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Tmaxx Trouble??? Runaway Flywheel

Tmaxx Trouble??? Runaway Flywheel

Old 11-12-2019, 02:52 PM
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Questions?? Tmaxx Trouble??? Runaway Flywheel

https://photos.app.goo.gl/DCfzcGEX25BR4CqGAHey Yíall, I bought an old Traxxas Tmaxx over 2yrs ago for $50 from a friendís neighbor. It was given to him by the original owner, but my friendís neighbor had no idea what to do with it. I think it may be from the first year they were built, but I could be wrong. It sure ainít anywhere close to new. If you read my Ďabout me,í youíll see that my occupation is listed as ďsmall engine mechanic...Ē cause it is. Iím familiar with engines. Besides lawnmowers and chainsaws, etc., Iíve worked on Mazda rotary engines, Nissan engines, chevys... so you can understand why Iím a little frustrated that I canít get this minuscule glow engine to go. On the day I bought the truck, I was able to get it to fire for a short moment of no more than 5secs, until the flywheel unscrewed from the crankshaft of the TRX .15 engine. Ever since, I havenít been able to start the thing. The flywheel/clutch assy comes off every time I turn the engine over. The carb works and delivers air and fuel to the engine, the engine has spark, and it has compression(as of 2yrs ago). I just donít know why the flywheel and clutch keep coming off. The video I took and put at the top of the post shows you what Iím dealing with. Any and all help is appreciated! My goal is to bring the truck to a local track on a practice day and drive it around when Iím not practicing. Iíve rebuilt the transmission, since I thought that may have been the issue at first. I donít think it was, and Iím not sure what I was thinking lol. The trans has no fluid in it now, and didnít when I bought it. Iím not sure if it needs fluid, since it does have a port on the top for it. Thanks in advance for your help!
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Old 11-13-2019, 07:24 PM
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the flywheel does not screw the engine its a tapered fit....take the clutch apart

these pics might help (scroll down)

https://traxxas.com/support/TRX-Engine-Rebuild

Last edited by imaxx21; 11-13-2019 at 07:36 PM.
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Old 11-14-2019, 06:32 AM
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Thanks, looks like I’ll service the clutch. I’ll report back, afterwards.
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Old 11-14-2019, 05:25 PM
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Alright. I rebuilt the clutch and it no longer comes off. Thank you. This little engine still won’t cooperate with me, though. I spent 2 hrs on it today. Ridiculous! I have burnt through a starter motor. Thankfully I had a spare. I changed the glow plug, even though I knew it was getting spark. I can get it to start, but it stalls instantly. No carb tuning can solve this, I tried. After some more research, I think the issue may be the one way bearing in the ezstart. The engine sounds like it’s thrown the rod when turning it over in the higher rpm’s. I took off the ezstart to check it, and it’s fine. It’s a little gunked up in the sump, and there are some metal sparkles in it and a bit of grime, too, but not terrible...but not great. I expected that. The piston is borderline immaculate. I have a spare, brand new engine, but I don’t think a new engine will solve the problem. TBH, I don’t want to put the new engine in. I am committed to forcing this original tiny block of aluminum back to life.
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Old 11-14-2019, 05:27 PM
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Old 11-14-2019, 05:36 PM
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are you using a glow ignitor or just the blue wire, get an ignitor

