STIHL ms650- 84.5cc 6.4hp 13000rpm need help with gearing

Discussion in 'Introduce Yourself' started by floppyBiker, Jul 3, 2010.

  1. floppyBiker

    floppyBiker New Member

    hey all name is Matt from memphis i am working on my first motorized bike
    STIHL chainsaw engine---woooo
    riding lawnmower gas tank
    stater off of 3 wheeler on crank ??
    Gary fisher marlin M.B. 26" rims
    I have a final drive ratio calculated with my gear reduction(11tooth on engine to largest chainring gear on crank and smallest chainring on crank to largest on rear casette gear... 11t-44t-22t-30t final drive ratio = .34-1 i have no idea how to calculate my top speed at 13,000 rpms with this gearing...
    any help would be greatly apppreciated

  2. professor

    professor Active Member

    Hi Floppy, welcome to Motoredbikes. Don't know about the gearing, most of the kits are around 20 to one with the two stroke engines.
    Please rig up a muffler on it, the less people that are annoyed at us - the longer these things will be legal.
  3. unior

    unior Member

    where'd you find the engine?
  4. unior

    unior Member

    you have the entire saw?
  5. floppyBiker

    floppyBiker New Member


    definitely putting a muffler on it ... im using one off of my honda 125m three wheeler--- it will whisper to the wind...
    i bought an entire chainsaw for 500$-- i know its alot of $ but it is a 1000$ saw new and it has been used 5 or 6 times... so it is a brand new engine barely even broken in... no problems with reliability or power, its why i went with a stihl... after all they are the best saws on the planet.. i just posted on craigslist in the want to buy section and told a bit about what i was doing and a guy called me three days later, and drove to memphis to meet me with it.... i love craigslist, no bank accounts necessary
  6. unior

    unior Member

    Thats cool man I was researching all the stihl saws last night. I agree with the professor though keep it quiet and we'll all benefit. 6.4hp is a lot of power for a bicycle lol.

    You should run that sucker through a log or two before you tear it apart also heh. Post vids.

    TREEWK Member


    Welcome And Have Fun. Recently Retired From My Tree Service Business Of Over 30 Yrs. Have Well Over 20 Good Saws, For Professional Work Sthil Is #1, Husky #2 Imho. I Have That Saw. Very Expensive For A Motor Bicycle And Maybe Dangerous!! Wow Lol. Hang-on!!

    I Think Your Gearing Is Close. I Have A 34 Tooth On My Rear Cassete, That Really Helps. Just Recevieved A 38 Tooth Cassete Off Ebay, Not Needed But Would Be Ok In The Woods. Good Luck With Your Build. Have You Checked You Tube Vids? Some One Posted A Pretty Good Saw Mount A While Back. Ron
  8. tjs323626

    tjs323626 Member

    Hi Matt,

    Good luck with your build. That engine may have you flying down the road. It sounds like it's too much for a bicycle frame. I think you will need more reduction than what you have planned. From your post it sounds like you only have about 5.45 ratio. You would need to at least double that or more to keep from bogging the engine. with a 12 to 1 ratio at 13000RPM's you would be doing about 80MPH- That is way too fast for a bicycle. I'm not saying it could actually go that fast. There are other factors involved wind resistance being the biggest of them. I have hit over 40MPH on my bike, but only do that in rural areas where it's safe to do so. The stopping power of your bike brakes must be considered. Make certain your insurance is paid up to date and good luck!
  9. plinko

    plinko Member

    Better watch It bro

    I love creativity and building bikes with chainsaw engines also.But I am gonna give ya 2 words of warning.First,In tennessee and some other states anything over 49 cc requires license,registration,tags,Insurance,and so forth.And In some states none of this Is required for anything under 50 cc's.You are looking at trouble with the law with this Idea If you don't have a license for a motorcycle.don't believe me?check out the dmv website on mopeds and motored bikes. Secondly and more Importantly,I have built 3 bikes now with the cheap 80/66 cc kits around 3 to 4 h.p. and I just had a rim Implode with spokes all over the place and a crack In my frame after 4 months of service.Make darn sure you got a seriously heavy duty frame and some really solid rims or you may be looking at the ICU unit or morgue.Many style wheels and frames are from chinese made schwinns and so forth and adding a 13000 6.4 h.p. motor In excess of 25 lbs with vibration out the yin yang Is way too dangerous to put on a cheap bicycle frame.Good luck to you.I am only saying this from experience and a few broken teeth and cracked bones.Build It right or don't build It at all.Not worth getting hurt or killed over.And btw,I lived In knoxville Tn for 5 years.
    Last edited: Jul 4, 2010
  10. plinko

