Onza-Nick

Crank slipping on my Zoot?

18 posts in this topic

So i've been experiencing this annoying problem for a while with my Onza Zoot which usually happens when i'm doing pedal kicks. Sometimes when I kick hard enough, rather than jumping forward there is a loud KLANG noise coming from the chain somewhere and afterwards my chain is slack. At first I thought it was something to do with the crappy chain tug bolts bending under load letting the wheel slip but i've just switched to some Gusset Kojak tugs I bought from Tarty after reading a recommendation on here and it's still doing it so it can't be that. It occured to me when it happened again the other day that it feels like it's happenning at the crank, when I put the power down maybe the crank slips but the chain doesn't move. Could that be happenning or is it something else? I don't know enough about the bike yet to understand what is happenning just from the way it feels. It's really annoying and doesn't give me any confidence in attempting moves at the moment.

So what could it be and how do I fix it?

Help appreciated!

Nick

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If the chain's becoming slack after it happens then it would be pointing to the wheel moving... However if it's just that the cranks are moving without driving you forward that would suggest the freewheel slipping (though this shouldn't really change the chain tension noticeably). This happens when the pawls either don't fully engage in the freewheel or slip allowing the cranks to rotate until the freewheel engages. That's usually accompanied by a bang as you describe...

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Thanks for the response. It’s the slack chain that also made me think the rear wheel is moving but I don’t see how, especially with the new tugs. The noise it makes is also really loud which I don’t think the rear wheel would do. If it’s the freewheel is there anything I can do to fit it. Take it apart and clean it maybe or will something need replacing?

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What components are you using on the Zoot? Is it front or rear freewheel and is the freewheel a screw on one? You can usually take freewheels apart and clean them out, clean up an rework the pawls with a file etc. before lubing with a light oil but (and it's a big but) first you have to get it off which can be a royal pain in the arse!

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It's pretty much standard as far as I know and from what I gather the freewheel is at the front on the zoot.. This would make sense given it feels like it is slipping at the crank. I don't know what type it is through. Is there a guide somewhere about how remove and service a freewheel?

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Stick your phone against a wall and film the drivetrain as you jump on the front pedal. Then you should be able to see what is messing up, if not, post it on here and I’m sure someone will spot what’s up. Even if you think it is the freewheel it’s worth checking to avoid wasting money on parts you don’t need.

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With things like this, it's generally best to try and separate issues off so you know where to look.

If the chain is tight, you hear this noise and then it's slack, the only cause of that will be the rear wheel.  The position of your rear wheel is what dictates chain tension, so it's going to involve that.

If the chain is still tight (or if it's only loose in spots - most freewheels don't spin perfectly concentrically around the BB axle, so you'll often get tight spots or loose spots.  This is especially true with Onza cranks due to the design of the threaded section for the freewheel) then it sounds like it'll be your freewheel skipping.

If the chain is going loose, then your best option is to take your back wheel out, take the axle bolts and washers off and give everything a good clean.  If it's been slipping in the past you might have bits of paint and metal built up on the end of the hub spacers which will stop them gripping the frame as effectively.  The big thing though is to make sure you've got plenty of grease in the axle threads and on your axle bolts.  Dry bolts will often feel like they're torqued up quite a lot before they really are, so putting that bit of grease on will help you get a lot more torque through them which should hold them in place.  If your old tugs broke, that will usually be from the wheel shifting, so it would suggest this is a likely cause.  The wheel suddenly shifting can sometimes make a noise too, incidentally.

For the freewheel, if you've got something like GT-85 you can flush the freewheel out to help perk it up a bit.  Just point the tip of the nozzle into the gap between the outer shell and the centre section of the freewheel (this will be easiest with the bike upside down, and you being on the non-drive side of the bike), and as you slowly rotate the cranks backwards start spraying into it.  If you've got any dirt or similar in the freewheel this can help get some of it out.  From memory, the Tensile freewheels on the Zoot come with some grease in them which will slow down engagement a bit too and make them more prone to skips (as well as being a magnet for dirt/grit) - the GT-85 will help reduce the 'stickiness' of that grease a bit as well.

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I've got an '09 or '10 Zoot, the black and green one. It lives at my Mother-in-laws house in Germany so I only ride it for a month every other year or so, but I've had the same problems. It's still got the stock freewheel, which feels fine. It does have a bit of precession, but no worse than I've seen in lots of other bikes.  I switched to more burly chain tugs just like you, but it didn't fully solve the problem. What I've finally decided is it's the chain trying to climb over a tooth and then slamming back into the trough because the whole rear frame is flexing during a good pedal kick. I'm sure you could film it with a higher speed camera and see it, but I'm fairly certain that's what it really is. I love how light my Zoot is, but that weight comes at a price. Even the newer Zoot Pro frames were pretty lightly built. I plan on replacing my Zoot next trip to Germany. If you figure something else out, let me know too. Otherwise I'll pass my Zoot on to a kid.

Zoot24.jpg

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14 hours ago, Swoofty said:

What I've finally decided is it's the chain trying to climb over a tooth and then slamming back into the trough because the whole rear frame is flexing during a good pedal kick.

 

For the chain to move over a tooth like that (if I read you right) there'd have to be a lot of twisting/flex - you wouldn't need a high speed camera to see it.  The Tensile freewheels aren't the best so if your chain tension isn't altering but you're just getting a skip then it's probably just the freewheel doing it's thing.  If your chain tension is dropping, it can only be the wheel moving in the dropouts.  

 

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On 07/02/2019 at 9:26 AM, Archie H said:

Stick your phone against a wall and film the drivetrain as you jump on the front pedal. Then you should be able to see what is messing up, if not, post it on here and I’m sure someone will spot what’s up. Even if you think it is the freewheel it’s worth checking to avoid wasting money on parts you don’t need.

