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  1. #1
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    Is it time for a motor rebuild?

    Hey guys, I havenít posted here in a while because recently itís just been too flippiní hot to do anything in the garage or outside or whatever to mess with the Revo but Iíve been doing a lot of thinking about new problems that have come up with my car which is making me wonder if maybe itís time to do an engine rebuild because the last couple times I ran my car, it starts up just fine but it seems like once it gets warmed up, it stalls really easy and then itís like almost impossible to start back up until the motor seems like it cools off a bit.

    I did quite a bit of googling on the subject a while back and it seems like a lot of the problems that people were having that was similar to mine, they were being told by not only some older threads on this forum but on other forums as well that it sounded as though their motor had finally lost compression and that it was time to either replace the engine or rebuild it.

    Sure, I probably havenít been the nicest to my engine because number one, its my very first RC car of this caliber and itís also my first RC anything thatís had a nitro motor on it so Iíll admit, there was a lot of times in the past where I never did put in any after run oil in the motor when I got done playing with it and because of things in my past, thereís been a lot of times this car has been in storage and some of those times and never had any after run oil put in there so I can only imagine what the inside of my engine probably looks like.

    So that being said, a little insight into the history of my car since Iíve had it for the last 10 years and with the symptoms I mentioned having, does it sound like itís just probably time to rebuild the motor? Which, I got no problem spending the 80 bucks on the piston and sleeve but what other parts should I replace since Iíll have it torn apart? Also, whatís a good resource to follow to tear it apart and rebuild it the right way?

    Thanks.


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  2. #2
    Marshal Double G's Avatar
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    You've found your answer.

    Either rebuild the engine with new piston, sleeve, bearings and o-rings or purchase a new one for the same price you'd pay for that.

    Under the Support button you can search to find Traxxas's set-by-step process on rebuilding the 2.5/3.3.
    The Super Derecho

  3. #3
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    Quote Originally Posted by Double G View Post
    You've found your answer.

    Either rebuild the engine with new piston, sleeve, bearings and o-rings or purchase a new one for the same price you'd pay for that.

    Under the Support button you can search to find Traxxas's set-by-step process on rebuilding the 2.5/3.3.
    So thatís pretty much what itís down to? I know the motorís old, and yeah, I know itís probably been neglected but I wasnít sure if that was totally my only option.

    But how is just buying a whole new complete motor the same cost as rebuilding it? I know these are just preliminary thoughts since Iíve yet to tear it down but I just figured a new piston and sleeve is mostly what Iíd need starting out and thatís only 80 bucks. Isnít a new, complete motor assembly like, $250 bucks? I know I could save a few bucks with their trade up program that I used to upgrade to the new transmitter and receiver.


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  4. #4
    RC Turnbuckle Jr. olds97_lss's Avatar
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    Man, when did the 3.3 get so stinking expensive!?!?!? Pretty sure the last one I bought was less than $140 at my LHS. Granted, that was a long time ago, but what's with the premium price on an RTR engine?

    If your going to spend that, just get the 21TM for a few more $. More power, less fussy tune (once broken in) and a long life.
    https://www.rcplanet.com/engines/eng...ifold-osm12241
    https://www.youtube.com/c/olds97lss

  5. #5
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    Quote Originally Posted by olds97_lss View Post
    Man, when did the 3.3 get so stinking expensive!?!?!? Pretty sure the last one I bought was less than $140 at my LHS. Granted, that was a long time ago, but what's with the premium price on an RTR engine?

    If your going to spend that, just get the 21TM for a few more $. More power, less fussy tune (once broken in) and a long life.
    https://www.rcplanet.com/engines/eng...ifold-osm12241
    I may be wrong, I thought that was what I saw the price was the last time I saw anywhere that sold one.

    But how does this 21TM compare to the 3.3? I really wasnít looking to buy a whole new complete engine but if this one that you recommended is a much better choice, Iíd almost rather try that. Iím not saying I have anything against the corporate motor in my truck but if thereís something better, Iím definitely interested.

    I guess I have no need to question itís possible more power output, but how does it last longer and what do you mean by less fussy of a tune?


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  6. #6
    RC Turnbuckle Jr. olds97_lss's Avatar
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    After I saw your post, I checked, it seems to be selling for $219 at various places, which IMHO is too much. $150 was a fair price. Guessing traxxas jacked up the price so people stick with the trx but use the trade in program to get the discount.

