# Tjet gear free travel and gear lash



## yellerstang

Hey all,

What would you consider ideal gear lash in the crown/pinion mesh? .002-.004"?

What do you prefer for endplay of arm shaft, the movement up and down?

Also how much play in the pinion/driven gear shaft up and down?

How much clearance between gear plate or chassis for the pinion gear?

I know that most of the average guys wont know this, I have been messing with this stuff for a long time, but would like some opinions. Thanks


----------



## yellerstang

Also, do you see much difference in CNC gears vs. those that were properly lapped in? I know the CNC gears have almost no break in period, they fit from new...


----------



## Boosted-Z71

Let me answer the gear question first. The CNC gears are awesome IF your motor plate is dead on, & I always check for straight holes that are the correct distance apart, .010 here on the hole spread on the top plate is equal to a ton of gear mesh / slop. I still like to lap everything together regardless. 

For the crown gear I like to see .002 max, less if I can get it without any binding on the gear, root to crown and watch your side of the tooth clearance. You can bottom out the gears and still have a ton of side tooth clearance, this leads to stripped teeth really soon. You also have to control the axle side to side play, and not bind / preload the gear boss. 

As for arm endplay and the drive shaft I start out setting them with a feeler gauge that has a clearance slot in it for the shaft, at .005 and again work down and avoid bind, most of the time .003 to .005 is where most chassis / plates fall at. Sometimes you have to leave the arm at .005 due to heat. 

Boosted


----------



## slotking

it depend on the track
I have found for both t-jets and inlines on toy sectional track I like more slop.
it reduces the shock vibration though the whole car.

On a routed track, I have been down to 1l on the axle slop (but be careful that the crown & pinion do not bind at some points.

on the gear plate, I try to make the motor gear and the driven gear the same height (which is most adjusting the motor gear)

other than that, as long as there is no rubbing, I am good


----------



## slotking

HA

while on the subject
I have a car I know that has a good motor in it, but both dyno and track was not showing it!:freak:
The car was fast, but what the freak happened!! 
So I pulled the motor gear, tached the arm, it was still looking good
put the as I looking to put the motor gear back on I noticed the rear gear it sitting kind of high, the cluster shaft was resting on the rear axle.

So I sanded it down, and it went from 1.64 to 1.72, much better but not where I think it should be. but better. sometimes I just have so many car apart I forget to stop and inspect each car as I should.

Just out of curiosity I took another car also running 1.72 and swapped gear plates. The 2nd car went up to 1.81 and the 1st car dropped to 1.63.

Ok time to try another chassis


----------



## Bill Hall

*That'll do-meter*



yellerstang said:


> Hey all,
> 
> What would you consider ideal gear lash in the crown/pinion mesh? .002-.004"?
> 
> In a perfect world, maybe. Boosted got straight to it. It's about where the crown of the tooth sits relative to the root. A lot depends on what gears you're using. Without knowing the run out of the gears in question your just guessing. Two wouldnt be uncommon for some factory gears, so you'd already be in the rough. Assuming all the RO is zero, then 2 is a good number. The advent of after market gears take most of the guess work out of it.
> 
> What do you prefer for endplay of arm shaft, the movement up and down?
> 
> At .015 stock, you have a mile. Pancakes armatures do not free float. They are pre-loaded vertically by comm pressure onto the thrust stop. I always check the underside of the gear plate where the thrust lands. You can usually squeeze the arm gear down a bit, but; what is really critical is how the arm gear relates to the idler gear. I like to watch what that first gear mesh between the arm gear and the idler does throughout the throttle range as well what happens off throttle. Then ease the arm gear down to get the best possible mesh.
> 
> Also how much play in the pinion/driven gear shaft up and down?
> 
> Im kinda fussy about the driven cluster. Verify the bottom side of the driven gear, and the top of the pinion are actually flat and that their lands on the gear plate arent boogered or worn first. I go trial and error, until its as tight as you can get it without binding or lifting the pinion gear up out of the crown teeth.
> 
> How much clearance between gear plate or chassis for the pinion gear?
> 
> As I mentioned above the mesh between the pinion and crown is the determining factor for me. The original engineers put the driven gear land on the gear plate and no thrust provision on the chassis. The vertical thrust control for the pinion shaft is that little bushing on the bottom of the gear plate. This way all the driven cluster thrust control is integral to the plate; and not dependent on how the chassis and gearplate interface when assembled. The pinion shaft bore in the chassis is only to index and keep center. The plate clearance shouldnt enter into the thrust discussion unless you have the cluster lash opened up beyond reason.
> 
> 
> I know that most of the average guys wont know this, I have been messing with this stuff for a long time, but would like some opinions. Thanks


My grumpy old man opinion is that folks put an awful lot of stock in adhering to specific numbers. AKA: The blue printing trap; where in order to actually do it right, one has to have sophisticated tooling and knowledge and go through the task from stem to stern. 

