Hi Lynda,
I haven't been able to find a repair manual for the 115. WIChix is correct about the instruction manual for your 115 can be found at the link she posted. Here is the direct link
http://ismacs.net/singer_sewing_mach...ine-manual.pdf Also, as she said "Sometimes the check spring is good on the tension, but isn't seated correctly. When you take it apart, be sure to photograph it and compare to diagrams for correct reassembly." It is possible that the tension assembly need a complete disassemble and thorough cleaning. My 115 has a newer assembly. I think your tension assembly is more like the 15-30. I think it is like the one shown on this thread -
VSMS: Difference between Singer 115 and Singer 15-30 machines?
Since it is very similar on the top to a 15-30 I would suggest taking a look at
https://quiltersstashbox.com/blogs/v...-1-disassembly especially the "Thread Tension Assembly"
I think the needle thread guide is a wire that screws on to the needle clamp. You can find the parts list at
http://parts.singerco.com/IPpartCharts/115-1_2.pdf On page 28 of the pdf you can see 55619 (needle bar thread guard). Perhaps you can fashion one from the image.
Janey - Neat people never make the exciting discoveries I do.
I really think you need to take it apart and clean thoroughly.
If it has the pin 15238 on page 29 of the parts pdf you can print out that page and compare the pin to the print out of that page. Only print "current page" and do not alter the page size.