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Monday, June 29, 2009

PBL Sn3 trucks modified for American OO

About a month ago I had a “sneak peek” of a pair of PBL Sn3 Andrews trucks converted to OO. I have now converted two more pair and have more details on how to do the conversion which makes into great American OO trucks.

As background, due to a quirk of scales and gauges the sideframes of these 4’ 8” wheelbase Sn3 trucks work out as very close to 5’ 6” in OO standard gauge and as such they are prime material to attempt to convert to American OO. Andrews trucks were still in interchange service before 1957 so they are perfect for some of the older cars on my roster. The PBL catalog may be accessed here.

In this first photo at right is the first pair of Andrews trucks I converted and at the left is another PBL truck design. This is the type of Bettendorf truck used on “Gramps” tank cars. It is not the most common type of Bettendorf, it is somewhat “flat” looking for standard gauge, but is still a good stand-in for a cast steel truck of somewhat elderly design in OO. As such it fits this particular stock car pretty well. The Andrews truck in the photo has wheelsets converted from Athearn HO 36” wheelsets which are slightly undersized, and the Bettendorf has North Yard 11.08 mm wheels on a 26 mm axle which are perfect for this truck. Both are quite a bit better looking and rolling than a Scale-Craft truck!

So, how do you make a pair of these fine trucks? In the final two photos we have construction photos of the last PBL type that seems well suited for OO conversion, the long arch bar as used on narrow gauge UTLX tank cars. This type of truck was banned from interchange service in 1940 but was the normal, standard type before WWI. The PBL sideframes are meant to snap into place on the bolster. Instead of snapping them on what I have done is just fit them to the point before they would snap on and at that point insert a thin plastic spacer, seen in the photos. The Bettendorf worked out well with a .015 spacer but the Andrews and arch bar seem to need a slightly thinner spacer, with the .015 spacer I had to use wheelsets with a slightly longer axle. I will work this out more with future conversions. In any case, with things set up square the next step is to super-glue the parts together. Drop one drop on and capillary action will do the rest. Let it set a while, you don’t want to disturb the sideframes until the glue is completely cured. (Plastic cement won’t work.) When it is cured, put in the wheelsets and if they are the correct length you are ready to roll. [See UPDATE at end of post for improved method of assembly].

It is really not a difficult conversion. One quirk is you can’t use a “standard” OO wheelset with roughly 28 mm+ axles in these sideframes if you do this conversion this way, you can’t manufacture enough width between the sideframes. This is why the 26 mm axles were used in the Bettendorf truck and the modified Athearn wheelsets in the Andrews truck. [And, in the case of this arch bar truck, I was able to split it back apart and remove one of the spacers, it now fits the 26 mm axles perfectly.]

I have three more pair of the Andrews trucks on the way from PBL to use on three composite wood/steel boxcars that are nearing completion, and have North Yard wheelsets set aside for them.

I can see another way to work out the bolster which I may try on a future batch of conversions. This method would be to cut the existing bolster in half and take square tubing of the correct size and cut it to length, drill a hole in the middle for mounting in the new bolster, insert each half of the bolster in the tube, and super glue that at the correct length. It would look visually a lot like one of the versions of a Scale-Craft bolster, big and square, and could theoretically be set up to use virtually any handy wheelset. [See UPDATE].

In conclusion, these trucks roll great and are among the best looking trucks available to us today in American OO. I plan to set up a number of cars with these trucks.

UPDATE: My standard method now is to discard the original bolster altogether as outlined toward the end of the original post and make a new bolster from Evergreen 3/16" square styrene tube--it is exactly the right size. I just super glue it all together very square; you could pin the side frames on for extra support if desired. It is a much better way to do the job as there are no small spacers to fuss with. These trucks roll and look great.

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