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  1. #1
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    Help resurrecting my 10+ year-old T-Maxx's 2.5 engine

    Good evening all--hope everyone is doing well during these trying times.

    To keep this post short: I'm trying to get my T-Maxx 2.5 running again. The backstory is that my dad gifted it to me back around 2003... We ran it together for years, always taking care to clean and lube all components after each use... around 2007 we stopped using it and it sat in the garage until 2015 when I brought it back out again for fun--the flywheel was badly stuck, but we got it loose, flushed the engine and carb with plenty of WD-40 and it was running fine... then it sat in the garage for a few years more.

    The other week I used some of my newfound/forced pandemic time to try and get it running again. Applied plenty of WD-40 to the engine and carb, applied some new white lithium grease to servo gears, charged up the EZ-starter battery which I purchased new in 2015... but the engine won't start this time. The piston turns over without a glow plug in it, but when the glow plug is inserted it won't start.

    I thought it might be old fuel stuck in the brittle fuel lines (fuel not making it to engine), or the glow plug. So I purchased new fuel lines and a filter, new glow plug, new glow plug lead (the old one was badly worn) and fresh air filter oil. The fuel I'm using was just opened this week, although I technically bought the bottle back in 2015... my dad and I figured it was still fresh enough for use since it was sealed all this time, but maybe we are wrong?

    After all that cleaning and replacing and priming fuel into the carb, then clearing the engine in case maybe it was flooded, it still won't start up. Without a glow plug, it's turning and blowing out the WD-40 I've sprayed in, no problem. But as soon as I tighten up the glow plug up, it seizes. I recorded the video below to share here (shown starting with a fully charged EZ-starter battery, new glow plug, new fuel lines and new (old stock) fuel):

    https://drive.google.com/file/d/1Aed...ew?usp=sharing

    Any help or guidance will be very much appreciated! Thank you in advance.

    -Dan

  2. #2
    Marshal Double G's Avatar
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    The engine sounds like it has good compression but it is either a weak battery and/or starter motor. Replace them or just go with a glow ignitor and pull start and it should start up.
    The Super Derecho

  3. #3
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    Yeah, I get this a lot when I forget to charge my EZ Start battery. Get a fresh battery and it should do fine, (I'm assuming the EZ start motor worked fine last time you used it)
    I'm not afraid of my fellow man.

  4. #4
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    I really appreciate your replies, guys. So you're recommending I replace both the EZ starter batter (handheld) as well as the EZ-start motor itself?

    I last replaced the EZ starter battery around 2015. I didn't use it much, but it technically has been sitting uncharged for years. The EZ start motor on the truck is original and could potentially be the culprit, but I'm not sure if there's any way to test that independently from the starter battery.

  5. #5
    RC Champion grizzly03's Avatar
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    I don't know if this applies to your battery, but when I switched out the NiCad battery in my EZ start to a NiMh battery it made a huge difference.

  6. #6
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    Quote Originally Posted by grizzly03 View Post
    I don't know if this applies to your battery, but when I switched out the NiCad battery in my EZ start to a NiMh battery it made a huge difference.
    I actually already use a NiMh battery in my EZ starter. Not sure if it originally came with one, but I upgraded to it back around 2015.

    Now that I am researching the EZ start system (handheld starter and motor) I am beginning to prefer just changing over to a pull start system. It looks like it would be less expensive and bypass the potential electrical system problems I could be facing. Hmm...

  7. #7
    RC Champion grizzly03's Avatar
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    Do you have another electric RC you could test the battery in? That would help you determine what shape the battery is in.

  8. #8
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    Quote Originally Posted by grizzly03 View Post
    Do you have another electric RC you could test the battery in? That would help you determine what shape the battery is in.
    Unfortunately I do not. I just have the one T-Maxx. From what I gather based on what everyone is saying so far, it sounds like I should either replace the EZ-start system and see if that works, or switch to a pull-start system and see if that works.

    Could there be another reason why my engine wouldn't start? Maybe some part inside that needs lubricating after all these years of sitting? Just trying to figure out what sort of basic at-home maintenance I can at least try before buying parts.

  9. #9
    RC Champion grizzly03's Avatar
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    After sitting in storage any residual fuel in the motor likely gummed up the bearings. So they aren't helping. The best thing to do would be to take the engine apart and check the bearings.

    Since you said it turns over without the glow plug you could try a trick that has worked for me in the past. Slightly un-tighten the glow plug and try starting. Sometimes this would lower the compression and aid in the engine turning over and still start. Once started then you would tighten the glow plug.

  10. #10
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    Quote Originally Posted by grizzly03 View Post
    After sitting in storage any residual fuel in the motor likely gummed up the bearings. So they aren't helping. The best thing to do would be to take the engine apart and check the bearings.

