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Python Paragon gear change problems

Posted: 5 Nov 2019, 10:10am
by Hornblower
I have just purchased a Python Paragon bike with Suntour XR300 gear changing mechanism.
The problem is the gear change isn’t smooth and struggles to change down into the lower front cog unless there is no torque whatsoever on the gears. I have to find an area of road where there is no slope, or even a slight downwards slope to get into the lower gear. This is the latest in a series of gear changing problems and I have taken the bike back to the shop where I purchased it 4 times now and I am assured It will ‘get fixed’. The shop has changed the front cogs amongst other things but there is still a problem. They have hinted it might be the way I ride the bike because when they ‘test’ it there isn’t a problem. Is this a common problem with this bike? I am at the end of my tether so where do I go from here, as I have no confidence the problem will get fixed by the shop. Would appreciate any comments on what to do next. Thanks

Re: Python Paragon gear change problems

Posted: 5 Nov 2019, 10:21am
by pwa
Just so we can work out what is happening, when you try to change to the smaller chain ring and it refuses to do it, could you stop, get off, and see if giving a sidewards push on the front mechanism where the chain goes through results in the mechanism moving a tiny bit further inwards. If that happens, what you have is probably a problem with a sticky cable. If it doesn't move when you push it the problem must be something else, so we will have narrowed down the possibilities.

Re: Python Paragon gear change problems

Posted: 5 Nov 2019, 10:32am
by Brucey
IIRC this bike is fitted with suntour derailleurs but they are pretty basic models. I wouldn't expect stellar performance from them, although it could vary from 'pretty dire' to 'acceptable' depending on the chainset. The reason is that chainrings have (or have not) got features on them which help the chain to derail from one chainwheel to another. Chainsets also can have built-in chainguards and sometimes the chainguard forces the front derailleur to be set too high, which usually causes the middle to inner shift to deteriorate. The type of chain used can make a significant difference too.

The other thing is that you shouldn't expect the front shift to go onto the smallest chainring when the transmission is under any real load; best to change down early, I.e. before you practically conk out and have to 'mash' the pedals.

cheers

Re: Python Paragon gear change problems

Posted: 5 Nov 2019, 10:38am
by Hornblower
Good point. I’ve just tried to change down on a slight slope and it wouldn’t go. So stopped bike and tried to move gear selector by pushing on it as you suggested but it wouldn’t move any further.

Re: Python Paragon gear change problems

Posted: 5 Nov 2019, 10:43am
by Hornblower
Thanks Brucey. I never change down under any real stress but this problem happens on the slightest slope.

Re: Python Paragon gear change problems

Posted: 5 Nov 2019, 12:08pm
by reohn2
It sounds as if the front mech inner limit screw needs backing off about 1/8th to 1/4 of a turn.

Re: Python Paragon gear change problems

Posted: 5 Nov 2019, 12:56pm
by Hornblower
AB3D9704-E446-4315-A699-BC52EF4AD379.jpeg


Can you tell me which screw I need to adjust and which way to turn. Thx

Re: Python Paragon gear change problems

Posted: 5 Nov 2019, 1:02pm
by Brucey
screw 'L', ACW

try half a turn at a time

cheers

Re: Python Paragon gear change problems

Posted: 5 Nov 2019, 3:31pm
by Hornblower
Thanks Brucey. I’ll try that later. Rgds

Re: Python Paragon gear change problems

Posted: 7 Nov 2019, 11:47am
by Hornblower
Hi Brucey. I turned L back half a turn and tested it. It didn’t appear to make much difference. So backed off ACW again half a turn. Tested again and once again didn’t make much, if any, difference. Still struggles to go down the gears. As a point of interest the L screw was already backed off quite a bit before I started.

Re: Python Paragon gear change problems

Posted: 7 Nov 2019, 2:00pm
by Brucey
after a certain point something may happen like

a) the mech will run out of travel and/or
b) the mech will start pulling on the cable (even though you have selected low gear on the front shifter)

If the 'L' screw is actually doing anything then you should see/feel the FD move when you turn the screw.

cheers

Re: Python Paragon gear change problems

Posted: 7 Nov 2019, 2:14pm
by reohn2
If the cable is slack with L screw backed off it could mean the the mech is at it's inner limit or is up against a part of it touching the frame usually either the seatube or the chainstay.If that's not the case and the cable is slack with the limit screw backed right off it means the BB axle is too short and the bike needs a slightly longer one fitting to bring the inner chainring outward slightly.

If the cable is still tight with the gear selector in 1(inner ring position) there should be an adjuster on the gear lever which may need screwing in to allow more slack on the cable which will allow the mech to move inward.

EDIT,With the bike in bottom gear ie; largest sprocket at the rear and inner chainring,how much gap is thrpere between the inner edge of the chain and the inn front mech cage plate?

Re: Python Paragon gear change problems

Posted: 8 Nov 2019, 9:53am
by Hornblower
Have backed off L by 3 turns and cable still isn’t slack. Changing down no better. The inner chain is approx 5 mill from outer cage. Should I do anything with W screw?

Re: Python Paragon gear change problems

Posted: 8 Nov 2019, 11:24am
by Chris Jeggo
As both Brucey and reohn2 have said, the cable should be slack when low gear is selected, and it clearly isn't. Try winding the L screw back in a couple of turns, and then getting the cable slack but without a lot of slop. Then get the L-screw right, if possible, followed by final adjustment of the cable. If adjusting the L screw with the cable slack still doesn't work, then further investigation is needed.

Re: Python Paragon gear change problems

Posted: 8 Nov 2019, 11:45am
by pwa
It sounds like the cable may have been attached wrongly. Turn to L screw until it doesn't turn very easily anymore, so that it is where it started. Then undo the allen key bolt that retains the end of the cable, and without releasing the cable completely carefully pull a mm or so through so that the cable is a tiny bit slack when on the low setting. That will allow the mech to move towards the frame when you adjust the L screw. Then adjust the L screw a quarter turn at a time and with a bit of luck it should move a tiny bit closer to the frame.