DeTomaso Mailing List: April 98, Message #391

Jim wrote:

Just wondering. Been thinking about D-Manns exploding Cleveland trick 
and
wondered why we don't hear about Motorcycle engines doing the same 
thing.  Can
you imagine what kind of damage a motorcycle piston could do to a 
persons butt
if it decided to remove itself from the motor at 10,000 rpm?

Are they built to take the high rpm and not explode?  What is the deal?

>>>Jim,

Production, bone-stock motorcycles are being built to rev in excess of 
15,000 rpm all day long.  So do automotive Formula-1 engines.  Simply 
put, they go like stink.  Why?

Little bitty parts.

Generally speaking, the mechanical limitation on an engine is mostly a 
function of the mass of the reciprocating parts.  You get a great big 
heavy piston going updownupdownupdown really really fast, and that 
immense inertia puts a hell of a strain on the connecting rods.  
Similarly, you have a camshaft smacking a heavy valve, which is being 
closed by a spring, and it too is going updownupdownupdown really really 
fast.  Drive these things too fast (as D-Mann and others have found 
out), and you start suffering failures in components like connecting 
rods, valves, etc. etc.

Motorcycles use teeny tiny pistons and valves that don't weight much, 
and thus have a lot less inherent inertia.  (I'll let the math wizards 
come up with the formula that lets you calculate this stuff.)  As a 
result, you can spin the motor that much faster before you reach the 
inherent limitations of current metalurgy, but things can still get 
spectacular.

FWIW, cylinder heads are pretty beefy, and thus pistons rarely come 
zinging out of the top of the motor.  If the rod breaks, the piston 
smacks the cylinder head and either stays there or falls back down and 
fouls the remnants of the connecting rod, which then blast out through 
the side of the motor.  This is usually followed by an impressive stream 
of hot oil, which on a motorcycle coats the rear tire immediately.  As 
often as not, this failure occurs when the bike is heeled completely 
over in a corner and the tire is right at its limits of available 
traction.  Coating it with a heavy bath of oil obviously adversely 
reflects the traction capabilities of the tire.  

>From the rider's perspective, it goes something like this:

BANGthuddirtskydirtskydirtskydirtskyTHUD! :>)

Mike (who fortunately has never blown an engine!)



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