    The 21Tm performs better than the 3.3. It's not the torque/power of an actual big block, but it puts out more power than the 3.3 and for me, tunes a lot easier. I run a THS pipe with mine.

    This is the last time I ran mine:
    https://www.youtube.com/watch?v=KKh_L-gf5jw

    I don't have footage of it with a 3.3 though I don't think. I didn't record my sessions back then. I have it geared down a bit to help with the grass and to help me get into 2nd gear quick enough for some of the jumps. I'm running the RRP full steel gear set with the standard ratio in it. Would probably work better with the close ratio for what I do.

    My big block revo does well there too. This was the first time I ever took it to that grass bmx track which was a couple weeks ago:
    https://www.youtube.com/watch?v=5O6LCNqOExM
    https://www.youtube.com/c/olds97lss

  7. #7
    RC Champion grizzly03's Avatar
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    Instead of rebuilding I would use the Power-up. $85 for a new 2.5R or $110 for a new 3.3. That $80 piston/sleeve doesn't account for bearings, connecting rod, o-rings. Depending on what items are worn the rebuild cost can add up.

    If your going to pay retail for the 3.3 ($220), I agree with Old97 that I would get the OS21TM instead.

    If you look around you can find a new take off 3.3 engine for under $150.

  8. #8
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    I did the power up option, but after tax and everything else it still cost me nearly $140

  9. #9
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    Quote Originally Posted by grizzly03 View Post
    Instead of rebuilding I would use the Power-up. $85 for a new 2.5R or $110 for a new 3.3. That $80 piston/sleeve doesn't account for bearings, connecting rod, o-rings. Depending on what items are worn the rebuild cost can add up.

    If your going to pay retail for the 3.3 ($220), I agree with Old97 that I would get the OS21TM instead.

    If you look around you can find a new take off 3.3 engine for under $150.
    Sorry for the late response but yeah, I havenít torn the motor down to see what all would need replacing. With this heat, I havenít done a whole lot out in the garage Lol, but I might just try that aftermarket motor that was mentioned because even though it may have been mostly my fault with questionable tuning on my part but even after breaking the motor in after I got it I just never really seemed all that impressed.

    But if I still decide to go that route when that day comes, am I going to have to buy all new glow plugs, or will all the ones that I have that I bought for the 3.3, will they work in this new motor? And I guess since were on the subject, is there anything else that I would have to get to make this new motor work with my car? Thanks.

    Also, Iím assuming the break in procedure for this motor is virtually the same as the 3.3? Iím sure itíll come with directions on how to do so but Iím just asking ahead of time.


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  10. #10
    RC Champion grizzly03's Avatar
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    The glow plugs betweeen the Traxxas engines and the OS 21TM are the same. If you order the correct engine for your style truck (Revo or T-maxx) it comes with the correct header.

    The break-in procedure from OS is different. They want you to run the engine and after each of 5 tanks close the HSN 30į. I just ran my truck back and forth across my lawn easy during those 5 tanks.

  11. #11
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    Quote Originally Posted by grizzly03 View Post
    The glow plugs betweeen the Traxxas engines and the OS 21TM are the same. If you order the correct engine for your style truck (Revo or T-maxx) it comes with the correct header.

    The break-in procedure from OS is different. They want you to run the engine and after each of 5 tanks close the HSN 30į. I just ran my truck back and forth across my lawn easy during those 5 tanks.
    Thanks. Which tuned pipe works best with that? I guess my carís old enough that it came with the regular blue ďnothin specialĒ dual chamber pipe and ever since I brought the car outta storage and started messin with it, I had bought the traxxas tuned single chamber pipe that I believe is the one thatís designed for more low-end power on the lower rpms.


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  12. #12
    RC Champion grizzly03's Avatar
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    I've used the Traxxas pipe and it worked good. I've also read good things about the THS pipes too. Right now I'm running a Trinity pipe on mine.

  13. #13
    RC Turnbuckle Jr. olds97_lss's Avatar
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    I run the THS pipe with my 21TM. When I bought it, THS had 2 of them, a low end and top end pipe. I bought the low end version. I had a 3.3 in it at the time and wanted a bit more on the bottom... the $70 pipe helped, but not enough. Then I tried a losi 3.4 carb (larger venturi), ran great for about 2 tanks, then no matter how I adjusted the linkage, it would bind. Gave up, got the 21TM. It was a nice happy medium between big block and 3.3.

