BMW G650 cam swap?

Discussion in 'Thumpers' started by Crisd, Nov 10, 2013.

  1. Crisd

    Crisd Adventurer

    Joined:
    Mar 14, 2013
    Oddometer:
    14
    Location:
    NC
    Hi all, well some of you will get this, most probably won't. About four years ago I bought a BMW G650 and rode it from the dealership to the garage and stripped it down to about a 100 or so parts, the proceed to use it as my donar bike for a replica 1939 Dresch motorcycle. Four years later and the bike is done (the story of delays would take pages). But now I want more power. I already did the Power commander and obviously custom exhaust and intake. I'm thinking a better cam might be in order... any one have any thoughts or input? If you want to see the bike look on You Tube and type in Dresch test ride. I just tried to paste the link but this site is not letting me.
    Thanks, Cris
    #1
  2. Crisd

    Crisd Adventurer

    Joined:
    Mar 14, 2013
    Oddometer:
    14
    Location:
    NC
    Is there anything?
    #2
  3. motorrat

    motorrat Been here awhile

    Joined:
    Mar 21, 2012
    Oddometer:
    182
    Hiya Chris!
    Nice bike!

    maybe pop your question here, http://advrider.com/forums/showthread.php?t=290240

    But I havn`t heard of hot camshafts for the G650X,

    I could imagine that your bike gained some weight, and topspeed isn`t where youre after, so replace the 47 rear for a 49, or swapping the front 16 for an Xchallenge 15 sprocket would be the simplest way to enhance acceleration.
    I`m staying away from 14 sprockets as they don`t fit to well on the driveshaft.

    <iframe width="420" height="315" src="//www.youtube.com/embed/HIM1FFGVs-U" frameborder="0" allowfullscreen></iframe>
    #3
  4. Crisd

    Crisd Adventurer

    Joined:
    Mar 14, 2013
    Oddometer:
    14
    Location:
    NC
    Thanks for the suggestion, I think I'll try the bigger rear sprocket, more surface area and teeth in contact with the chain helps spread the load and the chain will last longer.
    Also, thanks for pinning the link to my bike, how did you do that?
    Cris
    #4
  5. oldxr

    oldxr Long timer

    Joined:
    Jan 28, 2007
    Oddometer:
    1,170
    Location:
    central komifornia
    Somewhere I heard the g650 was a rotax 650 -if so try here http://rotax.net/ or Web Camshafts or Megacycle Cams.
    #5
  6. motorrat

    motorrat Been here awhile

    Joined:
    Mar 21, 2012
    Oddometer:
    182
    Hiya Cris, dunno if the 49 chainwheel is widely available on your side of the pond, I got it from www.bashplates.de
    changing the sprocket by 1 tooth will give you an even shorter gearing.
    (1 tooth less up front is 3 more at the rear)

    don`t take it as an offence, but you are not exactly reving it, and it is due to the low down torque character of the Rotax that it is still smooth sailing along.

    At 53 with tinitus, I allways ride with earplugs, the very exceptional occasion I ride a minute long trip without, the shear noise prevents me from turning the throtlle, so, my choice would be an OE 15 frontsprocket and earplugs:pynd

    about the link, somewhere under your youtube movie there is shearing and "enclosure" c/p that here (i`ve got the Dutch translated version so don`t know if the are the exact terms)

    15 X 47 here, mostly 3 gear
    <iframe width="420" height="315" src="//www.youtube.com/embed/uy3t4Dv-QyI" frameborder="0" allowfullscreen></iframe>
    #6
  7. Crisd

    Crisd Adventurer

    Joined:
    Mar 14, 2013
    Oddometer:
    14
    Location:
    NC
    Hi Marius,

    In the video my father was riding the bike and was going quite slow and easy. Later in the day I raced a Harley and he blew me away :( I am not looking for top speed, I just want to be able to beat Harleys from a dead stop at a red light to about 50mph.
    I will need to experiment with gearing, but want more power as well. Because the bike shifts by hand controls, I'm interested in being able to get the most I can in a single gear because once I remove my hand from the throttle to shift... the race is over. Being able to rev it to the red line will be a requirement obviously.
    #7
  8. michael1968

    michael1968 Long timer

    Joined:
    May 20, 2009
    Oddometer:
    1,092
    Location:
    Newcastle, Australia
    There are a few rotax tuners around, try looking for tuners of the DS650 quad. The engines aren't exactly the same but I believe the cams are.

    You could also try getting some cams out of a Husky Terra, same engine but a few more hp, they upgraded the cams and fitted larger valves. FYI from a performance perspective the valves are a little small in the BMW 650s, they could do with being about 2mm larger.

