Technical Insights
by Elden Carl
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Welcome to Technical Insights!

As you may know, the weather south of the border in Baja is getting to be just about
perfect for riding. Naturally, Elden and Pauline couldn't pass up an opportunity and are
traveling to Mulege with several other riders. Someone, however, has to keep the place
running, so I'm filling in on Technical Insights with a report on engine temperatures and a
comparison between the KLR-650 and DR-650.

Elden and I have talked many times about the pros and cons of the DR-650 and KLR-650.
The discussion often turns to engine cooling actual running temperatures. Earlier this
summer while investigating a popular aftermarket computer set-up, I noticed the company
was using a gasket-sensor to gather head temperature information for air-cooled bikes. I
searched in vain to find a sensor/display combination at a reasonable price that could be
used to check head and/or oil sump temperatures for the DR and KLR. By chance, I
happened upon a potentially useful tool in a Harbor Freight catalog – a non-contact
temperature sensor. Long story short, after listening to me talk about how this might make
for a good test and article, but knowing my tendency to procrastinate, my lovely wife
ordered one for me. When it arrived, I immediately tested it on everything in the kitchen
(much to Mindy’s dismay…).  We were in business!

For those of you with a scientific mind, we came up with the following controls for our test.
Both bikes were stock configuration with regard to the airbox, jetting, and exhaust. We
removed both bash plates. Elden and I happen to be nearly the same size and weight,
though etiquette prevents me from pointing out who is actually heavier… We took the
readings in the same order at each stop, and we started and stopped the engines at the
same time. We rode a meandering mountain road devoid of any sharp curves, allowing us
to run exclusively in top gear. One thing we didn’t intentionally try to keep the same was
RPM. This was intended to be a test of the two models under actual riding conditions. If
one bike was geared higher or lower, so be it.  The DR-650 was geared with 14/42,
equivalent to 15/45; and the KLR-650 was geared at 15/44. Note that stock for each bike
would be 15/42 for the DR and 15/43 for the KLR. Surprisingly, we found that our RPM
was the same when riding nose-to-tail at 4000 RPM and 4500 RPM. Since the DR was
geared the equivalent of one tooth lower on the rear sprocket than the KLR, it reinforces
the fact that 5th gear on the DR is higher. Another point worth remembering is that the DR
was geared essentially three teeth lower than stock (the KLR one tooth lower than stock).

Our real intent was to see the relative differences between the two bikes under normal
riding conditions, and also to note any trends that might reveal themselves. Although the
temperature sensor is advertised as accurate to within 2%, the actual figures should not
be relied upon for any reason.

We planned three stops measuring six different locations around the engine. The first
stop was approximately 25 minutes and 15 miles out of town; enough time to get the
engines fully warmed up and get out of the in-town traffic. This leg was fairly level, with the
last 10 minutes or so on the highway. The second and third stops were approximately 10
miles and 10 minutes apart, with riding conditions characterized by open road,
predominately up-hill to the second stop, and down-hill to the third. We took engine
temperatures at the following locations: 1. center of oil filter cover, 2. center of clutch
cover, 3. center of dyno cover (actually just to the right to avoid the cap), 4. oil sump
adjacent to oil drain plug, 5. center of cylinder wall, and 6. head adjacent to intake.
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