How a couple of new acquisitions revealed hidden track issues

I’ve recently gone left field with applying rule 1. I was tempted by the great Mallets of the US of A (whereas I have previously accumulated a motley collection of UK stock). The first, a Athearn 2-8-8-4 fell apart on me but was replaced following an offer for a new one I couldn’t refuse. A magnificent model with excellent running characteristics. It runs without issue on my layout. Then came an offer on the new Kato Big Boy.
I couldn’t resist it. Another fabulous model but I couldn’t get this one round one circuit of my tail-chaser layout. Now I know it requires a minimum radius of 11 inches, which just happens to be half the distance between the two parallel lines of my loop. I thought my curves were consistent, after all, I had used a tracksetta when fixing the two end end curves down.
I have also acquired a Dapol Super-voyager from my buddies in our N Gauge Society area group. This also wouldn’t run around until I realised it has a projecting piece under the cab that catches on Peco points. When removed, off it went but it growls like a frustrated guard dog on the curves. Now the pitch of the growl is not uniform. I guess the drive shafts are catching something but the pitch changes as the radius changes and a high pitch  conincides with where the Big Boy derails. So now I know not just where the change of radius starts, I also know where it ends.
Enter another Kato - the FEF 4-8-4 which in reality is half of a Big Boy. It derails just like its big brother. Much easier to handle though. A better Guinea  pig for track testing. it too is a superlative runner, apart from being hyper-sensitive to track characteristics. Time to get fixing.
I’ve just re-laid the end curves, this time using home-made 11 inch tracksettas that form a semi-circle, the tight points have been eliminated and the FEF now runs around smoothly. So does the Big Boy and I can really appreciate what wonderful models these two Kato steamers are.
My loop has a scenic side and a fiddle yard side. Rising above the fiddle yard, I have a spectacular elevator (raises the track 30 cm via a spectacle-shaped incline of over 10 meters length) in readiness for an upper tier terminus (yet to be installed). The Kato engines climb up most pulling impressively heavy trains but derail on a couple of the curves. The Dapol Super-voyager doesn’t derail but the growl does change pitch where the Kato engines leave the track. So, more curves to smooth out and all will be good.
So, now I have useful new tools in my kit and one step closer to revealing my layout (too much work in progress just now).

Looking forward to it,don't take too long.