    Cheers,
    Michael
    #8
  9. motorrat

    motorrat Been here awhile

    Joined:
    Mar 21, 2012
    Oddometer:
    182
    For "sprinting" maybe a recluse clutch and shifting left handed?

    I beat the HD 850 Iron roadster thingie easily
    But Harley`s can be decivive, their owners only joy can be from outsprinting seemingly faster opponents, so they spent huge amounts on tuning

    @Michael, usefull info, knew the terra has some more horses, 58 I thought.
    #9
  10. Crisd

    Crisd Adventurer

    Joined:
    Mar 14, 2013
    Oddometer:
    14
    Location:
    NC
    Michael,
    I just looked up your suggestions. ... excellent info, just what I needed! I have a machinest that is going to do a valve job using the Husky valves and cam swap. Unlike the higher Husky compression, it will remain stock. I am however contemplating a small nitrous bottle under the tank cover doing a dry nitrous install.
    #10
  11. itsatdm

    itsatdm Long timer

    Joined:
    Jun 19, 2004
    Oddometer:
    5,433
    Location:
    Nor Ca.
    You might want to check the ignition advance of the Terra to compare with your bike. Usually there is earlier advance with hotter cams. If so, there is a way to advance the cams using stock ignition.
    #11
  12. Crisd

    Crisd Adventurer

    Joined:
    Mar 14, 2013
    Oddometer:
    14
    Location:
    NC
    I'm not quite following you. Are you saying that I have to use the Husky ignition because it uses a timing curve that is more aggressive than the BMW because the cams are ground differently or if I use the Husky cams there is a way to advance the BMW timing using the stock BMW ignition? I don't understand what you mean by saying I can advance the cams using stock ignition. Are you saying that the Husky cams them selves are not different but rather they are merely advanced in the Husky along with the timing there fore just advance the BMW cams and ignition?
    Thanks - Cris
    #12
  13. itsatdm

    itsatdm Long timer

    Joined:
    Jun 19, 2004
    Oddometer:
    5,433
    Location:
    Nor Ca.
    I am saying the ignition timing curve could/probably is different between the bikes. The cams are going to have different advance, duration and overlap.

    Using the Terra ECU might work, but it also controls fuel injection, both timing and the amount.

    One way to change cam timing is to rotate the cams in relation to the sprocket to mimic Terra timing. You do that by elongating the cam sprocket bolt holes. Some popular street bikes have aftermarket sprockets available to do that.

    You won't find one for the 650 Rotax, so it is a DIY project and requires some knowledge and a degree wheel.

    Until you find out what the ignition curves are, it is supposition.
    #13
  14. Crisd

    Crisd Adventurer

    Joined:
    Mar 14, 2013
    Oddometer:
    14
    Location:
    NC
    OK, I get what you're saying now. I am unfamiliar with the internals of the Rotax engine and what the cam gear looks like but I have machinist skills and the facility to make those kind of modifications to existing parts. If a completely custom gear must be made I'll have to farm that out.
    If BMW uses the SAE J I can use a Crane adjustable ignition box, which will also come in handy if I decide to use nitrous.

    Knowing that taking the bike away from my father to tear it apart will be like taking chocolate cake away from a fat boy, I may hold off on doing the valves, cams, and adjustable cam gear and just do the adjustable timing right now since that is fast and easy. Besides doing dyno runs are fun and I can talk him into doing that. I'll have to wait to tear it apart when it's stripped down in order to paint it.
    In the mean time, I'm going to contact Crane Cams to see if they might have any interest in making me some custom cams tuned for my specific desires (Zero to 60 single gear drag runs.)
    #14
  15. Crisd

    Crisd Adventurer

    Joined:
    Mar 14, 2013
    Oddometer:
    14
    Location:
    NC
  16. aprilian

    aprilian Can I change this?

    Joined:
    Feb 20, 2009
    Oddometer:
    480
    Location:
    MinneSNOWta
    I bought strada cams and they have a longer throw which I feel would create an interference fit :eek1

    preliminary investigation indicates that the Husky vales are shorter stems to go along with the longer lobes and the piston crown may be different too.

    try daniel crower cams for a drop in for your engine. http://danielcrowerracing.com/i-5912880-bmw-rotax-g650.html
    #16
  17. aprilian

    aprilian Can I change this?

    Joined:
    Feb 20, 2009
    Oddometer:
    480
    Location:
    MinneSNOWta
    Update, I measured the Husky lobe sizes and depsite the BMW marketing material, they have the same throw as the 2007 BMW cams :cry I have sent them off to a cam specialist to see if the duration or overlap are different, I can't measure that with my home tools.


    #17