    Since you said it turns over without the glow plug you could try a trick that has worked for me in the past. Slightly un-tighten the glow plug and try starting. Sometimes this would lower the compression and aid in the engine turning over and still start. Once started then you would tighten the glow plug.
    That's a great idea about slightly loosening the glow plug, grizzly. Thanks for that tip, I will definitely give it a try.

    And I think I agree that it's time to take the engine apart and inspect for bad bearings and the like. Do you have any tips about how to clean and lubricate internal engine components? I use engine and carb cleaner on my motorcycle, but am not sure if that'd be too strong for the little Traxxas engine. Maybe just WD-40?

  11. #11
    RC Champion grizzly03's Avatar
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    You can use soap and water,denatured alcohol or Wd-40 on the engine parts. I just wouldn't use water on the bearings,LoL.

    Maybe this will help you take it apart if needed: https://traxxas.com/support/TRX-Engi...Instructions-0

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    Hope everyone is having a good weekend--here's my Saturday update:

    After reading earlier comments, I used my peak charger to charge my 7.2v 1800mah EZ starter battery at 2amps. Was reading out at a steady 8.4v after charging. Good so far...

    I also charged a separate glow ignitor overnight, which I used to test the NOS glow plug I had in my T-Maxx. The plug glows a bright orange and looked good to me. Good so far...

    Also unplugged my new fuel lines and blew into them to make sure there were no obstructions in either direction. When blowing into the engine with the high speed needle removed and into the muffler, air moved freely in both directions. Good so far...

    Using advice from grizzly, I loosened my glow plug in the engine and tried to start it up, and the motor started running! But it was only while I had the EZ-starter plugged in and EZ motor turning. Once I let go, the engine cut out. So I reset my high speed needle to 4 turns out and my low speed needle to about 1.75 turns out, and also checked the throttle trim which looked good. Tried starting it up a few more times, and every time the engine would run and smoke was coming out of the exhaust, but it would cut out immediately as I let go of the EZ-starter button.

    I tried tightening and loosening the glow plug some and every time, no matter my needle or throttle trim settings, the engine would cut out. I think I'm moving in the right direction because I believe this has proven that my glow plug, EZ-start motor, EZ-starter battery and fuel lines are all functioning. Only problem is I'm not sure where to go from here...

    Some light brown-ish liquid was oozing out from the glow plug hole during my attempts to start where the plug was slightly loose. Is the next step to take the carb and engine apart for bathing in denatured alchohol and WD-40? Any thoughts will be appreciated... thank you in advance!

  13. #13
    RC Champion grizzly03's Avatar
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    Sounds like you have a lot of old fuel residue. I would at least take the back plate of the engine and try rinsing (spraying) with WD40 to remove what you can. You can try that without any other disassembly of the engine. Drain the excess WD40 and put the cover back on and try again. If nothing else, you will be able to see what it looks like inside.

  14. #14
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    Quote Originally Posted by grizzly03 View Post
    Sounds like you have a lot of old fuel residue. I would at least take the back plate of the engine and try rinsing (spraying) with WD40 to remove what you can. You can try that without any other disassembly of the engine. Drain the excess WD40 and put the cover back on and try again. If nothing else, you will be able to see what it looks like inside.
    Hello again grizzly and all,

    About one month later, I'm proud to report that I've completely taken apart the engine and carburetor and rebuilt both with new o-rings where necessary--which was just about everywhere, haha. It took me the most time to track down Traxxas Part #5213, the engine backplate o-ring which is separate from all other o-rings that are included in Traxxas Part #5247. The engine was definitely gunked up, but it has been 100% cleaned, re-lubricated and re-sealed. I was very careful in my reassembly so as to ensure everything went back on exactly the way it came off. And that all being said...

    ...I still cannot get my T-Maxx to start. The engine and E-Z start spin much more freely and easily now, but the engine will not stay on. Both lights are green on my fully-charged E-Z starter. I have re-set the high speed, low speed and idle speed needles to factory settings. I have replaced all fuel lines and primed the engine, visibly seeing air bubbles moving freely through the fuel line (good pressure). I also removed and cleaned the muffler. What could I be missing? Here are two videos of my attempts to start the engine:

    https://drive.google.com/file/d/1FHh...ew?usp=sharing
    https://drive.google.com/file/d/1FFM...ew?usp=sharing

    Should I also disassemble and inspect the clutch assembly? Could that have something to do with the engine stalling? Or maybe it's the glow plug? Although as I said earlier, this was a new-old-stock glow plug that was sitting sealed in its package on my workbench for a few years (so yes, a few years old, but never removed from its package).

