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Discussion Starter · #1 ·
After having had two timing belts fail on my Peugeot 508 BlueHDI 150 within 500 miles of each other, on investigation I became aware of this issue, which may save some others some pain and expense.

If the timing of the high pressure fuel pump is not set correctly when repairs are done to the cylinder head, this can cause premature breakage of the timing belt, and possibly damage to the water pump that means the impeller fouls inside the block. The damage to the timing belt is seen as a number of stripped teeth on the belt.

A good explanation of this along with pictures can be found at REPXPERT

Further to this looking in the Peugeot Servicebox dealer information, for removal and refitting of the high pressure fuel pump, contains a warning that "Incorrectly fitting the high pressure pump may offset the timing and cause a risk of damage to the timing belt.
 
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Pity they didn't expand the meaning of this passage, 'Correct setting of the high-pressure fuel pump involves setting its maximum torque demand in a range in which the valve train requires a low level of torque. This ensures a relatively even distribution of tensile stress in the timing belt drive. ' to how this actually done.
 

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Discussion Starter · #3 ·
Having read the Peugeot removal refitting procedure it basically means the pump needs to be timed so that it doesn't apply load to the timing belt at the same time as any of valves opening.

If this is not done and the maximum strain of the pump coincides with the load caused by a valve being pushed open, it creates a pulsing effect in the belt, that causes the belt tension to vary, meaning the belt can jump teeth, and potentially damaging the bearings in the water pump.

Its a rather nasty potential issue, and makes a mockery of the conventional wisdom that common rail high pressure fuel pumps don't need to be timed, it also suggests that the cambelt and tensioner arrangement are a bit on the fragile side.

I'm just glad to have an explanation as to the timing belt failures I've had on this engine, fortunately the camshafts and rockers are sacrificial and have prevented catastrophic internal damage.
 

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