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  1. #1
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    Nitro RC Noob, Broken Revo 3.3

    A guy at work wanted a new RC car, so he sold me his Revo 3.3 for a hundo to help finance whatever new monstrosity he bought.

    Him and his kid have kinda been beating on this thing until it broke, and that's how it sits for me.

    Bear with me here, as I know exactly nothing about RC cars, nitro, none of it. I am mechanically inclined, and a geek by nature.

    Problem 1: Idle is about 44,000 RPM. I think I have this figured out, not sure how to fix it though. I backed the idle screw out all the way, and the slider didn't move. I applied the brake, and it closed. Now it won't start. I think that, plus a mis-adjusted low speed fuel screw is the idle issue. Once the batteries are all charge up I can play with that.

    Problem 2: Even at 44,000 RPM, the truck won't move. There is a gear on the rear of the transmission, I believe it's a spur gear matched to a slipper clutch, and it's destroyed, only about half the teeth are there. The metal gear attached to the clutch spins. Occasionally, the metal gear will catch the good half of the spur gear and it'll start spinning as well, and the truck will just shake, no movement. Safe to assume there is a broken gear in the transmission? Safe for me to take that thing apart, or just ebay another one?

    That's all I've got so far, other than wildly maladjusted front wheels, but I see how those work, just need to wrench them straight.

  2. #2
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    Update: I backed out the idle screw and attempted to set the low fuel screw to "flush with the grey ring" or whatever traxxas says (There are two grey rings...) and now I've got a no-starter. Nothing at all, won't even make a pop. The starter is also slipping off it's gear like crazy.

    Edit: Seems the starter issue might just be a dirty sprag clutch
    Last edited by Double G; 09-14-2019 at 08:15 AM. Reason: merge

  3. #3
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    Update again: I got it running, the idle is lower, but still seems crazy high to me, 3-5K maybe. The throttle trigger does something now, but I still have to apply the brake to lower the "idle" back down. Can't fart around with it anymore tonight, it's past midnight and this thing is nasty loud. Looks like my next steps will be to replace the header (PO mashed it with pliers) and the spur gear assembly. It came with a new glow plug wire, I replaced that, the old one was pretty beat up. I'll replace that gear, the header, and clean and lube the sprag clutch and report back.

  4. #4
    Marshal Double G's Avatar
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    1. Go to the Support button above and download the manual and exploded views of the truck and engine.

    2. Replace the header. The exhaust is used as a pump to push fuel to the engine. Air should only enter through the air filter and exit through the exhaust stinger.

    3. Assuming the engine is a Traxxas 3.3, the factory settings are 4.0 turns out from all the way in, LSN: 1.75 turns and the idle gap is 0.7-1.0mm open.

    Don't know what you mean by sprag clutch unless you are talking about the one-way bearing that is located on the back of the engine. There is a clutch on the front of the engine that works similar to a chain-saw clutch and is located inside the clutch bell. The clutch bell is meshed with the spur gear which is attached to the slipper clutch.
    The Super Derecho

  5. #5
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    Thanks for merging my double post.

    I'll order the header and spur gear today, not sure if the header leaks, but it's kinked, and 2 strokes are heavily dependent on the shape of the exhaust to run properly, so I'm sure that's a major issue.

    3.3 engine to the best of my knowledge. 4.0 turns on the high speed adjustment on top, 1.75 turns on the low speed adjustment in the throttle slider, yes? I think I have the idle in the ballpark.

    One way bearing is what Traxxas calls it, yes. Not sure why they don't just say sprag clutch (helicoptors have them and there's one in my Ducati) but that's fine. Looks like it gets fuel on it and will start to slip. I need to get the trans and engine out anyway to fix the spur gear and inspect the clutch, so I'll give that a once over as well.

    Exploded manual downloaded, thank you.

