GEBE Clutch slipping?

Discussion in 'Rack Mounted Engines' started by SpeedyG, May 5, 2007.

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  1. SpeedyG

    SpeedyG Guest

    So, I thought it was maybe a combo of an old belt plus a wheel that was out of hop but...

    I got my regular wheel back from the bike shop today after YET ANOTHER busted spoke (6 since the new year)... same problem.

    I hadn't noticed any problems before I was limping on the out of whack replacement wheel I was using. It 'feels' and 'sounds' like the belt slipping, kind of a grinding/slipping during high torque moments. Starting up and gaining speed and uphills. I can make it happen if I goose the gas on the flats as well... I checked the belt, looks fine... I checked my drive spline and clutch drum spline and those seem ok... Inside the drum is shiny and the clutch shoes have a bit of shine as well.

    So... you think I'm right about this? Anyone have any problems w/ their clutch (or other drive train slippage) before?

    I'm gonna just replace the clutch shoes and spring but as I just sunk $250 into a new rear wheel (byebye busted spokes) and an upgrade to the HTD system it's gonna be a hot sec before I can drum up some more funds. If it's the clutch I'm not concerned about riding it 'till it dies. However, if anyone knows that this may signify something different and potentially dangerous to my motor please let me know.

    I'd love to hear some feedback just to get some ideas and/or reassurance.

  2. Torques

    Torques Guest

    Is the system new, motor and drive system?
  3. Hive

    Hive Guest

    Could be a couple things

    Speedy and Torques,


    1.) The 25 cc motor uses small clutch assy, even going up hills may require pedal assist and if bike is geared, the proper gear engaged. Takes about 2000 hours to break-in. Best combo would be large clutch and 25 cc motor, but not made that way???

    Be sure the engine sits so the belt tensioner or idler wheels do move belt inward a lot. You can raise or lower engine with washers -stainless are thinner.

    You can also move the drive gear out with SS washers.

    2.) The engine and clutch will not take kindly to torqy or quick starts.

    In fact, it gets harder as engines grow larger. A 40CC Tanaka might rip the 14 ga. spokes out on a rabbit jump.

    If the belt slips you might feel it and will see some rubber on the ring. If the clutch slips, you may feel it but not always. The engine has more power than the clutch can handle with these neat 25cc engines.

    Typical spokes are 14 ga, maybe twelves are better but requires drilling of hubs etc.

    Ease the effort pedaling a bit to give engine a nudge and gradually get to speed. You are on a bicycle not a motorcycle and need no failures of light bike equipment or spills to put you in the tombs.

    I have one-speed cruiser and the little Honda GX25 is great, but needs help on hills. No rapid starts. With gearing, hills should be tamed. You just cannot gun-it and going up hills needs assist.

    Lots of riders run the engine and pedal at same time, but that is not what you seem to be doing, but it does not matter as long as you know limits. You have toget a "feel" for the interplay between motor and acceleration.

    The engine will get better - more power - as you ride.

    Call GEBE and ask Dennis for advice.
  4. Torques

    Torques Guest

    Re: Could be a couple things

    Did you mean to say "do NOT move belt inward a lot"? The way you say it is that there should be a lot of slack so that when the tension roller is engaged, it should move a greater than lesser distance. Can you clarify this? Thanks in advance.
  5. Hive

    Hive Guest

    My meaning was correct

    Should have been more clear.

    I had similar problem when I first ran motor, called Dennis, and we determined the tensioner should be more to its end or up, in its spring unload position, meaning more bend in belt.

    Ran a bit better after that.

    Forgot to mention that I used the standard gear for the 25cc motors, and that the others are not much better with small clutch engines on hill.

    Higher gear ratio may also increase spoke pressure.

    Easy does it, 'til motor breaks you in.
  6. SpeedyG

    SpeedyG Guest

    Re: Could be a couple things

    OK, you're both confusing... closer to 1 o'clock or closer to 11 o'clock? I'm right around 12 o'clock now.

