Technical Insights
by Elden Carl
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08/13/2008

Summer Gearing

Rod Morris recently talked to a customer concerning gearing his KLR650 down to 14/49
or 51.  In cool weather this might be an OK idea if the bike is equipped  with a Chain
Master upper chain control unit. All KLRs need a "Chain Master", but those with larger
rear sprockets need it more in order to keep the fast moving chain away from the gear box.

In mid-summer we fear that increasing the rpm at any speed might negatively change the
relationship between air velocity through the radiator and around the engine and the
number of times per minute that the engine fires on the compression stroke.  I would like
to see a mechanical engineering whiz like Kevin Cameron of Cycle World address this
subject.  Would Mr. Cameron conclude that a KLR650 engine turning say 5,000RPM at
60MPH would run hotter than one turning 4,000RPM at the same speed.  It would be
interesting to compare and contrast the effects on engine temperature in each case; the
increased load created by higher gearing vs. the increased RPMs resulting from lower
gearing.  Maybe the "Skipper" (webmaster Todd Vosper) can e-mail Kevin Cameron at
Cycle World for a scientific answer.  We'll see.

Cush-drive VS Solid Rear Hubs

The two rear wheels we have the most to do with are KLR650 and DR650.  Both have
cush drive rear hubs with rubber absorbing much of the shock caused by driving forces. I
hate unsprung weight like any dirt rider but the heavier rear wheel with the cush-hub is far
superior when it comes to protecting gearboxes and clutches.

Bikes with solid rear hubs that are ridden in rocky conditions sometimes have gearbox or
clutch problems. The most common symptom is "notchy" shifting and difficulty getting into
neutral.

If one were to remove the clutch basket and inspect its aluminum fingers you would  
probably find notches caused by clutch plates moving back and forth on engine reversals
especially hard acceleration in rocky sections.  None of my bikes with cush drive rear hubs
has ever exhibited this problem.

Is there a fix?  Yes, but it involves removing the clutch basket from its gear, filing the
notchy surfaces (not a good idea if the notches are deep), hard anodizing the basket and
reassembly to its gear by someone who can rivet.  The only one I know who does this
uses the most expensive process of hardening available.

The best solution for this problem is to buy a new clutch basket, install a cush-drive rear
hub, assembly and be easy on the gas in the rocks.
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