Tuesday, May 31, 2011

front bearing starving for oil on Mitsubishi 4d56 motor?

If the engine has an overhead cam, the resulting misalignment in the cam bores created by the warpage can gall or seize the cam bearings, or even break the cam. Anytime you encounter a warped or cracked aluminum head, or an OHC head with a seized cam, chances are the damage was caused by overheating.

Oil starvation is almost always fatal to any engine, and is usually the result of a failed oil pump, a plugged oil pickup screen inside the oil pan, or a low oil level. Bearings that have been damaged as a result of insufficient lubrication will be shiny and worn where the crankshaft journal wiped away the bearing material.

Overhead cam engines are even more vulnerable to oil starvation and low oil pressure problems than pushrod engines because the cam and valvetrain are farther from the pump. When an OHC engine is first started, it takes awhile for oil pressure to reach the cam bearings. If the oil viscosity is too heavy (especially during cold weather), it may delay the arrival of oil long enough to starve and seize the cam. For this reason, most vehicle manufacturers recommend using a 5W-30 oil in late model OHC engines year round, but especially during cold weather. Refilling the crankcase with the recommended viscosity oil can prevent a reoccurrance of this type of failure.

If you suspect engine damage may have been caused by a low oil level, check the dipstick to see how much oil is in the pan. A low oil level may be the result of neglect, oil leakage and/or oil burning.

Any evidence of oil leakage around the front or rear crankshaft seal, pan gasket, valve cover gasket or other gaskets, would tell you new gaskets and seals are needed. Most of these gaskets and seals will have to be replaced anyway if you are opening up the engine.

Bearings ruined by dirty oil will have foreign material embedded in the surface and/or be scored by debris. Check for a plugged oil filter and/or a missing air filter or oil filler or breather cap. The underlying cause here may be not changing the oil often enough.

  • Misalignment. If the center main bearings show much greater wear than the end bearings, the crankshaft may be bent or the main bores may be misaligned. The underlying condition must be corrected by straightening or replacing the crank and/or align boring the block. The same applies to camshafts and cam bearings (pushrod & OHC).
  • Failure to lubricate parts properly during engine assembly. Camshaft lobes require a high pressure engine assembly lube that will stay put until the engine is started and oil reaches the cam. Bearings and cylinders also need to be coated with oil or assembly lube to prevent a dry start.