How to trim bi-fold door?

I bought a bi-fold door at home depot and the size of the door is 36"x79"(Actual is 35.5"x79"). But my house was built in the 1960 and the door opening for the entrance closet is not a standard size. I measured the openning and the measuremeant I got were, 34" and 11/16 by 80" so I trimmed the width of the door to 34 and 11/16 of an inch but the door still doesn't close because it's too wide. Now I assume you have to leave a gap and you can't have the door exactly the same as the opening because were the door hangs on to the track is off the edge of the wall frame by maybe an inch but how much gap should I leave? I already cut both door panels once so I can't screw up a second time. Now since I have to cut some more off of the door I will probably have to reinforce it because the MDF wood on the edge is getting pretty thin.

 

When you trim a large amount off a bifold you generally want to take it apart and trim equal amounts off each side of each door. Generally the doors need to be at least 1/2" smaller than the opening.

 

Well I got it to fit by cutting it half an inch smaller than the opening. But I had to reinforce it with a cut 2x4 on both side but now at what distance from the edge should I drill the holes for the pins on the top and bottom so that it fits like it's suppose too?

 

Can't see your hardware from here, so its hard to say exactly. If your top and bottom brackets are adjustable, it really doesn't matter too much, and you would probably just center your pivot on the rail of the door. Put it too close to the hinge side and the door would swing too tight to the jamb.

1" would be a good guess. Look at where the pivot will fit into the track on top and bottom. There should be a minimum and maximum amount it will adjust, and plan to put your hole for the pivot somewhere in the middle of that. Figure in the gap along the edge of the door, and subtract that when you measure.

 

the bifold doors I've trimmed and hung said to leave a 1/4" gap to the jamb on the pin side, this gap allows the front corner of the pinned edge to rotate without binding.

One thing I did to reduce the amount of trimming necessary was to reduce the need for that gap by routing a roundover onto the front vertical edge of the doors on the pinned ends, with the roundover cut on the door, the gap could probably be reduced down to 3/32 or so (meaning if your door is currently cut to exactly the width of the opening, you'd need to trim 3/64 to 1/8 off each panel depending on which way you want to go on the roundover, a planer would be the best tool for this if you've got one). If you're really worried about retaining what's left of the outer edges then you could remove the hinges and plane this material out of the middle then re-mortise those edges and replace the hinges, but that's a bit more work.

If you have to re-drill the pivot holes in the doors (possible given how much you've trimmed off the sides), once you're trimmed to the final width, the pivot hole center would be in from the edge by 1/2 the thickness of the rail.