Re: Block Chain

On Sat, 07 Apr 2007 18:44:36 -0400, Marcus Coles <marcoles@xxxxxx>
wrote:

carlfogel@xxxxxxxxxxx wrote:
On Apr 6, 12:02 am, "rcous...@xxxxxxxxx" <rcous...@xxxxxxxxx> wrote:
On Apr 5, 1:28 pm, jobst.bra...@xxxxxxxxxxxxxxxxxx wrote:

http://www.midamericaauctions.com/showvehicle.asp?VehicleID=12098
Jobst Brandt
Can't really see the evidence for block chain in those photos, but a
lovely bike nonetheless.

Dear Ryan,

I could have sworn that I posted a reply about this, but I can't find
it, so here it is again.

Block chain would require a gap between each tooth:

http://www.sheldonbrown.com/gloss_ba-n.html#blockchain

I can see only two teeth clearly exposed on the front sprocket, just
below the right crank arm:

http://www.midamericaauctions.com/showvehicle.asp?VehicleID=12098

Enlarging the picture with a free viewer like IrfanView doesn't help
much:

http://www.irfanview.net

Even when I enlarge it, I can't make out what the sign on the lower
left of the picture says, much less tell whether there's a clear gap
(or non-gap) between the two front sprocket teeth.

So I used a free onscreen protractor:

http://www.markus-bader.de/MB-Ruler

The protractor suggests that the teeth are set ~10 degrees apart, or
~36 teeth on a front sprocket.

(Precise measurement is tricky, since the picture was taken at a
slight angle. The angle distorts the sprocket a bit and also requires
you to guess where the center of the sprocket is. But I get ~10
degrees, plus or minus a degree.)

A ~36 tooth normal-chain front sprocket is reasonable, given an
ancient moped.

A ~36 tooth block-chain sprocket doesn't seem likely. If a block chain
skips every other tooth, ~36 teeth would mean that the front sprocket
in the picture is the size of ~72 tooth normal sprocket, which it
clearly isn't.

Cheers,

Carl Fogel


Dear Carl,

From here it looks like a skip tooth chain wheel.
Take a look at the teeth above the crank arm in the upper picture where
they have the black chainstays for a background.
In the lower picture look where the chainwheel has the engine flywheel
as a background. http://www.ody.ca/~marcoles/MarksChain.jpg

Marcus

Dear Marcus,

Nice enlargement of the lower picture!

Here it is again, for those who want to check for themselves:

http://www.ody.ca/~marcoles/MarksChain.jpg

My onscreen protractor shows ~16 degrees per tooth, which works out to
~22 teeth, and is quite plausible for skip-tooth. And the gap in your
enlargement looks pretty clear to me.

Here's the original link with two pictures:

http://www.midamericaauctions.com/showvehicle.asp?VehicleID=12098

But the upper picture still looks like ~10 degrees per tooth for the
two teeth against the white background, which works out to ~36 teeth
and doesn't seem plausible for block chain.

This apparent contradiction puzzled me, so I looked some more.

When I enlarge the upper picture with the two teeth that look so close
together against the white background, I _think_ that I can make out
other teeth that are further apart, just like the lower picture.

For the best view of a skip or gap in the upper pciture, look at the
teeth against the black chainstay area.

So now I agree with you that it's block chain.

I suspect that the two "teeth" that caught my eye against the white
background in the upper picture are actually just one tooth and
something else in just the right spot to look like a tooth where
there's actually a gap.

I can't figure out what that false "tooth" is against the white
background in the upper picture--maybe some fitting hanging down on
the far side of the machine?

The upper picture has what looks like a light-colored bar running
under the chainstay, but I think that it's actually just the faint
_shadow_ of the chainstay on the white wall. But the false "tooth"
seems to be next this bar, not part of it, so I still don't know what
that false "tooth" is.

Anyway, my reconsidered dental opinion is that I was wrong and that
you're right--it's block chain with a skip-tooth front sprocket, just
as advertised.

Cheers,

Carl Fogel
.

Relevant Pages

  • Re: Block Chain
    ... Block chain would require a gap between each tooth: ... I can see only two teeth clearly exposed on the front sprocket, ... Enlarging the picture with a free viewer like IrfanView doesn't help ...
    (rec.bicycles.tech)
  • Re: Block Chain
    ... Block chain would require a gap between each tooth: ... I can see only two teeth clearly exposed on the front sprocket, ... Enlarging the picture with a free viewer like IrfanView doesn't help ...
    (rec.bicycles.tech)
  • Re: Block Chain
    ... Block chain would require a gap between each tooth: ... I can see only two teeth clearly exposed on the front sprocket, ...
    (rec.bicycles.tech)
  • Re: Over Cautious Dentist?
    ... Since utilizing his services, I've had to get 6 fillings, some so minor ... With tooth coloured fillings the ... dentistry or teeth for that matter to live productive lives. ...
    (sci.med.dentistry)
  • That dental surgery didnt exactly go as I had thought...
    ... DD1 had her appointment with the pediatric oral surgeon this morning. ... smashed her teeth right out of her head. ... The dentist there ended up just 'sealing' her one tooth ...
    (misc.kids)
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