Engine Seized – What happens when an engine gets seized

Normally when an engine is “seized up” it is frozen to the point that the crankshaft will not turn in the bearings. This is caused by heat most times the car has been run low or out of oil. The parts that have seized or melted together could be main or rod bearings, piston rings etc. If the engine will not turn over by hand it probably time for a complete rebuild or a new engine.

Generally, there is a thin layer of oil between the piston and the inside wall of the cylinder for lubrication purposes. When this dries out, the bearings”spin”. This causes Engine Seizure.

Another likely reason for engine seizures are due to driving through water which leads to “Hydrostatic lock”. In this situation, water enters the space between the piston and the cylinder, and since fluids are “incompressible” in nature, the piston while trying to compress water either leads to bent con rods, sheared cylinder heads, blown crank cases or even bent broken crank shafts. Depending on the damage magnitude it is decided whether original block and cylinder head will work or not. If its a crack, blown case engine needs to be replaced, if only con rod has bent then you can do away with only sets of new con rod, pistons and bearings but of course, crank shaft conditions and cylinder head and crank case planes need to be checked for perfect alignment before repairing.

What happens when an engine gets seized

What is Scoring :

To understand what is seizure and what causes it ,one must first understand what is scoring. Between the piston and the cylinder walls there is always a presence of oil film(lubricating oil) that avoids the metal to metal contact.Now consider a situation when an oil film is temporarily missing. This causes a metal to metal contact and a scraping sort of action takes place.Now this causes little lining indents in the cylinder walls.The problem is not a performance robber until the oil film is resumed shortly.The above is a condition called scoring.

Now consider the same situation only difference being the oil lubrication does not resume and this scraping continues for some time.After only a few strokes the piston and the cylinder wall start to draw material from each other.Imagine this metal drawn as a small ball which continues to grow with every continuing stroke.Then there is a time when it is significantly large enough to push the piston the other side generating large pressure on the opposite side of the wall where scoring initally took place till scoring starts at the other end of the piston as well.Now all this happens when your engine is running at its normal speeds.The final blow happens when this molten aluminium iron mix of ball accumulated due to metal drawn from piston and cylinder wall finds its way to cylinder ring and accumulates there.This is what causes seizure and the crankshaft motion is stopped.

There could be many reasons why seizure can take place.Some being improper lubrication or dirt logging in the lubrication system. Other could be improper clearance between the piston and the cylinder walls.Some other reasons could also include improper heat dissipation from the cylinder and piston walls causing them to expand and change clearances.