    I still enjoy my big block revo, but the 21TM revo runs a lot longer on a tank of fuel.



    Back in the day, I ran a fantom pipe with a 18TM. That really woke the engine up over a drilled out stock blue pipe.


    I think I still have one of those pipes somewhere. Had a very sharp "ping ping" sound to it. Might be worth trying on the 21TM, although, I do like the quieter pipes these days.
    https://www.youtube.com/c/olds97lss

  14. #14
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    Quote Originally Posted by olds97_lss View Post
    I run the THS pipe with my 21TM. When I bought it, THS had 2 of them, a low end and top end pipe. I bought the low end version. I had a 3.3 in it at the time and wanted a bit more on the bottom... the $70 pipe helped, but not enough. Then I tried a losi 3.4 carb (larger venturi), ran great for about 2 tanks, then no matter how I adjusted the linkage, it would bind. Gave up, got the 21TM. It was a nice happy medium between big block and 3.3.

    I still enjoy my big block revo, but the 21TM revo runs a lot longer on a tank of fuel.
    I'm with you there. Had a 3.3 with the LOSI 3.4 on it and spent a lot of time adjusting, cleaning, deburring the carb just to get it not to bind. Found out through reading the LOSI forums that it was a known issue. Discovered that as the barrel was pulled out by the servo it would twist a little and that was enough to cause it to bind and again, after some wrenching I got it to work smoothly. It did help with the power and tuning of the engine (sounded healthier) and once I put a THS pipe on it the 3.3 was a screamer. That 3.3 was built from a few different engines and had a repinched sleeve so once it died I wanted to see the hype of the .21TM. Love the engine but if I were to be in the market again for a new one $300 would be very tough to cough up.
    The Super Derecho

  15. #15
    RC Turnbuckle Jr. olds97_lss's Avatar
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    Yeah, I don't know that I'd spend that on another one either... It's the most expensive engine I've bought in 20 years of RC. I guess if you don't have a big block mount that can fit what you want, your kind of forced to. Even then though, if you just wanted a 21 and bought the mount, you'd still be in it for $200+.
    https://www.youtube.com/c/olds97lss

  16. #16
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    Well yíall, I think Iím just gonna use the power up program and turn this old motor in to traxxas for a new one. I took a pic of the old one with the cooling head off.

    If I remember right, when this truck was new over ten years ago, there was quite a bit of resistance when turning the flywheel even with the glow plug out of it and now, it turns with hardly any resistance at all so Iím thinkin maybe the sleeve is shot, I dunno. For only 115 bucks for a new motor, Iíll just start fresh. But Iím curious- when they say the backplate needs to stay with the old motor, are they talking about that adapter plate that the easy start assembly bolts to? Also, because I wasnít sure, since the directions said to keep the flywheel, Iím assuming the nut that holds the flywheel on, and the little cone-shaped thing that goes between the shaft and the flywheel stays with me as well, correct?




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  17. #17
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    Keep the flywheel, collet (the cone shaped washer), and I kept my clutch nut as well. I swapped mine at LHS and my engine came with a new clutch nut but no collet. Yes, the back plate is what the EZ Start bolts to. Your new engine will have a pull start. Just take it off and replace with the EZ Start.

  18. #18
    RC Qualifier nebulous.cow's Avatar
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    Dang man that is a beaten up motor! Definitely power up program, or if you see yourself using it a lot in the future, the OS goes a long way. I bought my revo 3.3 new this past year, and it was definitely not my first nitro, and the rear bearing exploded very quickly. Was so fed up with it I just dropped the cash on the OS 21 and I cannot tell you how much fun I have had with the truck since that upgrade. The fun I've been having has been priceless, bar none the best thing it has seen so far. But it sounds like a fresh 3.3 would be good for you as well, especially at that price.

    Just keep it from running lean and overheating, and you can't really go wrong. That and a nice, slow break in. Looks like your old motor had a couple lean spells, and either some stuff on your piston top there or like pitting from detonation, it's hard to see. If you have issues with heat like I do out here in the Arizona heat, finding a high quality oil additive for nitro fuel and adding just a hair more can help you maintain proper temps and enough lubrication.

