The online magazine on the history and operation of vintage scale model trains in American OO gauge

Friday, June 26, 2009

More on tuning up Scale-Craft trucks

Yesterday I had some time and ended up spending a good while working on many pair of Scale-Craft trucks, some that were on cars already that did not seem to run well and others that I just wanted to upgrade as they were cars I especially like. I did the things described in this previous post to improve the trucks, including trimming the bolster tabs and especially also putting in the spacers at the end of the bolsters to square them up better. I had to replace several bolsters with others from the parts box. Still, after all the work, while they all rolled great several pair seemed to be shorting out running on the layout and it just made no sense.

The insulation on the wheelsets was fine for sure; all of them that caused trouble in fact were types of wheelset that have a metal rim to the wheel, a plastic center, and solid metal axels. Or, stated another way, all the offending trucks had very nice replacement wheelsets, either by Schorr, Ultimate, or North Yard, which made the whole thing even more curious. They all rolled great, two pair of the freight trucks with Schorr wheelsets had been modified by a prior owner with brass bearing surfaces even, but they seemed to cause intermittent electrical shorts.

When you work on many pair of Scale-Craft trucks you realize that there are subtle (and not so subtle) variations of bolsters especially, the size/shape of the plastic part and also the size of the pins on the ends, and some have “aged” to a degree. What I discovered after some effort was that some bolsters no matter how hard you try to work it out still allow too much play in the truck, and a wheelset with a solid axle may short out intermittently due to the "play" built into the truck design. In some situations you are best to just convert them back to Scale-Craft wheelsets with the split axle. They are completely reliable in any S-C truck.

With enough effort most S-C freight trucks can be worked out to run well with upgraded wheelsets. It is a matter of finding the best sideframe/bolster combination and working out the play as much as possible. The bad news is for Scale-Craft four wheel passenger trucks it is extremely difficult to work out this issue to the point of being nearly impossible. The long wheelbase allows too much play in the truck. The designers at Scale-Craft certainly knew this, which was why they used the split axle wheelsets to begin with, they eliminate the problem. For me however, I had obtained a quantity of North Yard 36” (12 mm) wheelsets on 28 mm axles, and while the 4 wheel S-C passenger trucks I put them in looked and rolled great they were in fact unusable on my two rail layout due truck flex and to the shorting problem. Would be great on three rail, however.... [See UPDATE]

I worked on some other trucks today and will have news about new trucks for OO soon. Not RTR like you would have in any other scale but close!

UPDATE: Working through the parts supply is like a giant puzzle. I did note that I had one pair of S-C 6 wheel passenger trucks that work well on Ultimate wheelsets--with no shorting issue--so I decided to try the North Yard wheelsets that I have plenty of in a couple pair of those. In the 6 wheel trucks they will work, as there is less "flex" to the truck with the twin bolsters and especially with the span bolster in place. Over time I will switch out a couple more pair of these to free up S-C wheelsets for the 4 wheel passenger trucks that I have sideframes for but not enough wheelsets.

UPDATE II: Phil R. had one other suggestion I had not thought of, it would be possible to paint the backs of the truck sideframes with 3M liquid electrical tape in order to insulate the area that the wheel rims touch.

No comments: