A question for people who know a little about metal.

[kevbot]

I hope this isn't too stupid. I know the noise is because the metal the engine is made of is contracting, or expanding, I forget which.

Anyway, why doesn't his cause damage in the long run? I mean there must be close to a dozen different materials that expand and contract at different rates in my engine.

Also does it make the same noise when you start it up cold? I think it must, just that you can't hear it over the other noises.

Sorry if this is too dumb of a question.

 

[oynaz]

The metal is contracting, as it cools down. It itsn't dangerous, as the amount of contraction is relatively easy to calculate for an engineer, and thus the engine is designed to not take any damage from the contraction.

The engine of a modern car is quite hard to damage anyway.

 

[Calin]

If your engine has an iron/steel block and an aluminium valve block, the difference in the expansion rate could be the reason for ticking.

 

[Pulsar]

What they said.

I think your mistake is in thinking that things break rather than stretch. Bolts (by design) are allowed to stretch a certain amount. You don't normally think of bolts as streching.... but they do.

Likewise, you have seals and gaskets in your engine design to handle the differences in contraction. Head gaskets, front and rear seals, cam cover gaskets and front cover gaskets just to name a few.

 

[Jeff7]

Originally posted by: LsDPulsar
What they said.

I think your mistake is in thinking that things break rather than stretch. Bolts (by design) are allowed to stretch a certain amount. You don't normally think of bolts as streching.... but they do.

Likewise, you have seals and gaskets in your engine design to handle the differences in contraction. Head gaskets, front and rear seals, cam cover gaskets and front cover gaskets just to name a few.

Definitely.

I've been in some classes dealing with material expansion and stretching. One fun test was a tensile test. A steel piece, .50 inches wide, and .125 inches thick, is put under tension until it simply tears apart. It's loud when this happens, especially with the cold-drawn steel. That stuff isn't as ductile as hot rolled steel or aluminum, and it is really loud when it suddenly breaks.
There were also tests with thermal expansion. Some metals expand quite a bit when heated, others to a lesser degree.

 

[Calin]

Originally posted by: Jeff7
Definitely.

I've been in some classes dealing with material expansion and stretching. One fun test was a tensile test. A steel piece, .50 inches wide, and .125 inches thick, is put under tension until it simply tears apart. It's loud when this happens, especially with the cold-drawn steel. That stuff isn't as ductile as hot rolled steel or aluminum, and it is really loud when it suddenly breaks.
There were also tests with thermal expansion. Some metals expand quite a bit when heated, others to a lesser degree.

Metals expand at different rate. If you want a demo, take the thermostat from your car, put it in cold water and heat it. Starting from some 85* Celsius, it should start opening (fully open at around boiling point). There are also bimetal stripes, that twist then heated (two metal blades welded on each other - if their thermal expansion properties differ, they will twist one direction when cooled and the other when heated)

 

[CycloWizard]

Originally posted by: Calin
Metals expand at different rate. If you want a demo, take the thermostat from your car, put it in cold water and heat it. Starting from some 85* Celsius, it should start opening (fully open at around boiling point). There are also bimetal stripes, that twist then heated (two metal blades welded on each other - if their thermal expansion properties differ, they will twist one direction when cooled and the other when heated)

The rate of metal expansion will depend on a material's thermal diffusivity and its coefficient of thermal expansion (CTE).

 

[kevbot]

Thanks for all the replys, everyone.

I know the ticking is normal and nothing to be alarmed about, it just seems strange that all that noise is just a bunch of metal imperceptively moving.

 

[PowerEngineer]

I'm thinking that the "ticking" may be coming from your catalytic converter, which also gets very hot and is made of thinner metal that therefore cools and contracts more rapidly once the engine is off.

 

[Witling]

Engine blocks tick when they cool. They did this before aluminum heads and they did this before catalytic converters.

 

[OrganizedChaos]

Originally posted by: Calin

Originally posted by: Jeff7
Definitely.

I've been in some classes dealing with material expansion and stretching. One fun test was a tensile test. A steel piece, .50 inches wide, and .125 inches thick, is put under tension until it simply tears apart. It's loud when this happens, especially with the cold-drawn steel. That stuff isn't as ductile as hot rolled steel or aluminum, and it is really loud when it suddenly breaks.
There were also tests with thermal expansion. Some metals expand quite a bit when heated, others to a lesser degree.

Metals expand at different rate. If you want a demo, take the thermostat from your car, put it in cold water and heat it. Starting from some 85* Celsius, it should start opening (fully open at around boiling point). There are also bimetal stripes, that twist then heated (two metal blades welded on each other - if their thermal expansion properties differ, they will twist one direction when cooled and the other when heated)

engine thermostats usually open from the expansion of a wax pellet. the pellet expands pushing on a spring loaded plunger.