609 bike questions [photo]

On Sat, 08 Jul 2017 19:36:37 +0200, Emanuel Berg
wrote:

Sir Ridesalot wrote:

CHECK that stem and make sure there's at lest
2 inches (5cms)of it BELOW the top locknut -
more if there's any space between the top
lock nut and the fork steerer tube. The guy
will NOT like it if he hits a bump/pothole
and the stem breaks off or comes off
the bike.

My intuition was always that it was OK, but of
course I would hate if someone got hurt from
riding my bikes, not to mention (or I will
mention it) [s]he would hate it even more, so
I took the bike to a professional which
operates a bike shop in the city.

No doubt, the world of professional
practitioners is only as good as its worst
mechanic, but I trust this guy completely, he
is from Persia/Iran with all its talented
mechanics, and has tons of experience, anyway
without even looking closely he said it
was fine.

I tried to provoke him to elaborate on that,
but then he just grabbed the handlebar and
torqued back and forth and repeated not
to worry.

There is a couple of points though. You definitely want the expanding
"wedge" to be below the threaded portion of the steerer tube and you
want enough depth so that the stem is filly supported - true on seat
posts also. Probably 50 - 70mm as a minimum would work.

By the way, depending on the bicycle you may find forks with a tapered
steerer tube. Tapered on the inside, that is, and you can sometimes
insert the stem so far that it jams into this tapered portion, which
is not a good thing to do either.
--
Cheers,

John B.

On 7/8/2017 9:42 PM, Sir Ridesalot wrote:
On Saturday, July 8, 2017 at 1:36:42 PM UTC-4, Emanuel Berg wrote:
Sir Ridesalot wrote:

CHECK that stem and make sure there's at lest
2 inches (5cms)of it BELOW the top locknut -
more if there's any space between the top
lock nut and the fork steerer tube. The guy
will NOT like it if he hits a bump/pothole
and the stem breaks off or comes off
the bike.

My intuition was always that it was OK, but of
course I would hate if someone got hurt from
riding my bikes, not to mention (or I will
mention it) [s]he would hate it even more, so
I took the bike to a professional which
operates a bike shop in the city.

No doubt, the world of professional
practitioners is only as good as its worst
mechanic, but I trust this guy completely, he
is from Persia/Iran with all its talented
mechanics, and has tons of experience, anyway
without even looking closely he said it
was fine.

I tried to provoke him to elaborate on that,
but then he just grabbed the handlebar and
torqued back and forth and repeated not
to worry.

--
underground experts united
http://user.it.uu.se/~embe8573

NO GOOD! You need to make a mark with something where the stem is now. I use a marker or even a pencil. then you loosen the stem bolt and remove the stem and see how much is below the mark. If it's less than 5cm or 2 inches (at the start of thewedge) then the stem needs to go in further. Failure to have enough stem inside the steerer tube is risky as it can lead to the stem snpping off. It just takes a minute or so to check it so why not do it to be POSITIVEthe stem is in a SAFE distance?

So, I wonder how the position of the SAFE distance mark is determined
for each stem.


--
- Frank Krygowski

On 7/9/2017 10:18 AM, Frank Krygowski wrote:
On 7/8/2017 9:42 PM, Sir Ridesalot wrote:


NO GOOD! You need to make a mark with something where the stem is now.
I use a marker or even a pencil. then you loosen the stem bolt and
remove the stem and see how much is below the mark. If it's less than
5cm or 2 inches (at the start of thewedge) then the stem needs to go
in further. Failure to have enough stem inside the steerer tube is
risky as it can lead to the stem snpping off. It just takes a minute
or so to check it so why not do it to be POSITIVEthe stem is in a SAFE
distance?

So, I wonder how the position of the SAFE distance mark is determined
for each stem.

http://picayune.uclick.com/comics/ch/1986/ch861126.gif



--
- Frank Krygowski

Sir Ridesalot wrote:

It just takes a minute or so to check it so
why not do it to be POSITIVEthe stem is in
a SAFE distance?

I can take considerably more than a minute to
check as those wedges for some reason (?) gets
very rusty.

But the reason I'm not doing it is I trust my
intuition and my mechanic friend 100%.

--
underground experts united
http://user.it.uu.se/~embe8573

John B. wrote:

There is a couple of points though.
You definitely want the expanding "wedge" to
be below the threaded portion of the steerer
tube and you want enough depth so that the
stem is filly supported - true on seat posts
also. Probably 50 - 70mm as a minimum
would work.

Yes, these bike typically has a wedge that is
pushed to the side, not the half cone expanders
that pulls into the tube itself. Actually I've
only seen wedges so far.

By the way, depending on the bicycle you may
find forks with a tapered steerer tube.
Tapered on the inside, that is, and you can
sometimes insert the stem so far that it jams
into this tapered portion, which is not
a good thing to do either.

OK. The steerer tube is threaded but not
tapered. I've seen that on MTBs tho. I don't
know if it has been around earlier as well.
What is the advantage of that on a bike and
what do you do differently as a mechanic?

--
underground experts united
http://user.it.uu.se/~embe8573

On Sunday, July 9, 2017 at 4:02:32 PM UTC-4, Emanuel Berg wrote:
Sir Ridesalot wrote:

It just takes a minute or so to check it so
why not do it to be POSITIVEthe stem is in
a SAFE distance?

I can take considerably more than a minute to
check as those wedges for some reason (?) gets
very rusty.

But the reason I'm not doing it is I trust my
intuition and my mechanic friend 100%.

--
underground experts united
http://user.it.uu.se/~embe8573

Laziness is thy name. It takes a few seconds to check a stem that isn't frozen in place and a stem that has a rusty wedge can still be easy to remove.

I hope your friend gets the bike checked after she gets it. I'd never trust a mechain who is too lazy to loosen a stem to make sure there is a safe amount of it in the steerer. YMMV and it seems it does.

Your decision but I'm done with this discussion.

Cheers

Sir Ridesalot wrote:

It takes a few seconds to check a stem that
isn't frozen in place and a stem that has
a rusty wedge can still be easy to remove.

It can but not always. You can check out
YouTube videos with people spending hours (?)
on this particular problem, using half their
chemical arsenal before stuff comes apart.

But the reason I'm not doing it is I never felt
the need to. I doubled checked this with guy
I trust completely and he agreed.

--
underground experts united
http://user.it.uu.se/~embe8573

On Sun, 9 Jul 2017 14:02:38 -0400, Frank Krygowski
wrote:

On 7/9/2017 10:18 AM, Frank Krygowski wrote:
On 7/8/2017 9:42 PM, Sir Ridesalot wrote:


NO GOOD! You need to make a mark with something where the stem is now.
I use a marker or even a pencil. then you loosen the stem bolt and
remove the stem and see how much is below the mark. If it's less than
5cm or 2 inches (at the start of thewedge) then the stem needs to go
in further. Failure to have enough stem inside the steerer tube is
risky as it can lead to the stem snpping off. It just takes a minute
or so to check it so why not do it to be POSITIVEthe stem is in a SAFE
distance?

So, I wonder how the position of the SAFE distance mark is determined
for each stem.

http://picayune.uclick.com/comics/ch/1986/ch861126.gif

Actually there is a bit of truth in that cartoon. Or at least I always
assumed that the earliest bridge builders probably kept increasing the
timber sizes until it didn't break any more.
--
Cheers,

John B.

On Sun, 09 Jul 2017 22:02:28 +0200, Emanuel Berg
wrote:

Sir Ridesalot wrote:

It just takes a minute or so to check it so
why not do it to be POSITIVEthe stem is in
a SAFE distance?

I can take considerably more than a minute to
check as those wedges for some reason (?) gets
very rusty.

But the reason I'm not doing it is I trust my
intuition and my mechanic friend 100%.

Intuition is frequently wrong and simply reading this site ought to
convince you that there is considerable dispute about what is the
right way to do it. ("it" being anything). :-)
--
Cheers,

John B.

On Sun, 09 Jul 2017 22:09:47 +0200, Emanuel Berg
wrote:

John B. wrote:

There is a couple of points though.
You definitely want the expanding "wedge" to
be below the threaded portion of the steerer
tube and you want enough depth so that the
stem is filly supported - true on seat posts
also. Probably 50 - 70mm as a minimum
would work.

Yes, these bike typically has a wedge that is
pushed to the side, not the half cone expanders
that pulls into the tube itself. Actually I've
only seen wedges so far.

By the way, depending on the bicycle you may
find forks with a tapered steerer tube.
Tapered on the inside, that is, and you can
sometimes insert the stem so far that it jams
into this tapered portion, which is not
a good thing to do either.

OK. The steerer tube is threaded but not
tapered. I've seen that on MTBs tho. I don't
know if it has been around earlier as well.
What is the advantage of that on a bike and
what do you do differently as a mechanic?

The internally tapered steerer tube means that the tube is stronger at
the bottom of the tube where it is attached to the fork crown, or fork
blades. Where the maximum load will be.

A "raw", uncut, tapered steerer tube will be, typically, ~1 mm wall
greater in wall thickness in the bottom 50 or 60 mm, with about 30mm
taper.

Differently. Just make sure you don't push the stem in too much :-)
--
Cheers,

John B.