial pistons continue with the 14 mm
ring position.
A free floating, hollow piston pin is used to attach the piston to the connecting rod. Lubrication of the pin and
journal is accomplished by residual spray from piston cooling.
The piston pin end of the connecting rod is angle cut to provide additional bearing surface. The connecting rod
end is fitted with a bronze bushing.
In production, steel backed aluminum connecting rod bearings are used for naturally aspirated engines. Steel
backed tri-metal bearings are used in production for the additional loading resulting from turbocharging and
aftercooling.
To prevent incorrect use of the two bearings at time of repair, only steel back tri-metal bearings are available for
service.
Oversize service connecting rod bearings are available for use with re-ground crankshafts.
