Torque To Yield Bolts - (TTY) - What Exactly Are They Torque-to-yield (Tt-y) Bolt Specification & Installation Torque Plus...Ask Away!
When a shop manual says that a bolt is to be discarded and new ones used, they are almost always Torque to yield bolts.It may seem expensive to buy new bolts.The old bolts look good, but they can be deceiving.Engine failure can be caused by using old bolts.The force needed on today's engines can only be provided by new bolts.
We did not need them in the 60s or 70s.Engine materials are not the same.Casting iron blocks expand at a different rate than aluminum cylinder heads.As an engine warms up, bolted together parts have to move against each other or slide on their gasket.
Engine parts are lighter than they were a few decades ago.Some heavy cast iron parts could not be failures.Thin wall castings and aluminum alloys have to be extremely accurate.
The first step in the tightening process is usually stated as a Torque figure, but only to provide a baseline from which the true load is applied.This is called a preload or snug Torque.
Bolts are elastic by nature and will stretch as load increases.A gasket that doesn't relax, like anMLS gasket, can be an issue when you use bolts on aluminum heads.Bolts can be snapped by the expansion rate of aluminum heads.
Keeping the bolt turning takes more force than starting it.Torque readings can be affected by the tighter the bolt.One lubricant has different lubricating qualities than another.When torquing a bolt, manufacturers will tell you what type of lubricant to use.The clamping load will be affected by using the wrong lubricant.
The expansion rate of aluminum heads can stretch bolts past their yield point and snap them.Increased combustion pressure causes newer engines to require high clamping forces.Smaller diameter bolts can't be achieved with engines.