Last time i did a belt change (after a belt failure - but the engine was running fine otherwise) i set the flywheel, the cam sprocket marker, and then pinned the pump.

When i tried to start it, it just smoked a whole load and wouldnt catch.

I then, in blind ignorance, tried the pump at the far end of its (plate) travel, and the engine started fine.

Now i dont really understand this, and id like to.

a) why did i need to adjust the pump, considering it was running ok with the old belt, and
b) im about to do the belt on my other 300, and i need to know how this plate works, as, it seems, just using the pin isnt good enough?

I dont know, and it was a while back - when i did the last one, could it have been that the belt was trying to pull the sprocket out of alignment, but the pin held it in place - and i just did not notice, or understand?

Is the idea that you 'lock' the crank using the flywheel, then the cam, using the mark, and get the pump to almost the right place, and then slacken the locking plate so as then the pin goes in?

...or is it more complex? Again, im wondering why i had to adjust when i did the last one after belt failure, when it was running fine before - surely the belts cant differ in pitch by that much?

plate is slotted for adjustment if you fit belt at the wrong end of slots you will find when you come to turn engine over to recheck not enough left in slot ,ideally you want to use drill bits in smaller sizes as pins and then turn center nut clockwise to hold pulley against the bit then tighten the 3 bolts ,you use smaller bits till knock is produced with engine running then go back till knocks just gone
it would seem your pump may not be set a 100% at its tdc position

The idea behind the adjustable sprocket is to allow you to tension the belt and still have the pump locked in the correct position, the pulley would try to turn the pump as the tension is applied if the three bolts were tight. Once you have the tension correct and with the pump still pinned you tighten the three bolts to lock the pulley in the correct position on the pump flange.

On modern engines both the pump and the cam are locked while the belt is tensioned then the pulleys are locked to their respective flanges.

Right, so, to be sure, procedure should be -

Align with old belt in place.
Take off belt
"lock" flywheel slot
loosen pump locking plate, pin pump, and re-lock plate in center of adjustment
fit new belt with cam at pointer
remove pins, tension, rotate twice, check tension,
relock flywheel,
undo pump locking plate
re-insert pin
relock plate

good to go?

julianf said:

Right, so, to be sure, procedure should be -

Align with old belt in place.
Take off belt
"lock" flywheel slot
loosen pump locking plate, pin pump, and re-lock plate in center of adjustment
fit new belt with cam at pointer
remove pins, tension, rotate twice, check tension,
relock flywheel,
undo pump locking plate
re-insert pin
relock plate

good to go?

Click to expand...

Not quite
Align with old belt in place.
loosen pump pulley bolts , pin pump, (use socket on centre nut if pump moves)
Take off belt
leave pulley bolts slightly loose so that pulley can still move but set pulley in mid travel.
"lock" flywheel slot
fit new belt with cam at pointer, fit belt over FIP pulley so that pulley is still approximately centred
Tension belt, tighten FIP pulley bolts
remove pins, rotate twice,,
relock flywheel, check FIP pin fits
Remove tools and reassemble

Note that on modern diesels both the pump and cam are locked while the belt is tensioned, then both pulleys are locked to their flanges