Basic (noob) chainset replacement

[Jeremy Collins]

Hi all,

I've been given an old MTB, and to make it rideable it needs
a new chainset (amongst other more minor jobs).

Rather than attempt to fit new cogs, I want to replace the
whole lot - cranks, chainset etc in one go.

OK, so here are the complete beginner questions:

1. How do I determine the size and type of replacement that
I need? Browsing bike component websites confused
me...

2. Can anyone direct me to a guide for doing this job,
including any special tools I might need?

TIA,

--
jc

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[Derek Hodges]

"Jeremy Collins" <[email protected]> wrote in message
news:IzvEc.15$Ln6.10@newsfe4-gui...
> Hi all,
>
> I've been given an old MTB, and to make it rideable it
> needs a new chainset (amongst other more minor jobs).
>
> Rather than attempt to fit new cogs, I want to replace the
> whole lot - cranks, chainset etc in one go.
>
> OK, so here are the complete beginner questions:
>
> 1. How do I determine the size and type of replacement
> that I need? Browsing bike component websites confused
> me...
>
> 2. Can anyone direct me to a guide for doing this job,
> including any special tools I might need?
>
Advance warning: unless its a very good bicycle replacement
with new parts can get more expensive than finding another
old bike that's in better shape. That said:
1.Clean the gunk off and find any markings with make, part
numbers, sizes , so on.

2.Try http://www.parktool.com/repair_help/FAQindex.shtml

--
Derek Hodges Toronto

 

[Jeremy Collins]

Derek Hodges wrote:

> Advance warning: unless its a very good bicycle
> replacement with new parts can get more expensive than
> finding another old bike that's in better shape.

I guess you're right, but this is intended as a learning
project, so I'm hoping the money spent on this bike will pay
off in the future.

> That said:
> 1.Clean the gunk off and find any markings with make, part
> numbers, sizes , so on.
>
> 2.Try http://www.parktool.com/repair_help/FAQindex.shtml

Ah, nice one. I picked up a Park crank puller today, and
have successfully removed the chainset (very clear
instructions on the pack!).

The markings on the chainset tells me I've got 170mm cranks,
plus a little "SA" logo. The shifters and deraillers are all
Suntour. The chainrings have 28/38/48 teeth, so I'm hoping
that something like this: http://www.edinburgh-
bicycle.co.uk/catalogue/detail.cfm?ID=11196 will be a
suitable replacement.

I guess it's bottom brackets that confuse me when it comes
to buying a new chainset.

I removed one end of the bottom bracket, and the spindle
(axle?), here's a photo, along with the nicely bent
original chainset:

http://homepage.ntlworld.com/jd.collins/images/chainset.jpg

The spindle is 145mm long, and bears the markings 3S, I-12,
B

AIUI all modern bottom brackets are sealed units - this
doesn't appear to be.

So, do you reckon the above Shimano set will fit my existing
BB, or will I have to buy a new one of those too?

Cheers,

--
jc

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[Werehatrack]

On Wed, 30 Jun 2004 09:18:38 +0100, Jeremy Collins
<[email protected]> wrote:

>1. How do I determine the size and type of replacement that
> I need? Browsing bike component websites confused
>me...

Count the teeth on the large and small chainrings, look for
the length marking on the cranks (probably 170 or 175) or
measure the distance between the centerlines of the BB shaft
and pedal shatf, and match for those characterisitics. Buy
the recommended BB to match the new chainset unless you're
able to determine that it can use the same type and length
of BB as is currently present.

>2. Can anyone direct me to a guide for doing this job,
> including any special tools I might need?

The Park Tools site already mentioned covers it reasonably
well; if the current cranks aren't loose, and if you don't
want to risk damaging them in removal, you'll need a crank
extractor. Since you're new at this, a torque wrench might
be a good idea for tightening the bolts when reinstalling.
Most cranks go on to a tapered shaft, and tightening the
bolts correctly requires stopping at a point that's not
apparent to the untrained hand.

