We are rebuilding the differential cases for the rear end now and some folks are actually bending the flange trying to install the ring gear, the gear mic's about .007-.0012 smaller than the housing, if you try to use the bolts to bring down the gear then it can bend the flange, so is heat or a heavy press the best way to install the gear?
Are the new ring gears too small?
The gear should be a light slip fit.
You can safely heat the gear to 275deg and cool the housing Use a stud or two in the ring gear to align it while installing. If you don't have a temp gun, spit on you finger and touch the part. When it sizzles, it is hot enough.
We are looking into this these are used ring gears that customers are using, we just found that a Ford script ring gear is .0002-.0002 1/2 press fit, the non Ford script gears are the problem, the manual says to tap on with lead hammer but some folks are using the screws to tighten and draw the gear down which will bend the flange
I can do most things on a Model T, but if there is something I cannot do, I have no problem seeking the help of an expert. Sounds as if the ring gear is too small. Safest way is to take both parts to a machine shop and have them machine the ring gear to fit it. Should not cost too much and you will have the peace of mind of knowing that you did not remove the temper by heating, or bend or otherwise damage the gear by forcing. Jim Patrick
Heating aside, a .0012 press fit is kind of much. I'd be afraid to split the ring gear.
I had a batch of some of those ring gears you are talking about, I had to put the carrier in my lathe and remove a tenth of a cats hair to make it fit properly. Just my $.02.
Not to nit pick, but things seem to be called out to the wrong decimal in several places.
The unscientific rule for an interference fit is 0.001 per inch of diameter, so anything more than 0.005 would be stout on a gear with a 5" i.d. Even to install it heated would be a lot of crunch when it cools, especially at the tighter end of what you've found. The best thing would be to open them up to Ford spec, which I think you are saying is 0.002 - 0.0025 under and would be half of a standard interference fit, which sounds about right.
I think it would be best to dust whatever is necessary out of the i.d. of the gear. To install them too tight or turn down the o.d. of the carrier is setting up a future owner for a booby trap when it comes time to rebuild again someday.