manufacturers valve clearances bullshit?

[MaybeGuy]

are they just set to be on the VERY safe side?
Just thinking of linear expansion here.
without boring everyone with formulas and bullshit:

using coefficients, steel expands roughly 1mm per meter per 100 degrees

so if a valve is about 60mm long, and if you take the cam into it as well (as it is also a factor), say its roughly 40mm diameter.

at 100 degrees, the valve clearances should be just over 0.1mm to allow for a gap? ie: half what the manufacturers state? and seeing as an engine keeps a consistent temperature of about 70 degrees, should be even less?

or am i completely missing the point?
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Blue_SV650S wrote: it was a sh1te wheelie, but it proves that he can get it up in 3rd and can do angles. In summery, mattsprattuk is a gobby little sh1tebag, dopehead tw4t, but sadly for all of us, he probably isn't THAT full of sh1te!!
Kickstart wrote: Hi I tend to agree with Matt. All the best Keith

[neil.]

Seems right for my bike then... 0.08 - 0.12 on inlet and 0.10 - 0.14 on the exhaust. Remember the valves are right on/in the combustion chamber, where temperatures will be much higher than 100C (I read somewhere that it was hot enough to melt platinum which would be over 1700C!).
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CBT February 2008 | A2 June 2008 | Yamaha YBR125 (written off) | Honda CBF125 (current)

[Ichy]

You missed the bit about the engine casing expanding at a higher rate, roughly twice the coefficient of expansion of steel.

[Pete.]

The gaps are calculated to allow a certain amount of seated-time for the valves to keep them from over-heating at the lip. Simply having a clearance isn't enough to keep the valves from burning out.
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good