Rebuilding a T-Jet

 

Bobby and I recently made a trip to Huntsville, AL to learn more about building T-Jets.  The people with North Alabama Slotcar Association (N.A.S.A.) are way ahead of where we are in knowing how to do this.  The person we learned from has competed in some of the largest HO races in the nation.  While we were there they were in discussions about a race in Ferndale, CA they will be going to in March of next year.  The "Fray" is probably more prestigious than the H.O.P.R.A. National Championships.  These guys are serious racers and serious car builders.  We were extremely fortunate to have Kevin Riggs spend about 8 hours instructing us on how to do it right.

Rebuilding a car the way they do may take 6-8 hours or more, not the 30 minutes you may think it takes. You have to use specific tools to do the things we did under the guidance of an expert.  I tried to compile a list of tools we used and price them out.  My head was spinning by the time I finished.  To my count we used more than $1,500 worth of tools to rebuild these cars.  Mind you, that amount does not have to be spent on tools.  As I said these people are in a different league than us.  They build cars which can be competitive in any race in the nation.  They also have the know how and experience to use these tools properly.  Bobby and I were just stumbling along trying to follow instructions, our cars did not come out nearly as fast as what they can build.  But we did learn what it takes to do the job if you have the tools and the experience to do it right.  I repeat, you do not have to buy all these tools to enjoy HO racing and working on your cars, but it does take it to another level of enjoyment.  Who can argue that you can luck upon a car that is fast right our of the box.  Just look at Bobby's stock T-Jet, it is blistering fast and he did none of the stuff we learned to it.

The tools we used... Lets start this way, we didn't even know what most of them were when we started.  . Then Kevin pulled out an extensive quantity of parts, and a few donor cars to be used in the build of one car. TOOLS - A quality gear puller plus attachments to protect the chassis plate when you use it, A quality piece to peen the gears for when you put them back on the shafts and all the anchors they use for the different size gears A quality gear press, the lucky Bob's we have been using is not good enough. Various grits of sandpaper to sand every gear surface smooth and polished. You need a gauge to measure the flatness of an armature (this is not balancing). You need a tool to repair loose shaft holes such as armature, and pinion shafts, plus your axle holes. You need a Dyno or a replacement for one and an amp meter to measure your amp draw. You need good set up blocks which are perfectly flat and have something representing the rails measured to the rail height you are using. A gauge that measures tension when you rotate a gear. A gauss meter. Appropriately shaped pliers with flat jaws to adjust pick up shoes. Exacto knives and dental floss to repair brush springs. Proper oil including Dielectric oil for the arm hole by the brushes. A quality surface to check the flatness of chassis. A high quality set up to check for arms being out of balance. A device to clean and polish comms that goes way beyond what we have been doing. And a plate to set your chassis up with that is exactly true so your chassis is not crooked in aspect to the alignment of your axles. Now.....you have to know how to use each of these tools and when to use them.

I will try to explain the steps we went through. First you disassemble several cars to get a stock pile of part to build one car with. Every part has to be taken apart. Gears off shafts and everything removed except the copper plates on the bottom of the car. Find the chassis which seems to be the flattest with the best brush springs. Discard the rest of the chassis. Clean the chassis thoroughly. A little grit left where the magnets go could disrupt the handling of the car. Clean the copper completely. Straighten the chassis the best you can to get it exactly flat. This can be done by using a boiling plate and boiling the chassis for it to reset or by flexing the chassis until it comes back to its original shape. This takes a while and is very detail oriented. Once you have the chassis sitting flat check with an alignment tool to see if the axles may not be touching at all four corners. Once this is done you can start trying to adjust the brush springs. We learned the brushes have to sit up higher than we thought before.

Next select a top plate that fits the chassis the best. You want it tight but not binding. If the plate fits check it for flatness. Twist and bend the plate until it starts moving back to its original shape. Once it is flat according to a quality flat surface check again for fit. If it binds find another plate and start working again until you get one flat and fitting properly. Discard the rest of the top plates. The symmetry of the poles of the arm is what you are looking for. This is more important than having a low ohm rating. Once you have selected your best arm check using a run out gauge to see if the plates of the arm are all the same height. If not, loosen the clamps holding you lamanations together and squeeze together to get the right height then tighten it back down (this is not balancing an arm). You now have the arm you will be using, discard the rest.

Thoroughly clean your magnets. See if they fit in the chassis without binding. If they do, check for dirt in the chassis or get another pair. Find all the pairs of magnets you can that fit into the chassis properly. Check these magnets with a gauss meter to find the best matched magnets. Discard the rest of your magnets.

Inspect all your gears, look for spurs, bent or worn teeth, look for abrupt edges where the gears were stamped. Discard the bent or worn gears. Clean the remaining gears completely. Sand the gears smooth. Use a wire brush in the teeth of the gears to make sure they are clean. Polish the gears.

Check all the shafts gears will be on for pitting or dirty surfaces. Clean them and remove any tarnishing. Check axles for straightness. Discard any bad shafts or axles including the arm if necessary.

Look at your chassis and evaluate the hole that shafts and axles pass through. If any are loose you must tighten the holes up. Use a tool to pinch the hole in from both sides of the plastic and test the shaft for play. Remove as much play as you can without creating resistance.

Now you are ready to begin assembly. Install your pick up shoes and springs. Oil the hole in the bottom of the chassis for the arm to fit in and the hole in the top plate. Install you brushes. Drop your arm into the chassis. Install your top plate and clamp. Test the motor on a Dyno using an amp meter. Make not of the amp draw and how fast the arm is turning. Take the top plate off and find the idler gear that fits the shaft with the least amount of play while not binding. Discard the rest of your idler gears.

Now you are ready to start installing gears. Find your best armature gear. Use the peening tool on both sides of the gear (you don't want to spin a gear after everything is together). Using a GOOD gear press install the armature gear so it has as little gap between the shoulder of the shaft and the plate as possible without causing restriction. Put the plate back on the chassis with the arm attached and clamp it down. Test the speed and the amp draw of the motor again. If the amps have gone up a little it is ok. If the amp draw goes up considerably remove the gear and start over.

Once you are happy with your amp draw and the arm gear remove the top clamp, oil and install your idler gear. Use your tension gauge at this point to see how much tension it takes to move the idler gear. Change out the idler gear to each good one you have and test. Pick out the best one you have and discard the rest.

Disassemble your chassis again and find the shaft you have that best fits for your pinion gear. Discard the rest. Peen your pinion top and bottom (you do not want to spin a pinion gear in a race). Find your best driven gear (the one above the pinion) and peen it top and bottom. Using a high quality press put the driven gear onto the shaft until the shaft crowns slightly in the hole. Drop the shaft into the top plate and assemble the entire chassis again. Check for speed and amp draw again. If it goes up significantly find another gear and start over. Once you are comfortable with the gear you have chosen discard the rest of the driven gears.

Disassemble your chassis again and install your peeened pinion gear leaving as little gap between the gear and the plate as possible. Reassemble and test for speed and ampls again. If there is a big jump remove the pinion and start over.

Once you are comfortable with your pinion gear. Find you best rear axle and your best crown gear. Install your axle and crown gear. check once again for speed and amp draw. If there is a large amp draw go to another gear or axle until you are happy.

Once you have done all this you are ready to install your tires and check your shoes for contact. We spent an hour on this process. The shoe should have the most contact possible with the rail. Bend it until it works right.  I came away with the opinion all of the above helps, but what is more important than anything is how the pick up shoe meets the track.  You need as much contact as possible.