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  1. #1
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    Current direct fit motors avail?

    Hey guys, have had a T-maxx for a couple months now, that I bought on the cheap with a worn out 2.5. After lots of searching and digging around this site I determined it needed to be replaced. I figured I would go the easy route, and pick up a 3.3 @ my LHS. Slipped it in, proper break in, and began tuning (not something I am new at, spent years tuning race 2 strokes, all kinds of fuels, and set-ups)....this was atleast 2 months ago and I am still having a rough time with this (triggered language filter0 truck. I have tuned to temps, smoke, sound...and it always gives me some sort of problem... biggest is idling, wether its coming off a throttle pull, or just sitting. Sometimes it behaves as it should, for just a few seconds- sometimes it flat wont idle, others it idles just high enough to engage clutch. I've tried diff carbs, settings, even pulling off this brand new motor, and sealing all the places it was/could leak. Its driving me bonkers. I can NEVER get a full tank thru it without serious frustrations.

    I have read several places that there are other motor/carb combo's that will give me less grief, and more fun. How much truth is behind this? Since I am pretty new to the hobby I tend to get lost looking at all the different options, and ideas. That leads me here...you guys are the real Traxxas pro's, help me. Which, if any are true drop in? Who will give me the most reliable set-up, and why? Which set-ups are proven, and which are new/untested?... I dont mind small tuning, as long as I can actually take it out and play. Along with these questions, who will give me the best pricing?

    Thx fellas

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  2. #2
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    Before you buy a new motor, are you retuning every day you start up the truck? I had a 3.3 for 2 years before I replaced it.
    If you insist on a new motor, you can go with O.S. .21tm, RB TM523, picco .28 with or without the red dot. Those are probably the 3 drop ins with the most power.

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    TRXnot so Newbie21

  3. #3
    RC Turnbuckle Jr. Nitronaught's Avatar
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    I know you have 2 stroke experience with tuning but they are still different. These engines work on a blyby principle and have no reed valves. At one point both intake and exhaust ports are open unlike reeded setups.

    First thing I want to warn you about is that as your fuel level drops in your tank, the tune becomes slightly leaner... So tune with only 1/2 a tank, it is more stable this way. When you do as you first fill up it might be a tad rich but that prevents you from being too lean when you fuel level drops.

    Now, the LSN must be tuned properly in order for the HSN to function correctly, so with a warm engine do the pinch test to tune the LSN...

    If you read over this tuning sticky AND the owners manual which is available on the support section of this website, you should have much better luck with your tune...

    I've 4 TRX engines, have raced since 2005, rebuilt a quite a few and have done some modding/fuel porting, crank polishing, etc... Trust me this will help you find the Zen art of tuning Nitro's....

    If I had a penny for every 2 stroker out there New to Nitro who has scratched their heads and pulled out hair trying to figure it out I'd be rich!!!!!

    http://traxxas.com/forums/showthread....&goto=newpost

    RB TM523 and Picco .28 are NOT direct drop ins, they require special motor mounts, and I believe the .28 Picco requires a BB chassis, but the Picco .26 will fit with the appropriate motor mount... However these engines are a lot more powerful than the 3.3 and probably will require driveline upgrades to support... THe OS .21TM is a direct drop in fit, but double the price of the 3.3 practically...

    Try those tuning tips in that sticky and go over the section of the carb and tuning in the owners manual, it should clear things up...

    Especially when you see these to help explain the needle relationship of HSN and LSN they ARE different than diaphram operated carbs....





    I also do believe there is a Losi 3.4 that's supposed to be a drop in fit, but I've not heard anything on them as how well they are working... I'm happy with the TRX engines... Once you get the tuning down...
    Robin Williams
    He will be greatly missed...