    plinko Member

    In short!!!This Is your first build and no offense.But what you are building Is a recipe for disaster and being your experience Is limited on these.A very bad semi-dumb Idea.Please reconsider or at least enlist some help from some motorcycle mechanics or people who have built stuff like this before. and have them look over your build and help out.Seriously,There Is reason why most bicycle engines are 49/66 cc and limited to speeds of 30 to 40 mph.And even then you better have a quality frame and some seriously well made wheels Instead of the 14 or 12 gauge china junk quality rims.These guys are not thinking about your safety and should have said something way before I did.Sorry If I offended anyone here.But,Someone has to say something about this potentially dangerous contraption.Especially considering It's his first build and he's a newbie.Way dangerous and way Illegal.Ideas like his Is gonna cause this once fine hobby to be Illegal or require all kinda paperwork and registration and licenses.Or worse,get someone killed or crippled.
    Last edited: Jul 4, 2010
  11. TREEWK

    TREEWK Member


    You Are Correct, I Hinted At The Same Thing. A Post After Mine Also Did.

    Plus Saw`s Are The Worst To Look At Or Resale. I Wish Him Luck And Fun, But Hope He Sells The Saw For More Suitable Power.

    When You Are A Newbe It Is Hard To Decide Which Path To Take.

    The Old Saying Is Always Good Advice!!

    "When In Rome, Do As The Roman`s Do". It Is Hard To Go Wrong When You Do That. Hope He Stays Enthused!! Ron
    Last edited: Jul 5, 2010
  12. unior

    unior Member

    Gear it for 60, a balance between speed and torque ripping apart you wheels, frame, etc.

    He has been warned now it's his decision to make lol.

    Although dude, you could resell that saw for a lot of money, profit and purchase a 4-5hp gp460 or 2 for that matter. The value of the saw will be greatly reduced once it's in pieces.
  13. G-Superior

    G-Superior Member

  14. 5-7HEAVEN

    5-7HEAVEN Guest

    I agree. The GP460 engine will bolt onto any aftermarket drive systems available. If you're hard on it, this engine might rip thru tires, break belts, chains, etc.

    The 460 engine's weak link is its narrow power band. Once you learn to harness it, you'll have a VERY powerful setup.:bowdown:

    Not as reliable as the Stihl, though.
  15. aero07

    aero07 Member

    using gear rat this gear set up would put you doing 184.4.mph @ 13000rpm
  16. 5-7HEAVEN

    5-7HEAVEN Guest

    Your final ratio is 5.45:1, which is unusable. Not going anywhere, and your clutch will burn out. You need an additional 5:1 gear ratio, which would place 1st gear at 27.27:1, which is okay for starters.

    That's the disadvantage of using uncommon engine powerplants. You need at least two jackshafts to attain proper gearing, especially if you intend to wind up that engine to 13,000rpm+. Let's gear it to max out at 50mph at 13,000rpm::detective:

    1. Use 9-tooth engine sprocket to 36-tooth sprocket on jackshaft = 4:1.(SBP parts, bicycle chain)

    2. Use 11-tooth sprocket on jackshaft and 76-tooth sprocket on drive ring= 6.91:1.(Pocketbike parts, strong 8mm chain)

    3. 4 X 6.91 = 27.64

    4. 22/30 = 1.36(Your bike chainring and cassette-1st gear)

    5. 27.64 X 1.36 = 37.6:1.(Brutal acceleration!)

    6.6th gear sprocket is 16-tooth. 22/16 = .73:1; 27.64 X .73 = 20.18:1.....

    7. 6th gear is 20.18:1

    In 6th gear, 50mph @ 13,000rpm.

    7th and 8th gear is for cruising at highway speed.

    Now you're SMOKING!:jester:

    Unsure if bike chain and cassette will withstand this awesome power.

    You need to jump into the forum for more feedback on this!
    Last edited by a moderator: Oct 15, 2010