As specified, the characteristic that the 7 critical fastener bolts
of the engine have in common is precisely the “critical nature
” of the role they play.
In addition to this, each one has its own peculiar characteristics,
depending on its position in the engine and its specific task.Making critical fastener bolts
is nevertheless an undertaking that involves custom design
capability, since besides the general characteristics that these fasteners may have, every manufacturer
has its own particular requirements and precise performance to achieve, which are different case by case.
One practical example is this: there are critical fastener bolts
in both economy
cars and racing
cars, but the two vehicle categories are very different in terms of performance!
In this regard, limiting the overall weight
of the bolts in a car, including the critical fasteners
, becomes essential when an engine has to reach high levels.
This necessity leads to making choices of compromise concerning dimensions
and strength class
of the critical fastener bolts
, at times removing material from the fasteners without, however, impairing the engine’s performance.
Going into the details of the critical bolts, the cylinder head bolts
are a cornerstone of the engine, as they fasten the head to the engine block and have to respond to considerable thermal expansions
The main bearing cap bolts
keep the engine main bearing secure, and are not subject to the same thermal stresses, but are tightened twice
, so it is necessary to pay attention to their dimensioning.
The con rod bolts
tighten the con rod caps and are one of the critical bolts of the engine most highly stressed.
In addition to the same thermal expansions of the cylinder head bolts, they are subjected to forces in three dimensions
and are, for all practical purposes, moving components.
The flywheel bolts
, on the other hand, transmit the torque from the crankshaft to the gearbox and have to respond to important space limitations
that highly influence their design.
The camshaft cap bolts
tighten the camshaft caps and must retain their precise mechanical and strength
characteristics for the entire lifetime of the engine.
The crankshaft bolts
instead tighten the crankshaft.
They are critical fasteners
because they must always ensure perfect synchrony
between the components that they fasten.
The camshaft sprocket and VCT bolts
also must retain the exact timing between the gears or phase transformers and the crankshaft.
However, they are somewhat short elements, so they have to be treated with micro-encapsulated bonding agents
to perform perfectly.