November of last year I was working on my SILs 99K. I had found two problems with it that needed adjustments to fix.
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The first was the bobbin case position bracket. The screw that holds the bracket in adjustment is frequently mistaken for the screw that removes the bobbin case latch and loosened up. This messes up the adjustment by allowing the bracket to move. See the black arrow in the pic below:
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This screw in my SILs machine was loose. The b c position bracket was literally flopping around. This throws the adjustment of the spring to bobbin case out and that will create tension problems.
The specs I've found show the adjustment to be .010" to .015" gap between the heal of the bobbin case and spring. See yellow arrows in the pic above.
To adjust the gap use a narrow gap guage, I set it at .012", set the gap then tighten the screw good and tight.
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The screw to remove the bobbin case position bracket is underneath the bed. It has a small head and is accessed from the left near the hook casting.
The next problem was that the feed dogs were hitting the rear of the needle plate
and the casting under neath.
I looked and looked and asked here on the QB and a couple forum members if they knew of any adjustment instructions for the front to back position of the feed dogs. I was never successful in finding any instructions.
So I reverted back to when I took Rusty my derelict 99K apart to clean the rust off. I had to adjust the feed dogs on it so I decided to adjust my SILs the same way.
[(NOTE: I do not know if this is correct according to Singer as I never found any instructions. However it worked so this is what I did.)]
If you tilt the head back on the motor side the longer horizontal rod towards the front of the machine controls the feed dogs. The screw on the right that connects to the connection rod is eccentric.
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By loosening the lock nut on the inner side then turning the screw counter clockwise I was able to adjust the front to back position of the feed dogs.
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It didn't take much, and now the clattering is gone.
So, hopefully this will help someone if they have the same situation.
Joe