Renault Renault Scenic dephaser pulley failure
Damage caused by seized dephaser pulley on a Renault Scenic Megane f4r
These photographs show the damage of the valves and pistons in a f4r 464 Renault engine due to failure of the dephaser unit.

This is becoming more regular as some garages and mechanics do not know how to check this item correctly.

It is very important that the pulley is checked for excessive play when carrying out cam belt replacement.

If your Renault Scenic Megane or Renault engine fitted with variable timing has a top end rattle it is advisable that you get it checked by a reputable mechanic or garage.

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Cylinder head and valve damage



This engine had to be replaced due to the catastrophic damage caused.

Cam belt failure Renault Scenic Megane

Cylinder block and piston damage


The role of this pulley is to allow variable timing adjustment it works using a hydraulic system with oil pressure being supplied by the engines oil pump via a valve in the cylinder head.
On later models the valve is electronically monitored.