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RMI Prairie Step 2 - Tender Truck Construction

Printed From: Southern California Live Steamers
Category: Live Steam Miniature Railroading
Forum Name: Steam Locomotive Construction
Forum Discription: Discuss building live steam locomotives
Printed Date: Apr 01 2023 at 1:40pm

Topic: RMI Prairie Step 2 - Tender Truck Construction
Posted By: PhilC
Subject: RMI Prairie Step 2 - Tender Truck Construction
Date Posted: Jun 26 2009 at 9:58pm
It was decided to build the tender first as it was the easiest to complete and can then be easily moved to the club freeing up some room in the shop for the locomotive. Also once the locomotive is complete it would be tacky to drive it around with a bucket full of water and a jug of diesel fuel until the tender was complete.
The trucks are the first things to be assembled. Each truck comes as a complete kit of parts in a box like this. (very exciting, I knowSmile).
Tender Truck Box of parts
Here is what is in the kit of parts for each truck. All that is required is to paint the wheels and axles, insert the woodruff keys in the shaft press the wheels on and clip them into place and press the bearings on the end of the axles. Then bolt the various parts together to built the archbar portion.
There are no instructions how to do this included with the kit, so I will show the steps here to help out the next person that has to put 3.75" scale RMI truck assemblies together.
Step 1. After checking that all parts are there and accounted for you will need to degrease the shafts and wheels prior to painting with paint thinner or lacquer thinner as there may be some grease left on them from machining.
Step 2. Mask off the steps on the shaft with masking or painters tape.
Step 3. Prime and paint the shafts and wheels.
Step 4. Press the woodruff keys into the slots on each axle. I used a drill press vice and squeezed them in.
Step 5. Press on the wheels all the way against the step in the shaft and insert the retaining rings on the shaft in the groove using external retaining ring pliers.
Step 6. Press the bearings on each end of each shaft. (4 places) so that they are pressed up tight against the step in the shaft. I used an 11/16 3/8 drive socket on the press which was a perfect fit for the inner race of the bearing and allowed the shaft to protrude up inside the socket after being pressed.
 Archbars, notice the spacer shown in position above the lower bars to space the bolster up.
Place the bolster assembly into the archbars and then place the top bar in place. Install all of the bolts starting with the ones through the bolster. There are spacer tubes, not shown that are installed in the bolster next to the springs. You will need 4 inch bolts to go through everything. The bolts supplied were only 3 1/2 inch so were too short and were meant for the older trucks that did not use the spacer under the bolster. A quick trip to the hardware store and the correct length bolts were purchased.
spring assembly
A closeup of the spring assembly with spacers installed. All tight and ready to go. Notice nuts are on top all other nuts on the bottom as they have more clearance. I did this as this is the lowest part of the truck and didn't want the nuts to drag on the ground or get banged around during a derailment. Not sure it is correct, but I liked it that way. Make sure all of the springs are correctly seated in their pockets.
Completed tender truck assembly, very simple to put together. Really nice stuff, built like a tank too.

I used to be a rocket scientist, now I am just a space cadet.
You only need three tools in life - WD-40, Duct Tape, and a Hammer. If it doesn't move and should, use the WD-40. If it shouldn't move and does, use the duct tape. If you can't fix it with a hammer, you've got an electrical problem.

Posted By: WSSHAY14
Date Posted: Sep 22 2009 at 5:01pm
Since there were no instructions with the trucks, you might be interested in this info.
One of the members in our club, Redwood Empire Live Steamers, built 2 riding cars using the RMI archbar trucks, to use for our public train rides. The first weekend out, we spent more time re-railing the cars than pulling them.Confused
The problem seemed to be that the trucks were too tight, and unless the cars had a load on them they would derail.
The next weekend we turned the cars over, and removed the trucks. We noted that the nylon (?) strip on the top of the truck was sitting flat agaist the body bolster.  All RR equipment must have a little side play in the bolsters.
If you note there is an unusually large hole in the nylon strip were a 5/8" bolt goes through the top bolster of the truck into the body bolster.  We found that the hole is big enough for a 5/8" flat washer. Huh.
We had to shop around a bit, but we found that there are thin and thick flat washers.  The nylon we have is about .275" thick.  We found a pair of thick or heavy washers that were about .315" thick. After the cars were reassembled, there is a small amount of rock in the car body.
At the next public run the cars had no derailments, or in the last 5 months.Tongue
Dave F.

Posted By: PhilC
Date Posted: Sep 22 2009 at 5:50pm


Thanks for the input. The bottom of the tender crossbeam has a washer welded to it that I think provides the spacing. I will see if it is resting totally on the plastic or if it just kisses it and rides on the washer. The kit came with some additional washers that are the correct size so will see if they are needed.
Thanks again for the info and welcome to the SCLS forum.

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