Subaru Forester 2.5 EJ253 (2011): Valve Replacement and Cylinder Head Valve Seat Lapping

Part numbers are from the manufacturer's original catalogue. Check them against your VIN before ordering.

• torque wrench (range 10-100 N·m (7-74 lb-ft))
• socket set and ratchet
• long socket for cylinder head bolts
• valve spring compressor
• valve lapping compound (coarse and fine)
• suction-cup lapping tool
• micrometer and bore gauge
• caliper
• straightedge for checking cylinder head flatness
• compression tester
• drain containers
• marker and bags for sorting parts

1. Do a preliminary diagnosis: a compression test and a cylinder leak-down test will show which head needs work. Replacing valves makes sense when a valve head is burned, the stem is bent, or the seat cannot be brought back to specification by lapping.
2. Disconnect the negative battery terminal and drain the coolant and engine oil. Remove the air filter housing with its ducts, the intake manifold together with the throttle body, the fuel lines (relieve the fuel system pressure beforehand), the exhaust manifolds with the catalytic converters, and the front pipe.
3. Remove the drive belts, pulleys, and timing belt covers. Set the marks to TDC of cylinder 1, take a photo of their positions, and remove the timing belt. Do not turn the camshafts with the timing belt removed unless necessary.
4. Remove the camshaft pulleys (hold them against rotation with a special holding tool; torque per the service manual), the rear timing belt covers, and the valve covers. Lay out all parts in order and mark which side each came from.
5. Loosen the cylinder head bolts strictly in the reverse of the tightening sequence, evenly in several passes, then remove the heads. If a head will not come off, do not pry on the mating surface; carefully tap the protruding areas with a plastic mallet.
6. Disassemble the head: remove the rocker arms together with their shafts and the camshaft (remember the order and position of each rocker arm; do not mix the parts up). Compress the springs with the valve spring compressor, remove the keepers, retainers, springs, and valves, and sort the valves by cylinder number right away.
7. Clean carbon from the combustion chambers without scratching the mating surface. Flush the passages and check the head for cracks (pressure testing at a machine shop). Measure flatness with a straightedge and feeler gauge. If it exceeds the limit in the service manual, the head must be resurfaced; if the deviation is greater, replace it.
8. Measure the valve stems and valve guides: compare the stem-to-guide clearance and guide wear against the limits in the service manual. Worn guides are replaced at a machine shop, with pressing in and subsequent seat machining. Check the seats: if they have deep pitting or burn damage, they are cut (three-angle valve job) rather than lapped.
9. Install the new valves and apply clean oil to the stems. Lapping: apply a thin layer of compound to the valve face, lap the valve with the suction-cup tool using a back-and-forth rotating motion, periodically lifting and turning it, until you get an even matte ring around the whole circumference of the seat face. Use coarse compound first, then fine. Then thoroughly remove all compound from the passages and stems with kerosene or a cleaner.
10. Check the result for sealing: with the valves installed, pour kerosene or mineral spirits into the port and make sure there is no seepage after 5-10 minutes. Install new valve stem seals, springs, retainers, and keepers; lightly tap the end of the stem to seat the keepers.
11. Install the camshaft, rocker arms with their shafts, and the seals in order. Check and, if necessary, adjust the valve clearances (if your engine's design calls for adjustment; use the values from the service manual) and the camshaft end play.
12. Clean the block and cylinder head surfaces of gasket residue and degrease them. Install new cylinder head gaskets (dry or with a thin layer of sealant, as the gasket manufacturer specifies), seat the heads on the locating dowels, and tighten the new cylinder head bolts in several passes strictly following the pattern: first the preliminary torque, then the final torque and an angle turn. Take the exact torque and angle values from the Subaru service manual for the EJ253; they depend on the bolt type. Tighten with a torque wrench and do not skip any stages.
13. Install the valve covers with new gaskets (low torque, about 5-10 N·m (3.7-7.4 lb-ft), evenly in a crisscross pattern), the camshaft pulleys, the rear timing belt covers, and a new timing belt with idlers, tensioner, and water pump. Align all marks, turn the crankshaft two full revolutions by hand, and check that the marks line up.
14. Reassemble the remaining components in reverse order: manifolds with new gaskets, intake, fuel lines, belts, and hoses. Fill with coolant and oil, replace the oil filter, and bleed air from the cooling system.
15. Start the engine and warm it up to operating temperature at idle. Check for oil and coolant leaks and for fault codes in the ECU. Do not put the engine under heavy load for the first 500-1000 km, then check the oil and coolant levels and, if necessary, retighten connections per the service manual.

• Cylinder head bolts on horizontally opposed Subarus are single-use; reusing them risks a blown head gasket
• Do not mix valves and rocker arms between cylinders and heads
• The job requires a machine shop with equipment for checking flatness, replacing guides, and machining seats
• If you have no experience disassembling timing systems and cylinder heads, leave the job to a repair shop: a mistake with the belt marks causes the valves to hit the pistons