how's the compression, may be time for a piston/sleeve set
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Old 11-14-2019, 06:03 PM
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That engine is FILTHY, That is a LOT of gunk in the crankcase. Did you clean the carburetor? They need to be cleaned just like a atv/snowmobile or any other type of carb. Also, in the picture it appears to me that the carburetor is not fully seated. It looks like theres a gap between the carb body o ring and the case
If you've checked all that, and the engine still fires but doesnt stay running, try either turning the idle up or leaning out the low speed slightly, or both. You can also try holding the throttle slightly open and see if that keeps it running. (An easy way to tell if its just your idle too low)
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Old 11-14-2019, 08:26 PM
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Thanks again. Not using a glow igniter, since I don’t have one. I’d have a few if I raced nitro. Compression is surprisingly good. The carb is seated well. I’ve played with the carb and have plenty of experience with carburetors. I haven’t cleaned the carb yet, since it’s delivering air and fuel as it should. Lol I’m not sure what I was talking about when I said the engine wasn’t terrible. It’s pretty bad. I’ll look at it a bit more tomorrow. Then I’ll be off to work fixing lawnmowers. Once I get this running, I plan to completely rebuild the entire truck, including the engine, carb, etc. The thing probably has 20 years worth of encrusted nitro fuel and dirt on it.
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Old 11-15-2019, 04:21 PM
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Alright, so the one way bearing is fine. I’m stumped, and frustrated at this engine. I sprayed the crankcase out with carb spray to get a little bit of the gunk out and put the sump cover and everything else back onto the engine. Still won’t go. Any other ideas?
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Old 11-16-2019, 01:22 PM
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These carbs are not like lawnmower carbs. Just delivering air and fuel is not enough for it to start up and stay running. it needs to be taken apart and cleaned meticulously. The very small orings on the needles are also prone to dry rotting and cracking when sitting. Cleaning and rebuilding the carb will greatly increase the chances of it starting. Also do not spray carb cleaner in the carb unless every o ring has been removed, it will make them swell and ruin them.
You can also check quick to make sure the plug is actually heating up. Take the plug out and just leave the wire connected. Then just hold the threads of the plug somewhere on the engine and spin the engine over. The plug should glow bright orange hot. If it doesnt youve found your problem
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Old 11-16-2019, 03:14 PM
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Originally Posted by upbasher1 View Post
These carbs are not like lawnmower carbs. Just delivering air and fuel is not enough for it to start up and stay running. it needs to be taken apart and cleaned meticulously. The very small orings on the needles are also prone to dry rotting and cracking when sitting. Cleaning and rebuilding the carb will greatly increase the chances of it starting. Also do not spray carb cleaner in the carb unless every o ring has been removed, it will make them swell and ruin them.
You can also check quick to make sure the plug is actually heating up. Take the plug out and just leave the wire connected. Then just hold the threads of the plug somewhere on the engine and spin the engine over. The plug should glow bright orange hot. If it doesnt youve found your problem

everything he said, also when making tuning changes you can't spin the needles 'turns' at a time

think of needles like a clock divided into 12.... a common saying in RC is to lean or richen ''one hour'' that's where it comes from
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Old 11-18-2019, 07:04 AM
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Well, I got the engine running for about 30 secs. Like I said, the carb is fine and it’s getting spark. Now I think there’s another issue with the ezstart. The ezstart gears are all intact and the brushed motor works but it doesn’t turn the engine over.
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Old 11-18-2019, 07:18 AM
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Originally Posted by evhexrc View Post
Well, I got the engine running for about 30 secs. Like I said, the carb is fine and itís getting spark. Now I think thereís another issue with the ezstart. The ezstart gears are all intact and the brushed motor works but it doesnít turn the engine over.
That would indicate the OWB is bad or backwards.
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Old 11-18-2019, 07:57 AM
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Originally Posted by johnnydmd View Post
That would indicate the OWB is bad or backwards.
Yep. One way bearing. Take that bearing out and give it a good spray out with brake cleaner. Let it dry then stick a small drop of 3 in 1 or marvel mystery oil in the rollers and reinstall.
And just a fyi, IDK why it bothers me but...these nitro engines do not get "spark". The plugs dont spark they just get red hot to ignite the fuel.
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Old 11-18-2019, 03:10 PM
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Originally Posted by evhexrc View Post
Well, I got the engine running for about 30 secs. Like I said, the carb is fine and itís getting spark. Now I think thereís another issue with the ezstart. The ezstart gears are all intact and the brushed motor works but it doesnít turn the engine over.
There is no ďsparkĒ with a nitro engine. The glow plug just glows orange.
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