A new campaign to upgrade my locomotive roster with 6 axle diesels is not going well. Last of these I purchased prior to 2013 include Life Like, Athern and Atlas have always run great from the get go. Recent purchases (and returns) of Intermountain SD40-2 and a Walther Proto SD45 were disappointing. Both derailed regularly on a couple of 18" radius track I have in necessary locations on the layout - a reverse loop and 90 degree change of direction needed to get into an attic attic space. These are top of the line $300 locomotives. Hidden areas, so no concern about looks.
Best I can tell, a lack of lateral axle side play in the trucks is a root cause. Causes flanges to climb the rail. Removed the side frames to no avail. In one case there was obvious interference of the truck body and the ditch light wires in the frame preventing the front truck from traveling through its full turning angle. I say this too from close inspection and comparison with the older locos cited above that the older brands clearly have more mechanical play, or “slop” if you will, in their trucks.
I found some earlier threads on this topic recognizing the problem and recommending a variety of prototypes and manufacturers that have no problems. But I notice these, too, are several years old. I also notice examining the specs on the boxes of the above late models as well as poking around some manufacruers web sites that the “will run on 18” curves" promotional claim has / is disappearing from many of these products, both 4 and 6 axle.
Botton line - wondering if anyone has any suggestions / recommendations for purchasing late model, contemporary 6 axle diesels? Thanks, geoff
geoff, I don’t have any suggestions / recommendations for operable 6 axle diesels on your layout, but I do agree with your assessment of the problem. You are battling the laws of physics when trying to operate 6 axle diesels on 18" radius curves. In my experience, it is possible to successfully operate 6 axle diesels on 22" radius curves. Is it possible to modify your layout to accommodate 22" radius curves?
Also, the old Atlas-Roco SD35 and SD24 would go around an 18" curve without any problems, can find them on E-Bay.
Not much else in C-C trucked engines would go around and the Athearn engines mentioned above would derail if the handrail was pushed in to far on the front or back decks and it would catch on the truck causing it to derail, don’t ask me how I know this.
I, and probably most of us here, could probably give some such suggestions, but…
…they won’t likely avoid the problems which you’re encountering.
If the 18" curves on your layout are a necessary requirement, then a corollary to that requirement should be searching for locomotives (not six axle) which can handle those curves. Recognising your self-imposed limitations will lead you to a better solution, I think.
I think you are correct DrWayne. I have a lot of 18 inch curves and limit myself to 4 axle diesels, which is no big deal since I like the look of those RS’s, SW’s and the GP7/9’s.
Note also that the arrangement of the 18" curves matters a lot. If there are s-curves without a straight section in between at least as long as the loco, it exacerbates the situation. If using sectional track, apparently minor kinks at track joints can be extra troublesome for the 6-axle power. And any unevenness (tilt) across the railheads can also make things worse.
I rebuilt my layout with 22” radius to fix the problem. There are still a couple of spurs which have 18” but they are only for shorter length freight cars and 2nd generation GP locomotives.
Most Athearn blue box locomotives will run on 18” radius but the six axel diesels will have problems with turnouts next to curves. Tunnel motors need 22” radius. Also cars over 80 feet will need 22” radius. The newer passenger cars with correct couple pocket details will need 24” radius.
As for modern locomotive recommendations: The 4 axle Dash 8-40bw made by Walthers, coming soon by Atlas.
The minimum radius on my layout is 11 1/2" and my 6-axle electric has no issue negotiating a curve this tight without derailing, because it was designed to be able to!
Apparently, a number of manufacturers have no problem to reduce their customer base by excluding those customers, who do not have the space for curves in excess of 18".
It only takes .03125” of wheel side slop in the wheels of a three axle truck to clear a 18” radius. In randomly checking three axle trucks most have more than .0360”, some as much as .040”. I suggest checking for problems with the truck swing/swivel on the locomotives that have a problem.
I have several versions of Proto 1K & 2K three axle SD, PAs and E series locomotives and all easily clear an 18” radius as well as Atlas #4 turnouts. My entire yard/locomotive storage is made up of Atlas #4s with 18” radius approaches and several S turns and the only locomotives that have problems are Bowser 4-8-4 (SP GS4s) and a Bowser Big Boy. The Bowser GS4s will clear everything in my yard at a creep, the Big Boy was dead meat in my yard so It’s history.
