Bike is not much different than a modern car engine. Unless one is losing oil through poor sealing gaskets, poor sealing piston rings or valve guide seals, etc., oil loss is very minimal between normal change intervals. The oil sight glass is sensitive to suspension changes from tires, suspension springs and shock air pressure, parked surface anomalies and even varied between bikes, etc. On some bike, sight glass was totally filled no matter the attitude.
Hence came the wise sage advice toward most for changing oil and don't bother with checking level.
On the other hand, my 1986 Suzuki LS650 Savage single cylinder air cooled was a different story. It ran hotter especially in warmer weather. Although it had tight compression, good valve guide seals and no oil leaks, it would consume a quarter quart of oil every 500 miles when temperatures got above 90 degrees F (32 C). There, I religiously checked the oil every other fill.
![Confused :-?](./images/smilies/icon_confused.gif)
(Fuel fill was roughly every 100 miles, as I had a 2.8 gallon tank. Why manufacturers insist on cute looking small gas tanks on mid size cruisers beats me. Yet their 250 cc single cylinder GZ250 Marauder had a 4 gallon tank.
![Shocked :shock:](./images/smilies/icon_eek.gif)
Some have ruined the engine by failing to check and maintain oil level.
![Embarassed :oops:](./images/smilies/icon_redface.gif)
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After riding the 250 Honda Rebels and Suzuki Marauders at an MSF course (employer safety training requirement on government installations regardless of riding experience), the Savage felt and throttled like a "big bike" when riding home.
![Laughing :laughing:](./images/smilies/laughing021.gif)