This is sight unseen of course but I was left wondering if your curve is slightly under gauge? I have effectively sharper than normal curves, led into by a transition curve. My experience of AHM/Rivarossi engines as such is that the flanges have picked the rail and lifted, sometimes off, from the track.
Do your tender trucks and your drawbar have a degree of lateral play as well as "roll and yaw"? Is the drawbar free but not loose on the tender. The force exerted by the engine could be lifting your tender wheels or forcing the body straight thus lifting the truck.
I have had to make sure that all of these are free... but not sloppily loose for reasonable operation on my layout... one day I'll get the bigger curves!
Hope this is of help!
Cheers from Down Under
Trevor www.xdford.digitalzones.com FYI
Charles,
I don't think your 20-inch radius is the problem. I have BLI Mike that deals with my reverse loop, which has 18-inch radius curves. And does it in both directions. My Niagara with its centipede tender, and my grandson's Challenger both negotiate the reverse loop in either direction as well.
All of my steamers will travel my layout's 20 1/2" and 22 1/2" curves in either direction at any speed and will negotiate the 18" radius curves on the reverse loop in either direction at any reasonable speed, with or without a train.
The only time I had trouble backing the Mike through the reverse loop it turned out the tender was close coupled. Moving the draw bar out to the end hole fixed the problem.
My BRVRR is flat so I have no experience with the complexities that grades and transitions into them bring to the question.
If your new tender is lighter than the original, I would weight it to be at least equivalent or maybe a little heavier than the original BLI tender. The larger wheels may contribute to your problem as well. I would go with 33" metal wheels to add some weight down low. Less chance of 'climbing' in my opinion.
My worth.
Good luck!
Remember its your railroad
Allan
Track to the BRVRR Website: http://www.brvrr.com/
When this happens, are you pushing a train backwards up a hill? In this case, it may be the non-linear forces acting on the tender which are pushing it outwards on the curve.
Is the curve flat, or superelevated (banked)? Any such tilting of the track would cause the tender to tip inwards, particularly if it's top-heavy.
Does this always happen at the same spot on the curve? You may have a slight dip in the track, either where the wheel comes off, or downhill a bit where the other truck is. If the tracks aren't even, the tender may be tilting to follow the track. Check carefully with a straightedge, and also verify that the track is in gauge all the way. And while you've got your NMRA gauge out for the track, check all the wheels, too.
Is there a kink in the track near where you have the problem? Even a smooth-looking joint could have a small "ledge" that's catching the stressed tender as it rounds the curve with a load.
My BLI Hudson has 2 settings for the drawbar with the tender. On the wider-spaced setting, the unit will take 18-inch curves. If close-coupled, though, there is interference between the back of the locomotive and the front of the tender, and it can't take those curves. Check the spacing of the engine and tender to make sure there is clearance.
Replacing the wheelsets is probably cheaper than replacing the trucks. Even if the plastic wheels are not the problem, putting in metal ones will be better in the long run.
It takes an iron man to play with a toy iron horse.
Charles--
Just a thought--add a little weight to the tender and change out your 36" wheels to 33". That might make a difference in the tracking. NWSL makes 33" wheels that have some pretty good weight to them.
Tom
Tom View my layout photos! http://s299.photobucket.com/albums/mm310/TWhite-014/Rio%20Grande%20Yuba%20River%20Sub One can NEVER have too many Articulateds!
Some follow-up info.. The original (HO) BLI Light mike easily makes 18 inch radii and had no problem with the 20in curves - interestingly enough the stock tender is heavier than the converted AHM tender. The C&O K-8 Mike's used a roughly 40 ft tender, and the old AHM plastic tenders are a near match for them (I think they came on their Pacifics), I did subsitute 36 in wheel sets for the ones that are on the orginal tender (31 in wheels). If I remember the AHM models that used these, they would work with 18 in radii as well.
Charles
Were the C&O K-8 Mike tenders longer than regular Mike tenders? Or, to put it another way: Is the brass tender you are now using longer than the tender that came with the BLI Light Mike?
My BLI and Trix Mikes can navigate 18" radius curves with no problem. However, I do have shorting issues when my Trix Mike goes through a #4 Atlas turnout.
Anyway, I was just curious about the length of the tender.
https://tstage9.wixsite.com/nyc-modeling
Time...It marches on...without ever turning around to see if anyone is even keeping in step.
I assume this is in HO, as I don't think BLI does anything in N...
That 20" radius is waaaay too sharp for a steamer of that size, only meant for switchers in the steamer department.
hi,
I think your options one and three are the best an the easier to do.
Put the adding wheight as down as possible to the floor of the tender.
Take a look at the secure system of the trucks to the floor of the tender to see there not to much play too.
Good luck
Photos of my Nscale Maclau River RR at www.nscale.org (personnal album/ letter "M"/ Marc Magnus)
Marc Magnus
A bit of background - converted a BLI light Mike to a close visual stand-in for a C&O K-8 mike. As part of the project swapped the BLI tender with an older AHM 6-axle tender as this was the type/size used on this loco. On the whole this has worked out real well, except for a bit of a be-deviling issue. When rounding a 20 inch radius curve on a grade (roughly 3.25%) in reverse the rear tender truck will lift the outside wheel from the rail and of course derail. Watching this action very slowly it appears as if the tender is tipping to the inside and lifts the rear truck frame enough to also lift the wheel clear of the rail head.
Since this tender is very light for its size, my thoughts are:
1. increase the tender weight2. replace trucks with brass trucks (the current ones are plastic)3. add snubbers to the trucks to restrict tipping motion of the tender body
Open to ideas on what to try.
thanks