engine won't start, clutch is engaged but wheel spins

Discussion in 'Frame Mounted Engines' started by flyingafro, May 27, 2010.

  1. flyingafro

    flyingafro New Member

    ok so i had this problem starting a few days ago and now im finally having some time to fix it and i can't find anything that has to deal with my problem.
    so the problem is that when i engage the clutch i can tell the clutch is engaged because i can hear the piston move but when i start to pedal on the bike it seems almost like a gear is slipping because i can hear the piston slowly moving. so i thought it was the clutch pads at first so i decided to take off the the clove looking nut and check but compared to others ive seen they look like they are in good condition.
    im not sure if this is a clutch issue but the problem seems to be like a stripped gear or something but honestly have no clue...any help would greatly be appreciated, i start school in 3 days and this is my only way to get there lol
    thank you

  2. AussieSteve

    AussieSteve Active Member

    If your clutch is in good condition and adjusted correctly, then it sounds like you might have sheared one of the woodruff keys. (The little 'D' shaped keys, used to locate gears on shafts, so they don't slip.) There's one on the clutch shaft and, I think, one on the primary gear that drives the clutch. Also, there's another on the countershaft sprocket and one on the magneto rotor.
    Check the one on the countershaft sprocket first, since it's easiest, then the primary drive gear and finally the clutch. You'll need the supplied puller for the countershaft sprocket and the clutch.
  3. Al.Fisherman

    Al.Fisherman Active Member

    First off yes Steve there are only the 4 keys where you said they are. If ever removing the magnet super glue the key in place before installing the magnet. No need on the other 3.

    If the clutch is adjusted correctly and disengaged, and you peddle, the engine/piston shouldn't move. Only when the clutch is engaged (hand off clutch handle) should the crankshaft rotate from the turning of the rear wheel...(talking about a non shiftkit, haven't worked on a bike with a shiftkit.)

    Unless I'm missing something, your clutch is slightly engaged while peddling. To make sure we are talking on the same page, remove the clutch pads and pressure plate and peddle to test. Now you should have NO piston movement at all.

    In your title "engine won't start, clutch is engaged but wheel spins" you have me Buffaloed. What do you mean??? Under NORMAL operations. Disengage clutch (pull on handle), peddle to speed needed to start engine (crankshaft not turning at this point). Engage clutch (release clutch handle), rear wheel rotates chain, chain rotates chain sprocket, chain sprocket rotates crankshaft. Crankshaft rotates magnet, and hopefully supplies electrical power to CDI and then onto the plug. And GOD willing engine starts.
    Last edited: May 28, 2010
  4. AussieSteve

    AussieSteve Active Member

    Ron, if I understand correctly, the problem is that when the clutch is engaged, the engine only turns very slowly when pedalling and not at normal starting speed, indicating slippage of some sort.
    Hopefully flyingafro will clear things up.

    And no, with a shift-kit turning the wheel doesn't spin the engine over, (unfortunately).

    Thanks for the tip about the super-glue. I've heard that it can be a PITA removing the magnet if the key sticks to it. I guess the glue stops that happening.
    Last edited: May 28, 2010
  5. Al.Fisherman

    Al.Fisherman Active Member

    Peddle faster...:)

    You telling me that I can't start my bike going downhill? Anyway of locking the two sprockets together to start? Only way to start is peddle or a pull chord? I use the down hill method for my first start up of the day, then no problem after first start. I guess I need to rig up a way to start the engine with a 1/2" drill or impact wrench:( Exactly why I super glue the key, no problem if it needs to be removed. Super glue isn't what they make it to be, but good enough.

    If that's the case there are only three reasons I can think that can cause this problem. Clutch out of adjustment, sheared clutch key, sheared chain sprocket key, and or clutch drive gear key in that order.
    Last edited: May 28, 2010
  6. AussieSteve

    AussieSteve Active Member

    'Fraid so. It takes a little getting used to, but I'm 50kg and have no trouble.
    I usually pedal-start on the centre-stand, but if you pedal up to speed with the clutch in, then let it out and pedal through half a turn, the engine starts OK. ie Set the RHS pedal at 2 o'clock, then 'kick' to the bottom of the stroke.
    It's surprisingly easy on a hill.

