Make sure all the holes that should be threaded, are threaded. I have assembled two kits and one of them had two parts with unthreaded holes. Of course, the ones that were unthreaded were the ones that are the hardest to get to with the screws and I spent a lot of time assuming I did not have them aligned correctly.
There is one other tricky part to get together and I spent a lot of time getting quite upset to my stomach before I realized how EASY it is to assemble them...
The Walshaerts valve gear has a curved link with a forked Radius rod that fits into it and a small square Link Block between the forks and contained inside the Curved Link. You have to place the fork inside the link and then slide the Block down one fork tine halfway into the link and then push it sideways so it will fall between the tines. I had a terrible time because every time I tried to slide it sideways, it fell over and then would not fall between the tines. ARRRRRRGH! TWENTY MINUTES of: put in the fork, lay the block on it, tip the fork so the block slides into the link, it falls over, remove the fork, shake the block out, drop it on the floor, hunt for it, do it all again.
Then I discovered that the small screwdriver that comes with the kit could be inserted into the link from the side and into the hole in the block to keep it vertical. Then it could be slid sideways and down between the tines.
The first one took me 20 minutes and 3 seconds, the second one took 3 seconds. The second engine also too just 3 seconds per side.
Don't be afraid to file off burrs around punched out parts... especially the Link Block (it should be smooth on all the edges, but don't file it smaller, just break the edges a bit!) Also the paint seemed to have subtracted a wee bit of width from the frame axle box horns. A light, fine file will do. I used the file on my Swiss Army Knife for all of it... it is not too agressive.
Mark Horovitz wrote a review of the Mike for Garden Railways Magazine back when the kit came out. I would heartly recommend reading it. I think it used to be available on his web site, but I could not find it just now.
He said he felt that the kit was not for beginners and that had me quite nervous as I had purchased my first one before I read the review and I was a klutz assembling plastic models as a kid. I think he also said that Aster expected the assembly to take between 20 to 40 hours and he felt that was a bit short. He also listed some errors in the assembly instructions... if Royce does not provide them to you, say so and I will get them to you somehow.
I decided to spend no more than 1 hour per evening and maybe 4 hours on Saturday and Sunday afternoons just to make sure I didn't "burn out" on it. I assumed it would take me a couple of months to get it done.
I started on a Tuesday night. I read the whole instruction manual and studied the assembly drawings (and made markups per Horovitz's article). I then got a bunch of plastic cups (ice cream cups... low and wide so they won't tip over easily) to hold some of the really small parts and the bags of screws. I kept the bags of screws and such in alphabetical/numerical order on my table so I could find them easily. The parts for each step of the instructions all come in one box per step. That was the first night's "work"... that and being mesmerized by the beauty of the tiny parts!!! It should not have taken me 3 hours to do this step, but I spent way too much time admiring the parts... and it is a good indicator of how well I kept to my plan of just 1 hour per night.
By Friday night I had the chassis running on air, but discovered I had missunderstood the instuctions in setting the valve gear and when I put it in forward, expecting to catch it with my right hand, it went backwards and almost into the glass front of my china cabinet!
By Sunday afternoon, I had it boiling water and running on steam. It took me less that 20 hours to do the assembly. (This was without the axle pump, but with the tender pump.)
The second engine... well it took me slighty OVER 20 hours to assemble it.
ONE, there were two parts that were not threaded and one was the smokebox base where you have to slip the screws deep into the frame almost blindly to attach them together. I spent a long gut wrenching time on that one before I pulled the smokebox off (a tricky step due to some of the parts in the smokebox you have to thread through the hole in the bottom) to see why I could not get the screws started... NO THREADS... easy fix, but took a trip to the hobby shop to get the right metric tap.
TWO... Male EGO! I had already assembled one of these things! It was EASY! RIGHT!??!?!? I kept skipping steps in the instructions, putting things together that needed other things attached first. Had to do a LOT of dissassembly to correct things. I also still got the valve gear reversed, but I was smart this time and put a couple of big books on the ends of the table to catch it!
If you have problems, feel free to ask here... also do a search of the archives for notes by those that have assembled it. Also check the Southern Steam Trains website for more notes.