worn chainring?

[mister g]

Right, I've made a start. Just purchased a Shimano UN55 BB and a KMC X8-93 chain. Now, rear sprockets? I've just been looking at a couple of options Shimano Acera HG41 & Altus HG31. Would these be compatible and is one better than the other?

 

[shadow master]

Right, I've made a start. Just purchased a Shimano UN55 BB and a KMC X8-93 chain. Now, rear sprockets? I've just been looking at a couple of options Shimano Acera HG41 & Altus HG31. Would these be compatible and is one better than the other?

Either cassette will do not much between them......don't buy the chain set online you'll never get the same standoff for the bb,wander in to your local bike shop with it ask for a exact match

 

[mister g]

Oh bugger, I should have checked back here first! I've just bought a crankset going off the same ratios!!! Will it make a lot of difference? Do cranksets state what length Spindle they are for?

 

[Nigelnaturist]

Being an 8 speed cassette you have to change the chain and cassette together as they wear as a pair,in short about £50+ for bb chain set cassette and chain

Any components working together like gears will wear as a set, no matter the number of rear gears.

Any chain that's been running on that middle ring will be totally knackered, i see can most of the riding has been done on the middle ring only hence the wear!bike needs bb,chain set,chain and almost certainly rear sprocket,relatively expensive for a very basic bike.wouldn't mess with ratios at front,probably lead to shifting problems.

If a replacement chainset has the same ratios, its usually easy enough to go up or down a few teeth, the main pronlem for a novice is then resetting the height/angle of the FD not so much in the components

@mister g if its say 115mm and you have 113, chances are it will work ok, much more than the odd mm it will lead to problems.

 

[Gravity Aided]

Measure 2 things for the new bottom bracket (sealed) Un 55 (because both cups are metal, the plastic ones with others may go out faster than the BB)
You want to measure the bottom bracket shell, just the painted part which is part of the frame, and the spindle length. Exactly. Maybe even get a digital micrometer, they cost about $15 here. Read the measure in millimeters.
Here's a guy replacing a bottom bracket.

View: https://www.youtube.com/watch?v=1BrVjDFqotE

 

[Nigelnaturist]

@Gravity Aided the biggest problem I find with plastic shells is getting them out after a while, last one I had to drill the plastic out in bits you can imagine how careful I was.

 

[Gravity Aided]

I've seen cracked ones on some bicycles I've repaired, but it gets a little colder around here. I always splurge for UN55, no worries then. I can also use some grease on the metal cups, not so on plastic. (very little, just enough to keep anything from seizing.)

 

[shadow master]

Any components working together like gears will wear as a set, no matter the number of rear gears.

If a replacement chainset has the same ratios, its usually easy enough to go up or down a few teeth, the main pronlem for a novice is then resetting the height/angle of the FD not so much in the components

@mister g if its say 115mm and you have 113, chances are it will work ok, much more than the odd mm it will lead to problems.
I agree on chain/gear wear,but was just pointing out cassette systems are sensitive to chain renewal as freewheels are much more tolerant.

 

[shadow master]

Oh bugger, I should have checked back here first! I've just bought a crankset going off the same ratios!!! Will it make a lot of difference? Do cranksets state what length Spindle they are for?

Same ratios are best, next top ring is commonly 48t means having to move front mech up,or size down is 42t and means moving again and 42 is a bit low geared...No cranksets do not state what axle they are for that's the problem...its easier to buy the bb length to match the new crankset than the other way around,you may be lucky,but so often the new crank will be too close to the chainstays because the bb is too short,or perch on the end ie too long,and the front mech although adjustable via the H and L screws simply can't cope with the increased travel...bit of trial and error I'm afraid

 

[raleighnut]

TBH you'll always be better to take the bits into a shop to get them replaced, even experienced cycle fettlers occasionally manage to f*ck up and buy the wrong bits on-line but a basic Shimano crank was standard across so many bikes so that shouldn't be a problem likewise a BB suitable for a triple is normally OK.
With the cassette though its so much easier to wander into a shop, buy the same one and say "can you just swap that over mate" and very often they'll do it for free.

 

[mister g]

Measure 2 things for the new bottom bracket (sealed) Un 55 (because both cups are metal, the plastic ones with others may go out faster than the BB)
You want to measure the bottom bracket shell, just the painted part which is part of the frame, and the spindle length. Exactly. Maybe even get a digital micrometer, they cost about $15 here. Read the measure in millimeters.
Here's a guy replacing a bottom bracket.

View: https://www.youtube.com/watch?v=1BrVjDFqotE

Ok thanks. I have digital calipers and measured the shell at 68 and the spindle at 122 and last night purchased a shimano un55 of the same size. But I've also now bought a crankset with the same ratios as the old one thinking that would be ok. I suppose I'll have to live in hope that they go together ok (but with my luck... )

 

[Nigelnaturist]

Same ratios are best, next top ring is commonly 48t means having to move front mech up,or size down is 42t and means moving again and 42 is a bit low geared...No cranksets do not state what axle they are for that's the problem...its easier to buy the bb length to match the new crankset than the other way around,you may be lucky,but so often the new crank will be too close to the chainstays because the bb is too short,or perch on the end ie too long,and the front mech although adjustable via the H and L screws simply can't cope with the increased travel...bit of trial and error I'm afraid

Most square taper chainsets do quote axle length, when I got mine it was quoted as being 113mm my previous one I know from the bb I took of 116mm though I ran it on a 115mm UN55, I have another that is 110mm, I did run this one on the 113mm BB not ideal but it worked, though not something I would do on a regular basies

@raleighnut these are all triple chainsets

 

[Nigelnaturist]

@mister g forgot to mention, it is normally marked on a sealed BB for future reference. Though not always. I have aUN55 115mm that doesn't say its size.

 

[shadow master]

Most square taper chainsets do quote axle length, when I got mine it was quoted as being 113mm my previous one I know from the bb I took of 116mm though I ran it on a 115mm UN55, I have another that is 110mm, I did run this one on the 113mm BB not ideal but it worked, though not something I would do on a regular basies

@raleighnut these are all triple chainsets

MOST SQUARED TAPER CHAINSETS DO QUOTE AXLE LENGTH....? Really, I have just check about 10 various makes and models,I see brand, code for model number,country of origin,CRANK arm length,but no numbers that resemble bb axle length eg 110\113 etc...I don't ever recall seeing this,and with varying chainlines and seattube diameters they would have to range 2\4mm anyway?Even more difficult on an unbranded chain set like in this case.

 

[Nigelnaturist]

@shadow master try sourcing from a different place, or try looking up the specs.

http://spacycles.co.uk/products.php?plid=m2b0s109p2801 touring 110mm

http://spacycles.co.uk/products.php?plid=m2b0s109p2657 mtb touring 107mm


just a set of cranks ( I use these, with rings, my current setup on a 105 FD 26/38/50, and shifts superbly ) http://spacycles.co.uk/products.php?plid=m2b0s109p3051 103/107 for the double and 113mm for the triple.

I wouldn't buy anything with out first knowing sizes, if its not quoted don't use them.