The Head Bolt Tightening Sequence for a Subaru 2.5L Engineby Ron Sardisco
The Subaru 2.5L engine is made from aluminum alloy. In order for the heads to properly seal and to prevent warping, a special sequence must be followed when installing the head bolts. Not only is the tightening method critical, so is the order. You will need both inch and foot pound torque wrenches as well as a torque angle gauge.
Clean All Surfaces
Clean the cylinder heads and the block mating surfaces thoroughly with lacquer thinner or acetone. Avoid any scraping tools that could mar the surface.
Position New Parts
Lubricate all bolts and washers with engine oil and place the new gasket on the head locating pins. Position the head on the block and finger tighten all bolts.
The Tightening Sequence
The order for tightening is as follows: top center, bottom center, left top, bottom right, bottom left, top right. Follow this sequence for each step.
Tight but not too Tight
Tighten all bolts to 22 foot-pounds. Tighten all bolts to 51 foot-pounds. This first sequence sets the gasket. Loosen all bolts in reverse order. Loosen them again another 160°. Tighten bolts one and two to 25 to 36 foot-pounds. Tighten bolts three, four, five and six to 132 inch-pounds.
Use the torque angle gauge to tighten all bolts another 90°. Follow the sequence again and tighten them another 45°. Tighten bolts one and two only an additional 45°(turbocharged models only).