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[Jeremy Collins]

Jeremy Collins wrote:

> I'm hoping that something like this: http://www.edinburgh-
> bicycle.co.uk/catalogue/detail.cfm?ID=11196 will be a
> suitable replacement.

That link doesn't seem to work...

http://www.evanscycles.com/product.jsp?style=29224

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jc

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[Leo Lichtman]

"Jeremy Collins" <[email protected]> wrote: (clip)
Rather than attempt to fit new cogs, I want to replace the
whole lot - cranks, chainset etc in one go. (clip)
^^^^^^^^^^^^^ Since you are a "noob," in my opinion, you
should try to get the bike rideable with cleaning, oiling,
and minimum replacement of parts. You will learn more doing
one thing at a time, make fewer mistakes and probably save a
fair amount of money. For example, the crank arms don't wear
out. The chainrings are probably still usable. Unless the
chain is really rusted, it may also be usable, at least for
a while. After you start riding, you may want to play with
the gearing, upgrade your shifters, etc. If you try to do
too much too soon, you may have to replace some things more
than once.

 

[Jeremy Collins]

Leo Lichtman wrote:

> "Jeremy Collins" <[email protected]> wrote:
> (clip) Rather than attempt to fit new cogs, I want to
> replace the whole lot - cranks, chainset etc in one go.
> (clip) ^^^^^^^^^^^^^ Since you are a "noob," in my
> opinion, you should try to get the bike rideable with
> cleaning, oiling, and minimum replacement of parts. You
> will learn more doing one thing at a time, make fewer
> mistakes and probably save a fair amount of money. For
> example, the crank arms don't wear out. The chainrings are
> probably still usable.

The chainrings are bent - badly [1]. I've already done all
the basic maintenance you mention, having stripped it down
and cleaned the frame, chain, deraillers etc. I've replaced
the brake pads and cables, plus the gear cables. Despite the
chainrings, the rest of the bike is now working quite well.

I'm fairly competent (compared to the general population)
in /basic/ bike maintenance, but still consider myself a
"noob" in the context of the level of knowledge in this
newsgroup.

Gaining more knowledge and experience is something I want
to do, even if it costs me some money. And I'm enjoying
the process!

The thing that's confusing me at the moment is bottom
bracket specifications - do I need a new one, and which one
do I need.

[1] This photo doesn't really do justice to how mashed the
chainset is, but I think you'll see the problem! http:/-
/homepage.ntlworld.com/jd.collins/images/chainset.jpg

Cheers,

--
jc

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[Jeremy Collins]

Werehatrack wrote:

> Count the teeth on the large and small chainrings, look
> for the length marking on the cranks (probably 170 or 175)
> or measure the distance between the centerlines of the BB
> shaft and pedal shatf, and match for those
> characterisitics. Buy the recommended BB to match the new
> chainset unless you're able to determine that it can use
> the same type and length of BB as is currently present.

OK, so I've got 28/38/48t chainrings, and 170mm cranks. I've
seen a reasonably cheap (< 30 GBP) Shimano chainset with
these specs, and as you say they recommend a particular BB.

Now this is where I'm in the dark. How do I know whether a
given BB will actually fit the bike? The BB goes inside that
little lateral tube at the bottom of the frame - mine
currently has a little bearing assembly threaded into each
end with a spindle in between, and all the BBs I've seen for
sale don't seem to look like this.

The spindle and one of the end bearings are in this photo:
http://homepage.ntlworld.com/jd.collins/images/chainset.jpg

> The Park Tools site already mentioned covers it reasonably
> well; if the current cranks aren't loose, and if you don't
> want to risk damaging them in removal, you'll need a crank
> extractor.

I got a Park crank extractor yesterday and it worked
perfectly.

> Since you're new at this, a torque wrench might be a good
> idea for tightening the bolts when reinstalling. Most
> cranks go on to a tapered shaft, and tightening the bolts
> correctly requires stopping at a point that's not apparent
> to the untrained hand.

