NG 900/9-3 Oil Pressure Reducing Valve
The pressure reducing valve (relief valve) controls maximum oil pump pressure. It is located below the balance chain area. The valve piston moves up and down with oil pressure and is easily damaged by metal particles from a worn balance chain or from the balance chain sprockets. If the valve sticks open, oil pressure will be low. If closed, pressure will exceed maximum pressure at high rpm. The oil pressure reducing valve can be inspected along with the timing chain tensioner, valve cover, oil pan and oil pickup screen to assess the condition of the engine.
Pictures and other content below were provided by jonnyfgroove on SaabCentral Forums. Thanks also to Anders (Swedecar) for documenting reducing valve scoring and other balance chain issues on SaabNet.
Access and Inspection
The oil pressure reducing valve is accessible from under the car, after removing the plastic right front air shield. The right wheel, and the plastic shield over the crankshaft pulley can be removed for more room to work if necessary.
The cap may be rusted in place and hard to brake loose. A small amount of oil will be released with the cap. If the pressure relief valve is moving freely, the spring and piston should drop out on their own when the cap is removed and pressure is taken off the spring.
If the piston sticks in the bore, it may have to be removed using a pick or a similar tool. In that case, the pick must be inserted carefully into the hollow piston to avoid scratching the walls of the bore.
The valve consists of a cylindrical piston, a spring, and a cap with a gasket. The spring fits inside the hollow portion of the piston.
The piston in Fig. 1 came from a '96 SE turbo with a noisy balance chain which had to be cut and removed from the engine. Closeup pics show significant scoring, but the piston moved freely, and did not appear to stick inside the bore. If the piston shows excessive scoring, or no longer moves freely, it must be replaced.
It is important not to allow any rust or dirt particles into the valve bore! The washer, spring, and piston should be cleaned of metal particles and tar, and coated lightly with clean engine oil before reassembly. Verify that the piston can move freely inside the bore. If not, replace the piston and any other damaged parts. If the cap is rusted, clean the threads using a wire brush, and coat them lightly with anti-seize. Then tighten the cap to 22 lb-ft.
- Plug: #7508955
- Gasket: #9130600
- Spring: #9309998
- Piston: #9167784
- Torque Wrench
- 17-mm socket
- Pick (if needed to remove piston)
- Wire brush
Relief valve cap, 22 lb-ft
Haynes Ch. 2A-11.11
Saab EPC 2-0330