oil top-up?

Does this engine have a Briggs and Stratton engine? if so their webpage has owners manuals to download. Normally there will be a dipstick that unscrews it position depends on engine model and make, unlike a car engine you do fill some if not all B&S engines through the dipstick hole. Can you find the serial number of the engine it will read something like 10A900 you just look on the maker’s site for this model?
Briggs and Stratton link below:

http://www.briggsandstratton.com/maint_repair/manual_and_more/doclist.aspx?category=Engines&manual_type=Operator%20Manuals&menu=nav3&subMenu=3

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February 2008