How much main bearing bore misalignment is allowable before a bore alignment is required?
Main bore alignment is also very important, with perhaps no more than 0.0005-inch misalignment between the adjacent bores and only 0.001-inch overall, when using conventional tri-metal bearings. That overall tolerance should be no more than 0.002-inch when using aluminum bi-metal (lead-free) bearings.
What causes engine rod failure?
Thrown rods or piston rod breaks happen due to oil problems, over-revving the engine, faulty piston bearings or normal wear and tear. Over-revving the engine can lead to rod breaks. The revving causes rod failure due to a valve’s spring failing or being sucked into the engine.
What is used to correct for a main bearing bore alignment issue?
Any and all of these bearing bores can be misaligned. The correct way to check for main bearing bore alignment was to have an accurate straight bar that is laid on the main bearing saddles. Then the space between the bore and the straight bar is measured.
What kind of bearings are used in an engine?
Virtually all modern engines use bearing shell inserts for the crankshaft, rods, and camshaft. Mains and rods use a split bearing with upper and lower half-shells. Cam bearings are mostly single-piece, ring-style inserts that are pressed in place with an interference fit in each housing bore.
What should the temperature be for crankshafts and bearings?
Bearings, crankshafts, rods, and micrometers are manufactured from various steels that expand and contract differently according to temperature. Micrometers are designed to be used at a standardized temperature of 68 degrees F. For best results, all components and measuring equipment should be close to the same temperature.
When to use oversized or undersized crankshaft bearings?
An oversized bearing is used after a block has been line bored. The opposite is true for an undersized bearing because it has more material on the inside facing the journal, and the same amount facing the bore it fits into. Undersized bearings are for a smaller diameter or machined crankshaft journal.
Do you know the position of the bearings?
One of the most critical steps (and the first one mentioned in the guide) that many enthusiasts may not even realize the importance of is making sure that each connecting rod and main bearing cap is properly identified by position and orientation.