Saturday, April 12, 2014

Timing belt pulley positioning on belt drive Ducatis

There's a thread going on one of the forums about replacing belts, and the point of marking the belts has been raised.  I made the comment that I found the marking of belts an over complication of the procedure, but some people do find some comfort in it.  In particular for locating the vertical camshaft correctly (vertical inlet on a 4V), due to the load the vertical inlet closing spring places on the camshaft when the cam is at the correct position.  Coupled to the fact that on most of the 2V models the vertical cam pulley has a surround covering it and making it hard to get a good hold of it.  I can understand the issues this brings to those who do this very infrequently.

So, to confuse people further, I thought I'd introduce another method to bypass this.  I did teach this method to a previous workmate, who them went and bent some valves, so if you don't understand it, don't use it.  But it seems pretty simple to me.

The timing shaft pullies traditionally have 4 holes in them, and the locating dot on the outer edge.  See the picture below:

In this instance, the locating dot is lined up with the mark on the primary drive cover.  This denotes the engine is at TDC firing on the horizontal cylinder, which is the master position for most setting procedures.

As the timing shaft turns at half crank speed, it rotates 180 degrees for one crankshaft rotation.  From the RH side the crankshaft rotates clockwise and the timing shaft rotates counter clockwise.  Vertical TDC firing is 270 crankshaft degrees after horizontal TDC firing, or 135 timing shaft degrees.  If you look at the above, you can see 4 holes spaced at 90 degrees, and conveniently located at 45 degree spacing either side of the locating dot.  This means that the second hole clockwise from the locating dot is 135 timing degrees from horizontal TDC firing, and as such, it's a locating dot for vertical TDC firing when aligned with any of the aligning marks on the primary drive cover or camshaft surrounds.  As below:

On the engines with adjustable cam pullies, these holes aren't present.  But of the three locking screws that hold the halves together, one is in the correct position.

The locating dot still gives the position anyway.  On the 2V pre DS motors, when the timing shaft dot is at 3 o'clock, the vertical camshaft dot will be at 4:30.

On the later 4V Testastretta and 2V DS style engines with the 20 tooth pullies, the small holes are still there.  But there are many larger holes, just to confuse the issue.

And, as always, when done, the locating dots on the timing shaft and all cam pullies must align with all the correct marks once set back to horizontal TDC firing.


Unknown said...
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