When did the 2.5L engine switch over from DOHC to SOHC?
Previous to ’99 all 2.5L were DOHC and the crankshaft thrust bearing was on the #3 main bearing. This caused a see-sawing at high rpm due to the 2.5’s longer stroke (everything was seemingly fine on 2.0 and 2.2 motors using this design). In addition, the 97-98 DOHC 2.5L used a piston with no skirt, which looked a bit like a pancake. This was an attempt to get better mileage, but the result was broken ring lands and excessive piston slap, not to mention decreased durability under “modified” applications. In MY99 Japanese engines went to the PhaseII design for all displacements, and on the north american market 2.5L this included a change to SOHC ‘tumble port’ cylinder heads. They also got rid of the skirtless pistons and reverted to a conventional design, and moved the crankshaft thrust bearing to the #5 main. Since they are built in Japan, MY99 Imprezas and Foresters have the PhaseII engine. However, MY99 models built in Indiana have the older engine. In MY00 these models received the
