beach_cycle

Causes of chain drop?

Greetings, I received a new Schwinn Meridian 7 speed 26” adult tricycle for Christmas; it came in a box, so I assembled it. The derailleur came off during shipment, so I put it back on; however, couldn’t get it adjusted right, but The Bicycle Tree Co-Op showed me it needed to be installed at a different angle. Now it shifts responsive and every gear… and no other assembly issues were discovered.

However, the chain periodically drops (~once a week). Back in December, a rough road seemed to cause it, and then the secondary chain would come off when I put the primary chain back on. The Schwinn Meridian has a primary chain from the chain wheel to the rear cog(s [my model has 7]) connected to a freewheel unit that spins another cog the secondary chain wraps around spinning a cog on the secondary axle that rotates the tires. I tightened the secondary chain and shortened the primary chain using the Park Tools Method: bypassed the derailleur, wrapped the chain around the chain ring and largest cog then broke the chain an inch (two 0.5” links beyond where they connect). That solved the chain dropping on rough road issue. But the chain still drops occasionally during a shift (between 4-7 sometimes during an up shift and other times during a down shift). The lower derailleur pully appears to be aligned with the chain in all 7 gears. I’m wondering what else can cause the chain to drop!?

The bike is still in good shape, but over 250 miles so road grime is starting to accumulate. I only rode 15 miles today but my hands got greasy from putting the chain back on. My last 4 Adult Trikes did not drop the chain; just this one and I’d like to resolve the issue, but don’t know the cause.


1.4.2022 offshore from Port of Long Beach

Andrew R Stewart 

Der chains are made to shift easily which is what we call "wanted drop offs", so inadvertent drop offs are no surprise. I suspect the secondary chain drop was from a loose chain tension. Trikes have a lot going on with their cogs, chains, frame/dropout elements. Adult trikes also live a hard life for a few reasons and we see more than a few with loose chains. Now the primary chain drop could be from the chain jumping about during the shifting. Sometimes a wave of chain is created when it shifts. This wave can travel to the chainring and if any sideways vibration or jolts are also happening at this moment the chain can shift off the ting. I'll bet the trike has no chain guide or retention design/device to best keep the chain engaging the ring in a straight line. This is why so much effort and $ has been spent on single ringed systems that are used on rough surfaces (1x MtB drivetrains as example). For x2 or x3 ringed systems the ft der cage acts as a guide, BTW.

The low cost solutions deal with rider controlled things, like when to shift, how smooth is the shift, how smooth is the surface of the road/trail. The expensive solutions are adding chain guide devices or replacing the rings/crank with a design that better keeps the chain on the teeth (wide/narrow tooth profiles as example). Andy

JoeTBM 

As you have a Meridian trike, you should check the chain lines of both chains. Also verify that the main chain is not too long. Drop offs at the crank chain ring are possibly due to misalignment or chain length being too long. Drop-off at the DER sprockets may require resetting of the derailleur limit screws and possibly cable length issue. Their are many good videos on properly setting the limit screws as the rear DER is the same as on a typical bicycle.

The secondary chain coming off is normally due to misaligned sprockets or chain tension (adjusted by the frame bolting).

The sprockets are held in place typically with two set screws with locknuts, Verify that they are in the proper horizontal position and that the set screws are tight.

Andrew R Stewart 

Checking the cog/ring alignments (besides the chain tensions) is a good point given the three elements that are in play. The main frame with the crank/BB, the rear axle sub frame and the axle's cog and the intermediate cogs (in this case a freewheel with der) which "floats" between the first two. It's not uncommon for the rear sub frame to become cocked WRT the main frame, the need to keep both "stays" and the sub frame at the same amount of pull back to achieve chain tension while also keeping the two sides balanced so the trike tracks straight can be hard to do without a spare set of hands, or some little tricks. If one side's bolts slip the sub frame 9and the axle/cog it contains) can become crooked. The "hub", the floating middle element, can be aligned WRT either the sub frame of the main frame (hopefully both at the same time as this middle hub also has two ends that slide in "drop out" slots. Getting the three elements aligned and with proper chain(s) tension is often a trial and re try again effort, not one a shop likes to quote for. Andy