On those occasions during the cooler months when I went insane and laid track when the temperature in my non-climate-controlled layout space was in the 30s I deliberately left 2mm gaps in my rails. By the time the layout reached its seasonal high of 120+ those gaps had closed to near-invisibility.
If it's cool in your layout space and you solidly fill an anchor the gap (or lay track with no gap) don't be surprised at the heat kinks that show up in August.
If the gap is on tangent track (or on the inside of a curve) and you have body-mounted couplers, it will not cause problems in normal operation if you have 'battered' the ends of the rails at the joint to remove the sharp corners at the top inside of he railheads. Unless your oversize gap is located in the outer rail of a curve, I wouldn't even bother with it. (And I am obsesso about derailment-resistant trackwork!)
Chuck (Modeling Central Japan in September, 1964)
I would use a two part epoxy. Get the kind that comes in sticks and is kneaded together. Work it into the gap shaping it as close to the rail as you can. When it cures touch it up with a file.
I did this on my last layout when I was a little too enthusiastic about leaving a gap for insulating the rail into blocks. Had no trouble with it.
Enjoy
Paul
I am having a bit of a hard time visualizing exactly what the issue is here. Are you using flex track, sectional track, or section track with built in roadbed?
Assuming we are talking sectional track, I'd go back and see if by chance you created this gap with smaller gaps earlier in the tracklaying, such as curves that do not fit tightly or with slight gaps on just one side. Assuming there is nothing wrong there, I'd investigate cutting two pieces of snap track to come up with the final length you need. My experience is that very small sections are an invitation to problems -- if you need 10 inches of snap track, rather than use 9 inches plus one inch, I'd go with two sections of 5 inches each. In fact this may be a place to use a cut up piece of flex track.
Of course in HO Atlas does make a variety of very short lengths of snap track to fill gaps but not 1/8 inch gaps!
When facing a fixed end point like this my instincts are to cut the track too long and then file or grind it down to size based on trial and error, rather than think you can measure and cut exactly right on the first try.
Dave Nelson
I have a straight track plan in a specific section that now as a gap of about 1/16th to 1/8 in gap. What is the best way to fill in that gap? What procedures would you advise?
THanks
Mike