CRF250L Research - 7/29/14 version

Rick's Home Page

Click pictures to supersize.

Alert - CBR300R news October 18, 2013:

"Honda unveiled a freshened-up and bored-out CBR300R at the China International Motorcycle Trade Exhibition to fire back at Kawasaki's Ninja 300R."

"Details on the 300 have surfaced in the form of a Chinese spec sheet (pictured). The motor has the same bore, but has been stroked 8 mm to 286 cc total displacement. Claimed horsepower jumps from 26 to 30.5 at the same 8500 rpm, while torque takes an even bigger jump (percentage-wise) from 17 to 20 foot/pounds."

Spotted: Honda CBR300R and Triumph Mini-Single

This will surely result in a CRF300L (286cc) in a year (or two)... and many will rejoice.
But Bill Blue will be the happiest:


A CRF350L would be a dream come true for many small-bore dual-sport riders; I know I would have to have it at any cost.

The question is not "How much would it cost?" but rather "Can it be done in my garage?"

Rather than talking to someone who might actually know the answer (Bill Blue), I decided to jump in with both feet and figure it out myself. How hard could it be?

I decided that there were two options:
Buy a complete CBR300R or CRF300L motor and shoehorn it into my CRF250L frame,
Buy the parts (crankshaft, cylinder, piston, whatever) and install them myself.

The first option will be very expensive, and I'd probably be waiting for 6 months or more for just the CBR engine (in a frame, as a complete bike - Honda doesn't sell complete engines). The CRF300L hasn't been announced and so waiting for it is not a good idea.

Well, on to the second idea, build it myself from parts ordered on-line. The drawback here is that there is no way to know exactly what to order. A crankshaft for sure, because Honda announced it as a stroked version of the 250 engine. But what other parts would I need? And would the B&B kit fit?

I looked on-line for a CBR300 parts catalog - no luck. So I waited.
And waited.
And waited.
And waited.
And finally, added a 2015 section to their on-line catalog, and there it was - CBR300 motos in several flavors.

I captured the parts info in an Excel spreadsheet and went about editing it and adding CBR250 and CRF250L parts. Then I added Excel logic to compare parts from the three models and mark the parts that were different, like so:



Click the sheets to supersize or right-click to download and print your own copies.

The sheets show part assemblies for the engine and transmission; other differing parts on the body, for instance, are not relevant.

Note that the sheets are incomplete; required quantities are missing in several places, and I haven't worked out some mis-matches as yet. But these are details that I'll get to later. For now, the big picture is as you see it. And it's a pretty big picture.

The task at hand is to decide which parts to order. In an effort to simplify the task, I made this sheet showing parts that have teeth, and that often are related to heights of various levels and distances between various surfaces in the engine/tranny. This will help me decide if the cylinder height is changed, for instance.


Stay tuned for more info as I crawl through the sheets and measure, measure, measure...
Updated sheets, as I write this; added DIFF info.

4th of July, time to celebrate. Or not. I have bad news. I have discovered that the 300 crank will not fit the 250 cases; a little blue bird told me. I want to find out exactly why before I call this whole thing off and sit on my hands, waiting for a CRF300L.

More updates; corrections.


Cylinder deck height

Looking at the cam chain and related parts, I see:
• The cam chains are identical with the same number of links (128).
• The gears on the camshafts have the same number of teeth (34).
• The primary drive gears have the same number of teeth (26).

IF the crankshaft and camshaft center lines are the same distance apart for all three, then the cylinder deck height is the same for all three. It is plausable that the center lines are the same distance apart, considering their locations in the crankcase and head. If the cylinder height was changed, then engineering new center line locations would be much more difficult than just changing the cam chain length, so the simplest assumption is the deck height is unchanged.


Tranny and gearing

   C300         C250         250L     
Primary  73/26 2.808  OA↓   73/26 2.808  OA↓   73/26 2.808  OA↓
1st 41/12 3.417 0.041   40/12 3.333 0.039   40/12 3.333 0.037
2nd 36/16 2.250 0.062   36/17 2.118 0.062   36/17 2.118 0.059
3rd 33/20 1.650 0.084   33/21 1.571 0.084   33/21 1.571 0.079
4th 27/20 1.350 0.103   30/23 1.304 0.101   30/23 1.304 0.096
5th 28/24 1.167 0.119   29/26 1.115 0.118   29/26 1.115 0.112
6th 27/26 1.038 0.133   26/27 0.963 0.136   26/27 0.963 0.129
Final 36/14 2.571     38/14 2.714     40/14 2.857  
Spread   3.29       3.46       3.46  

OA is the overall drive-train gearing, including the primary, tranny, and final gearing but NOT the tire size.

Stay tuned...

 Rick's Home Page