# T-jet Tuning Guide



## Reaper

I did this info & pics years ago and have posted these tips elsewhere but thought I'd post it again here... Hope these tips help folks out. These help with both drag & road racing t-jets.

When selecting a good motor I look for one that has a flat comm plate. Doesn't do any good to have the face of the metal plates not making contact with the motor brushes. Even small waves on the face of the comm plate can cause the motor brushes to bounce up & down in their cups/holders - no electricity transfer in the system means no power overall. You've got to think of the whole electrical system as one wire - any breaks in the wire and you get less power through the whole system.
I chuck the motor up in my dremel (the chuck is available at Walmart for ~ $11 and it holds the motor perfectly centered by holding the shaft.

Here is a stock motor that has nasty fouling on the comm plate.









I then use a flexible very fine grit polishing wheel (I bought a gunsmithing polishing wheel kit with a wide variety of grits) that I hold in my hand and touch it against the shaft & comm face while it is spinning and also to remove the old crusty layering that has built up on the copper face of the comm plate. Clean as a whistle afterwards.










After the polishing is complete I can rotate the Dremel shaft by hand very slowly and I hold the motor at this angle so that I can look across the face of the comm plate and look for how flat it is. While you are rotating it you can see if it is flat or has rolling hills. Believe me you can't imagine how wobbly the comm plate can be. There are remedies to fix a comm plate that isn't flat but they doesn't always work.


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## Reaper

Since it's all about reducing friction in the drivetrain then this is a simple method. Take a dremel wire wheel and attack the teeth of the gears. Remove the top plate from the chassis first then take the center (idler) gear off the top plate and hold the wheel 90 degrees to the idler gear and remove some of those super tiny burrs on the teeth with the wheel. Make sure to wear eye protection as those wire brush pieces will fly off. They will embed in everything, soles of feet etc...
If you can't or don't want to remove the other gears from the top plate then you can attack them with the wire wheel while they are still attached to the top plate. Make sure to put a little bit of oil on the shafts since they can spin up and you want that shaft lubed before doing so. The idea is to grind the teeth not get the gears spinning at 50 million rpm. Keep the gear rpms to a minimum if possible and work on the teeth. You will notice a difference in smoothness. This is the easy method. There is a messier method called lapping in the gears with paste or polishing compound. Works better though to lap them in but the wire wheel method works pretty darn good too.










So you think you've got a fast car? Could be lots of vibration that makes it sound fast when it really isn't. I used to use the old "ear dyno" but it lies to you big time. So the simplest solution is to make an inexpensive dyno. Radio Shack or eBay sells this voltmeter. I got a motor from a tape deck and glued it onto the voltmeter. Then I soldered the leads to the motor, put a hub and tire on the motor shaft...voila! Instant, portable dyno.
Just make a power supply and solder alligator clips onto the wire ends. Then attach the clips to the pickup shoes of the chassis and then lower the rear wheel until it contacts and spins the dyno wheel. It will read a number on the volts - the higher that number then the faster the motor is spinning. You can use this dyno to help you find the fastest combo for your car.
Swap between top plates, try different motor brushes in each cup, gently press up against the motor brushes on the underside and if the motor wants more spring pressure then it will respond with more rpms... Be VERY careful when adjusting the motor brush springs upward - you can ruin them easily by putting too much bend in them. You must remove the topplate and motor brushes to be able to properly adjust the pressure of the motor brush springs. Remember to match your power supply to what the power supply will be for the track that you are going to be running on since some motors run very well at 18 volts but terrible at 13.8 volts. One simple solution for an adjustable power source is an old train transformer that has the handle on it to allow you to increase/decrease the amount of power. Use your newly acquired voltmeter to set the DC power output of the train track transformer.


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## Reaper

Air Gap Adjustment
What is air-gapping? It's cutting/grinding down the outside dimension of the metal lams to make them all the same distance from the motor shaft. Sort or making the outside of the circle center around the motor shaft. Why do it? It allows the motor to be centered in the chassis and you can also shim the magnets closer to the motor for more power/torque.
Sometimes a motor that isn't air-gapped will strike a motor magnet if the magnet is shimmed too close to the motor. You also get an equal attraction force from the metal lams towards the magnets. That smooths out the motor - sort of like when you rode your Huffy bike as a kid and each time you'd push downward on a pedal the bike would surge forward then slow down until you pushed downward on the other pedal. The motor behaves like this if the lams are differing distances from the motor shaft.
I use a fine stone and hold it against the edge of the motor while it is spinning at a high rpm. Make sure you do this step before you balance your motor as you are removing metal.