  6. #6
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    Quote Originally Posted by DoubleJ View Post
    ...The throttle trigger does something now, but I still have to apply the brake to lower the "idle" back down...Looks like my next steps will be to replace the header (PO mashed it with pliers) and the spur gear assembly. It came with a new glow plug wire, I replaced that, the old one was pretty beat up. I'll replace that gear, the header, and clean and lube the sprag clutch and report back.
    Throttle linkage is set up "wrong". What I mean is when throttle lever in neutral the throttle barrel itself should be resting on idle adjustment screw. If you hit the brakes the idle should not change. Have a look here:Throttle-and-Brake-Linkage-Adjustment.

    Getting exhaust fixed would help with tuning and running if its not right. Check the silicone coupler, if it's cracked or has a hole in it replace it. Also there is a gasket or o-ring where header attaches to engine. As Double G said it uses exhaust pressure to pressurize the fuel system(the setup acts like a fuel pump.)

    If your replacing the header I would suggest the spring mount one. Less likely to bend/break in a crash. Header 5340X and the spring/gaskets to hold it on 5254

  7. #7
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    That would probably explain why the pipe is pliered. I'll get the flexible setup.

    Here's something else odd I've noticed, the truck doesn't roll on it's own. If you turn a wheel, the other wheel will spin the opposite direction, but if you put it on the ground and push it, it'll just lock up and not move. Is that some sort of built in engine braking? According to the PO, they were driving it around their yard 2 days before I bought it, but it was either stuck in 1st or stuck in reverse, they couldn't get it to sit still. Now I've got the opposite going on.

    Once I get everything replaced I'll check that tutorial.

    Last thing for now: What's my best bet for buying parts? No one seller on ebay has everything I need, so I'm stuck paying 4 different shipping charges for a bunch of 3 - 15 dollar parts.

  8. #8
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    Quote Originally Posted by DoubleJ View Post
    If you turn a wheel, the other wheel will spin the opposite direction, but if you put it on the ground and push it, it'll just lock up and not move. Is that some sort of built in engine braking? According to the PO, they were driving it around their yard 2 days before I bought it, but it was either stuck in 1st or stuck in reverse, they couldn't get it to sit still. Now I've got the opposite going on.
    One wheel turning opposite is normal, it's the the differential. As for not sitting still, check your clutch spring and shoes on your engine, sounds like a spring broke keeping clutch engaged. This would make it so you couldn't push it also. You should be able to push it on the ground and see if things are moving.
    Quote Originally Posted by DoubleJ View Post
    Last thing for now: What's my best bet for buying parts? No one seller on ebay has everything I need, so I'm stuck paying 4 different shipping charges for a bunch of 3 - 15 dollar parts.
    If I need to buy a bunch of smaller priced parts: (Ebay is not very good for multi part purchases)
    A: Go to my local hobby shop or B: Online retailer

  9. #9
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    The clutch on the front of the engine could be bad. If the tires spin when the engine is turned over that is one sign. Another is that when the truck comes to a stop the engine stops. A third is that if the truck is lifted off the ground, the tires spin but when it is placed on the ground it dies. If you leave your Ducati in gear and come to a stop without releasing the clutch what happens?

    If you pick up one end of the truck and roll it and the opposite axle rolls the opposite way then a differential is installed upside down. You'll have to pull the bulkheads and look at the differential case for "UP" and an arrow.
    The Super Derecho

  10. #10
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    those support links are great and after you get it running well you should check out these performance tips as well

    https://traxxas.com/pitpass/howto/ne...t-Guide-part-1
    https://traxxas.com/pitpass/howto/ne...t-Guide-part-2
    https://traxxas.com/pitpass/howto/ne...t-Guide-part-3

    also id pick up a temp guage so you dont overheat and ruin your engine. and a glow igniter wouldn't hurt either.

  11. #11
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    Thanks Billy, I'll check those out.

    I just pulled the trans and engine. If I spin the spur gear one way, nothing happens. If I spin it the other way, both output shafts spin. Both diffs seem fine. Plenty of meat left on the rotor and brake pads.

