Studebaker Engines ( oil pressure relief valve )

The components of the Oil Pressure Relief Valve assembly
1) Cap bolt (1.5")   2) copper washer    3) spring    4) sliding piston


Other indicators

    5- Crank/cam gear lubrication port - The internal Orifice, machined from the sliding piston area through the block to the apex of the cam and crankshaft gears. This orifice allows engine oil to be sprayed on the two gears for lubrication. The upper gear being made of Celeron, which is a cellulose fiber type of material and the lower steel crank shaft gear. In some truck and R-series engines, and cloverleaf blocks, the upper gear is aluminum.

    6- indicates the oil pressure valve piston, which has a small hole drilled through the center to allow oil to pass, while the piston is at any position in the cylinder. In the engine off mode, the piston rests at the base of the cylinder, behind the upper gear, at the right side of the machined lubrication hole.

    When the engine is started, the oil pressure immediately presses against the piston, sliding it outward against the heavy spring. Oil to lubricate the crank/cam gears bypasses the piston through the center bore hole, whether or not the oil is at operating temperature. Oil that lubricates the gears drains back into the pan at the base of the timing cover

    When the oil is cold, pressure will press the piston against the spring tight enough for it to bottom out. This greatly increases the amount being supplied to the gears and to prevent overpressure causing a leak and regulate the oil pressure normally, another orifice is machined on the opposite wall of the cylinder that directs oil back into the crankcase

    As the oil warms up, the spring pressure forces the piston back towards the gears, possibly covering both these escape orifices, depending on the weight of the oil. With oil at the operating temperature, the small center bore piston hole provides enough lubrication to the crank/cam gears.

    The OPRV system is meant to be serviced during routine maintenance, but is ignored much of the time due to the placement of the cap bolt at the flange of the oil pan. To compound this situation, many of the early engines were not fitted with an oil filter. The ones that were, used a partial flow filter. Further, the oils in the early days may not have had any detergent and would allow residues, gummy deposits or varnish to settle inside the engine. The could cause problems with the OPRV if not serviced regularly.

    If the engine has been sitting for a long time unused, the OPRV piston can get stuck in the base of the cylinder and once the engine is restarted, will not move.
    A piston that is stuck will cause very high oil pressure and that can be a problem to gaskets and seals throughout. If you have a partial flow filter, it can pop the canister lid and spray oil over the hot engine. If you have a full flow filter, this problem is greatly diminished, but a stuck valve still has the energy to burst a spin on filter. The later oils were better formulated as were the filtration characteristics. Still a problem, nonetheless.

    If you have a stuck piston, the following means can be used to remove it.
    1) Remove the cap bolt, remove the spring and replace/tighten the cap bolt. Start the engine and run for a few minutes. Stop the engine and remove the cap bolt to see if that loosened the piston. Try again until the block gets warmer. If the engine is at operating temperature and the piston won't budge, then other means have to be used.

    Under no circumstances should you leave the cap bolt off and start the engine, cold or warm. The piston could be dislodged and fire out of the block like a bullet.

    )If you cannot start the engine or the piston will not move from the cylinder, you can clean the area with alcohol, then spray a rust or varnish solvent into the cylinder and replace the cap bolt maintain a level of solvent, wait a few days and try again. Be aware that too much solvent will spill into the crankcase.

    )Barring any luck with the above, you should try to use a tool to remove the piston. Never use any action that might force the piston farther into the cylinder, as that may cause more serious damage.

    )Hammering on the piston will likely expand it and seal it in forever.

    Try something like a crochet hook through the piston orifice to to get some purchase behind it and pull it out.

    )Try an oversized drill bit to wedge into the hole and cause it to spin. Shear forces on the circumference may work better to get something started. You'll not be using the piston again if you have to destroy it somewhat.

    )Generally, it will finally come loose and just cleanup and replacement of parts will suffice.

    If the gears are not being lubed adequately, here are some pics of what the damage can look like.