What causes these Trucks to go out of Timing?

[nicksorenson]

Just wondering what makes these engines go out of timing after the years? I just retimed my IDI and it starts and runs great now. But I don't understand how a geared injection pump can go out of time.

On my mercedes where the pump and cam are chain driven I can completely understand because the timing chain will stretch as it ages. But with the Stanadyne pump on my IDI I haven't a clue on what could cause it to go out???? Anyone know?

 

[dbarilow]

Wear inside of the IP changes timing, also as the injectors age the pop pressure decreases making it easier for them to fire.

 

[subway]

yep just driving the truck and the IP will wear over time. When they wear they wear to the retarded side.

much safer than constantly advancing while wearing.

 

[Agnem]

There are several areas that can cause the timing to retard. First is the lobes which are responsible for pushing the plungers in to inject the fuel. The lobes get smaller, and this causes the leading and trailing edges of the lobes to receed, thus pushing the plungers in later than before the wear. This recesion also causes lower fuel delivery because the lobes are no longer as tall. Another area is the advance ring on which the lobes are placed. The ring is rotated by a piston and linkage that works off of fuel presure at cruising RPM's. The piston, and linkage can wear resulting in less advance for a given fuel presure. I don't know any of this as gospell. It's just my assesment from having taken pumps apart.