    Either way you go, I think you'll be happy. Never hurts to tear down your nitro motors and give them a good cleanout too every once in a while! Hope you get it running good soon.

    -Mike

  19. #19
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    Quote Originally Posted by cjtamu-redux View Post
    Keep the flywheel, collet (the cone shaped washer), and I kept my clutch nut as well. I swapped mine at LHS and my engine came with a new clutch nut but no collet. Yes, the back plate is what the EZ Start bolts to. Your new engine will have a pull start. Just take it off and replace with the EZ Start.
    Thanks. Itíll come with a pull start? Thatís a 20-dollar part I donít need. Lol.


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  20. #20
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    Quote Originally Posted by nebulous.cow View Post
    Dang man that is a beaten up motor! Definitely power up program, or if you see yourself using it a lot in the future, the OS goes a long way. I bought my revo 3.3 new this past year, and it was definitely not my first nitro, and the rear bearing exploded very quickly. Was so fed up with it I just dropped the cash on the OS 21 and I cannot tell you how much fun I have had with the truck since that upgrade. The fun I've been having has been priceless, bar none the best thing it has seen so far. But it sounds like a fresh 3.3 would be good for you as well, especially at that price.

    Just keep it from running lean and overheating, and you can't really go wrong. That and a nice, slow break in. Looks like your old motor had a couple lean spells, and either some stuff on your piston top there or like pitting from detonation, it's hard to see. If you have issues with heat like I do out here in the Arizona heat, finding a high quality oil additive for nitro fuel and adding just a hair more can help you maintain proper temps and enough lubrication.

    Either way you go, I think you'll be happy. Never hurts to tear down your nitro motors and give them a good cleanout too every once in a while! Hope you get it running good soon.

    -Mike
    Is it really that badÖ LOL? I mean, I donít know that much about nitro RC cars to be able to tell right away how it aged motor should look like but, maybe it isÖ LOL.

    But yeah, I thought about that OS motor but like I said, for 115 bucks for a brand new engine and carburetor I figured you canít go wrong. I liked the old motor when it was new that it came with, it was good enough for me for how I play with my RC car but I really think the reason why itís longevity was compromised was because of just plain ole neglect and probably never had it tuned right since I never really understood the tuning process until just here back in the spring when I pulled it out of storage and really learns how to tune it. But there was also a lot of times where I would put it away without using after run oil like I shouldíve. And a couple times it got put into storage like that for over 2 to 3 years. So yeah, even though this engines only seen maybe between a gallon and a gallon and a half fuel combo a lot of why Iím having to replace it is probably because of myself more than anything. But hey, Iíve learned a lot so maybe this new motor I can make last a whole lot longer. Hopefully the way I broke that other motor in wasnít anything to do with it, because at that point I didnít know hardly anything about RC cars of that caliber but if I remember correctly, I followed the break-in instructions to the T.

    I think there might of been a few times where I did run it a little bit to lean because like I said earlier, I didnít really have the tuning process down like I do now so I think there was a few times I did run it a little bit to lean but the only fuel that Iíve ran in this car is been the traxxas brand 20% nitro fuel with a only one quart bottle of some other brand of fuel that I got from Hobby store.


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  21. #21
    RC Qualifier nebulous.cow's Avatar
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    Interesting. Only a little over a gallon for real? That's quite a short life span man. I have an old OS 18 motor in my classic Maxx, and it probably has about 20 gallons on the same motor. It's old, and its hard to start, but once shes running, it runs absolutely fantastic and doesn't overheat. I even got the motor used from someone else, so it's seen a life of shenanigans.

    After run oil is hit or miss for people. I stopped using it after just running my nitros, and resorted to just firing them all up once a month for half a tank and tuning them just to keep the juices flowin and keep the gunk at bay. Always run the engine dry for storage though. I do however use AR oil very liberally when it comes to assembling nitro engines. When I clean them out maybe once a season or so, I always put a few drops on every part and bearing as it goes together to get a perfect start the first time it's fired back up. But yeah if you are going to store the motor for even a year, a couple drops of AR oil and maybe put the piston half way up the stroke. That way it keeps the combustion chamber sealed off to the elements, and keeps the exhaust port closed off so moisture can't get in the crankcase easily. Works perfect for me.

