Friday, July 10, 2015

Further comment on the Ducati ST3 crank slot incorrectly machined.

I thought I'd put up a photo to better explain what I was talking about with the incorrectly machined crank slots, using a photo of a crank.

The crank has two slots machined in the end of it to locate the factory locking tool, and you also use these to locate the turning tools. I've never seen these slots machined off before (not once that i can recall), but these ones certainly were. It would either be an error in or damage to the machining jig I expect. I doubt anyone made the decision to machine them 10 degrees off, as it would be a simple production process.

In the pic you can see the two slots for the tool (red arrows), the alignment slot used to align the flywheel dot (yellow circle) and the timing gear keyway (green circle). The timing and cam pulleys appeared to all be correctly aligned, but I don't recall if this bike had a timing window to see if the flywheel marks lined up with the pointer, or if it was one of the later threaded plug covers. I would expect all these slots would be machined in pretty much one pass though.

As a consequence, using the factory cam timing tools would see the crank locked in the wrong place.

The only way you would know is by doing what I did, so it's not something that would come up often. Using the tools as intended would see this result, but it would be unintended and unknown. The assumption that the tool is right is the assumption you work with when using any tool pretty much, unless anecdotal evidence shows you otherwise. This is the first anecdotal evidence of incorrectly machined slots that I have seen.


Unknown said...

I found this page after I degreed my cam a few years back. My 2004 ST3 is the same way, which explains why the cam timing was off.

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