what does "timed with engine pulses mean" and is the crank gear really oval shaped? or is it the teeth that are oval shaped?
yancey
To be honest, I'm not sure, just remember reading oval sprocket somewhere, it may refer to the spacing of the teeth, or a tiny change in the actual sprocket shape, or that the teeth spacing makes it slightly oval vs. evenly spaced teeth which would make it round. In any case, T10050 and T10100 are different and watch out for the bad T10050s out there.
All I can find right now is this from VW's study materials and service manual:
High pump forces are required to generate an injection pressure of up to 2000 bar. These forces subject the components of the toothed belt drive to high loads.
Some of the teeth on the crankshaft timing belt gear have a larger gap clearance in order to reduce toothed belt wear.
To relieve the load on the toothed belt during the injection cycle, the toothed belt of the crankshaft has two pairs of teeth which have a larger gap clearance than the other teeth.
This is how it works:
During the injection cycle, the high pumping forces exert a heavy load on the toothed belt. The camshaft gear is slowed down by the pumping forces. At the same time, the combustion process which now begins speeds up the crankshaft timing belt gear. The toothed belt is stretched and the pitch is temporarily increased as a result.
On account of the firing order, this process occurs periodically. As a result, the same teeth on the timing belt gear are in mesh every time. The teeth have a larger gap clearance at these points in order to compensate for the change in tooth pitch and thus reduce toothed belt wear.
On a crankshaft timing belt with a uniform tooth gap clearance, the teeth of the toothed belt abut (not a typo that's what is typed in the guide don't know what "abut" means) against the tooth edges of the timing belt gear when the toothed belt is placed under heavy strain by high pumping forces. The upshot of this is that the toothed belt wears quickly and has a short service life.