    This is NOT a new engine, It does have new rings... plus it has the old school XT drivetrain... upgrade to HTD iminent...

    I'm worried that with the new 'more effecient' system I will just wear out the clutch that much faster...
  7. Hive

    Hive Guest


    Under full tension, the rollers will push the belt in so belt forms a decided zig zag and the knob, I replaced with a SS acorn nut, is pulled down (forward) by the spring tension and it will flex as belt eases and tightens to keep tracking.

    Say the belt should be pushed to point straight down toward 6 o'clock (belt pointing downward to 6 o'clock) seems right, maybe a hair more. When I first installed, I boosted motor with SS washers and it was too high. I thought the tensioner should have only pushed the belt a little, but not according to Dennis.

    Also, if the belt is on a bias on the gear, it might wear prematurely on one side or not make full contact with the gear.

    HTD or older variety, the idea is not to hammer the throttle so much as a happy medium between the pedals and the engine to get it going and once going, still not run it up too fast. The small clutches have but two shoes and the little motor easily out powers it. Like I say, if the 25s had large clutches, a perfect world weight to power, but not so.

    Maybe the HTD is harder but if the old gear does not show signs of wear, why change it? Same for belt.
  8. SpeedyG

    SpeedyG Guest

    ok, something is definately slipping... I'm past believing it's the clutch or the belt and I think it must be in the drive shaft... I'm definately gonna have to just be gentle because I know not where to find replacement parts for that...
  9. Hive

    Hive Guest

    Slipping stuff

    can be hard to figure out.

    I take it you believe the drive shaft is slipping but that might only happen if its connection to clutch is not proper, but I know little about engines per se and cannot comment. It just seems that the drive shaft connection is straight forward and should not be slipping as I thought it is one piece to clutch.

    If you were gunning it a lot, it might be that the clutch shoes are worn and that the face they contact is also worn. Might be good idea to remove and look over or have small engine guru check it. Could be as simple as nothing wrong, needs shoes or shoes and clutch housing.

    If engine runs well, has to be something like that. These engines take a long time to wear out or break. If they do, you know it right away.
  10. SpeedyG

    SpeedyG Guest

    Ok, first I want to thank you for hanging in w/ me on the advice and my horrible descriptions... I'm going to explain my conclusions about the clutch and then hopefully better explain what I think the actual problem is...

    Ok, it can't be the clutch... because:

    Well, I decided that my clutch shoes and drum just aren't worn out so I spent some time just staring at the mechanism and it occurs to me that a centrifugal clutch really only has 2 states... engaged (flung out) or disengaged (retracted to center)... The spring provides variance and smooth retraction.

    To me, it seems like worn shoes would manifest as continuous slippage, probably getting 'slipperier' as more throttle is applied. Further, I have power and torque required to start from near dead stop with no 'slipping'.

    This is the time I would expect the clutch to start showing if it has problems because the engine rpms are still relatively low and there is less force to actually spin the clutch shoes out but, no probs...

    If the spring was worn I would expect clutch engagement to just occur really suddenly, and I expect it would put audible stress on the motor (perhaps even shutting it down)...

    Also, I ruled out the belt because there's not rubber dust everywhere.

    What I think it is:

    I didn't mean 'drive shaft' I guess, not the one that comes directly out of the motor and attaches to the flywheel/clutch plate. I mean at the other end of the drive line... The gear that drives the belt is attached to a spline. This spline inserts into a ??? Sleeve? Shank? I'm not sure what to call it but it is attached to the back side of the clutch drum, and I think this "part with no name" is what is failing...

