Why my Yamaha FZ-S engine makes rattling sound after long run?
You should check the following possible reasons and repair suggestions.
(1) Engine oil level may be low, an engine relies on oil to supply lubrication to the inner moving parts if the engine oil level is low the engine cam followers or lifters will lose pressure allowing excessive clearance in the valve train causing a rattling noise.
(2) Engine's drive belts may be broken or slipping so Tighten or replace belts.
(3) A belt tensioner is used to hold pressure against the serpentine belt, when this tensioner fails it can make a rattling noise.
(4) A mounting bracket is used to support the various accessories such as the power steering pump, air conditioner compressor, if the bolt becomes loose or the bracket breaks it can cause a rattling noise.
(5) The electric cooling fan may not be working properly so repair or replace cooling fan, repair wiring, replace cooling fan temp sensor.
(6) The engine may have mechanical problems so check compression to determine engine condition.
After assuring and working on above suggestion if still the problem persists then we advise you to get your bike checked to your local Yamaha service center.