[Biturbos4] I think I really did it this time

[Keman]

It's mostly a noise and wear issue. Belts are quiet, smooth, and transmit
less harmonic vibrations into the valvetrain. They're also lighter which
accounts for less rotating mass. Chains last forever but are a lot heavier
... they take up less space though. Gears have backlash (gaps between
the teeth) so as the cams would be driven, they could skip forwards and
backwards depending on if the valves were in a position that applied
resistance or forward force. Those old timing gears on V8's from
yesteryear that sounded trick at the quartermile generally destroyed
valvetrains and made for high oil temps ... even old domestic race V8's
use timing belt conversions in the high end arena.

The materials technology that goes into a timing belt which allow it to
last 120+ million revolutions is pretty incredible.

- Keman


----
How come they're still belts (or chains as on the 4.2), rather than
just another cog on the side of the engine? It's never made much sense
to me.



andyt