Using your own senses to develop "the fundamental feel" is far more important; rather than being on a first name basis with your calipers and your mics. Good build habits and track test and tune are really where its at.


----------



## Boosted-Z71

The inclined roll test will tell you more about your gear setup than anything else, and if you want to measure it will only throw one measurement of inches at you. 

I agree Mr. Hall, blue printing is a mess, and you have to understand how tolerance stackup can effect everything from front pinion to rear crown, every number in between has to line up accordingly. Its much easier check a few key features like shaft straightness in the chassis / top plate and then put your good ear on the sound of the gear mesh and let the incline plane be the judge, it either rolls or it dont.

Boosted


----------



## alpink

what angle incline do you prefer?


----------



## slotking

sloping down:wave:


----------



## Boosted-Z71

slotking said:


> sloping down:wave:


Nice

I have an approx 30 deg block I cut from a 2X4 and added a piece of Formica (kitchen counter top material). I say approx 30 deg, because I am no wood worker, but I do my best.

Point em down hill and measure away

Boosted


----------



## Bill Hall

Pitcher!


----------



## yellerstang

*gear meshing and coasting on formica*

Ok, you have me a bit confused with this.. 

First the ramp... A tuning ramp would be easy enough to build, I get it. Simple ramp, make it smooth and wide enough to run a car and watch the results. So... what wheels and tires in your testing cars? This could skew the events easily. Or am I reading this wrong?

Coast down... I dont have a ramp, never tried this. I clean, deburr, polish, install, lap, clean and then I test for a free running chassis. Compressed air with a needle for blowing up a foot ball, I blow air at an oiled chassis. Blow air right on the gears. If it spins very freely and takes time to stop spinning (car assembled without magnets and brushes) then I know I have a chance at a fast car. It must have great coasting at this point.

Something to consider, gears hold debris from running/lapping/running. Oil acts like a glue, it holds the crap in the teeth. You can put some lighter fluid, lantern fuel, or denatured alcohol on the gears, then try the air. It really cleans out the crap and will show you if its free or not.

One final note on the compressed air... OIL everything freely or you will melt plastic at the metal contact points. (Some people do this same thing but using a dremel as the wheel spinner. Air is better, at least for me.)

The compressed air will take a stock tjet into super high rpm, just sayin...


----------



## slotking

yeller

It is not tha hard.
I used the ramp method to test the axle/tire for being true.

For gears I use my hands 1st.
If I fell anything, I use a dremel to clean the teeth.
i also use the dyno and amp meter to check for binding.
if a fray car is below .15amps I do not worry (in general) about binding


----------



## yellerstang

slotking said:


> yeller
> 
> It is not tha hard.
> I used the ramp method to test the axle/tire for being true.
> 
> For gears I use my hands 1st.
> If I fell anything, I use a dremel to clean the teeth.
> i also use the dyno and amp meter to check for binding.
> if a fray car is below .15amps I do not worry (in general) about binding


The details that we inspect and adjust can be mind boggling. 

I started this thread because an idler gear is jumping a bit at high rpm.

I want this car to run faster than a 1.002 et on my 1/8 mile AW drag track. So, I dig deeper... Im going to work on tolerances...


----------



## Boosted-Z71

I have access to sink cutouts for kitchen counter tops, so getting the laminate which is nice and smooth is simple for me for material. 

Yes the ramp is easy, I test with the tire wheel setup I am going to use on the car, Chassis is set up with everything except, magnets, brushes, pickup shoes, springs and no guide pin, otherwise the rest is there, again all I am testing is everything that is rotating. 

Test before and after but you will find that a smooth setup will deliver similar distance results regardless of wheel choice, as long as everything is rolling round and smooth and your not dragging the chassis. 


As for cleaning I always clean everything with a toothbrush and some all purpose soap like simple green etc, then I clean it in an ultrasonic cleaner, any dark marks on the gears generally is crud or lapping compound ground into the space between the teeth. 

Mike is also correct that you can use a dyno to check amp draw but I like to know that I have my friction in the drive train to the minimum and the ramp along with spinning it by hand for feel will tell you that.

You can change the amp draw on an armature to an extent by brush tension or lack of. 