    Any help or advice will be greatly appreciated. Thanks all!

  15. #15
    Marshal Double G's Avatar
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    Hopefully you put the cut-out on the piston facing the carb. If you are unsure, remove the header and spin the engine by hand and if you see the rod the piston is backwards. If not, you are good.

    If you have a multimeter, confirm that you have full battery voltage coming out of the corresponding wand ports for the starter and 1.5v for the glow plug. If so, make sure the same voltages are present at the end of the wires.
    The Super Derecho

  16. #16
    RC Champion grizzly03's Avatar
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    It's trying to start. Try putting a block or something under the truck, to lift the tires off the ground. This way your able to give slight throttle without it taking off. Then try starting again. Instead of holding the throttle half way or at any point, try pumping the throttle from idle to 1/4, as it's trying to start. Similar to squeezing the trigger on a water squirt gun.

    Excess fuel is actually called a rich setting.

  17. #17
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    Quote Originally Posted by grizzly03 View Post
    Excess fuel is actually called a rich setting.
    Whoops, I misspoke--you're absolutely right, Grizzly.

    Another month has gone by, but I wanted to update anyone reading with the news that a brand new glow plug combined with feathering the throttle from idle to 1/2 as I attempted to start the engine did the trick! I guess that first, new old stock glow plug I had sat a little too long for it to be reliable enough.

    Two final things I'd love a little feedback on in regard to getting the engine running normally again are:

    1) Even after tuning my LSN (flush with the slide), HSN (about 3 3/4 turns out from closed) and idle speed screw (about a 0.6mm gap), my truck jerks forward pretty aggressively at idle. No jerking for the first 20 seconds or so, then it starts to jerk forward once every couple of seconds, getting progressively worse until I kill the engine manually. I see the slipper clutch spin in the reverse direction for a moment every time a jerk forward happens... Any idea what this could mean?

    2) After about three minutes of running, I notice a very thing, small bit of smoke coming up from the glow plug area. Glow plug is on tight with the EZ start lead attached firmly. It's not a huge amount of smoke, but it does make me worry that I'm running a bit hot or maybe some fumes are escaping upward somehow... Any more ideas?

    Seriously big thank you to Grizzly and Double G for advising me as I went. Now that the truck is back up and running in ANY capacity at all, I feel confident that I'm doing something right, haha. Looking forward to making more upgrades in the near future.

  18. #18
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    The gap for idle should be 0.7-1.0mm open so open it up a little bit. The combo of a too small idle gap and possibly lean LSN (yes I know stock setting is flush - or 1.75 turns from closed but I've found that with my Traxxas engines you need to richen it) causes the engine rpm to slowly rise while sitting still which will raise the temps of the engine. Off throttle the engine should be cooling a degree or so every few seconds. Let the engine breathe and give it a drink and it'll settle down. As for the jerking, the way I see it is that the clutch is at that point of grabbing and releasing and trying to spin the transmission. Should be nothing to worry about.

    2. The washer on the glow plug should be tapered and when you install it you want it to look like an upside-down bowl - /---\ .
    The Super Derecho

  19. #19
    RC Champion grizzly03's Avatar
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    It does sound like a lean condition at idle. You can check it with the pinch test. 3-5 seconds before it dies is a good setting.

    The jerking or bucking is a normal trait of the classic transmission. It has internal clutches that grab as the spin up. I'm thinking if you richen your LSN setting that should help the idle and the excessive bucking.

    There was a no-buck mod (if you want to try) that got rid of the bucking. Maybe Double G remembers more about it?

    Here is a good article to read:https://traxxas.com/support/How-Star...-Racing-Engine

  20. #20
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    Ah, no buck mod. With reversing transmissions, there was a pawl system much like the system used to engage second gear but it was to engage the transmission. Starting from a stop the truck would buck like someone learning how to use a manual transmission in a car.

    Snook Man, THE guru of all T-Maxx and transmissions had this to say:
    https://forums.traxxas.com/showthrea...=1#post6095064
    Quote Originally Posted by Snook Man
    For what its worth, back in the day when I did run reverse in the black transmission a lot of us did the no buck mod.
    We would remove the pawls from the F&R gears and add screw pins to the gears that engaged the clutch bell instead of the pawls.
    This would allow the accidental switching from forward to reverse while the truck was moving. Not once in quite a few years of
    running that way did I ever accidentally hit the reverse switch. I did however do it on purpose a few times for scientific reasons...
    The Super Derecho

  21. #21
    RC Champion grizzly03's Avatar
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    That would be the one. Sure do miss his "nitro speed mods". Now that ceramic bearings are much more affordable I wonder how much easier his modifications (3 speed) would have turned out.

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