One of the more mythologically relevant parts of a car,
the big end is actually quite simple; being a
part of the larger connecting rod.
In vehicle folklore, one of the worst problems you can
have is if "Your big end's gone". Accompanied by loud
knocking, and loss of power, it is quite a serious problem
and expensive to repair - requiring a total strip-down of
The big end is the end of the connecting rod
which is attached to the crankshaft of the car. The end
attached to the piston is conversely the little end. The
reason for the name is purely that the big end is larger than the other.
The big end assembly actually consists of the end of
the connecting rod, a bearing attached to the crankshaft,
and clamp to hold the whole assembly together - with relevant nuts and bolts. Problems occur because of the immense stresses and forces applied.
Consider that the big end is spinning in a circle, being
pulled around by the crankshaft, except for half of its
turn on every other revolution during which time it is being
pushed from the other end and forcing the crankshaft around.
Now consider that this may be occuring at 6000 revolutions per minute, at high temperatures. No wonder it
can go wrong.
Problems and remedy
The bearings can wear, bolts can come loose, and parts can break off. All of these problems require a complete strip down of the engine. It is not actually a difficult problem to fix, but will take many hours of labour - and this is where the expense is incurred.
It is often cheaper to scrap an engine with a broken
big end, and have a new engine fitted. If you are quite handy,
it can be worth fitting a new engine - but keeping the old
one, stripping it down and rebuilding as new in your spare time. It can then be sold on, or kept as a backup.