From: tim@intrepid.gsfc.nasa.gov (Tim Seiss)
Subject: Re: CR250 vs. XR250(long)
Organization: Goddard Space Flight Center
Date: Wed, 16 Dec 1992 21:04:26 GMT

In article Message-ID: <1992Dec16.152427.13871@nlm.nih.gov>
Dr. Daniel R. Masys) asks:
>1) how does one learn to ride such a beast in a way that minimizes risk
>   of injury?  
>
>2)-Are there any maintenance gotchas with the 1988 CR250, or things to
>  look out for beyond what the owner's manual says (analogous to snapping
>  the swing arm linkage on recent KX's)?  The owner's book is almost a
>  shop manual, with maintenance procedures and specs for all the systems
>  on the bike, and while its cold and wet we may disassemble the beast
>  and put it back together by book specs.  Anything special to look for
>  in terms of hidden damage?

I might be qualified to answer this, since I used to own an '88CR250 and
my father has an '87XR280 (<--highly modified, GREAT bike BTW, and those
comments are coming from a lover of 2-stroke racing bikes...).

I start with question #2
   The one problem I remember most about that specific CR250 was with some
hardened bushings in the rear suspension linkage.  Two bushings in particular.
There is a part of the linkage that is called the "delta" arm because it looks
somewhat like a triangle and has 3 holes in it (I think...).  The bottom of
the shock bolts to it.  If I remember correctly, it also bolts to the frame
and through the underside of the swingarm. The bushing in the delta arm
where it bolts to the frame is an odd shape where it's diameter in the middle
is larger than the diameter out near its ends:
				   				   
				    
                            Thicker here than over here...
                           \/                    \/
       _____________________________________________ 
       |                                           |
       |_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _|
       |                   /\                    /\|	 
       |                                           |	 
       |_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _|
       |                                           |	 
       |___________________________________________|

This causes the rear suspension to bind up, and eventually break these
bushings if you do a lot of high jumping.  

There is another part of the linkage that has 2 thin parallel arms.  This
arm also has one of these type bushings...This design was only with the '88
models, fixed for '89.  If you talk to a mechanic at a dealer, they might
verify that '89 bushings will be OK in the '88 linkage.  Keep the linkage
lubed and not over-tightened when you assemble it. (I'm not completely
sure about the assembled relationship these parts have, but the bushings
are sort of large, like 3" long or something, you'll see 'em after you
finish cussing over how much work it is to take the linkage apart...)

Gotcha #2:  This is a personal peeve, and may not bother other pre-92 
CR250 owners. The HPP (Honda Power Port) is a complete and total pain
in the butt to service.  It consists of 2 "fingers" at the top of the
exhaust port that slide in and out of the exhaust port as engine RPM changes.
They are "in" at low RPM, to lower the exhaust port height and provide
better bottom-end torque, and they slide "out" of the exhaust port with
increasing RPM to raise the exhaust port height for higher top-end
horsepower.  The tolerances between the sliding fingers and the cylinder
are fairly tight and easily gunked up with carbon, rendering the system
sort of inoperative.  Also, there is a rather complicated series of 
arms, linkages, and gears operating the fingers which are actuated by
a connection to a governer-thingy near the water pump on the right side
of engine (beneath the exhuast pipe)...I noticed my system jammed up
one time and the fingers were stuck in the "out" position...No major
trauma, but the system wasn't working as it was designed.

Gotcha #3: This is related to the last part of #2.  It you ever take
the cylinder off the motor for piston and/or ring replacement (BTW,
I put new rings in my bike after 48 hours of racing time, and the old
ones were still at "new" specifications.) you'll see this tiny little
lever near the front right side of the crankcase opening.  This lever
is what operates the aforementioned arms, linkages, and gears which
operate the power-valve (the fingers).  When you put the cylinder back
on, you have to position the lever in the OPPOSITE direction than the
one described in the service manual.  My dealer had a service memo on
it.  The manual was wrong.  You can't get the cylinder to fit down all
the way onto the cases until that lever is in the correct position.

Gotcha #4:  The STOCK suspension stinks on that bike.  Way too much
damping in the middle of the fork and shock travel.  It will have 
you bouncing all over the place on stutter-bump type terrain not too
mention cripple your forearms.  I had Race Tech redo my entire
suspension, including new fork and shock springs.  Made a big
difference.

Also, the exhaust pipe bracket on the skinny part of the pipe broke.


Now question #1:

  Experience!  The CR250 is not a learner's bike.  My father was scared
to ride mine.

  Suggestions: To tame the motor down a bit, you can do any or all of
  following: 1) a 36mm carb from a CR125, 2) A flywheel weight(I am a
  big proponent of flywheel weights), 3) Several head gaskets to lower
  compression, 4) some kind of mechanism that keeps the carb slide from
  opening all the way. 5) smaller rear sprocket and/or larger rear tire
  to reduce the abruptness of the bike's powerband.  (However, the '88
  didn't really have a powerband, it just oozed power every place them
  screamed to infinity.)

  There are 3 big differences between a CR250 and XR250.  
  1) Besides the obvious differences in power and acceleration, the CR250 
     is harder to slow down or stop because there's very little engine
     breaking like there is on a 4-stroke.  You can fix this a little
     by putting on a larger rear sprocket (opposite to what I said above).
     Fortunately, the CR250 has very good breaks.

  2) The CR250 has a longer wheelbase and less steep rake, making for
     better stability at high speed, but slower, more cumbersome handling
     at slow, casual trail riding speed.

  3) The transmission ratios are completely different.  The CR's first gear
     may be higher than the XR's second.  
       As I get into thinking about this, I don't think there are qualitative
     do's and don't you can observe in the interest of reducing the risk
     of injury except to be careful.

     The CR250 is a handful.  Truly, the harder you ride it, the better it
     works.  All I can really say with regards to learning to ride one safely
     is just to make sure you're pointed in the direction you think you want
     to go in before adjusting that little thing your right hand turns.

     The MD Competition Riders put on a Hare Scrambles on the first Sunday
     in January every year up at the track in Hagerstown.  If the ground's
     not frozen like it was in '88-'91, you can bring the bike out and
     ride it.  The ground was really nice in '92.  We haven't had much
     cold weather yet, so it will probably be good this year,too.

-Tim Seiss
   

  

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