I also have several manufactures of large articulated steam and all easily clear an 18” radius. My minimum radius outside my yard is 24” and minimum radius of my main line is 26” with the majority being 30” or more.
Indeed it is. None of our models is really a true to scale representation of the prototype. Allowing for that little extra leeway in the ability of the trucks of a 6-axle Diesel to swivel to be able to negotiate a 18" radius curve is not at all compromising an accuracy, which exists only seemingly.
After all, show me a prototype railroad with curves equating to a 24" radius in HO scale which operates even a 4-axle Diesel!
Geoff First thing I would check are in gauge. Then make sure the wheel flanges are inalinment and with 3 wheel sets it is hard.
Next I would make sure the trucks are not warped. Set the engine on a pices of glass and see if the wheels all touch.
Are you dragging freight or are they derailling with no rolling stock?
I have a PK1000 Erire Bulit B unit with a warped truck and had to pull the center wheels and make shafts for the gears so front and rear wheels where driven. Pain in the caboose but it is running.
Far as the Athearn, try pulling the center wheels, much easier than the Proto engines. Just remove and give it a spin.
Far as 22" turns, god I wish I did it that way and I knew better when I did it! [banghead] But with a little effort you can over come! I run SD 7’s and 9’s, Ge Ac 6000’s, E-6’s and E 8’s and larger steam with 18" turns.
Yes, model railroading is full of compromises. But, I think, the fewer the better. When I started, one compromise was cast-on ladders and grabs. There are now enough manufacturers that offer models with these details free-standing that I can exclude ALL “cast-on” rolling stock.
And then couplers. Sergent couplers have arrived. And I have been using them for awhile.
But. I don’t mind a “little extra leeway”, as you call it. I mind giant leeways in multiple areas. Like articulated steam engines that aren’t. Articulated.
OK (though these curves are a bit smaller–more like 11", I think):
Thanks everyone for your thoughtful comments. Good points all. Disappointed for sure that for the design, engineering and quality of modern HO diesel locomotives that they generally won’t accomodate 18" radius track. Final words on the phone by the Walthers rep to myself and LHS manager “we strive to have all of our (HO) products run on 18” track". Well, so much for that. Meanwhile, I’ll use several of the tips voiced above to deal with the limitations of my layout.
Sorry that you have had the issue. I have had to do a little modification to the swing of trucks inside the frames of the locos by filing clearance etc.
In the relatively recent past however I have had to rebuild parts of my layout replacing my flextrack with Peco set track curves in a compound mode and following some other advice on this forum, I super elevated the outside of the curves by about .020" using styrene… I would have gone higher but my main area is a 4x8 and I did not want the curves to have a slot car appearance with the banking.
I found that this improved the running considerably and certainly the appearance and the bigger locos seemed to handle the curves better although I only have a few 18" radius sections.
The other thing to check is that the joins do not have slight burrs that will “trip” the loco. I am still in the testing phase of redoing the layout after a fairly distant move and the Atlas FP7 units I had notoriously found the faults in the trackwork including the tiniest of small burrs at the joiner end of the curves. That situation has now been eliminated by relieving those burrs. If you are not sure, PM me and I will make you a small drawing of what I have done.
You can see what I have done on http://yourmodelrailway.net/view_topic.php?id=15547&forum_id=21 and I feel that I could have saved myself a bit of modification of the frames of the locos I did over the years with superelevation and deburring done earlier.
I’ve been in this hobby for the better part of 33 years. And for 33 years it’s been an axiom that 18" radius and 6 axle locos don’t mix. Even 22" is getting at the hairy edge in some cases. It sounds like some in this thread have had success with certain models and careful track arrangement. I would note what works, what doesn’t and approach any purchase with a mindset that 18"+6axle is never recommended.
Bravo to those who can get a six-axle loco to operate on a 18" radius. While this distance is workable for 4-axle, I don’t see positive news for a onger loco. The debate about what radius work for different loco types creates confusion. To alleviate, I suggest that people try on a test track before committing the resources to building a larger one with a narrow radius.
While only on my 2nd layout, I try to follow the motto of going for the broadest radius as possible. If that’s not possible, just have a series of straight tracks working with some turnouts. Nothing wrong with that!
