Friday, August 22, 2014

Multistradas and dirt...

I'm not going to get into whether the MTS1200 is a real "ADV" bike or not.  Each owner will use it as they see fit.  I would like to address a couple of points that should be given some thought if you do use your bike off-road.

First are the timing belt covers.  Ducati actually puts a foam filter in the front belt cover, apparently to prevent dirt ingress.

This is a sensible approach since dirt or other debris in the timing belts can never be considered a good thing.  Unfortunately the effort is for nothing because the rear belt covers do not even meet.
Take a look at the gap between the upper and lower halves of the rear belt cover.  So much for that idea.

Next up is a lesson in how not to design an airbox.  The air filter is a trapezoidal tube, open at each end.  It is constructed of pleated paper and has rubber gasket ends.  The left end sits up against the inside of the airbox and the right end is captured by the airbox snorkel.  The seal at both ends depends solely upon the compression of the rubber seals.  Here is where the problem arises, what do you think happens when that filter retainer is tightened down upon the PAPER filter.  Well, what happens is that the entire filter compresses thereby allowing leakage past the end seals.  Here are some photos of the "clean" side of the airbox.

In the second photo you will notice a few things.  First is that there is no register or shoulder to positively locate the filter element.  Second is the paths of dirt that have leaked past the filter seal.  Third is the homemade "improvement" via a soldering iron.  This is apparently a popular modification on internet forums, along with removing the external air supply to the airbox.  While I've not flowbench tested a modified vs. stock MTS 1200 airbox, I'm pretty sure that that sharp-edged ragged hole has succeeded in nothing beyond destroying the airbox's rigidity and therefore its designed-in resonance.  Removing the duct that channels cool outside air to the airbox certainly is not a way to increased airflow since the now cut-off snorkel is sharp-edged, and airflow does not like sharp edges.  But who am I to argue with internet experts.
I have compared a number of popular "free HP" airbox modifications for other bikes that are popular on the net.  Rarely do they work as touted.  One example is removing the rubber inlet snorkel from the airbox on the Aprilia Caponord.  This results in a sizeable DECREASE in airflow due to the fact that the airflow is encountering a sharp-edged hole and becoming choked by turbulence.  Many armchair horsepower junkies believe that airflow behaves intuitively, IT DOES NOT.  Unless studying airflow is your hobby and you have pretty good grasp on fluid dynamics and the effects of Helmholtz resonance, you should probably rethink cutting, drilling, sawing or otherwise mutilating your airbox.

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