Coast down is hard to measure consistently, you really dont know when your at max rpm by blowing on it and then as i see it the only measure is time it takes it to stop. but you can listen to see how quite it is, smoother less noise the better. And like was mentioned I dont like to spin things up to high speeds with a dremel tool without being lubricated 

Boosted


----------



## Boosted-Z71

If the idler gear is rising, you either have a gear that the teeth are not parallel to the bottom surface, it can be the driven gear walking up too, or the idler post is not straight, worn etc, How much clearance do you have between the clamp and gear? 

I take it your seeing this in a free rev situation? Just try turning the idler gear over, I am sure it will make a difference in a lapped gear setup as far as the free-ness of the gear set, but it might point out the troublesome gear. 

Boosted


----------



## alpink

hey guys, Jesse was very fast in a few classes at the fall drag meet in Skippack.
and, as you can see, he is working every parameter to find more speed.
I heard a rumor at the Merchant Square slot car show yesterday that some of his cars are already faster than they were in the fall.
based on the thread's substance that Jesse has been willing to share, I know he will be a force to be reckoned with on April 9.
sometimes I wonder if Jesse already knows the answer to the questions he poses and just wants to provoke/promote some serious thinking by others.
regardless, I am enlightened by most of the discussions he initiates, among many others.
there are many things to be learned from a lot of folks here.


----------



## Boosted-Z71

Al, for me its always good to see people sharing ideas and such about the how's & why. 

You know it never hurts to get an answer to a question that matches your thoughts or maybe a totally different angle. I too appreciate all the knowledge that exists here on HT. 

I wish that I lived in an area that racing existed like you guys do out East and be able to participate in some of the events, especially the drag racing, I caught the bug, have a little half track I test on when I can. 

Boosted


----------



## alpink

Boosted, your reputation precedes you.
I had the honor of being present for the final runs at Jim Sgrig's place when your car made such spectacular run on his 1/4 mile dragstrip.
so, I respect your input as well as many other proven competitors and even just tinkerers here and elsewhere.
the day I stop having an open mind and fail to learn from others will be a sad day indeed.


----------



## Boosted-Z71

Hey Al, I meant to tell you the other day, I saw an auction of a police car on ebay, new in the package, with the Radar gun turned around backwards, I had a good laugh.

If I can find the link I will post it 

here it is 
http://www.ebay.com/itm/AFX-Tyco-To...463187?hash=item3d11130113:g:1KcAAOSwL7VWr~dV

Boosted


----------



## slotking

going along with boosted said.

I would add a few thing to look at.

if using aurora gears.
mic them because they are often not round, try to use round ones or if legal true them.

as he said, try turning the gear upside down.

if it still rises, the it is the other gear(s).


----------



## alpink

Boosted, LOL
yeah, I guess some were installed backward at the factory too.
if that is, indeed, an unmolested NOS package.


----------



## yellerstang

Hey Al, thank you for the kind words. Im glad that so many fellows here have decided to chime in on my questions too, its very nice to see that some fellow racers freely share information, some of it hard earned and very technical. Kudos to those fellows. The drags racing at Skippack is just a few months away, Im hoping to have some cars ready for some of the other classes, it all takes time.

Btw Al, it was nice to see you at the Allentown show with your drag strip. I saw quite a few younger (and older) racers trying out their new cars on your drag strip.


----------



## alpink

Jess, likewise, it was good to see you as well.
thank you for spelling me awhile.
you seem to have an affinity with slotters of all ages


----------



## Bill Hall

We kinda glossed over the idler gear. Frequently overlooked is the actual center bore of the idler.

It's one of the first gears to check because it translates the conversation between the motor and the final drive when your on throttle, and vice versa when your off throttle. 

Typically you can just pick up the chassis and pin the armature gear with your thumb while rolling the rear wheels back and forth slightly. If the idler arcs on it's post and moves from side to side .... it isnt optimum. You'll be scrubbing speed before it ever reaches the wheels; as well as not coasting down properly off throttle.

I usually pull some 1200 through the center bore both ways. This will highlight any imperfections that need to be addressed or outright rejected. Grinding away the idler post and porking out the gear center are a fact of life. 

RTHO makes a swedging tool for spreading the post diameter.


----------



## yellerstang

So, is it better to work the plastic for a better fit than to work the gear? Its easy to make the gear opening a little tighter too.


----------



## Boosted-Z71

Jesse, you can use a steel ball bearing slightly larger than the hole in the gear to peen the hole in the gear, it will close the diameter of the hole, this is something that takes a little practice to get right. The make tools to do this, called a doming block & punch, its a steel ball welded on the end of a punch and a steel block with half holes machined into it.
http://www.harborfreight.com/25-piece-doming-block-and-punch-set-93539.html

The process is set the gear on a smooth hard surface, place the ball bearing in the hole tap lightly with a hammer on the ball, turn gear over and repeat, then polish it out to get the fit on the post you like.