    There is a spring around the clutch friction material, it's broken, so I believe this would leave the clutch engaged permenantly, resulting the complaint that they couldn't get the truck to stop. This probably also resulted in the spur gear getting destroyed as they messed around with it.

    The sprag clutch was literally dripping 2 stroke oil...in fact everything is absolutely covered in the gunk. Further investigation of the header shows that it's been removed, destroyed with pliers, and reinstalled. Holes in the head to bolt it to are suspect as well, so I'm glad I ordered the spring mounted unit.

    I think a clean up, tune up, a couple parts, and some TLC and this thing should be a runner. I'll report back as I find more broken stuff...or break stuff myself.

    Edit: Also found that there is a boot that seals the throttle slider and it was off, exposing some internals. I bet that was my idle problem.
    Last edited by DoubleJ; 09-14-2019 at 10:16 PM.

  12. #12
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    Your headed in the right direction. Oil covered usually is an indication of a leak in the exhaust. Keep up the great progress.

  13. #13
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    Ok, new parts arrived along with some long allen wrenches, I got everything installed minus a new zip tie for the pipe-to-muffler coupler, and got it fired up. Idle seems normal to me, maybe even low...there's a bit of take up before the clutch engages and the truck moves.

    Had to move the muffler about a half inch outboard on it's bracket to fit with the new header.

    Tipping into the throttle slowly will allow it to accelerate, but punching it causes it to bog. I have the 4 turns and 1.75 turns set up, but I'm guessing those are at sea level, so I'm probably rich in Colorado. I'll check out the tuning advice in the links above.

    Wasn't sure how to set the mesh between the engine's output gear and the input spur gear on the trans, so I mooshed them together, then backed out 1.5 hairs. They don't bind, but they don't feel loose either, figure it's a similar arrangement to the gear mesh on my slot cars.

    Hard to drive at night, gets out of view too quickly and too many cars to possibly hit (almost did ram the neighbor's house, radio seemed to disconnect for a second, no brakes). I'll probably mess with it this weekend again. Thanks all, I'll report back with updates.

  14. #14
    RC Champion olds97_lss's Avatar
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    The settings from the manual are general break in settings I believe, which tend to be on the rich side anyway.
    Expert rigging at it's best!

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    Quote Originally Posted by DoubleJ View Post
    ...

    Here's something else odd I've noticed, the truck doesn't roll on it's own....
    Yeah, the brake adjusting knob was cranked down, so the brake was always on.

    Also, what's the run time on a tank of fuel, 45 seconds or so? It's running so rich that it lays down a stripe of oil out of the stinger on the road when I drive it and the two stroke smoke will linger in my grass like fog for a minute or two. I downloaded a fuel card of some sort from Traxxas that give some tips on changing the mixture, so that'll be the next move.

    Second also, what should the range be with the radio? By the time it hits near what sounds like the top of second gear, I'm losing control of it and have to walk a few feet to pick it back up. Fresh batteries in the controller, batteries in the truck could be low.

  16. #16
    Marshal Double G's Avatar
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    Run time depends on driving and tune. I don't keep track of time but I would say around 12-15 minutes to drain the tank.

    What radio? Range issues usually are due to the antenna - check the one on the receiver and make sure it is not kinked or bent.
    The Super Derecho

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    ...what's the run time on a tank of fuel, 45 seconds or so?
    I never really payed attention . Double G's answer 12-15 sounds right.
    It's running so rich that it lays down a stripe of oil out of the stinger on the road when I drive it and the two stroke smoke will linger in my grass like fog for a minute or two. I downloaded a fuel card of some sort from Traxxas that give some tips on changing the mixture, so that'll be the next move.
    A good tune will help. With a bog it sounds like a rich setting.
    Second also, what should the range be with the radio? By the time it hits near what sounds like the top of second gear, I'm losing control of it and have to walk a few feet to pick it back up. Fresh batteries in the controller, batteries in the truck could be low.
    If you have a 2.4GHZ radio range is very dependent on antenna. Any damage will shorten the range.