The outside edge of the lam will look like so when finished. I try to hit 60-70% of the exposed edges - not all of it but nearly all of it. I don't want to remove too much metal. In this pic I pretty much hit 100% of this end - that means that one of the remaining two ends doesn't have much metal removed.


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## Reaper

Balancing The Armature
How to balance a motor? I like razor blades, long ones too. I bought some at Home Depot and then got a couple bolts, washers & nuts and sandwiched the razor blades in between the washers. Works well enough for me. I do the initial balancing on this device then move the motor over to a jeweler's balancing tool. It's got very fine/sharp edges to rest the motor shaft on to do very detailed balancing.









Once the motor stops turning I use a Dremel diamond wheel to cut a slot into the metal lam and remove metal. Remember it is the side that ends up on the bottom that you want to grind away at. Remember it's a diamond wheel - it will buzz clean through the metal lam in a hurry so go slow and don't take off too much. You'll also cut into the wires and ruin your motor if you get careless. (BTDT).










Here are some slots that I cut into the lams to remove weight.









Another method of balancing is to add lead weight. You can cut slivers of lead off fishing
weights to add to the motor. Remember, if you use this technique that you will have to add
the lead weight to the TOP of the motor when it stops on the razor blades. You can see a
square of lead on the right side of the motor that I added on the top of the comm plate and
to the inside of the end of the lam. I use super glue to attach it to the comm plate.


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## Reaper

About Plates
Not all top plates are created equal...
Look at these two pics and you can see the difference in the idler gear posts. One is rounded at the top and a tiny bit more narrow, the other has sides that go straight up and is a bit wider. If you've used the wire wheel trick to grind at the teeth of the top plate gears but your car still sounds loud & raspy then you might have some sloppy gear lash. Hold the motor pinion and keep it from moving then use your other free hand to move the rear gear on the top plate back and forth and watch what happens to your middle (idler) gear. If you've got the round top center post I bet you've got some sloppy movement of the center gear when you go back and forth with the outside gears.









If you've got the top plate that has the straight sides going upward then you are in luck since you've got one that doesn't have lash problems.










Solution??? A fellow named Rick Terry at RT-HO.com has built a tool that will expand your anemic round top post outward and therefore eliminate the slop in your drivetrain. Notice that his tool drives a metal point into the plastic idler post and therefore expands it. Make sure your idler gear is ON the post when you are smashing the post otherwise you could mash it too much and bind your idler gear.


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## Reaper

Brush Adjustments
So how do you adjust the motor brush springs for more upward pressure.
Here's a stock chassis with no adjustments. Notice one side is lower than the other. They don't necessarily have to be even - I just adjust upward the one that responds to higher rpms when I push against it while the car is running on a power supply. Remember you want to test your car at the power level that you will be participating at. If the race is at say at 13.8 volts then make sure to setup your car at that voltage.









Notice the tiny screwdriver pushing upward from the bottom of the chassis. Be careful to not push too much at first - start small and see what happens.










Here it is after adjustment.










Here are some that have been adjusted for LOTS of pressure. Of course you can adjust them too much and totally dork them up ruining the chassis.










Ruined motor brush spring:











Something that can rob horsepower is the motor brushes spinning in the brush cups. The JL
brush on the left already has a notch in the bottom of it. What do you do with a stock
replacement brush? The Wizzard brush on the right has a notch carved into it with an Xacto
blade. Be careful when doing so as you can slice through the motor brush with too much
downward pressure.










Another method is to make a tool from a pair of needle nose pliers that has a U shaped end.
You can then grab the motor brush spring and squeeze it to make the end of the brush
spring a U shape. The points on the ends dig into the motor brush and keep it from rotating.
This can be a dangerous exercise as I've ruined more brushes than helped. If the rules
stated "motor brushes cannot be altered in any manner" then this is a good method from
keeping the motor brush from spinning in the brush cup while the motor is running. (Bunny
hairs on the chassis are no charge).


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## Reaper

Trued Parts
How round or out of round are your parts? Things spinning perfectly around an axle work better than items that are out of round. Both of these are stock crown gears - I'd prefer the one on the left.









Is the hole in your idler gear centered? I marked the idler gear then made measurements with a micrometer.










Here are pics of the 4 different sides being measured.


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## Reaper

Efficient Electrical System
Since an automobile engine is basically an air pump and how fast or efficiently you move the air through it determines how fast you go then it stands to reason that a t-jet is an electric pump. You need to make sure that the electrical connections are optimum and that the electricity flows unrestricted through to the motor. How many electrical connections are on a t-jet chassis?

1. Track rail to Pickup shoe. 2. Pickup shoe to hanger plate 3. Hanger plate to bottom hanger plate (notice the rivet that holds them together?) 4. Hanger plate brush spring to motor brush 5. motor brush to motor comm plate
Your job is to make sure there is little or no arcing across those connections. How to do it? I dunno - I've been trying to figure out all those connections ever since I've been racing these things.

