llZer0

hello everyone, I have a t-maxx 3.3 4908. Yesterday 6/4 I went bashing and I saw some problems and new problems...

1. I got my t-maxx with 1m gap for the idle, I can brake good and keep running, but if I fully stop the engine dies. It doesnt idle when sitting still.
2. My engine is new, this was my first time bashing with this new engine( I did break in the engine, traxxas method), I cant get my t-maxx do wheelies, how can i tune it right..
3. When i was landing a jump the engine was bogging out, almost dieing.. I pull full throttle and the truck doesnt move until like 3 seconds.....
4. I was using a new traxxas digital 2070 steering servo, and it just broke, i can turn right but i cant turn left it makes a lot of noise. What aftermarket servo do you recommend me....I wouldnt like to buy the same one.
5. When ^ that happen I notice another problem. Without touching the controller the throttle servo was at full throttle, when i hit full throttle on the controller the throttle servo closes and then open close and open...So i dont know whats going on, can it be my receiver??? ( I am using an ofna fail safe, and traxxas 2075 throttle servo)

Thanks a lot, I now thats a long list , but i now i will fix it with your help

thxs...

dug44

My Feedback: (2)

I would have to say that your gap is less than 1mm. It's the thickness of a credit card. The high speed should be at 4 turns out from snug, the low speed is flush, which is about 1 3/4 turns out from snug.

This is from a guy named Robin, he is from rc mods... and it works well.

This is the way that I tune engines, there are many other ways to tune but I figured this is the most simple way to do it so I will share my info. This technique is for a fully broken in engine that is ready for a full performance tune. This tuning procedure will set your needles where they need to be for optimum performance, a temp gun is not required (other then high temp safety check) because there is no guessing, the engine will tell you.

For this to work the engine has to be at running temps (or as close to it as possible) as well as having the standard 1mm gap for the carb opening.

#1) High Speed Needle.
Pull a wot pass a couple times and listen what the engine does when you let off the throttle. As long as the rpm drops right to idle, the HSN is either good or on the rich side. At this point you can lean the HSN in 1/12 increments until the idle seems to hang a little after a wot pass, when it starts to idle high after a pass it is just on the lean side of a perfect tune. Back the HSN out 1/12 turn at a time after a wot pass until the engine drops right to idle after a pass. Now your HSN is set.

To give an explanation to what is happening is simple. If your HSN is too lean, after a wot pass when you let off the throttle the engine is still lean causing the idle to hang and idle high until the LSN has a chance to take over and meter the right amount of fuel to bring the idle down to normal running speed (given the LSN is set correctly)

Now if the opposite happens, after a wot pass when you let off the throttle, if it drops to a good idle right away and then starts to idle back up too high, this is a sign that the LSN is too lean. If it comes off wot with a good tune and will drop rpm nicely then the HSN is metering the fuel properly but once it hits idle the LSN being too lean will quickly take over causing the rpm to go back up.

#2) Low Speed Needle
Most of this setting was explained above but there are a few little tricks you can use to make sure the LSN is adjusted perfectly. We all know that you don't tune for temps but a temp gun is very handy for this part. After some wot passes with the engine good and warm, bring it in and let it sit for about 10 seconds. At this point take your temp gauge and hold it as steady as possible on the head, what you want to see is the temp dropping a degree every 4-5 seconds. You want the temp to drop very slightly at idle because when your off throttle the engine should be cooling, if not, the temps will keep pushing higher with on and off throttle running and will cause temp issues.

This is how I do it and I have tuned a lot of engines for people whether bashing or racing. I have seen across the board from beginners to veterans that when they hear the high idle after a pull, the first thing they go for is the LSN when in fact it is the HSN causing the issue. The veterans are surprised when we richen the HSN an hour or two and the problem goes away. I hope it's not too hard to understand as typing it out is much harder then explaining it to someone first hand, if you have any questions feel free to ask.


Take out the failsafe and see what happens as well.


AGAIN, these are not my words.... I got them from another forum... I just got lucky and found it....

llZer0

thanks for that information...

dug44

My Feedback: (2)

your welcome, hope you get it figured out.

that.dank

This should be sticked. That was the perfect how-to on to tune by the way. to the letter.

gettnbetter

Sounds like the engine could use a tune. Good summary dug44!

After you get it tuned, if it still happens, check the clutch spring, a broken clutch spring will make it hard to keep idle and the car will tend to creep forward even at lower idle RPM's.

It's common for that steering servo to break, it doesn't have metal gears. You can go with something inexpensive like an [link=http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXUZ89&P=7]HS-645MG[/link] or a mid-range servo with more power like an [link=http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXMUS4&P=ML]HS-985MG[/link]. Traxxas sells a convienent [link=http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXHGB3&P=7]kit[/link] with stock type servo horns to fit the Hitec or other aftermarket servos. Either servo will last a long time and are exact drop-in replacements.