  4. #4
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    Quote Originally Posted by Nitronaught View Post
    I also do believe there is a Losi 3.4 that's supposed to be a drop in fit, but I've not heard anything on them as how well they are working... I'm happy with the TRX engines... Once you get the tuning down...
    The Losi carb is a drop in with a little trimming of the outside of the carb to that it fits nicely. A couple other little mods for it to work. So far mine has been causing me issues so I put the Traxxas carb back on. Recently found a hairline crack in the lower part of the body so I'm planning on sealing it up and trying it again.
    The Super Derecho

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    TRX- yes, its seems to need tuning every single time I fire it up. Its getting to the point I usually just pick up the VXL Rusty, because its all thrill, no fill.... It erk's me to no end, because im a motor head I would much rather drive the maxx.

    NN- you are correct, these carbs are very diff that diaphram carbies. I learned that day one of having this janky ol' truck. Once I figured that out I went to google to learn. I have read all the items you mentioned, even have those illustrations saved on my desktop. I always start w a bit more than a half tank, so I can run and warm it up, before I start the tuning. From there I start with the HSN and tune till it seems happy (sound, smoke, temps) and then move on to the LSN. At this point it usually seems to lose its mind- i'll get it to where it feels/sounds good, then its like a switch gets flipped. It will idle funny, if it idles- or wont come off a pass well, it sounds like and old chainsaw (lack of better description) its kind of flutters on its way back to idle, where it usually dies. Once this happens, its usually a booger to start.

    With 4 TRX engines, and how you talk of them I have no doubt your tuning capabilities are better than mine. But I feel it shouldnt be this difficult. Maybe I am missing something. I tend to think with as much tuning as I have done on this truck, I would have it in a drivable condition, but I don't.

    As for the motors you guys mentioned, thank you. Not that I know what any of those are, but google does, and its a fine educator. I will certainly look into them, as the modding of carbs, and/or diff motor mounts aren't too big of a deal. I know it will never be as simple as pushing the button on the VXL, but if another motor set-up is MORE reliable/easier to tune it would def be worth it to me.



    aaaaaagh, all this talk is giving me the itch. Time to crack this lil motor off, and try again.

  6. #6
    RC Turnbuckle Jr. Wildman4910's Avatar
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    You have an issue, I find I normally only have to tweak the tune unless there is a major weather change.

    Check the fuel lines, exhaust coupler, header o ring, tank seal for damage leaks.
    Any of these will cause you no end of headaches till fixed & can cause you to chase your tune all over the place.
    Look out for the tree/crunch!

    LiPo? Naw NITRO!!

  7. #7
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    I have had those same issues before waffle it ended up being the exhaust coupler had a hair line crack in it that you could not see unless it was off the truck.
    Drive it, Break it, Upgrade it

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    I have checked fuel lines (new w motor) header o ring, and tank seal...I only get the occasional air bubble in the tank to carb line. I have noticed there is usually some fuel in the exhaust line. What should I see here? Slight amounts? Only one I havent checked is the coupler....will get right on that one. Thanks fellas.

  9. #9
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    Fuel in the exhaust pressure line? Sounds like you've got some junk gummed up inside the exhaust pipe..... Can you try a different exhaust pipe or maybe try to clean that pipe...
    It can also happen if you are running too rich, but you would also see a lot of fuel coming from the stinger as well...

    +1 you've got something working against you like Wildman said...

    If there is a leak your needles will be compensating for the leak... That will send you in circles.

    Fuel lines, check for splits at the connecting points
    Head Bolts, tighten in a star pattern like a 1:1 car tire
    Header bolts and o-ring, check if they are tight and look for any brownish coloration, if you see some there's a leak the o-ring may need attention on the exhaust outlet of the motor.
    Fuel tank, make sure the lid is sealing well, there is an o-ring in the lid and a screw you can tight to create more pressure on the o-ring if necessary.
    Check for any puddling of fuel under the engine or around the engine. If the flywheel is wet the front bearing has a leak and needs replacing. Mainly happens to engines that have been ran a bit or they did not perform an after run leaving nitro inside the engine...

