Front chain ring won't turn when pedaling

[MattyMcC]

Hi,

I just got a new adult tricycle that is an 8-speed. It only has one chain ring in the front, no derailleur, and the gears are in the back. I assembled it and at first, it was working fine but then the bike stopped moving when I pedaled. I noticed the crank arms move but the front chain ring does not. It will however move if I pedal backyards. Any idea what it could be? I assume it is something loose in the bottom bracket.

[liam122]

HI! Based on the information you've provided, it sounds like there may be an issue with your front derailleur or chain. If the chain is not engaging properly with the front chainring, it may be slipping and causing the crank arms to move without turning the chainring.

It's also possible that there is a problem with the bottom bracket, such as a loose or worn-out bearing. In this case, the crank arms may be moving freely without properly engaging with the chainring.

To diagnose the problem, you may need to inspect your bike more closely. Check the front derailleur to make sure it is properly aligned and adjusted. Inspect the chain to make sure it is not excessively worn or damaged. You can also check the bottom bracket to make sure there is no play or unusual movement.

If you're not comfortable performing these checks yourself, it's best to take your bike to a professional bike mechanic for a proper diagnosis and repair.

[Sybian]

(04-12-2023, 01:00 PM)liam122 Wrote:  HI! Based on the information you've provided, it sounds like there may be an issue with your front derailleur or chain. If the chain is not engaging properly with the front chainring, it may be slipping and causing the crank arms to move without turning the chainring.

It's also possible that there is a problem with the bottom bracket, such as a loose or worn-out bearing. In this case, the crank arms may be moving freely without properly engaging with the chainring.

To diagnose the problem, you may need to inspect your bike more closely. Check the front derailleur to make sure it is properly aligned and adjusted. Inspect the chain to make sure it is not excessively worn or damaged. You can also check the bottom bracket to make sure there is no play or unusual movement.

If you're not comfortable performing these checks yourself, it's best to take your bike to a professional bike mechanic for a proper diagnosis and repair.

I am not sure what is going on here, but the owner specifies that the bike is new without a front derailleur, and it only has a single chainring. I doubt there is enough wear on the chain to be a problem; and obviously with a single chainwheel a front derailleur problem is nonexistent.
I cannot wrap my head around this since it would be more than obvious if the chain was not engaging the ring teeth, and the chainring/chainwheel, crank arm spider, and bottom bracket spindle should all be mechanically connected regardless of pedalling forwards or backwards. Is there some sort of clutch or slip differential on this trike?
If the pedal (I assume crankarm) is moving when pedalling forward, but the chainwheel does not then I would assume that chainring/chainwheel is slipping on the spider. I have no idea how because the same thing should happen when backpedalling. This is very confusing since the front connectivity between parts is simple and directly bolted to each other (chainring bolted to spider/crankarm, crankarm bolted to bottom bracket spindle). I can only think that the crank arm has somehow loosened from the bottom bracket spindle (is it a square taper, splined, cottered, etc. connection?) that is allowing the crank to "free spin" on the spindle going forward, but at the same time engaging when pedalling backward. I have never seen or heard of it, but without seeing the bike it is complicated in determining the cause and solution.
A photo(s) needs to be shown for some clarification as to the front drive configuration (chainring, crankarm, bottom bracket). I may be interpreting your words incorrectly, or your description is somehow in error; but again, tough to come up with a solution based upon your statement.
I hope someone with modern trike experience will respond since this may be unique to trike drivetrains.

[enkei]

What Sybian said.

Unless there's some odd crank technology I've not heard of before, the way the OP describes the problem doesn't make sense.

I think the only way forward is to start by posting photos of the bottom bracket/crank/chainring area.

(04-14-2023, 03:20 AM)Sybian Wrote:  I am not sure what is going on here, but the owner specifies that the bike is new without a front derailleur, and it only has a single chainring. I doubt there is enough wear on the chain to be a problem; and obviously with a single chainwheel a front derailleur problem is nonexistent.
I cannot wrap my head around this since it would be more than obvious if the chain was not engaging the ring teeth, and the chainring/chainwheel, crank arm spider, and bottom bracket spindle should all be mechanically connected regardless of pedalling forwards or backwards. Is there some sort of clutch or slip differential on this trike?
If the pedal (I assume crankarm) is moving when pedalling forward, but the chainwheel does not then I would assume that that chainring/chainwheel is slipping on the spider. I have no idea how because the same thing should happen when backpedalling. This is very confusing since the front connectivity between parts is simple and directly bolted to each other (chainring bolted to spider/crankarm, crankarm bolted to bottom bracket spindle). I can only think that the crank arm has somehow loosened from the bottom bracket spindle (is it a square taper, splined, cottered, etc. connection?) that is allowing the crank to "free spin" on the spindle going forward, but at the same time engaging when pedalling backward. I have never seen or heard of it, but without seeing the bike it is complicated in determining the cause and solution.
A photo(s) needs to be shown for some clarification as to the front drive configuration (chainring, crankarm, bottom bracket). I may be interpreting your words incorrectly, or your description is somehow in error; but again, tough to come up with a solution based upon your statement.
I hope someone with modern trike experience will respond since this may be unique to trike drivetrains.