Noted, thanks.

--
jc

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[Werehatrack]

On Thu, 01 Jul 2004 08:52:20 GMT, Jeremy Collins
<[email protected]> wrote:

>OK, so I've got 28/38/48t chainrings, and 170mm cranks.
>I've seen a reasonably cheap (< 30 GBP) Shimano chainset
>with these specs, and as you say they recommend a
>particular BB.
>
>Now this is where I'm in the dark. How do I know whether a
>given BB will actually fit the bike? The BB goes inside
>that little lateral tube at the bottom of the frame - mine
>currently has a little bearing assembly threaded into each
>end with a spindle in between, and all the BBs I've seen
>for sale don't seem to look like this.

Measure the length of the tube that the BB goes into, and
measure the end-to-nd length of the BB shaft. The specs for
a BB are in two bits; the first is typically either 68 or 73
(the mm length of the tube), and the second is the length of
the shaft (also in mm). The 68 or 73 needs to be a match for
the tube on the bike, and the other number (which is
somewhere over 100, often around 113) needs to match the
requirement of the cranks. A number of different BB designs
are supplied; the majority of local bike shops will probably
carry cartridge-style units, which most likely look very
little like what you have now. The appearance is not the
important thing. The chances are near to certainty that your
bike will accept the ommon types of cartridge BB without a
problem. However, if the length of the existing shaft is
within 2mm of what's required for the replacement cranks,
and if it's not in bad shape, there's no reason not to
continue to use it.

One more thing; when measuring the shaft length, if the
shaft has threaded studs on each end, ignore the studs;
measure just the distance between the outboard ends of the
square tapers.

You will probably need either one or two more tools to
install the replacement BB if you're going to swap it to a
cartridge unit. The tools required will be determined by the
type of bearing you buy; ask the lbs about it.
>The spindle and one of the end bearings are in this photo:
>http://homepage.ntlworld.com/jd.collins/images/chainset.jpg
>
>> The Park Tools site already mentioned covers it
>> reasonably well; if the current cranks aren't loose, and
>> if you don't want to risk damaging them in removal,
>> you'll need a crank extractor.
>
>I got a Park crank extractor yesterday and it worked
>perfectly.
>
>> Since you're new at this, a torque wrench might be a good
>> idea for tightening the bolts when reinstalling. Most
>> cranks go on to a tapered shaft, and tightening the bolts
>> correctly requires stopping at a point that's not
>> apparent to the untrained hand.
>
>Noted, thanks.

--
Typoes are a feature, not a bug. Some gardening required to
reply via email. Surrealism is a pectinated ranzel.

 

[Jeremy Collins]

Werehatrack wrote:

> Measure the length of the tube that the BB goes into, and
> measure the end-to-nd length of the BB shaft. The specs
> for a BB are in two bits; the first is typically either 68
> or 73 (the mm length of the tube), and the second is the
> length of the shaft (also in mm). The 68 or 73 needs to be
> a match for the tube on the bike, and the other number
> (which is somewhere over 100, often around 113) needs to
> match the requirement of the cranks.

Ahhhh, now I get it!

> A number of different BB designs are supplied; the
> majority of local bike shops will probably carry cartridge-
> style units, which most likely look very little like what
> you have now. The appearance is not the important thing.
> The chances are near to certainty that your bike will
> accept the ommon types of cartridge BB without a problem.
> However, if the length of the existing shaft is within
> 2mm of what's required for the replacement cranks, and if
> it's not in bad shape, there's no reason not to continue
> to use it.

Now I know what (and how) to measure, I was able to get a
chainset which fits the existing BB perfectly from my LBS.

> One more thing; when measuring the shaft length, if the
> shaft has threaded studs on each end, ignore the studs;
> measure just the distance between the outboard ends of the
> square tapers.

Thanks - this explains why I was having a hard time finding
replacements for a "145mm" shaft!

Your post was incredibly helpful - thanks for taking the
time to reply.

Cheers,

--
jc

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