    Emperical data in review:

    This happens when I try to give too much throttle at the top end... I could be moving at 15mph with my bike in the middle chain group... if I try to speed up and get into the throttle it will start 'slipping' and making a grating noise. If I switch to the bigger chain group and pedal just a little it will speed up a bit but, again, there will be a limit as to how much throttle I can give it w/o slippage... If I am heading downhill this is no problem and I continue to pick up speed on the backed off throttle, I can also add more throttle little by little (up to a point). If I am heading uphill it is definately causing a problem. Speeds up hills that used to be 25mph all day long are now down around a labored 18mph... asking any more provokes the slip.
  11. Hive

    Hive Guest


    And I believe I understand what you are describing. Very likely and I never thought that part could fail, but there it is.

    If that is case, maybe call Julia or Dennis at GEBE cause you might have a warranty problem, or they will tell you what problem is. They are very nice and know their business. If I get it, you are saying the spindle the gear is on is buzzed, meaning that dark portion just inside the gear, right?

    I uploaded pic of gear and clutch assy. Maybe they will send new assy...?

    It also just occurred to me that if one (or parts of both) shoe is broken, that may also cause grinding and slippage, but...

    Might remove from motor and take a look before you call, just to have all the answers.

  12. Torques

    Torques Guest

    I like the nut on there, lol, I might do something like that.
  13. Hive

    Hive Guest

    Yourefer tothe acorn

    It is easier to manipulate and small...
  14. locoWelder

    locoWelder Guest


    OOooo I see whats wrong, You've got no belt :grin:

    sorry I just had to :razz:
  15. SpeedyG

    SpeedyG Guest


    you've got a much more compact driveline... my motor has the long goosey looking grey part that sticks off the motor as seen in the picture above. I wish I had a compact clutch assembly like yours!
  16. Hive

    Hive Guest


    That is the assy that is used with the 2-cycle motors GEBE first introduced with their kit, Zenoah. The Tanaka, Robins and others all use the one you see in the above pics.

    "No belt!" - Good one! Funny!
  17. Torques

    Torques Guest

    I was starting to wonder about that too when I saw that pic. I will have the eho25 complete drive system here on Wednesday to put on a 15 speed bicycle. I am looking forward to see how that performs.
  18. gone_fishin

    gone_fishin Guest

    a wheel and clutch saving thread for me.

    to me, break-in is about engine runtime and not miles on the bicycle. i have plenty of time, so i'm taking the load off the bike and the tiny clutch i obviously have to get used to...looks like i got more of a mellow cruiser now, instead of a smoky-bandit, but i think i can endure that hardship ;)

    i changed to the #12 as soon as i searched "clutch slip" in the rack-forum and read this thread.
  19. Spokes and Clutch

    First of all SpeedyG, you are not alone with the spoke breakage issue and GEBE. I have had the same problem, and I can't honestly say if I've solved it yet. I just recieved my rebuilt rear wheel, consisting of a Sun RinoLite rim, a Shimano hub, and 10 guage spokes from "The Wheelmaster" in Auburn, WA. I have only put a little over 200 miles on these heavy spokes. My 14 guage spokes lasted maybe 2 weeks without breakage. Only time will tell. I think it takes time to find all the bugs in any kit. It's funny you should mention the clutch slipping, because I just called to price clutch shoes, and spring for my Robin Suburu 35cc. I think the clutch is already starting to slip a little with 500 miles on the motor. I feel that this is largely due to my weight, (over 350lbs), and the fact that I hadn't figured out just how to use my Eagle until recently. GEBE has only one gear, and that is "high". YOU have to "be" the low gear by strongly assisting the engine by pedaling, and maybe even shifting gears until the bike reaches around 15 mph, and then the engine is at an acceptable rpm to continue accelerating under it's power alone. Once you master this smooth transition from muscle to motor, you will experience much less wear on the clutch, and engine....not to mention less stress on the spokes from overtorquing the drive ring at speeds too low for the motor to handle alone. Remember that any peddling you do, is that much less flexing your spokes will endure under the torque of the drive ring during acceleration to your desired speed. At any rate, Good Luck.