Slide Bar Play in 29K71

[Harfindel]

I am rebuilding some parts in a 29K71 to try increase the stitch length.  Already identified the bell crank lever as an issue.  I am wondering, though, if I need to work on the feed motion cam or the slide bar's roller and stud.  With the feed motion cam held stationary in an assembled machine, what is an acceptable end play for the slide bar?  I am measuring 0.007" at the moment.  How close am I to needing to replace the roller and stud? What is the best position of the feed motion cam to use to check for end play?

Thanks in advance for the help.

Carl

Edited December 10, 2016 by Harfindel

[brmax]

Just from your part names the feed motion cam is the item to have more duration for lengthened stitch in my "figrs"

I also believe the .007" clearance is perfect and being between .004"-.008 for flat land type bearing surfaces, many times oil film thickness is proportional to surface.

Keep us posted on the work

good luck

Floyd

[Harfindel]

Floyd:

Thanks for this information.

[Harfindel]

OK, so I have moved on, to the gearbox.  Dismounted it, disassembled it.  Drive pinion and long rack have unsightly wear on the teeth (I can feel the wear marks with my thumbnail), and so I ordered replacements.  I think I should replace the pinion bushing, too, though.  Any advice on how to get it out of the gear box?  Do I just persuade it out with a punch?  A gear puller?

[Constabulary]

When you replace just the long rack it could be that it does not play well with the other parts of the gear box. When the gears / racks are in "good" condition they have a flat tip when they are worn the have a sharp tip. But there is of course something in between.

I have replaced a pinion bushings on 29K´s twice and both were extremely (!!!!) tight. I heated the gear box and hammered it out with a big punch. Not sure if they were just badly gummed or heat shrinked. The new bushings did not fit very well as they were a bit oversized so I had to sand them down. That something I don´t like to do again as I feared to ruin the gear boxes.

Edited December 21, 2016 by Constabulary

[Harfindel]

Constabulary, thanks for this.  With the current parts, I have about .107" play in the shuttle carrier, when measured at the periphery, which is about 15%.  There is considerable side play between the pinion and the bushing, too, but the shaft of the drive pinion shows uneven wear (its formed a cone by about .006"), so maybe the new pinion will fix things.  If it comes to replacing the bushing I think I may need an arbor press and a torch.