    Bottom line, when you get a new 3.3, you should be getting way more than a gallon of fuel through it. My onroad engines get run as hard as possible, and spend most of their lives tuned at peak power, and I still get 4-5 gallons of full send through it before the piston and sleeve are done. And after that, the used piston and sleeve were the perfect golden brown. I'll try and post a pic for reference.

    I'm sure you'll have better luck with the new 3.3!

    -Mike

    Picture of my totally used up piston and sleeve from my touring car. Notice the gold in the piston oil ring as well, and no black spots. I ran this as hard as it would go, and I consider myself a pretty good tuner. This is how it should look when its time to pull it out and get replaced.

    https://imgur.com/a/lwTSe7d
    Last edited by nebulous.cow; 09-22-2020 at 10:31 PM.

  22. #22
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    I'm no nitro guy, but looking at the pic, if that was a dirtbike engine say, I'd say its running rich. Black on top of a piston indicates either carbon build up, or burnt oil. In this case, looks like oil. I'm assuming nitro has an oil mixture in it, and its not adjustable right? If no, its ruch, if it is, too much oil. Also looks like the sleeve is perfect, almost looks like you can still see the old hatch marks. A set (or it looks like just one?) of rings and a light hone, and it'll run like new agian. But nothing wrong with upgrading, who knows what the crank bearings are like after sitting for so long.
    Anyway if this is all wrong in the nitro world, I'd love someone to explain why.

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  23. #23
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    Quote Originally Posted by nebulous.cow View Post
    Interesting. Only a little over a gallon for real? That's quite a short life span man. I have an old OS 18 motor in my classic Maxx, and it probably has about 20 gallons on the same motor. It's old, and its hard to start, but once shes running, it runs absolutely fantastic and doesn't overheat. I even got the motor used from someone else, so it's seen a life of shenanigans.

    After run oil is hit or miss for people. I stopped using it after just running my nitros, and resorted to just firing them all up once a month for half a tank and tuning them just to keep the juices flowin and keep the gunk at bay. Always run the engine dry for storage though. I do however use AR oil very liberally when it comes to assembling nitro engines. When I clean them out maybe once a season or so, I always put a few drops on every part and bearing as it goes together to get a perfect start the first time it's fired back up. But yeah if you are going to store the motor for even a year, a couple drops of AR oil and maybe put the piston half way up the stroke. That way it keeps the combustion chamber sealed off to the elements, and keeps the exhaust port closed off so moisture can't get in the crankcase easily. Works perfect for me.

    Bottom line, when you get a new 3.3, you should be getting way more than a gallon of fuel through it. My onroad engines get run as hard as possible, and spend most of their lives tuned at peak power, and I still get 4-5 gallons of full send through it before the piston and sleeve are done. And after that, the used piston and sleeve were the perfect golden brown. I'll try and post a pic for reference.

    I'm sure you'll have better luck with the new 3.3!

    -Mike

    Picture of my totally used up piston and sleeve from my touring car. Notice the gold in the piston oil ring as well, and no black spots. I ran this as hard as it would go, and I consider myself a pretty good tuner. This is how it should look when its time to pull it out and get replaced.

    https://imgur.com/a/lwTSe7d
    It might be closer to two gallons. It ainít much, but the engine is as old as the truck and I bought it back in 07-ish.

    But if itís not from not using after-run oil every time Iíve put the truck away whether itís just for a day or as long as three years at one time, I dunno. 13 years was along time ago and although Iím pretty sure I followed the directions on break-in, there coulda been something wrong with how I ran it when it was brand new. Maybe I ran it enough while it was probably too lean, I donít know. There was always a steady stream of light smoke out the exhaust but hey, itís a two-stroke motor that burns the very oil that lubricates it so itís gonna smoke regardless, isnít it?...lol.

    But I dunno, it didnít start to have those issues I mentioned at the beginning of the discussion until it was a pretty hot day I ran it after putting what I eventually thought was too tall and too wide of tires on it without changing the gearing. Maybe that had something to do with it, maybe it didnít. Iíve long since took those overly-large tires off and went back to the stock size. I think also that those large tires is what destroyed the clutch inside the clutch bell too, since it had been over three years from the last time I ran the car so I canít really pinpoint when exactly that happened, I just assumed that it was because of them large tires.

    I donít think I ever sucked any water into the engine because I was pretty good about keeping it out of the mud puddles. I have ran it some in wet grass, though.