Notice the pickup shoe on the right is properly adjusted since the whole shoe is contacting the track rail. Now notice the left rail needs some adjusting as the rear portion isn't in contact with the track rail. Speed is being lost because of this improper adjustment.









I made a tool from a tiny screwdriver and using a steady hand and the Dremel diamond wheel I cut a slot into it.









Notice where you grab the pickup shoe to adjust the angle - twist the shoe to bend it ever
so slightly then run it again and see what the results are. This takes time so be patient. You
can also set the car on a piece of test track (small piece you cut of of some old track) and
look from the sides to see if the pickup shoe pad is resting flat on the track rail.


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## Reaper

Truing The Wheels
What about your hubs - if you are using stock hubs I can probably guarantee that they will be out of round. Here is an AFX hub on an axle inserted into the Dremel. I hold it very steady and slowly take little bits of the wheel down by grinding it against the metal file.









I stopped to show that the hub was in fact out of round as you can see the paint missing on one half as I'm truing up the hub.


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## Reaper

Other Tips
Ok last of the tips - I've got to save a couple of them for myself.
I'm probably taking this a little far but if reduction of friction is the overall goal then what about these tips.
I bevel the bottom edge of the top clip so that if the idler gear bounces up while the motor is running then the teeth don't run into a sharp edge but rather a beveled edge that doesn't cause as much friction on the gear.









What about the comm plates - I take an Xacto blade and draw it across the leading edge of the comm plate that first comes in contact with the motor brush. If the brush has a nice ramp to ride up onto and not a sharp edge then it will most likely make a smooth transition to the next copper plate. Otherwise I'd imagine that it would bounce the brush when it hits the leading edge if it isn't beveled resulting in less time that the electrical connection is being made.









Make sure to clean the crud out from between the comm plates - after all the dust that comes off the motor brushes conducts so if enough of that dust got in between the comm plates theory would seem that it could short between the copper comm plates.









You might notice the fact that there is some mounting slop on the rear shaft when it comes where the gear is located. Notice there is a gap between between the 9 tooth gear and the bottom side of the top plate. I'd drive one of the two gears (top gear or the 9 tooth gear) towards the other one to remove some of that excessive gap. Be careful and don't drive it too far and bind up the gear against the top plate.









Lastly - remove the motor magnets and motor brushes. Re-assemble the t-jet without those two components and then spin the rear tires to see how smooth your drivetrain is. It should spin freely - try this in both directions. If not then you've got some work to still do. Where to get the tools to work on t-jets? ( I remember back in the day that a screwdriver, needle nose pliers and a tiny hammer were all that we had.) I use a lot of stuff from Rick Terry and there are many other tool makers as well.


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## pfindeis

Great stuff..Thanks alot..


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## Reaper

Having trouble keeping the gears from spinning off their shafts on higher powered drag cars?
This works well for me to put some bite marks on the shaft then when you press the gear back onto the shaft it will hold better.
Another idea is to take a thin dremel cutting wheel and to nip the shaft & gear where they meet which transfers material from each surface onto the other and creating a bond.

































An addition to the post (thanks to Bill Hall for reminding about it !)

Make doubly sure that you put the bite marks from the pliers teeth into the shaft ABOVE where the top plate will be spinning on the shaft. Otherwise you'll be grinding the teeth marks into plastic top plate and causing friction.


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## Bill Hall

Very nice tutorial Reaper!

I've used the splining trick on armatures successfully for years. I align the tip of the pliers with an arm pole and make the bite. Then rotate to the other two poles in succession. In this manner the splines stay neat and arent accidentally doubled up anywhere. Care should also be taken to keep the splines above the gear plate journal.


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## glueside

Thank you Reaper!!!


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## joegri

thanx reaper for takin the time to show us what methods you use to make a good chassis!i will employ them on my next chassis build.the last 3 or so builds i have spent hours to make the gears fit n spin real nice and have been rewarded with some of the fastest and smoothest on my trak to date. nice job reaper. got anymore tips? that is only if ya wanna share ,em. thanx man


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## Hornet

edit.


