Chain slipping Between Chainrings
Re: Chain slipping Between Chainrings
Mine has one of those Tiagra front mechs, but what you say isn't quite right regarding the seat tube angle.
With a Moulton TSR, the bike doesn't have the BB below the chainstays, but above it
Bikes, generally, are defined by "BB Drop" as in that the BB is lower than the centres of the wheels.
Moulton TSRs have the BB above the wheel centres and as the outer chainwheel is larger than "normal" bikes, the angle of the chain to the cassette, and the front mech angle too, isn't "normal" by any means.
With a Moulton TSR, the bike doesn't have the BB below the chainstays, but above it
Bikes, generally, are defined by "BB Drop" as in that the BB is lower than the centres of the wheels.
Moulton TSRs have the BB above the wheel centres and as the outer chainwheel is larger than "normal" bikes, the angle of the chain to the cassette, and the front mech angle too, isn't "normal" by any means.
Mick F. Cornwall
Re: Chain slipping Between Chainrings
I think you have the previous model, FD-4603, which does not have the channel in the outer part of the cage that the OP's FD-4703 has. Most of the online photographs of the FD-4703 on retailers' websites show a model with a very distinct channel in the outer side of the cage, although Shimano's own website shows a cage without a channel in the outer side (I suspect that might be an earlier version or pre-production model).
Incidentally, according to the Bike Components listing for the FD-4703, the derailleur is supplied with the Shimano cable setting tool, which is for front derailleurs with a choice of two settings depending upon the angle of the cable, but I cannot see the corresponding protruding pin on the back of the derailleur body.
https://www.bike-components.de/en/Shima ... ur-p43860/
FD-4603
Re: Chain slipping Between Chainrings
Slowster, I had considered your theory about the chainstay angle (well spotted) but the correct part of the front mech is making contact with the chain and dropping it off the big ring. The real problem is not enough movement in the mech for the chainset, so if I set it up to make clean shifts from the outer to middle and middle to inner then I get chain rub when on the outer and on the smaller sprockets. If I set it up to get no chain rub on the outer then I get poor shifts from outer to middle (with the chain struggling to engage) and difficulty engaging the inner ring because I've run out of cable travel (not mech adjustment). As you have noticed the FD-4703 front mech doesn't have the pin giving a choice of settings depending on cable angle that the FD-4700 has. But why?
Re: Chain slipping Between Chainrings
But the front mech is angled back much more to compensate.Mick F wrote: ↑27 Jun 2022, 7:50pm Mine has one of those Tiagra front mechs, but what you say isn't quite right regarding the seat tube angle.
With a Moulton TSR, the bike doesn't have the BB below the chainstays, but above it
Bikes, generally, are defined by "BB Drop" as in that the BB is lower than the centres of the wheels.
Moulton TSRs have the BB above the wheel centres and as the outer chainwheel is larger than "normal" bikes, the angle of the chain to the cassette, and the front mech angle too, isn't "normal" by any means.
Triple Chainset.jpeg
Re: Chain slipping Between Chainrings
Last night I put my previous chainset on and there are no issues whatsoever with the chain failing to engage with the middle chainring when shifting from the outer. Although it isn't easy to measure, visually the spacing between the rings is less on the previous chainset. When I get a moment I will carefully take a file to the spider and report back.
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Re: Chain slipping Between Chainrings
The focus on mechs here was bemusing to me, always seemed more likely to be chainset related.iandusud wrote: ↑28 Jun 2022, 6:14am Last night I put my previous chainset on and there are no issues whatsoever with the chain failing to engage with the middle chainring when shifting from the outer. Although it isn't easy to measure, visually the spacing between the rings is less on the previous chainset. When I get a moment I will carefully take a file to the spider and report back.
Re: Chain slipping Between Chainrings
Hmm. That will then create a bigger gap between middle and small chainrings.iandusud wrote: ↑28 Jun 2022, 6:14am Last night I put my previous chainset on and there are no issues whatsoever with the chain failing to engage with the middle chainring when shifting from the outer. Although it isn't easy to measure, visually the spacing between the rings is less on the previous chainset. When I get a moment I will carefully take a file to the spider and report back.
The older I get the more I’m inclined to act my shoe size, not my age.
Re: Chain slipping Between Chainrings
No, I'll take the material off the outer face.
Re: Chain slipping Between Chainrings
How does chainline compare with the two chainsets?iandusud wrote: ↑28 Jun 2022, 6:14am Last night I put my previous chainset on and there are no issues whatsoever with the chain failing to engage with the middle chainring when shifting from the outer. Although it isn't easy to measure, visually the spacing between the rings is less on the previous chainset. When I get a moment I will carefully take a file to the spider and report back.
Chainring spacing is best compared by putting the big ring of one against the granny ring of the other, that way the rings line up better. (maybe thats obvious?)
Bike fitting D.I.Y. .....http://wheel-easy.org.uk/wp-content/uploads/bike-set-up-2017a.pdf
Tracks in the Dales etc...http://www.flickr.com/photos/52358536@N06/collections/
Tracks in the Dales etc...http://www.flickr.com/photos/52358536@N06/collections/
Re: Chain slipping Between Chainrings
I have a micrometer and, when I have a chance I will measure the amount of aluminium between the two faces Ian.
Its easier I guess if I measure the spare Thorn and Spa spiders I have that are not on the tandem ATM although ideally I should measure the spider that is currently installed on the tandem and generating issues (a Thorn one - tolerances?)
Hoping we can share measurements...
Re: Chain slipping Between Chainrings
Ok, I measured the lugs on the spider at 3.5'm and the spacing between the teeth on the outer and inner chain rings at 4mm, giving a spacing of 7.5'm. Shimano give the spacing on their road triples at 7.1 mm, so I filled 0.5 mm of the outer face of the lugs, reassembled and it has been transformed! Works perfectly.
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Re: Chain slipping Between Chainrings
Nice one. And thanks for sharing.iandusud wrote: ↑28 Jun 2022, 12:07pm Ok, I measured the lugs on the spider at 3.5'm and the spacing between the teeth on the outer and inner chain rings at 4mm, giving a spacing of 7.5'm. Shimano give the spacing on their road triples at 7.1 mm, so I filled 0.5 mm of the outer face of the lugs, reassembled and it has been transformed! Works perfectly.
Re: Chain slipping Between Chainrings
Whoa! Thats a result. Ok ..time to measure and (probably) file mine. Many thanks for sharing this Ian.iandusud wrote: ↑28 Jun 2022, 12:07pm Ok, I measured the lugs on the spider at 3.5'm and the spacing between the teeth on the outer and inner chain rings at 4mm, giving a spacing of 7.5'm. Shimano give the spacing on their road triples at 7.1 mm, so I filled 0.5 mm of the outer face of the lugs, reassembled and it has been transformed! Works perfectly.