Basic (noob) chainset replacement

"Jeremy Collins" <[email hidden]> wrote in message
news:IzvEc.15$Ln6.10@newsfe4-gui...

Quoted message said:

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

Derek Hodges said:

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.

Quoted message said:

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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Jeremy Collins said:

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

--
jc

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Jeremy Collins said:

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.

Quoted message said:

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.

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

"Jeremy Collins" <[email hidden]> 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.

Leo Lichtman said:

"Jeremy Collins" <[email hidden]> 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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Werehatrack said:

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

Quoted message said:

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.

Quoted message said:

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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Jeremy Collins said:

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.

Quoted message said:

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

Quoted message said:

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.

Quoted message said:

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.

Werehatrack said:

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!

Quoted message said:

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.

Quoted message said:

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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