bike point of view.....
engine temperature and operating temperature:
the more high performance the engine is tuned, the more sensitive it is....
bikes are hypersensitive to this
there are several reasons why to warm....
ex: you must preheat the oven before you can bake the cookies...
ummm,,, ever hear... lick it before you stick it,, munch it before you punch it?
same applies.
its much more difficult to peal apart a cold grilled cheese sandwich.
for engines sitting for long periods of time, could/prolly be lubrication issues, thanks to gravity.
oil falls to the bottom.
if not mistaken, on the oil bottle, 10w40 means, when cold its not thicker than 40, when hot no thinner than 10.
engine, and oil designed around operating temperture.
again, all depends on design
generators designed to run at or around idle for hours at a time, most of its long life.
motorcross bikes, designed to run at wide open throttle for 20 mins at a time, short life
1. fuel mixture:
engine requires much more fuel to run when cold. i.e. choke/enrichment circuit
- starting the engine and turning it off, before operating temperature, causes rich condition making it very difficult on the spark plugs. the plugs will never reach a ''self cleaning'' state of operating temp to maintain life. repeated exposure resulting in premature plug failure
dont want to make it confusing, but a cold motor (specially carbed) is more prone to hesitate'' when you punch it, because its to lean while beyond/below operating temp range
2. cold seizure: piston to cylinder
the higher performance, the more sensitive.
engine designed around clearances and temp expansion.
ex. 2 stroke motors highly prone to cold seizure due to dramatic piston and cylinder expansion. the piston will heat and expand quicker than the cylinder, resulting in 4 point piston skirt contact to the cylinder. - not good- you may get away with this a few times, but then again, anyone can win the lottery. todays high performance 4stroke bikes, losely based on F1 technology (short skirt, light weight, quick rev) are very sensitive to this as well. resulting in severe cylinder damage and premature failure
piston/cylinder is the most typical damaged when cold, but not limited to, everything that turns has a designed operating temp.
your older motors, with worn clearances of course are not as sensitive, well to anything really...
basicly, metals change size with heat, so its best we give them time to change before we pin it.
those are the main issues that come to mind.