Brand new Chainring...........chainslip ?

Serious Cat

I really hated the gap between the cogs on my 50/34 compact so I had a brand spanking new 36 tooth chainring fitted tonight. The 10 speed chain has about 400 miles wear and is nowhere near 0.75% worn yet. I can use any of my 10 gears with the 50 chainring without issue, If im using the new 36 chainring I can engage cogs 1-5 on my rear 12-25 cassette with no issues, if I were select any of the cogs 6-10 I can pedal away with the chain not providing any resistance until it bites after a bit of hard pedalling . I wouldn't use those cogs with a 36 tooth chainring , but in theory the chain should not be skimming over any rear cogs.

The tech says the new 36 chainring has zero wear on it and needs bedded in and after a bit of use will provide resistance when used with any of the 10 gears. Is this normal or do you think I need a new chain despite the existing one having very little wear.

I forgot to say the chainslip only occurs when I change from the 50 ring to the 36 ring, if im on the 36 ring to begin with I can change through all 10 gears with no issue. Very confusing and thanks for any advice on this one.

Hewitt Cycles

This sounds more like the gap between the inner and outer ring is too wide, meaning that rather than the chain dropping onto the inner ring (when changing from the outer ring) it is sitting on top of the teeth, then consequently slipping until it drops properly on to the inner ring, it may be that the inner ring has been put on the wrong way round. The recesses for the chain-ring bolts, if there are any, should be on the side of the ring nearest the frame.

As you move to the larger sprockets the chain is gradually pulled away from the outer ring, this would explain why the larger sprockets work fine, once the chain is on the inner ring properly it wont slip again until you change down from the big ring again.

http://www.hewittcycles.co.uk

Serious Cat

The technician is very experienced and a superb rider , thanks for your suggestion but id be flabberghasted if he mounted a chainring the wrong way round. The whole thing is very puzzling to me.

mattv

Some chainrings have a different offset. I have come across this with some FSA parts, which won't fit shimano spiders. Or even some FSA spiders....

mercia_man

It does sound as Hewitt Cycles says as if the gap between chainrings is wider than before. Is the new ring the same make as the original? As mattv says some makes of rings are slightly different.

You could probably improve things by re-indexing the gears on rear mech so that the upper jockey wheel tracks accurately over each cog. I often find that even minor changes to drivetrain components will mean having to do a little bit of adjustment to the indexing.

mercia_man

Also you could try adjusting front mech inner stop screw so the chain moves a bit further inboard when you go from 50 to 36.

JayKosta

Serious Cat wrote:

...
I forgot to say the chainslip only occurs when I change from the 50 ring to the 36 ring, if im on the 36 ring to begin with I can change through all 10 gears with no issue. Very confusing and thanks for any advice on this one.

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So, the shift from the outer ring to the inner is the real problem.

Adjust the front deraileur so it properly positions the chain for seating onto the inner ring.
Also make sure that up-shifts work too, after a change is made.

Jay Kosta
Endwell NY USA

Old_Timer

Serious Cat,
One thought, make sure the front derailleur position in relation to the rings is correct. Its height above the big ring (outer) and its angle in relation to the rings should be correct. I use the SRAM recommendation of 4mm above the big ring for mine, if the derailleur is too high it will cause problems with both big ring to small ring and the reverse. Too low and it can contact the big ring.

The angle is some what subjective but check the SRAM website for their recommendations on your specific model derailleur. These don't need to be absolutely perfect but, they should be within tolerance for your equipment.

I use a simple machinist rule from a caliper to check mine when I have serviced the crank set or the derailleur. How is the equipment working for you now?