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CBR250 - CBR305 Big Bore Kit

Discussion in 'Modifications and Projects' started by AD-HUI, Aug 26, 2014.

  1. I would like to share my CBR305R build, firstly I would like to say. This was the most fun build/project I have had. Never done anything to such extent like this before. I thought a single cylinder small engine is a perfect starting point.

    Read Me First

    I can already hear you all typing or saying.

    "Why not get a XXXcc with XXXhp from XXX bike"

    Some answers:
    • I love my CBR, its not the quickest but I have had no issues with the bike from the day I picked it up (almost) new with 4kms on the clock, I know exactly what the past 14000km has done, every single fuel up (stored and logged), every service completed. So buying a used bike will not happen.
    • I have considered in the past on upgrading to a Daytona 675R (Dream Bike), after factoring the price of the bike and insurance, I figured its not worth it due to my financial status. (Insurance for me on the CBR is currently $480 a year whereas to insure the Daytona will cost me $2600 a year) Maybe down the road I will buy it, but not at the moment.
    • Excessive speed and power never seem to appeal to me, in my mind. The quicker you go, the quicker shit happens. Yes its nice to have the power in reserve but I always prefer to ride a slow bike fast rather than a fast bike slow. Given the strict tolerance on speed here in Victoria, Id say only 15% of riding on a ride will have some over the speed limit fun. (Trying to keep a clean record here :) )
    But wait, if you say speed never appealed to you why are you doing this modification?

    • The bike was great fun in the twisties. Just enough power to have fun yet forgiving if you made a mistake. But I have had situations where the lack of power has made several of my overtaking moves unsafe (in my book). Given that there are many roads in the country that has a speed limit of 100, and the top speed of the cbr was 157KPH indicated (130/140? Actual). Overtaking is difficult, some extra power will definitely solve this problem (still not justifiable to get a bigger bike).

    The Modifications

    What I have here is a Takegawa Bore Up Kit, it changes the engine piston and bore, up from a cast 76mm to a 84mm forged piston. Also increasing the compression ratio from 10.7:1 to 13:1. The kit I bought also comes with a sports camshaft as well as a fuel controller module. Being a Japanese made product. Everything was so nicely packaged and protected for shipping.
    (More info on the product HERE)

    Stay tuned for more
    • Like Like x 5
    • Winner Winner x 3
    • Agree Agree x 1
  2. Doesn't really make sense to me but if it makes u happy then go for it
  3. He he. Modding good.

    Understand. Man discharge negative energy when work on engine.

    Very therapeutic and learn lot in man cave.

    approve (y)

    Picking up towbar kit for xr4 tomorrow. Do you approve? Ha ha ha .
    • Like Like x 6
  4. his top end was fcuked anyway, he was fast on it as a 250, god nows how im going to keep up with him now
    • Like Like x 4
  5. The taking apart of the bike

    [​IMG] [​IMG] [​IMG] [​IMG] [​IMG]

    Taking apart the bike was the easy part, every bolt and nut removed was placed into a tray with a small post-it note of where it should go so I will not forget. I thought of doing this job with the engine in the bike. All was well until I realised the exhaust bolts was in the way of the frame. So the engine has to come out.

    [​IMG] [​IMG] [​IMG]

    A simple 4 bolts and the engine slides right out. (using a car jack underneath to the support the ~30kg engine).

    Now that the engine was out, the cylinder and piston was removed

    [​IMG] [​IMG] [​IMG]

    Comparison with new vs old

    [​IMG] [​IMG]

    Next up, installing the new cylinder.
    • Like Like x 5
  6. So all up that kit's a shade over $1100.00 delivered?

    Looks like a fun project, all the best.
  7. Great little project! You don't see too many people doing engine mods on bikes these days.

    Just a quick question just for my own curiosity... When it comes time to sell, will this bike be able to be sold legitimately as a LAMS bike being modified? I'm going to assume it will still sit within the prescribed power to weight ratio?

    Please keep the posts coming and the results of the mods. Will you be getting it dyno tuned as well?
  8. Im not too sure about that, I always had an assumption if you modify any engine related components (that are not factory supplied) it is not a LAMS bike any more. (e.g. removing a throttle stop on a restricted bike will not make it a LAMS bike).

    The mods are all done already riding it around to and from work to test it out before a ride this weekend. Finding the right fuelling for a kinda basic device is going to be an issue, but it seems like the map they provided is pretty good. (maybe down the road with a PCV fuel controller I will do some dyno tuning)
    • Like Like x 1
  9. #9 AD-HUI, Aug 28, 2014
    Last edited: Aug 29, 2014
    Putting it all back together

    [​IMG] [​IMG] [​IMG] [​IMG] [​IMG] [​IMG][​IMG]

    Nice and simple, fitting everything back in, torquing all the bolts to specific values (borrowed the epic snap-on torque wrench from work). Did have to take the head off and on around 3-4 times as I kept forgetting to route the chain guide under, or the bolt dropped down the chain guide thingy. Same for the camshaft, accidentally mixed up the intake and exhaust cams and only noticed that when I went on to turn the cylinder by hand (could have ended badly OOPS). [​IMG]

    Problems I Ran Into

    1. Crank rotation nut cap was damaged after I did my 1000km service from Peter Stevens. To get it out, had to drill that piece off
      1. .[​IMG] [​IMG][​IMG]
    2. Timing chain was kinked when I was about the put the bike back together. Took me a while to get that sorted out.
    3. Not understanding enough Japanese to read the instruction manual to set up the fuel controller. bike couldn't start without setting up (took me 2 days and a heap of google translate)
    • Like Like x 1
  10. I think it's a great idea - modding a bike you already like to improve on it.

    It's funny - a mod like this in most of Asia wouldn't raise eyebrows or draw silly go buy XXX bike instead. Then I am getting sick of looking at new bikes at the moment, there's a 1999 VFR which is speaking to me.
  11. Can you service my 675R please? :)
    • Funny Funny x 1
  12. Could the top end of a Honda CRF450 fit on it? ;-)
  13. Very interesting story and project. How does she feel to ride now?
  14. A heap of difference on the lower end. Seem to be going through the gears much quicker and pulls nicely up until 140ish.
  15. Service will include road tests and require you to leave the bike for a month to ensure everything is ok!. Normal to add 5000km to the ODO. ;)
    • Funny Funny x 3
    • Like Like x 1
  16. [​IMG] [​IMG] [​IMG] [​IMG] [​IMG] [​IMG] [​IMG]

    A nice clean bike and a upgraded sticker to give the extra 10kw.

    Currently, setting up the fuel controller to get the bike running better. Had the bike running too rich initially, but slowing turning it back down to find the perfect mixture. Will report further after the ecu adjusts the ignition timing.
    • Like Like x 3
  17. How do you find the Ixil exhaust? I had the same on my weebee. Nice sound, but for some reason the header pipe they supplied was too small diameter to fit over the exhaust gasket. Ended up using exhaust tape and replacing it every 6 months. Gave me a good chance to closely inspect the bike twice a year :)
  18. Exhaust heat wrap and slotting it over. Seems to be fine for the past few months.
  19. The exhaust heat wrap may tend to burn through like mine - keep an eye on it :) In the end, I used exhaust putty to create a seal, then some extra putty to fill in the slots and finally exhaust tape over the whole lot to ensure an airtight seal. That did the job :)
  20. i would really like to know what setting you used with the fi con2. also what octane fuel is required after installation.