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## wheelszk

Different strokes for different folks. Plain and simple.:thumbsup:


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## Reaper

Hornet said:


> And now we know the answer to why i'll never run a T-jet,ain't got that many spare hours to waste on a tiny toy car.
> How many hours do you guys actually spend building one of these hotrods
> I thought i was an anal magnet racer,but i don't hold a candle to a die-hard T-jetter that's fer sure:wave::wave:
> Ain't got that many hrs to spare Rick


I used to have LOTS of spare time to build chassis but no longer with kids running amok in the house. Someday I'll have the time to spend on it again. I used to get enough top notch/hand selected parts to build 5 chassis. I'd take my time and do them all exactly the same with all the speed "secrets" (yeah right) that I know to use. End result?? Last time I did this I got 2 absolute screamers, 1 above average and 2 so-so cars. You never know what you are going to get after the build. I usually spend 1 full day on each chassis. Takes a while to prep a car just right - it's ALL about friction reduction (and having a good motor helps...)


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## Ralphthe3rd

Good thread, thanks for the info. I had been away from HO slots for over 35 years, and coming back I am more attracted to T-Jets and non magnet Tyco Cars than any of the SuperSonic 2000 Scale MPH "Magnet" cars. So I appreciate threads likes this, on how to bring back an old T-Jet and get her running straight. 
PS- ya know, I'm a Biker guy, and running/ tuning
/rebuilding T-Jets is alot like doing the same on an old Harley.....it's not for everyone, and I'm glad


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## Boosted-Z71

I figured on average I will spend 36-40 hours on a Fray-legal T-jet, that's chassis & body
I am not so fast at the paint work either, but I love T-jets, They are way better for me than the Inlines, and I have built a couple of inlines as well.

Boosted


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## slotking

> What about the comm plates - I take an Xacto blade and draw it across the leading edge of the comm plate that first comes in contact with the motor brush. If the brush has a nice ramp to ride up onto and not a sharp edge then it will most likely make a smooth transition to the next copper plate. Otherwise I'd imagine that it would bounce the brush when it hits the leading edge if it isn't beveled resulting in less time that the electrical connection is being made.


2 steps to make this better, 1 use a comm truer! I use the VRP set cause it has 1 tool for the dremel and 1 for the hand. this makes sure the plates are even.

the 2nd tip is i use a ball point pen (also works with inline arms) to run over the air gap, this will bevel the edges to make the transistion from each plate very smooth


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## Hornet

edit.


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## alpink

I build some myself and I buy some from very fast guys who are well known. about $150.00 for a competitive FRAY type chassis. there probably are some guys that charge less and I know one guy who builds whatever I desire. I ply him with parts. neither of us is ever sure what the value of his services are to me or mine to him. it is a platonic sort of situation that allows him more parts and me fast cars. now then, controllers and other accessories... what can ya afford? LOL


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## Brixmix

takes me about 3 to 4 hrs to build a car, with about 1/2 to 3/4 of an hour of the car build on shoes


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## slotking

he has very good cars!!
and makes a sweet controller!:thumbsup:


For those of us that are more mortal it can take some time, 
That what I enjoy about t-jets, unlike inlines that get put together and with very little work(at lest for me) are competitive, t-jet make you think and scratch your head cause no 2 are alike:lol:

smarter builders like brix may have an answer though


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## slotking

speaking of 

I had nice car, handles well, but out of after racing vs some big guns the other week, it just slowed down:confused ::freak::freak::

been playing with tension ie increasing or decreasing but no luck, gears and everything still seem free

may have to try a new arm


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## Boosted-Z71

I have seen brushes get glazed and cars slow down a bunch, you might try a good cleaning on them & the polish the comm plate, before you start tweaking on it. I have found when you take your time and build them right you get what you get, maybe a good one, maybe average etc. If they slow down, especially quickly its generally the brushes or a tensioner that is letting up under heat. You can carefully add some resistance (stiffness) to the copper tensioner with a soldering gun and cold water. Just be careful its a very quick process.

Boosted


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## XracerHO

Thanks Reaper for taking the time & sharing your techniques. ..RL


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## slotking

> You can carefully add some resistance (stiffness) to the copper tensioner with a soldering gun and cold water. Just be careful its a very quick process.


sweet
totally did not think about that

will give it a try, may have to practice 1st with the cars from my competition


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## Reaper

slotking said:


> speaking of
> 
> I had nice car, handles well, but out of after racing vs some big guns the other week, it just slowed down:confused ::freak::freak::
> 
> been playing with tension ie increasing or decreasing but no luck, gears and everything still seem free
> 
> may have to try a new arm


Clean the comm plate face off and toss some new Wizzard t-jet brushes into it. That usually solves most of the cases like that.


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## slotking

> Clean the comm plate face off and toss some new Wizzard t-jet brushes into it. That usually solves most of the cases like that.


worked on it last night

not the motor, but the slottech brushes still give higher reading(more speed) than the wizzard brushes.

chassis is free, gear plate is free, have to remove the mags an brushes and test the plate on the chassis


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## slotking

axles was binding


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## Boosted-Z71

Friction kills, Glad you found out the problem

Boosted


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