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  24. #24
    Marshal Double G's Avatar
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    Quote Originally Posted by Steve g View Post
    I'm no nitro guy, but looking at the pic, if that was a dirtbike engine say, I'd say its running rich. Black on top of a piston indicates either carbon build up, or burnt oil. In this case, looks like oil. I'm assuming nitro has an oil mixture in it, and its not adjustable right? If no, its ruch, if it is, too much oil. Also looks like the sleeve is perfect, almost looks like you can still see the old hatch marks. A set (or it looks like just one?) of rings and a light hone, and it'll run like new agian. But nothing wrong with upgrading, who knows what the crank bearings are like after sitting for so long.
    Anyway if this is all wrong in the nitro world, I'd love someone to explain why.

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    What you know about dirt bike, automobile or other small engines does help tremendously with using RC nitro engines but there is a little more to learn. That piston looks pretty much perfect for a nicely tuned engine; you want that light golden color. What you don't want is the very dark brown or black staining as well as pitting on the top which tells you it is lean and suffering from predetonation. Nitro fuel comes with oil mixed in and different brands have different % oil (castor and/or synthetic). The percent nitro you get changes the tune of the engine as well.

    Nitro engines do not have rings on the pistons. The sleeve is tapered at the top so that the piston gets squeezed as it gets to TDC to build compression. Then the glow plug - unlike a diesel engine the RC's stays lit - reacts with the fuel and ignites it.

    Quote Originally Posted by corneileous View Post
    Maybe that had something to do with it, maybe it didn’t. I’ve long since took those overly-large tires off and went back to the stock size. I think also that those large tires is what destroyed the clutch inside the clutch bell too, since it had been over three years from the last time I ran the car so I can’t really pinpoint when exactly that happened, I just assumed that it was because of them large tires.

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    Years ago when more people were running Revos and nitros in general many went with Big Joe's or similar tires and reported breaking parts, having to gear way down and/or going to a big block engine. IMHO, the 6.3" Maxx tires that come on the T-Maxx or the 6.3" Geode that come on the Revo are getting to the too big size for the 3.3 to push around. The 5.75" Talons seem to be a good size. Since I had some Traxxas rims lying around I bought some Pro-Line Badlands and glued them together last weekend. Perfect size/weight.
    Last edited by Double G; 09-23-2020 at 07:25 AM.
    The Super Derecho

  25. #25
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    Quote Originally Posted by Steve g View Post
    I'm no nitro guy, but looking at the pic, if that was a dirtbike engine say, I'd say its running rich. Black on top of a piston indicates either carbon build up, or burnt oil. In this case, looks like oil. I'm assuming nitro has an oil mixture in it, and its not adjustable right? If no, its ruch, if it is, too much oil. Also looks like the sleeve is perfect, almost looks like you can still see the old hatch marks. A set (or it looks like just one?) of rings and a light hone, and it'll run like new agian. But nothing wrong with upgrading, who knows what the crank bearings are like after sitting for so long.
    Anyway if this is all wrong in the nitro world, I'd love someone to explain why.

    Sent from my SM-G970U using Tapatalk
    Since you didnít quote anybodyís post, which picture are you talking about, the one I posted or the one that nebulous posted?

    If itís mine youíre referring to, I guess I couldíve ran it a little rich at one point but I donít think I ever ran the high speed needle any richer than four turns of the screw counter clock wise which is where these little motors is set to from the factory when theyíre brand new. If anything, Iíve probably ran it too lean more than anything.

    But yeah, since these are two-stroke motors, theyíre basically like a chainsaw or a weed eater where they use a fuel/oil mixture and the only to adjust that mixture unless you make it yourself, is dependent on what percentage fuel you buy. The higher the percentage- like on traxxas brand fuel, 10% has the least amount of nitro- 20% has more with 33% having the most.

    But no, I didnít see any pitting in the top of the piston, just the black discoloration. The sleeve did look fine, but as I stated before, there was hardly any resistance at all when the piston reached top dead center with the glow plug out of the head. I did however decide to take the back plate off just so that I could look and see inside the bottom of the crank case and the bearing on top of the rod and the bearing down that connects to the crankshaft was all nice and tight with no slack.