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    And I'm out of gas.

    I've turned in the low speed fuel needle about a full turn to get it to die 2-3 seconds after I pinch the line. It's right at 3, I'm ok with a little rich there. Idle is back up to the point that the car will roll away slowly on it's own, I can't get it back down.

    On the high speed fuel, it says to lean out to max performance, and then richen 1/8 turn. I have no idea what max performance is. I'm still using way too much fuel (about 10 minutes run time on a cup of fuel) and laying down a cloud of blue smoke, so I figure I'm still safely on the rich side.

    These things are too fast for driving in a neighborhood.

    Figured out my range issue, the PO yanked the antenna wire out of the crystal (Is it still called that?) and it was flopping around in the body of the controller. Re-attached, and I'm in business.

    I need to go find a hobby shop and get a gallon of fuel. Here's a surprise, everyone on the internet says something different about each type of fuel, and for each person that likes brand X, another person had it blow up their motor. Weird.

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    Double Post

  20. #20
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    After tuning the engine have you tried lowering the idle with the idle screw? High speed needle: running on the rich side is good, but running too rich can also be bad. If your engine is too cold it puts extra wear/stress on piston/sleeve. Your engine temps should be above 200F. Do you have raw fuel coming out exhaust?
    Fuel is personal preference. Back when Traxxas sold fuel in metal cans I had trouble tuning and switching to another brand made a difference. I'm back to using Traxxas brand fuel again and having no issues with it, they must have changed their fuel formula. Best advice I can give is to use what ever your local hobby shop keeps in stock.(just make sure it's not airplane or boat fuel,they have different oil content)

  21. #21
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    Quote Originally Posted by grizzly03 View Post
    Fuel is personal preference. Back when Traxxas sold fuel in metal cans I had trouble tuning and switching to another brand made a difference. I'm back to using Traxxas brand fuel again and having no issues with it, they must have changed their fuel formula. Best advice I can give is to use what ever your local hobby shop keeps in stock.(just make sure it's not airplane or boat fuel,they have different oil content)
    Yeah, in the 20 years I've been running nitro, I'd never blame a fuel for killing an engine. I've tried quite a few and find that byrons 25% works best for me in all my stuff. Fuel is ridiculously expensive to ship, so hopefully you have a local shop to buy it at or you will end up paying a real premium for the stuff otherwise.
    Expert rigging at it's best!

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    Quote Originally Posted by olds97_lss View Post
    Yeah, in the 20 years I've been running nitro, I'd never blame a fuel for killing an engine. I've tried quite a few and find that byrons 25% works best for me in all my stuff. Fuel is ridiculously expensive to ship, so hopefully you have a local shop to buy it at or you will end up paying a real premium for the stuff otherwise.
    I use to run O'Donnell fuel. Worked good for me. At that time only had the two choices at hobby shop. The new hobby shop only carries Traxxas. I don't get much of a selection locally.
    Absolutely, Rc fuel is ridiculous to ship as most places charge hazard fee.

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    Update: I got a gallon of VP basher 20% fuel and messed around with the tune. I've got it pinch dying in just about three seconds from idle, so I'm a hair rich on a 65 degree day, which will probably be very rich on an 80 degree day, I'll have to lean that out a hair I think. I've got the high speed screw leaned out a bit, with temperatures around the heat sink and glow plug ranging from 215 to 250 after I wail on it a little.

    How's that sound?

    I've found a stuttering issue at high throttle, low speed occasionally, but there's no spur gear damage, so maybe it's sticking in 2nd gear (I can tell sometimes that it is, there is no shift, but it reaches top speed from a slow 180 turn) and loading up the clutch as it tries to get moving. reducing throttle clears it.

