Glue

Try Contact cement.

You might be able to rough up the surface a little.

Rich

If it is made of Delrin

Quickly pass the blue corona part of a propane torch flame over the surface and then apply 3M DP8005. It is known as flaming. The flame corona temporarily ionizes the surface making the 2 part acrylic adhesive stick well.

[EDIT] I should note the above process is what we used to modify slot car chassis. It worked better than any of the normal hobby shop goos. 

Contact cement won't work

Contact cement won't work either.

The plastic used in the sideframes is sometimes called "engineering plastic", and is not glueable with most adhesives, even ordinary CA glues.

There ARE some CA-type glues that will work, but they're not cheap. You'll sometimes see them with a little kiosk selling the stuff at train shows. Let me see if I can find an old bottle I have around here and get the name of it.

Cypox

Mike Rose has found Cypox is usable in many applications that other glues won't work in, including gluing delrin/engineering plastic.  See the link for more information.

http://www.mrhobby.com/store.php/pg10120/cypox_tips_amp_techniques

Marc Simpson

Cyanopoxy from Cool-Chem was

Cyanopoxy from Cool-Chem was the one I was trying to think of... Looks like they've gone out of business, but this outfit claims to be same kind of stuff.

http://www.c-pox.com/home.html

If you can't find that, look for a hobby shop that carries ZAP products. Their "Poly ZAP" might fit your needs as well. (Blue label, second one down on the page below)

http://www.zapglue.com/special/

ZAP also makes a foam-safe CA that I've found useful. Any hobby shop that carries RC planes should have it, and can probably get the Poly Zap as well.

Gluing Delrin

Alan is right, flaming will give the plastic "tooth", helping the adhesive to bond to the plastic.  Creating a rough gluing surface is said to help also.

Locktite claims their product will glue Delrin.

Welding is the typical way that Delrin is joined, I believe.

Microscale Adhesive

The Microscale adhesive works very well too, just like the Cypox and Cyanopoxy adhesives.  Just be sure to use the Micro-prep first as it seems to improve the adhesion on slippery engineering plastics.  

Dan R.

Loctite

Loctite is likely the right now I can drive and buy it approach.  Likely Wally World of the local hardware store has this.  If it don't work there are plenty of uses through out the year for it.  Good to have in-stock around the house. 

The Cypox seems like the best but $35+ to test it just stinks! 

This link has some pretty good info:  http://www.plasticgenius.com/2009/04/plastic-glue-and-adhesive.html

Another Loctite product

I've used this  http://www.loctiteproducts.com/p/sg_plstc/overview/Loctite-Plastics-Bonding-System.htm with some success on handrails.  I just bought some at Menards. If it is structural I would not trust it.  If you have enough thickness you can plastic weld it with a soldering iron.  Practice first and yes it will stink.

Is it just side frames or is it structural?

Cosmetic sideframes can be attached with a rubbery cement like goo or barge. If it's a structural part I'd look at ways to pin it with metal along with whatever glue is used......DaveB

Gluing sideframes

Loctite has a product called plastics bonding system which uses a heptane primer. I picked it up at a big blue home improvement store and it was'nt very expensive. So far it has worked pretty good.

LocTite 770 Poly-olefin primer

Dear ???

Loctite 770 Poly-Olefin primer + Zap-a-Gap Green ACC has allowed me to stick Grandt-Line delrin Climax driveshafts to metal motor shafts, and use them under torque-load conditions to drive On30 locos hauling actual 2-kilo trailing log loads...

http://www.loctite.com.au/3320_AUE_HTML.htm?nodeid=8802638135297

Happy Modelling,
Aim to Improve,
Prof Klyzlr

Structural

It is used to hold the sides of the frames to the top tower part of the frame.

Bumper Epoxy

Well I had a brilliant moment flash through my mind.  I did a repair on my Mustang bumper a few years ago with a 2 part epoxy called Bumper Repair by 3m.  I figured it worked there why not on a HO loco truck.  It sets up quick and it is pretty tacky stuff.  Spreads pretty easy at first.  Dries black and is trimable and sandable.    Seems to have worked.

 Jason