The issue with the throttle servo sounds like it could be the failsafe not set properly or even the throttle servo has died. Hitec makes an inexpensive high speed servo that will work nicely in the Maxx, the [link=http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXUZ87&P=ML]HS-625MG[/link], or again, like the steering servo, the HS-965MG is a little faster and a bit more powerful.

I wouldn't use alkaline batteries with those servos, they draw quite a bit of juice and I've seen them pop and leak from over amperage... Upgrade to a 6v NiMh RX hump pack or use rechargable NiMh cells.

only1battman

another possible explination that your T-Maxx is not idleing while sitting still it because your clutch spring is broken. the pads are now touching the clutch bell and cannot retract when the RPMs go low enough.

llZer0

Thanks ... will the HS-625MG work good for the steering and the throttle? are they fast and strong... like the traxxas 2075 or better... I will check the spring, if its broken should i upgrade the shoes or stick with the stock..... but i will try to tune it right first....

the problem of the throttle servo i will make sure the ofna fail safe is not causing the problem..

thx

gettnbetter

The 625 will work but it's too weak for a steering servo. The 645 is almost as fast as the traxxas 2075 servo but a lot more durable. The 985 is stronger and faster.

You can also help ease some of the steering and throttle effort by replacing the nylon bushings (tra2545) in the steering gear and throttle bellcrank with bearings. I believe the 4908 has two in the right steering bellcrank and two in the throttle. AvidRC sells them for a buck each [link=http://www.avidrc.com/product/8/metric-bearings/78/5x8x25-Rubber-MR85-2RS-metric-bearings.html]5x8x2.5 rubber sealed[/link].

llZer0

is this a good servo?

http://cgi.ebay.com/ws/eBayISAPI.dll...fvi%3D1&_rdc=1

for steering or throttle? or both?

gettnbetter

Hitec, JR, Airtronics and Futaba make "good" servos.

llZer0

Does a wing help in some way.... have you guys try the tekcno mount kit for a t-maxx...

and will this wing work..

gettnbetter

You have to also install aluminum bulkheads or the wing will snap the mounts for the shock towers.

llZer0

do you guys use locktipe on aluminum bulkheads??

z400riderr

hey guys ive been having tuning/idling problems with my 3.3. it seems to run fine for the first few mins, but then it just goes all down hill from there. it consistantly cuts out, and has power gains an power loss. the glow plug is good, and the pipe is blowing out a nice blue trail of smoke when you zot it so i assume that its not running lean. could it be the gas or carb?? it seems to have decent compression.

gettnbetter

Yes, any metal to metal screw should be loctited with the blue stuff. If you want a permanent hold, use the red stuff. Loctite makes plastic brittle so be careful not to use loctite in plastic screw holes.

thechap76

My Feedback: (26)

hey zoo rider u say it runs good 4 the first few min the goes away....could be a air leak or loss of compression...how old is ur fuel...and just cause the plug seems good its a cheap way of insuring it is by just replacing it

z400riderr

chap76 the fuel i have is about 6 months old, and is traxxas top fuel 20%. the glow plug is good to. ive changed it a few times sence it started having ploblems so i dont think its the plug. also i dont see how it could be lossing compression because when metal gets hot it expands so it would gain more compression as it runs.

that.dank

The expanding and contracting of the metals (which is what break in is for) causes a special "fit" together.

if you broke in your engine wrong, you would still have compression right up until your engine started heating up, your "fit" wont be correct so as your engine approaches "running" temps it will lose compression.

Does your problem with the engine happen faster if you do WOT passes right from starting and get the kit hot fast?

and does it hold compression longer if you don't wail on it the moment you get it started?

z400riderr

i did not break in the motor i bought it used off of ebay, and it ran great when i got it. also if i let it idle it wants to stall out so it likes to be reved up and moving. an i dont know if they sell a compression tester but theres no other way to check it besides taking it out an checking it for feel type pressure on the flywheel, and by the time i got it out it would have started cooling down.

that.dank

Sounds like a compression problem, you can get it pinched for like 35$

only a temp fix though, ALWAYS take apart an engine you buy used and check for problems before running it.

z400riderr

yeah ive seen the pinch tools on ebay for cheap, but do they work or just mess up the sleeve?? also rip down my motors every few months or so to inspect, and clean them like you said.

dug44

My Feedback: (2)

+1 on that, the 645mg is def. enough... Sometimes too much...

REEGSf

Hi guys.
I need to replace my TRX 2.5 with the 3.3 . What tranny upgrade will I need and could you guys post some part numbers for me.
will I also have to replace my brakes ? they say the 3.3 is in a league of it's own.
Thanks

_____________________________

aerostar55

Your tranny will probably be fine with the 3.3, all the newer T-maxx's com with the 3.3. A 2.5 cc is actually a .15 CU In engine. A 3.3 is about a .20 Cu In. You may want to check your clutch shoes, and possibly adjust the slipper clutch for the additional power.

Just a hint: Traxxas has the engine exchange program running right now, you can trade in your old engine for any new one for a big discount.

Your brakes will work fine.