Pedal Washers

[David N. Makinson]

What is your take on the use of pedal washers to protect crank arms?
David

 

[[email protected]]

David N. Makinson writes:

> What is your take on the use of pedal washers to protect cranks?

The problem is that pedals with flat faced spindles will move radially
in their threads. Washers will not arrext this motion so as the pedal
wobbles in place, it will either begin eroding the washer, after which
it will find a preferred position and cause the same damaging motion
between it and the crank, or it will do this from the start. As long
as there is relative motion of the pedal spindle and the crank, the
crank will be eroded and develop cracks.

The history of automobile lug nuts, that once had this affliction
before being made with a conical pressure face shows what the remedy
is. Short of that, I see no solution to the problem other than some
clever machining:

http://www.chiark.greenend.org.uk/~damerell/bikes/brandt-cranks.jpg

Jobst Brandt

 

[David N. Makinson]

[email protected] wrote:
> David N. Makinson writes:
>
>
>>What is your take on the use of pedal washers to protect cranks?
>
>
> The problem is that pedals with flat faced spindles will move radially
> in their threads. Washers will not arrext this motion so as the pedal
> wobbles in place, it will either begin eroding the washer, after which
> it will find a preferred position and cause the same damaging motion
> between it and the crank, or it will do this from the start. As long
> as there is relative motion of the pedal spindle and the crank, the
> crank will be eroded and develop cracks.
>
> The history of automobile lug nuts, that once had this affliction
> before being made with a conical pressure face shows what the remedy
> is. Short of that, I see no solution to the problem other than some
> clever machining:
>
> http://www.chiark.greenend.org.uk/~damerell/bikes/brandt-cranks.jpg
>
> Jobst Brandt

OK. I understand. And I suppose the tapered washer is split so that it
clamps to the pedal spindle. Did this solve your 1/yr crank breakage
problem?

David

 

[* * Chas]

<[email protected]> wrote in message
news:[email protected]...
> David N. Makinson writes:
>
> > What is your take on the use of pedal washers to protect cranks?
>
> The problem is that pedals with flat faced spindles will move radially
> in their threads. Washers will not arrext this motion so as the pedal
> wobbles in place, it will either begin eroding the washer, after which
> it will find a preferred position and cause the same damaging motion
> between it and the crank, or it will do this from the start. As long
> as there is relative motion of the pedal spindle and the crank, the
> crank will be eroded and develop cracks.
>
> The history of automobile lug nuts, that once had this affliction
> before being made with a conical pressure face shows what the remedy
> is. Short of that, I see no solution to the problem other than some
> clever machining:
>
> http://www.chiark.greenend.org.uk/~damerell/bikes/brandt-cranks.jpg
>
> Jobst Brandt

Jobst,

1. What's the angle countersink?

2. Where did you get the angled washers?

I've used washers on TA and Stronglight cranks. They have a slight
counterbore for a washer and at one time the washers were provided by
the crank manufacturers.

Chas.

 

[[email protected]]

David N. Makinson writes:

>>> What is your take on the use of pedal washers to protect cranks?

>> The problem is that pedals with flat faced spindles will move
>> radially in their threads. Washers will not arrest this motion so
>> as the pedal wobbles in place, it will either begin eroding the
>> washer, after which it will find a preferred position and cause the
>> same damaging motion between the washer and the crank, or it will
>> do this from the start. As long as there is relative motion
>> between pedal spindle and crank, the crank will be eroded and
>> develop cracks. Look at the face of any well used crank when the
>> pedal is removed.

>> The history of automobile lug nuts, that once had this affliction
>> before being made with a conical pressure face shows what the
>> remedy is. Short of that, I see no solution to the problem other
>> than some clever machining:

http://www.chiark.greenend.org.uk/~damerell/bikes/brandt-cranks.jpg

> OK. I understand. And I suppose the tapered washer is split so
> that it clamps to the pedal spindle. Did this solve your 1/yr crank
> breakage problem?

This question gets asked often. No, I have not had any crank failures
since installing this modification and am using the same DuraAce
cranks that were all bought at the same time. These are as the
picture shows, the same old style Shimano square taper cranks.

I also no longer inspect the cranks with a magnifying glass before
going on longer rides on weekends as did in the days when I broke at
least one crank per year for close to two dozen cranks.

Jobst Brandt