    The rear freewheel stops the wheel turning the motor. If the freewheel wasn't there, the strain of starting would go onto the derailleur pulleys.

    A pull-start might work for you, but with my billet head I'm not sure that I could pull it over left-handed.

    This was one of my main concerns when I bought the shift kit, but in the end it isn't a problem.
  7. t-bone_zach

    t-bone_zach New Member

    more help?

    Okay, so I'm having a very similar problem with my bike. I've been trying to start the bike by pedaling up to about 12 mph with the clutch disengaged, then engaging the clutch. The rear wheel continues to spin, I can hear a kind-of smooth grinding noise (which I assume is the piston moving in the engine?), but the engine does not start.

    There has also been a lot of leakage into the engine, with gas even coming out of the air intake and exhaust pipe. (this is after my gas valve has been ON when I am trying to start the bike).

    I'm a pretty big newbie when it comes to mechanics - I had no idea what this was talking about and had to google it :confused::

    I don't even know where to find the clutch shaft or the countershaft to be able to check them? (but thanks to google, I now know what they are for!)

    I appologize for my lack of mechanical knowledge, but any help would be appreciated

    oh, and my motor is an 80cc boygofast
  8. Al.Fisherman

    Al.Fisherman Active Member

  9. AussieSteve

    AussieSteve Active Member

    A smooth grinding noise indicates that either the clutch is slipping or a woodruff key is sheared. It doesn't sound like the engine is turning over, by your description.
    If you remove the RHS side-cover, at the front there is a small (primary) gear, on the 'crankshaft'. Roll the bike forward with the clutch engaged, (lever out) and watch to see if the crankshaft primary gear turns. If so, the engine is turning over when you try to start it. If the primary gear does not turn, then the clutch or a key is the problem.
    Let us know the result of this test.

    You'll need to resolve this. Remove the carby and check that the float isn't punctured. (If it is, there'll be fuel in it.)
    Also make sure that everything is tight, then clean the carb with fuel and compressed air. Ensure that the float needle seat is clean.
    If it's an NT carb, double-check that the float level is set at 21mm.
    For more carb info, see NT Carb Tuning Basics

    The countershaft is the clutch shaft. It extends from the clutch through the casing to the LHS, where the countershaft, (drive), sprocket is mounted.
    The crankshaft is at the front, going through the crankcase, with con-rod/piston attached in the middle, primary gear on the RHS and magneto rotor on the LHS, under the front side-cover.
  10. t-bone_zach

    t-bone_zach New Member

    When I went out to test this today, I realised that there were a lot of issues I'd forgotten about (I haven't touched my bike for a month or two, I'm just now getting enough free time to work on it again). The first main problem was that, with the clutch DISengaged, it took a whole lot of effort and momentum to get the rear wheel to turn. I had to kind of rock it back and forth to get it "un-stuck", and even after it got going, it would catch every now and then, and I realized that the smooth grinding noise I was talking about in previous posts actually occurs here, with the clutch DISengaged. The "stickiness" is more noticable at lower speeds, or when stopping/starting.

    When I tried to start the engine by engaging the clutch, I was rewarded with a mutch louder, crunchier grinding sound.:surrender:

    I did take off the clutch cover and found the inside in not-so-good condition (IMG 1277.jpg). I scraped out a bunch of junk with a nail and found 10 tiny metal balls amungst it (which I assume need to be replaced somwhere). (IMG1284.jpg)

    I then tried moving the bike again (clutch disengaged), and it was a bit smoother, but the grinding sound persists. This makes me wonder if my clutch is not being disengaged enough with its current setting on my clutch lever. It has been at this setting for as long as I've had the bike, however, and it has never been a problem before. IMG's 1278 and 1279 show the different posistions. I did notice that squeezing the clutch lever only moved the clutch flywheel by about a millimeter.