    Also still having random radio or receiver cut outs, but they only seem to affect the throttle (or maybe there's a fueling issue?) as it'll take off, then coast for 10 feet, then I cycle the trigger and it takes off again. On second thought, no, it's a radio issue, as I almost creamed myself once when the brake wouldn't engage, wouldn't turn either. Only for a second, but this thing moves alot in that one second.

    None of these things are enough to take away from the fun though, this thing is a blast, I did a front flip with it. My neighbors and their dogs...not so happy about it.

  24. #24
    RC Champion olds97_lss's Avatar
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    Does it have the "optidrive" module in it? It's an electric box that keeps you from shifting into/from reverse when the transmission is spinning. Those were known to be kind of fussy and to cause strange radio issues. Most people removed them and just relied on their common sense to not shift when the truck was moving. Many removed it and put in a forward only conversion (FOC) to simplify things even further, which also removes some rotational mass from inside the transmission and makes for a stronger drive train as the primary gear used in the FOC is wider if I remember right.

    I haven't had reverse in anything for so many years that when I got my first electric truck 3 years ago, I smashed into myself when I was trying to apply the brake to keep the truck from rolling down a hill I was standing on.
    Expert rigging at it's best!

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    It does have optidrive, but it does not do any reversing. I forgot about that. I was told you brake to a stop, and then cycle the trigger back to brake and it'll back up. It does no such thing. Seems to be a servo next to the throttle/brake servo that doesn't do anything, maybe that's the one?

  26. #26
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    That process is for electric. The red thumb trigger is CH3 which is what controls the servo to switch between forward and reverse. Once in reverse you give it throttle and it will move. Pushing forward on the trigger only engages the brake.
    The Super Derecho

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    Ah, I tried that too, couldn't figure out what that red switch was for, PO said he didn't know, but that he drove it in reverse all the time.

    So if I flip the red switch I should see the tiny servo move and put the trans in reverse, I engage the throttle and then it should go backwards?
    Last edited by DoubleJ; 10-02-2019 at 09:08 PM.

  28. #28
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    Quote Originally Posted by DoubleJ View Post
    Ah, I tried that too, couldn't figure out what that red switch was for, PO said he didn't know, but that he drove it in reverse all the time.

    So if I flip the red switch I should see the tiny servo move and put the trans in reverse, I engage the throttle and then it should go backwards?
    Yep. If the linkage is setup right and the servo is working.
    Expert rigging at it's best!

  29. #29
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    Quote Originally Posted by DoubleJ View Post
    Ah, I tried that too, couldn't figure out what that red switch was for, PO said he didn't know, but that he drove it in reverse all the time.

    So if I flip the red switch I should see the tiny servo move and put the trans in reverse, I engage the throttle and then it should go backwards?
    Yep. Just like the engine in your car it only rotates in one direction. The transmission reverses the direction of rotation to the tires.

    There have been others in the past who have reported that they bought the truck from someone else only to find the truck was permanently put in reverse and the differentials flipped around so that the truck will run forward.
    The Super Derecho

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    That's hilarious

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    Quote Originally Posted by DoubleJ View Post
    ...

    Also still having random radio or receiver cut outs, but they only seem to affect the throttle (or maybe there's a fueling issue?) as it'll take off, then coast for 10 feet, then I cycle the trigger and it takes off again. On second thought, no, it's a radio issue, as I almost creamed myself once when the brake wouldn't engage, wouldn't turn either. Only for a second, but this thing moves alot in that one second.....
    Well, the Revo is down. The issue above, random radio disconnect and apparently no built in safety that engages the brake, happened at the top of second gear and it hit a curb doing about 30, square on, about 8 inches tall. There's basically nothing left of the lower front suspension and differential mounting points. Everything is so shattered I'm not even sure what was supposed to be there, back to the schematics for me. Also just got hit with a $17,000 repair bill on the house that I'm due to cover 10% of, and I bought a BMW, so I'm going to stop playing RC nitro cars for a while. Thank you all for your help.

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