I'll see if I can do this at the weekend if I have time and the weather isn't too bad.

 

 

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On 07/02/2019 at 11:37 AM, Mark W said:

If the chain is tight, you hear this noise and then it's slack, the only cause of that will be the rear wheel.  The position of your rear wheel is what dictates chain tension, so it's going to involve that.

If the chain is going loose, then your best option is to take your back wheel out, take the axle bolts and washers off and give everything a good clean.  If it's been slipping in the past you might have bits of paint and metal built up on the end of the hub spacers which will stop them gripping the frame as effectively.  The big thing though is to make sure you've got plenty of grease in the axle threads and on your axle bolts.  Dry bolts will often feel like they're torqued up quite a lot before they really are, so putting that bit of grease on will help you get a lot more torque through them which should hold them in place.  If your old tugs broke, that will usually be from the wheel shifting, so it would suggest this is a likely cause.  The wheel suddenly shifting can sometimes make a noise too, incidentally.

For the freewheel, if you've got something like GT-85 you can flush the freewheel out to help perk it up a bit.  Just point the tip of the nozzle into the gap between the outer shell and the centre section of the freewheel (this will be easiest with the bike upside down, and you being on the non-drive side of the bike), and as you slowly rotate the cranks backwards start spraying into it.  If you've got any dirt or similar in the freewheel this can help get some of it out.  From memory, the Tensile freewheels on the Zoot come with some grease in them which will slow down engagement a bit too and make them more prone to skips (as well as being a magnet for dirt/grit) - the GT-85 will help reduce the 'stickiness' of that grease a bit as well.

The chain is deffinately slack after it happens as that's why I assumed it was something to do with the weak chain tugs to begin with cos I kept having to adjust them. The problem with the old tugs was that the threaded part and the washer section where the axle bolt passes through were 2 seperate pieces, the threads kept bending where they join the washer. However these new tugs are 1 piece but it's still happenning so I guess they wern't the root cause in that case.

If I get time at the weekend i'll take the rear wheel off and have a look.

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15 hours ago, Swoofty said:

I've got an '09 or '10 Zoot, the black and green one. It lives at my Mother-in-laws house in Germany so I only ride it for a month every other year or so, but I've had the same problems. It's still got the stock freewheel, which feels fine. It does have a bit of precession, but no worse than I've seen in lots of other bikes.  I switched to more burly chain tugs just like you, but it didn't fully solve the problem. What I've finally decided is it's the chain trying to climb over a tooth and then slamming back into the trough because the whole rear frame is flexing during a good pedal kick. I'm sure you could film it with a higher speed camera and see it, but I'm fairly certain that's what it really is. I love how light my Zoot is, but that weight comes at a price. Even the newer Zoot Pro frames were pretty lightly built. I plan on replacing my Zoot next trip to Germany. If you figure something else out, let me know too. Otherwise I'll pass my Zoot on to a kid.

Exact same bike (mines also black and green)  and same problem by the sounds of it! I also live in Germany but I can't imagine that has anything to do with it :lol: Do you also get the KLANG noise when it happens and is the chain slack afterwards?

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1 hour ago, Onza-Nick said:

The problem with the old tugs was that the threaded part and the washer section where the axle bolt passes through were 2 seperate pieces, the threads kept bending where they join the washer. However these new tugs are 1 piece but it's still happenning so I guess they wern't the root cause in that case.

The Gusset tugs are definitely stronger so they won't break like the standard Onza tugs, but it'll just be the rear wheel slipping being the root cause.  Basically, M6 bolts are pretty small and need a lot of torque to really hold everything in place.  If you try and screw in an axle bolt to most trials hubs by hand you'll feel quite a bit of resistance or friction (when shooting photos of hubs at TartyBikes I'd usually need to mess around with bolts, and quite often I'd have to dick around with allen keys and spanners to move bolts in hubs, and that is using a brand new bolt in a brand new hub - just without grease).  If you add to that the tension naturally ramping up as you tighten the bolt it means that bolts will often feel tight without necessarily being tight.  Using grease helps out more than you might think - as shown here: https://www.engineeringtoolbox.com/torque-lubrication-effects-d_1693.html

It's just something that happens with M6 axle bolts and horizontal dropouts.  It's why for comp style bikes with snail cams most riders will go for notched snail cams as they are much harder to make shift or slip compared to chain tugs or smooth snail cams.

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Well I feel pretty stupid now :blink:

Managed to get the rear wheel off today and this is what I found:

Sprocket.jpeg.8ef45b98f22b5502bfe2b01301728e35.jpeg

As you suggested Mark the contact points of the hub spacers are pretty clogged up which can't help much with them gripping the frame. However whats more worrying is I seem to be missing 3 teeth from the sprocket! Don't know why I didn't check that before.

So looks like I need to get a new rear sprocket. Any ideas how I get this one off and any suggestions on a good replacement?

Nick

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And the rest! I count 5 missing/very worn teeth! 

From about 1:30

 

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Thanks for linking the vid! Problem is i'm living in a flat at the moment and don't have access to a workbench or vice. Is there any other ghetto method to get the sprocket off? Tried with a chain whip but think that's a lost cause with it screwed on so tight. If all else fails i'll have to get the local bike shop to do it but i'd rather manage it myself if I can.

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I think you'll struggle without a vice I'm afraid! Not unless you get adventurous with a dremel/angle grinder and sacrifice the sprocket (which is dead anyway) to get it off. You'd be risking damaging the hub though so probably asking nicely in Halfords if you can borrow their vice I'd say!!

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If you cut enough teeth off on both sides you can use a real wrench to get it off. I've tied the wheel to a street sign post to hold it steady before and then go at it with a wrench and breaker bar. Viel gluck!

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