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  26. #26
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    Quote Originally Posted by Double G View Post
    Then the glow plug - unlike a diesel engine the RC's stays lit - reacts with the fuel and ignites it.
    Itís funny that you say that because I always assumed that these little motors were actually kind of like a diesel engine that it was compression that caused the combustion and not the glow plug because I figured the only time the glow plug was lit was when you were starting it when you were putting electricity to it.

    Years ago when more people were running Revos and nitros in general many went with Big Joeís or similar tires and reported breaking parts, having to gear way down and/or going to a big block engine. IMHO, the 6.3Ē Maxx tires that come on the T-Maxx or the 6.3Ē Geode that come on the Revo are getting to the too big size for the 3.3 to push around. The 5.75" Talons seem to be a good size. Since I had some Traxxas rims lying around I bought some Pro-Line Badlands and glued them together last weekend. Perfect size/weight.
    Like I said, Iím pretty sure those large Duratrax tires I had at one point is probably what broke my clutch but those tires with no gear reduction, even on a hot day, would that have caused my motor to overheat? At that time I didnít have my heat gun yet so I have no idea how hot the motor was.


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  27. #27
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    Thanks guys, I'll dive into the nitro engine rabbit hole someday soon and properly educate myself. Double G, i was referring to the ops blackened piston picture. Surprised there's no ring, the grove on the linked pic looked like a ring grove. Makes me wonder if they even hone these motors. Got me some learning to do. Don't mean to hijack a thread. Thanks again.

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  28. #28
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    Quote Originally Posted by corneileous View Post
    It’s funny that you say that because I always assumed that these little motors were actually kind of like a diesel engine that it was compression that caused the combustion and not the glow plug because I figured the only time the glow plug was lit was when you were starting it when you were putting electricity to it.
    Yes, there is a catalytic reaction between the glow wire and the fuel. That is why an engine will stall due to a dead plug.

    Quote Originally Posted by Steve g View Post
    Thanks guys, I'll dive into the nitro engine rabbit hole someday soon and properly educate myself. Double G, i was referring to the ops blackened piston picture. Surprised there's no ring, the grove on the linked pic looked like a ring grove. Makes me wonder if they even hone these motors. Got me some learning to do. Don't mean to hijack a thread. Thanks again.

    Sent from my SM-G970U using Tapatalk
    I guess I don't see much black in the pic provided. These are ringless engines and again the sleeve squeezes the piston as it nears TDC. Obviously the more gallons put through the engine that pinch wears off so it is either a new piston and sleeve or a repinch. There are a couple companies out there that will repinch the sleeve for a fraction of a new P&S and you can get a few more gallons out of it. I've had it done once with a piston and sleeve taken out of different 3.3 engines and it ran beautifully.
    The Super Derecho

  29. #29
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    Quote Originally Posted by Double G View Post
    Yes, there is a catalytic reaction between the glow wire and the fuel. That is why an engine will stall due to a dead plug.


    Hmm.


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  30. #30
    RC Qualifier nebulous.cow's Avatar
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    Yeah my worn out piston picture shows that it may look totally good, and be totally worn out. Like it was mentioned, its the tolerance between the piston and sleeve that allow compression at operating temps. This piston would slide all the way thru the sleeve and thus would just not run anymore, it had no compression. The 'ring' slot is just a cavity for oil to buildup and stay.

    It's a little different with nitro, but in my experience, (unlike dirtbikes or other small engines) the richer you run them, the cleaner the insides stay. I always open up my engines after break ins just to make sure everything looks good and seated right, and after a rich break in, it is always spotless, shiny, barely golden in the combustion area, and clean. It's only after running too lean or too hot have I ever seen blackening, pitting, carbon deposits, ect.

    I would say this difference is due to the differing combustion reactions and temperatures between nitro fuel ingredients and gasoline.

    I have found also that high loading on a nitro motor, such as the big joe tires or too tall of gearing doesn't directly affect pitting or 'scorching' of your nitro engine, but it obviously produces more heat in the engine, which leads to those things. I actually geared my revo down from stock, with the stock tires. Desert heat, and I don't need top speed. If its fast enough to jump, then I am happy. Consider gearing yours down too, helps it do wheelies nicely, and if you spend a lot of time mowing it through tall ish grass, it'll keep it from bogging there too.

    Inspect your engines often, fellas! Even just popping the plug out and checking the color or peering down in there can help if you don't have a temp gauge or are not sure how its doing.

    -Mike

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