Hello All,
Thanks for having me!
I have an IBM Model B that, when I type in lowercase, some of the type bars fail to strike the platen. I've done some surface-level research and read about how the letter cams need to be a certain clearance from the power roll, which is between 0.15" and 0.20". So I checked this with a feeler gauge set to 0.15", and alas, the letter cams are too close to the power roll.

"Cam clearance must be equal across all cams in order to have uniform impression and keyboard touch. Excessive clearance will cause failure of cams to engage power roll as keylever bottoms, or failure of trip lever to restore as key lever restores. Insufficient clearance will cause weak impression and repeating cams."
http://bitsavers.informatik.uni-stuttgart.de/pdf/ibm/typewriter/model_b/241-5141-1_IBM_Customer_Engineering_B-1_Adjustment_Manual_Jan1963.pdf

[color=#303030][color=#303030]And insufficient clearance was what my problem was! Well, sort of. (I think....). I say this because the gauge clears the space on the left side of the power roll, but tightens considerably as one goes along its length.

So I ask: How can I adjust the clearance of the letter cams to the power roll? Or is this fault coming from another problem? Is the power roll simply worn out?

I have looked through the aforementioned manual, and it does (with a lot of technical jargon and glossing of details) go through how to adjust the clearance, but following these steps didn't help me. (I tightened all nuts that I loosened after this unsuccessful venture...)

I hope I have added sufficient information!
Thanks,
Oli

*At least I think it is a Model B, although it says "Model 12" on the underside.[/color][/color]