    Attached Files:

  11. t-bone_zach

    t-bone_zach New Member

    I just figured out what the balls were for. Is there a way to replace those between the clutch gear and clutch hub?

    I've also learned that I need to apply grease to the gears in the trasmission, and maybe to the ball bearing behind bucking bar. Do you think this is all that needs to be done?
  12. Al.Fisherman

    Al.Fisherman Active Member

    Looking at your engine there would be no doubt to me...I would do a complete tear down (that's even if you can do it), and get everything cleaned and lubed. Quite honestly, if you fix your problem and get it started, I don't know how much I'd trust it. Not much I know.
  13. AussieSteve

    AussieSteve Active Member

    I'd recommend a pull-down, clean up and a new clutch and possibly primary gear, depending on just how bad it is.

    I've never needed to remove or replace those balls, but it looks like the top collar is heated then shrunk into place. (Pic below.)

    How did it get so rusty in there? (Laying on it's side in the rain?)

    (Note the rust-pitting on mine - that's how it came from the factory.)

    Attached Files:

    Last edited: Jul 15, 2010
  14. skuzzy

    skuzzy New Member

    How do you disassemble the top collar ring?? to get to the bearings?, Heat and what tool?

    I also need to know how to tighten it, I have been through three clutches that get loose and are about to lose the bearings.???
  15. AussieSteve

    AussieSteve Active Member

    skuzzy, I've personally never needed to do it, but you'd need to (quickly) heat the collar, then turn the assembly upside-down and the collar would fall off, with virtually no help.

    Re-assembling would be harder. you'd need to use feeler gauges or similar to get the correct clearance, then heat the collar and drop it onto the feeler gauges, or a similar method. It'll cool and contract into place. (Like they used to do with wagon-wheels.)
    Not sure what clearance to allow.

    If it's any consolation, they all flop around everywhere when the clutch is disengaged.
    Last edited: Jul 24, 2010
  16. skuzzy

    skuzzy New Member

    Thank you Steve, so it doesn't have a thread to unscrew, it just drops with heat, intriguing, looks like it needs to get very hot for the metal to expand?

    I think its about a 1mm clearance, tight clutch wheels with minimal noise has a 1mm gap, and you aren't supposed to be able to see the bearings, if you can see it, it is too loose and it will be a screamer. I purchased a grubee engine, the clutch broke from first use..

    and I have only had it a few weeks, third clutch now, & a tight engine. Lots of slip, not a tight grab. Lots of pedal pushing on clutch before it starts, but it is completely engaged.

    I investigated it and found the shaft spring was damaged, the nuts holding the spring into place had jumped the thread and stuck jammed in. So engaging never happened until I replaced the shaft. Dodgy shaft

    Grubee clutches use bigger woodroft keys and the keys were loose. I had to change the whole clutch with one that used smaller keys and a tighter fit. But I still have a slippy clutch. It 'slowly' engages when it should just grab and start.
  17. GearNut

    GearNut Active Member

    When pushing the ring gear to one side of the clutch hub (radially) I could see the bearings on the 4 different clutches I have serviced. It is how I get the white lithium grease in there to lubricate the tiny ball bearings.
  18. GearNut

    GearNut Active Member

    By the way, is that engine a Katrina victim? Those transmission gears look like they were in contact with salt water and left to rot. :(
  19. skuzzy

    skuzzy New Member

    LOL ... did you accidentally lose the cover?
  20. skuzzy

    skuzzy New Member


    Yes ...On my good clutch assembly it is tight and noise free, 1mm is healthy, and you can see a small gap where the bearings are from the side when you push. I have a 2.5 mm gap in one I need to fix, I can see the bearings easy. and has death noise.

    Do you squeeze the white lithium grease in with a needle or something?