Right side sync chain on Adventure and Discovery 2000 - 2004

[martyn]

We bought a 531 Adventure from 2000 or 2001 a few years ago and the through drive gave us a bit of grief. In particular the sync chain tended to drop outwards from the rear 26t chainwheel onto the 22t inner drive ring. The first time I didn't work out what had happened until I tried to use the inner drive ring. For a while it worked OK as long as I did very frequent adjustment on the eccentric. The last straw was a major snarl up on a hill with a double break in the sync chain just before we were due to go on a tour. To our club mates' amusement we arrived at the coffee stop under stoker power.

I was mulling over various option to make it work more consistently when I remembered I had a NOS crossover Deore DX captain's chainset in hand and so could move to crossover at minimal expense and effort. This has been fine although it is heavier than the hollowtech Deore chainsets and can't provide such a low bottom gear.

We have just bought another Adventure, this one with S & S couplers and XT chainsets. This 2002 version has through drive but with alloy 30t sync chainwheels. I'm keen to make the through drive work well on this bike and encouraged to see the Discovery used by Marcus OTP for the round the world ride had same side drive.

What experiences do fellow Thorn tandem users have of this system? Are there any modifications or additions (such as a chainguide ahead of the sync chain wheel) that have proved useful?

Martyn

[martyn]

We have now got more experience of Thorn derailleur tandems with same side drive. The second Adventure with Thorn/Talon 30 tooth sync chain rings has been a great success with no chain tangles or over shoots. We recently found a Thorn 725 Discovery from the same period and that had the 27 tooth steel rings and was resting with the drive chain well stuck between the sync and granny rings, confirming that this original configuration was somewhere tricky to hopeless.

I have bought a couple of new alloy Thorn/Talon 30t chain rings but that is, it seems, the end of SJS stock. I've also got some TA Chinook 30 tooth rings and plan to put TA on the front to save the Thorn/Talon for the back because they make a better blocker as they are not cut away. Both SJS and Chain Reaction/Wiggle only had one of these rings in stock. Using a worn out ring as a 64mm to 94mm BCD converter looks like a possible future option. I would welcome comments from other Thorn Discovery and Adventure riders from the vintage derailleur years.