Having used our new Dawes Edge for some 600 miles I adjusted the timing chain with the eccentric bottom bracket to take up the slack and all was well. After a couple of hundred more miles I found there’s still more slack than I’d like (about 2 inches vertical mid-span) but the eccentric is as far as it will go, and if I remove a complete link the chain isn’t long enough to go round with the eccentric adjuster at it’s closest. It seems that the maximum adjustment range you get is less than one link of the chain, so as the chain stretches you will always end up in the situation of a slack chain until it stretches enough to get a link out. I have measured the chain stretch using both the Park tool and the trusty steel ruler and it’s about 0.5% so would not need replacing.
Is this normal for timing chains? Do I have to live with a slack chain until I can get a whole link out or is there another way of keeping the adjustment?
I would be interested to know what anybody else does to keep the adjustment as the chain wears.
First, a half link will shorten the chain by half an inch rather than one inch. This uses a link that has an outer bit at one end and an inner bit at the other. Unfortunately this requires the bringing together of 1/8” and 3/32” chain technology, but the resulting hybrid does work.
Alternatively, and possibly a long term solution, is to increase the size of the L/H chainrings.
The problem is caused by the geometry of the frame and the length of the beam. Some proportions seem to cause synchro chain tension problems.
I also have a Dawes Double Edge and had the same problem we just lived with the slack timing chain until it became a problem at about two and a half thousand miles, the chain came off twice on one ride and it still wasn’t stretched enough to take a link out so I fitted a new chain and so far its going beautifully!
Seems a bit daft not to have enough adjustment to get a link out, but I guess that’s just the way it is. Looks like I have to live with a slack chain for a while as I object to buying a new one so soon. If it starts to make a habit of coming off I’ll get a new chain, but so far no problems in that department.
Another solution is to insert a ‘ghost chainring’.
Check out your parts box . . . find a chainring about 2 teeth or so larger than the size of your crossover chainrings. Pop this ghost chainring between top/bottom of cross over chain so it ‘floats’ in the middle.
After a bit, chain will stretch sufficiently so you can remove one link of the crossover chain. Warning: this may elicit some comments from your cycling pals . . . but it’s a great conversation starter.
Been there. done that!
Pedal on TWOgether!
Rudy and Kay/zonatandem/USA
Thanks for that idea - but I guess it looks a bit odd with nothing holding the ring in there.
I have just changed the timing chain anyway as the rear chain was worn out after about 1000 miles so I bought 3 chains and did the whole lot in one go. I used Shimano DuraAce 9speed chains as I got a good deal on them so I’ll see how well they last.
The surprising thing is how many miles we’re now getting up to on the Tandem now we’ve got it compared to when we had two solo bikes.
Cross over/timing chains can last w-a-y much longer than the drivechains.
Do not need to use expensive 9-speed chains for crossover unles like you say ‘got a good deal.’ Timing chain gets less wear as there is no ‘de-railing’ involved and as long as you can keep proper tension on it they are good to go.
We are fortunate to live in a dry climate (8 to 10 inches of rain per year) and are rather metriculous about keeping chains/drivetrain clean. However living in the Arizona desert, there can be a bit of dust and even experienced dust devils (mini-tornado of swirling and visible and stinging dust particles) to grit things up. For that reason we use the hot wax method to keep cains lubed and exterior of chain quite dry.
Drive chains have lasted us into the 6,000 mile range and some timing chains over 20,000 miles.
A clean tandem is a happy tandem!
Pedal on TWOgether!
Rudy and Kay/zonatandem/USA
Can anyone tell me what tool I need in order to adjust the eccentric bottom bracket on a Dawes Galaxy Twin - ie. to rotate it? There are two small holes which I presume a tool can fit into but am really not sure?? Big tank you to anyone who can point me in the right direction
Loosen up the eccentric bolts.
Then, depending on the eccentric design (there are several) you can do the following:
If there are 2 small holes/indentations, you need to use a pintool to rotate eccentric.
If there is a larger hole you can insert a thin regular steel screwdriver into that hole and rotate pedals backwards so crankarm will move the screwdriver blade and rotate the eccentric.
Reverse procedure to tighten.
Pedal on TWOIgether!
Rudy and Kay/zonatandem/USA
I made a tool for this job, in about 1 minute! Take a small flat piece of metal, a little longer than a tyre lever. It need not be too thick 2-3 mm. Drill a hole at one end, and fit an M5 bottle cage bolt and nut, about 20mm long. Once the eccentric bolts are loose, simply place the screw in one of the adjuster holes, and butt the thin edge of the lever against the bb axle. Providing the eccentric is not totally seized, it provides enough leverage to turn in either direction. I love a good bit of Heath Robinson! Right, I’m off to the Patent Office....
Jeepers I am amazed at the milage zona tandem gets from chains. I use 9 spd for both chains so everything is compatable and interchangable and so I can carry just a couple of sram links to repair a broken chain.
However we get about 500 - 1000 miles from a rear chain and 1000-2000 from a timing chain - and that is with meticulous cleaning and lubrication. In a year we go thru 4 chains - 2 rear 1 timing (which is two chains) 4 chainrings and two cassettes. Its as much as a superbike in terms of chain costs per mile.
We do however ride in wet muddy conditions. Peat mud is about the nastiest thing going for wearing stuff out - fine, acidic and mixed with quartzite dust.
