Gummy Wheel Fix


I have downloaded details of how to replace the drive wheel on an old HP67 but no details on the correct O Rings to use. Size must be critical. Can anyone help with the O Ring specification or type ?


You can also use a piece of a rubber fuel- or oil-tube. I repaired my 41 card-reader with a piece of a rubber tube used (I guess for brake fluid or fuel) in a small motorcycle. When you have opened the card reader you can usually estimate what the outer diameter must be by inspecting the remains of the old rubber wheel or the distance from the wheel-axis centre to the card. Exact fits with an accuracy of 1/10 of a milimeter are not really necessary as long as the rubber gets in touch with the card: after all it is flexible and will give way to the card even when it is (slightly!) too large in diameter.


Thanks to all for the prompt answers and suggestions. Suppose I should open the thing up and have a look before I go any further or ask anymore questions....Thank You.


The inner diameter is crucial. You can check it by measuring or estimating the diameter of the axis. The wheel should fit tightly enough to the axis so that there is no slipping during operation. The outer diameter can be estimated from the remains of the old rubber wheel or by estimating the distance between the centre of the wheel axis and the card surface. The outer diameter is allowed to be a little too large since the rubber is flexible enough to give way and be pushed aside, but one should not overdo this of course.


If you MUST use o-rings you need size 005. These are 1/64" smaller than what almost every place stocks (size 006). Silicone ruber fuel line works much better. One problem can be finding it that has the inner and outer diameters well centered.

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