Certainly on KTMs and 'Bergs (dunno about the BMW).
Whereas the DR-Z 400 has an oil capacity of 2.4 litres, the EXC KTMs only have about 1 litre of oil. It's important, therefore, to use fully synth and to change it regularly as it is worked pretty hard.
Greg
Thanks Greg - sounds like another reason to stick to the HP2