I have done both remedies, peening & the post expander to fix a loose idler gear, neither work as well as having a good gear and post to start with, but they do work, its just 1 more thing to deal with friction wise on a setup. 

Boosted


----------



## yellerstang

I have a gear installation tool with the optional ball end screw. I dont have a post expander. I wish that I had training as a jeweler....


----------



## Bill Hall

*Bang Bang*

It's one thing to whack a gear in order to get a good press fit on a shaft. It's quite another for the idler. I'm not particularly keen on peening the center bore of a floating gear.

( ) This an exaggerated idea of what happens to the bore. We're banging both ends of the bore, in order to swedge material towards the vertical center. The effect is a "lipped" bore that requires correction. Arguably a very effective method, but it requires diligence to follow up and inspect/dress the new fit. 

It takes a pretty good lick to move enough material to allow the re-creation of a smooth vertical bore. Conversely the natural human tendency is to pussyfoot and clang them on both sides and "call her good", without actually moving the meat in the center. Then you have two lips assuming the bearing load of what was originally intended to be dispersed across the entire bore. Note how the engineers later changed the idler post. It prevents the gear from kiting, as well as providing the maximum bearing surface to distribute the load.

Peening the idler gear and expanding the idler post is an acceptable method when properly done. It's just not my first choice for a hot rod project.


----------



## Boosted-Z71

Bill your right on the fact it takes a decent hit to move enough material to tighten the center of the hole on an idler, My explanation, I wanted to start him out lightly tapping first, I am sure he would see what it did and increase the force from there, rather than clobbering it the first time, I have seen taco'd gears from guys trying this method and did not want him ruining a gear. And your dead on about the bearing surface issue, I also don like that with the post expander you get an inverted cone on the post or I have seen a bulge in the center. 

I look for round gears 1st, then flatness, then address issues with the hole & post fitment, then lap. 

When I build a race car I get 5 or 6 gears out that pass the round and flat test then best fit on the post and try my best not to use the expander tool or to tighten up the hole in the gear. 

Boosted


----------



## Bill Hall

Oh sure, no sweat. I know we agree! I still bonk a gear from time to time.

I was trying to carry on your idea about dutifully following up the all important fitment afterwords; because hammers aint magic wands. Every T-jet lives in fear of slotters with El-Kabong. Mashing the hole is the easy part. That dont make it round or straight. Fitting it correctly separates the wheat from the chaff.


----------



## RT-HO

On many of the Aurora idler gears the hole is way oversize.
As much as .007 larger than a good one.
I don't use the peen tool on idler gears.
You don't have enough size control.
Best to just toss them in the garbage.

I'm not a fan of expanding the idler post.
It does alter the shape of the post.
It may also slightly alter the post location.
Yes I designed & make the tool. Racers requested it.

I didn't have any luck peening with ball bearing & hammer.
It was off center every time.
Peen screw & tool to hold gear on center solved that.


----------



## Rich Dumas

I have both of those RT-HO tools. It is easy to expand the idler gear post too much, if you do that the gear plate will be useless. If the idler gear is REALLY loose I first use the expander tool, but I don't try for a perfect fit. I finish off with the swaging tool, you would have to really crank down on that to make the hole in the idler gear too small. In any case if you had the right reamer you could open the hole up to the correct size.


----------



## toomanyhobbies

RT-HO said:


> On many of the Aurora idler gears the hole is way oversize.
> As much as .007 larger than a good one.
> I don't use the peen tool on idler gears.
> You don't have enough size control.
> Best to just toss them in the garbage.
> 
> I'm not a fan of expanding the idler post.
> It does alter the shape of the post.
> It may also slightly alter the post location.
> Yes I designed & make the tool. Racers requested it.
> 
> I didn't have any luck peening with ball bearing & hammer.
> It was off center every time.
> Peen screw & tool to hold gear on center solved that.


Thank you for being honest!


----------



## slotking

i still like his post expander
i get visible results

just to note, in general the gears suck, but here is the video 
http://www.ho-tips.net/showthread.php?tid=1774


----------



## yellerstang

Bringing back an old thread..... I have noticed that gears that are reworked too much tend to have a sharp ridge on the inside of the hole.

A mildly reworked gear will give you a little oil "resevoir" (sp) where the taper on the gear finally meets the plastic post on the gear plate. This will hold a tiny bit more oil than a gear that has not been reworked. Just an observation...


----------

