Bicycle Mechanics - child stoker kit Burley Rivazza

I am trying to purchase a Burley Rivazza Tandem with a Burley child stoker kit. The bike mechanics said it would take a day to have it ready. Now they are saying that the Rivazza with a 39 tooth timing chainring and octalink splined bottom bracket are not compatible to the 36 tooth stoker kit they had and they may not be able to make it work. Today they said they ordered a different burley stoker kit. It appears to me that the only other choice was a 40 tooth child stoker kit. Does anyone know how they can make it work any better an not have issues with my child stoker being out of sych? It seems they think I am a nag for asking detailed questions but I am not sure how this is any better and I am having trouble getting a call back on what exactly they are going to do?

I'm having a hard time visualizing the problem. Where, exactly is the interference they are complaining about?

I am trying to purchase a Burley Rivazza Tandem with a Burley child stoker kit. The bike mechanics said it would take a day to have it ready. Now they are saying that the Rivazza with a 39 tooth timing chainring and octalink splined bottom bracket are not compatible to the 36 tooth stoker kit they had and they may not be able to make it work. Today they said they ordered a different burley stoker kit. It appears to me that the only other choice was a 40 tooth child stoker kit. Does anyone know how they can make it work any better an not have issues with my child stoker being out of sych? It seems they think I am a nag for asking detailed questions but I am not sure how this is any better and I am having trouble getting a call back on what exactly they are going to do?

The chainwheels on the cranks have to match. If they don't, the cranks will gradually get out of sync as the kid crank travels at a different rate. This will eventually lead to interference from the lower crank depending on where the kid crank is positioned on the frame. Surely Burley has this figured out. Call them and find out what they say to do. If nothing else, you should be able to change the chainrings to match. A 38 or 39 tooth ring should be readily available.

The chainwheels on the cranks have to match.

I don't think so. When I've installed the two child stokers that I've done, the kit came with two matching chainrings, one of which is installed onto the existing crankarm making it a double. As long as those two chainrings are the same, it doesn't matter what the timing rings are that go to the front of the bike assuming of course that they match one another also.

I don't think so. When I've installed the two child stokers that I've done, the kit came with two matching chainrings, one of which is installed onto the existing crankarm making it a double. As long as those two chainrings are the same, it doesn't matter what the timing rings are that go to the front of the bike assuming of course that they match one another also.

I'm reading this as the timing rings don't match. The inner ring on the stoker bottom bracket is a 40 and the the one on the kid crank is a 36. But it should be easy to find two chainrings that have the same number of teeth.

It sounds to me like the bike shop is worried because the chainrings on the child stoker kit don't match the chainrings on the timing gears between the front and rear cranks. They don't have to match. A revolution is a revolution. If the chainrings that connect the front and rear cranks are the same size, those two craksets will turn at exactly the same speed. If the chainrings that connect the kiddy crankset with the rear crankset are the same size, those two cranksets will turn at exactly the same rate.

If they're having that much trouble with this part of the process, I don't have much hope for them getting the chain line right, figuring how high to mount the kiddy crank and bringing the handlebar reach to something reasonable.

It sounds to me like the bike shop is worried because the chainrings on the child stoker kit don't match the chainrings on the timing gears between the front and rear cranks. They don't have to match. A revolution is a revolution. If the chainrings that connect the front and rear cranks are the same size, those two craksets will turn at exactly the same speed. If the chainrings that connect the kiddy crankset with the rear crankset are the same size, those two cranksets will turn at exactly the same rate.

If they're having that much trouble with this part of the process, I don't have much hope for them getting the chain line right, figuring how high to mount the kiddy crank and bringing the handlebar reach to something reasonable.

I looked at the Burley website and the component group is Ultegra (I think). I think the problem is that the kid crank comes with a 36 tooth chainwheel and the timing crank only goes down to a 130mm bolt circle which would limit it to a 38 minimum so the cranks could get out of sync. Is this correct, ragbraiboy? If it isn't and you are correct Retro Grouch, then yes, it wouldn't matter if the kid crank timing gear is of a different size than the timing gear on the bottom bracket. I've done that myself without problems.

Yes they are stating that they can't use a 36 tooth because it is too small. Now it is starting to make sense. So if they order the 40 tooth kiddie crank it will have a 130 bolt.

So what you all are saying is that as long as the upper and lower chainring on the kiddie crank are both 40 it won't matter if the front and back timing chains are 39 tooth, the kid peddals will still stay in sync as long as the dimensions of the chainrings are the same? Or do you think that they will need to change the timing rings to 40 tooth. If so how difficult or expensive is it to fing 40 tooth timing chainrings tandem and ultegra compatible. I am no mechanic and have a hard time understanding what the difficulties are for the mechanics. Thanks for all the input. Ragbraiboy

I think the problem is that the kid crank comes with a 36 tooth chainwheel and the timing crank only goes down to a 130mm bolt circle which would limit it to a 38 minimum.

Bolt circle diameter. Of course. Why didn't I think of that?

Yes they are stating that they can't use a 36 tooth because it is too small. Now it is starting to make sense. So if they order the 40 tooth kiddie crank it will have a 130 bolt.

So what you all are saying is that as long as the upper and lower chainring on the kiddie crank are both 40 it won't matter if the front and back timing chains are 39 tooth, the kid peddals will still stay in sync as long as the dimensions of the chainrings are the same? Or do you think that they will need to change the timing rings to 40 tooth. If so how difficult or expensive is it to fing 40 tooth timing chainrings tandem and ultegra compatible. I am no mechanic and have a hard time understanding what the difficulties are for the mechanics. Thanks for all the input. Ragbraiboy

As long as the teeth count from crank to crank is the same there isn't a problem. For example, if the captains timing crank has a 44 tooth chainwheel then the stoker's chainwheel has to be 44 teeth. If you add a kid crank and it has a tooth count of 36, then a second chainwheel is added to the inside of the stoker's timing crank (making it a double chainring) which has to have a tooth count of 36 but the size doesn't have anything to do with the main timing chain and cranks. It will all stay in sync since the cranks all will turn at the same speed.

Your problem lies in the fact that the timing crank on the stoker's crank has a different bolt circle diameter than the kid crank. The stoker's crank is limited to a minimum size of 38 teeth but 39, 40 and 42 are more common. The kid's crank they ordered has a smaller bolt diameter because it uses a 36 tooth chainring. I would suspect that the kid's crank uses a 90mm bolt center diameter (bcd). The mechanic should be able to just swap chainwheels to match the number of teeth on the Ultegra so that you use 40 tooth (that would be the easiest) chainwheels all the way around. Much easier than ordering a new kid crank.

I would have thought Burley would have had this all worked out before hand.