    Another quick thing you can do is make sure there is not a hairline crack in the composite carb. How you can check this is get the engine running and spray a little WD-40 at the base of the carb, if the idle changes there's a leak...

    Believe it or not a bad glowplug where the platinum on the coil has been worn or is not very good will cause tuning headache's as well..

    Besides that, changes in tune should happen when there are changes in temps more than 8 degrees F or more... Usually you never have to touch the LSN once it's happy unless you change fuels, exhaust or intake, then it's a full re-tune...

    Hope this helps man... Good luck
    Robin Williams
    He will be greatly missed...

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    I didnt think fuel in pressure line was right. It seemed to range from just small amounts, to alot at times.

    As for exhaust... Checked both the coupler and the pipe this morning. Found a small tear in the coupler on engine facing side, and a torn boot that sits just in the neck of a 2.5 pipe. So stoked! This has to be my problem I thought! Ran down to the LHS, picked up a new pipe (Traxxas doesn't sell the lil insert seperate) and a new coupler, along with a few new plugs. Ran home, excited to finally get to run this lil truck...Bolted it all together, stepped outside and hit the starter...Max fired right up, and idled like never before. Im sure my face was lit up like a kid at xmas! But it didnt last long... Not long after warm up, it started acting erratically again, sputterin on accel, fluttering on decel. Also, the fuel in pressure line is back, and the fuel tank seems to be more "bubbly" than usual. Grrrr, here we go again.

    So I brought this jank truck back to the table, and decided to give it a look over. Flywheel/Carb side seem to be clean, so im pretty sure its sealed correctly there...but towards the back of the motor, where the easy start bolts in its seems to be wet. At first I thought maybe I didnt get the couple back on right, or the o-ring @ mani was leaking. Pulled mani, looks good, re-aligned everything and sinched down coupler ties...Back out to test....No change. Still stutters on accel, flutters on decel. Smoke seems to be eraatic as well, confirming theres a leak somewhere...

    Remember its a new engine. Seals are new. Carb is new. Now exhaust too. I have pulled the ez start, and checked behind it to make sure bolts are tight, and seals are good. Usually I wouldnt rtv anything, im a firm believer in gaskets doing there job...but for kicks I put a ever-so-small bead around the base? plate (bolts directly to engine), and an ever-so-small bead around where the ez start bolts in since it only has three bolts....But this area still seems to be leaking? What else could it be!?!? I have pressure checked tank, new fuel lines, clean air filter, new plug....I even tossed a new mount in when I put the motor in for gigs..

    Im at the point now, where I would sell this truck if I thought I could make it run long enough to do so. But I cant sell anyone a truck I know isn't good, nor could I get what I now have in it. uugh.

  11. #11
    RC Turnbuckle Jr. Wildman4910's Avatar
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    Any chance of getting it on video when it's running irraticaly?
    Look out for the tree/crunch!

    LiPo? Naw NITRO!!

  12. #12
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    It could be the rear bearing I know you said it is a new motor but it is possible at this point. Also how does the compression feel on it? How does the top of the head look by the glo plug? Is it wet or dry? If it is wet you could have that little washer on upside down.
    Drive it, Break it, Upgrade it

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    well...I decided to go ahead an pull this lil engine down, and toss all new seals at it, just in case they were the source of my problems. upon tear down, I think I might have found a leak at the rear most o-ring...but I also found this.





    Im pretty sure this wasn't the problem, but is most def the result. Looks like its time to try again!

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    NN, and you other veterans..... where would you go from here? Piston/Sleeve kit? I would think all new seals too, just for kicks....or just do the Traxxas replacement prog @ my LHS?

  15. #15
    RC Turnbuckle Jr. Nitronaught's Avatar
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    Quote Originally Posted by waffle-n-chicken View Post
    NN, and you other veterans..... where would you go from here? Piston/Sleeve kit? I would think all new seals too, just for kicks....or just do the Traxxas replacement prog @ my LHS?
    The dark brownish and blueing on the side of the piston is definitely signs of high temps, not for very long though...

