I have a Heljan turntable that hold a 13 1/2" engine, what are my options as far as engine size i.e. 2-6-2, E8 AB, also brand. Most adds don’t give overall length and I don’t want to install the TT and find out that I can’t get the locos that I want.
In HO scale, your options would be any locomotive that’s no longer than 90 or 100 Scale Feet. Most turntables on the major railroads were removed shortly after the diesels took over, so you could almost consider the turntable and roundhouse a steam era type thing. They may have existed for a while with the diesels, but soon fell into disuse.
My BLI 4-6-4 fits well within the limits of the bridge rails for my Walthers 90’ TT. Basically, if you let your bridge rails extend past the bridge ends by 1/4", on each end, you buy yourself another 4’ in scale, give or take. You should be able to get a Mountain class loco onto that bridge, but your couplers may hang well out there.
I mated an Atlas Cornerstone 3-stall house to the Walthers TT, and ended up having to place the house about 1.5" away from the rim of the pit. That gave me the opportunity to make longer, if highly aprotypical, bridge rails…they would be right for a 100’ TT. However, this allows me to back my P2K F2 A/B set into one stall of the house using my ‘extended’ TT rails. Suits me just fine. [:D]