    The debris concerns me. Not sure if it was a glowplug failure where the coil breaks off inside the engine (EXTREMELY RARE), or if there was a bearing failure....

    Rule of thumb, no internal debris = rebuild with a piston and sleeve AFTER checking your conrod... With the piston and sleeve in the engine with the crank put 1 drop of household 3-1 oil or any light machine oil (WD-40 is too thin motor oil too thick) on the spot where the conrod meets the crank, if the drop of oil pushes all the way out when you rotate the flywheel back and forth 1.2 a turn each way then the conrod has seen it's day....

    Average pricing
    Ebay Piston and Sleeve $40.00
    Ebay Piston Sleeve AND conrod $60.00
    Engine Bearing replacment $25.00 $35.00 for ceramics
    Ebay brand new pulled motor $105.00 (no rebuild required).

    With debris in the engine I replace the engine bearings if rebuilding the motor,,, but only if I'm going to upgrade the bearings to ceramics.

    So you can rebuild one yourself for around $100.00 complete bearings, conrod, piston and sleeve for under $100.00 or spend $105.00 and have a new motor no rebuilding needed. I like mechanics and enjoy rebuilding so I do it not out of money but out of pleasure of the task and the reward..

    Hope that helps...
    Robin Williams
    He will be greatly missed...

  16. #16
    RC Turnbuckle Jr. Wildman4910's Avatar
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    I agree with NN, no debris rebuild it if you wish, but with debris I would just clean up the good parts left & either keep them as spare's or Ebay them.
    Look out for the tree/crunch!

    LiPo? Naw NITRO!!

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    Good, glad to see were all pretty much on the same page. I figured with the debris that I found inside, a bearing had to be at fault, and that they would all have to be replaced. NN- tell me, or shoot me a link to find out more of these ceramic bearings? I have never used them in an engine, only on longboards that we drifted alot (mostly wet surfaces) What are the benefits to running a ceramic bearing, if any?

    Also, you mentioned that the coloration of the piston itself told you about engine temps.I did briefly have a heat issue, probably attributed to the handful of leaks this truck had.... Where can I go to find more information/pics on this? What about glow plugs? Do they have signs of how the motor is running like spark plugs do? I have spent countless hours learning how to read diff plugs in diff situations. While i'm sure they're completely different, it can't be that hard to pick up.


    I guess im off to the interwebbings to find a new power plant. Now that we've come to this point, maybe we can talk options? Im positive now that I have any air/fuel leaks under control, as everything has been replaced (minus tank- but pressure checks ok)... So what should I opt for? I'm pretty sure there wont be much racing, unless its for fun- will be more of a play/bash type truck. Since I am not having alot of luck with this truck so far, I think i'd rather stay with the lower priced options. Im guessing that's gonna be a traxxas motor? It's the 4910, originally equipped with the 2.5, I put a 3.3 in it. I dont really know the performance difference- should I stick with the 3.3? Is the 2.5r much diff than standard 2.5? ohhhhhh...I have so many questions. Is there somewhere I can read a good comparison online?

    Wildman- dig your sig....tired of running my LiPo- I need to burn some nitro! I miss the smell.

  18. #18
    RC Turnbuckle Jr. Wildman4910's Avatar
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    3.3 is a good choice. Ebay is about the cheapest place to get a new one.
    Boca Bearings
    http://www.bocabearings.com/bearing-...es-trx-3-3-3-3

    For all your other bearing needs I use AvidRC.com, most of their bearings are $1 each so you can stock up & never be sidelined by a bad bearing again!

    Look out for the tree/crunch!

    LiPo? Naw NITRO!!

  19. #19
    RC Turnbuckle Jr. Nitronaught's Avatar
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    I use Avids myself, not as expensive as Boca's usually... http://www.avidrc.com/product/16/engine-bearings/
    Robin Williams
    He will be greatly missed...

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