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  1. #1
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    TRX 3.3 connecting rod failures!!

    hey guy's does anyone eles have issues with the 3.3 connecting rods I got a T-MAXX 4907 bought in jan. ran about 2 1/2 quarts of fuel through the engine and the rod just split right down the center of it and spit open like a V leaveing the piston at TDC . the engine was running about 225 degrees nice blue smoke trail not lean at all when this had happened . so anyways does anyone know of a connecting rod that will work better than stock I've heard of a davis rod but don't know anything about it !

  2. #2
    RC Turnbuckle Jr. Nitronaught's Avatar
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    The conrod and the piston skirt and the engine bearings of ANY Nitro engine are going to be what usually fails when an internal failure occurs.

    Can you post pics of the piston, a shot of the underneath, the side and the top of the piston, a shot of the sleeve might help as well.

    It's not uncommon for fatal engine damage to take place After the actual damage has been done....

    Example, Engine ran with high rpms for an extended period of time can cause stress to the internals. But they haven't let go just yet... A few tanks later of normal operation and wham,,,, it goes.... But at that particular time your temps and driving style was not warranting internal damage.


    Anytime an engine goes, it usually is going to happen in the area of where there is a pinion point, such as the wrist pin area.... I've rebuilt more 2.5's 2.5r's and 3.3's than I can count now. Some coming to me with conrod damage... But anytime I did see this I also fund the following.
    1, Chipped piece from the piston skirt, this is the are of the piston with the least amount of material on it, it will become brittle if it has seen high temps.
    2. Scoring on the crankshaft from the internal debris. (sometimes).
    3. Conrod split at the wrist pin, sometimes as far as the entire rod.
    4. Dark coloring on the top of the piston (if ran lean).
    5. Conrod stretched frm high rpms and low temps.... Not enough expansion and high rpms = internal stress..
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  3. #3
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    yeah i hear alot of people say the trx engine have conrods fail alot, but its like my mgt8.0, my ofna hyper 7 .28, all the forums say those engines have the same issue... so basically all engines do

    i think on the 2.5/3.3's electric start has alot to do with it, same with my mgt8.0, sometimes you dont realize your fuel locked till after its been cranked a few times and thats really hard on the conrod
    Traxxas is good, but so are other Manus

  4. #4
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    I would get some pics but I already swaped the engine into traxxas on they're replacment plan they have I think I'm goin to order the davis rod for the new 3.3 I got .... when I first got it I was haveing problems tunning it and it would run around 280 290 and thats probly were the problem had started for that engine... then I got it tunned it ran around 210, 220 degrees and was running good with loads of power right up to it's time of failure so deff. goin to take my time with this engine

  5. #5
    RC Qualifier westoakmech's Avatar
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    Shift point can also cause a conrod or piston failure. If the shift point is to high and letting the engine rap out to far before it shifts. IMO I also think what happens is guys dont let the engine properly warm up, gun it and take off, over reving a cold, poorly lubed enngine. I have a davis diesel rod a 3.3 and have had no issues with it, very beefy unit.
    Rusty 2.5R,T-max 2.5 & 3.3,Summit VXL Nitro 4-tec

  6. #6
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    ok thanks for the info on the rod how long should you let the engine worm up before to run it ? and what do you think about oversized cooling heads for the 3.3 are they worth the money or not

  7. #7
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    Quote Originally Posted by jpsny108 View Post
    ok thanks for the info on the rod how long should you let the engine worm up before to run it ? and what do you think about oversized cooling heads for the 3.3 are they worth the money or not
    not sure on a better cooling head, but as far as warming it up most people say use a hair dryer or something to heat the engine up before starting it, me personally i do what i do with my full sized real vehicles, i start it and let it idle till im reading proper temps, i drive my nitro engines once they are close to 200 degrees.
    Traxxas is good, but so are other Manus

  8. #8
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    ok thanks. and yeah were I run my truck a hair dryer is outta the question lol thanks for the help

  9. #9
    RC Qualifier westoakmech's Avatar
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    I have never used the other cooling heads, but I have heard stories about having problems getting enough heat. Heat is your friend and enemy at the same time. I just idle around for a few minutes before I make any high speed runs.
    Rusty 2.5R,T-max 2.5 & 3.3,Summit VXL Nitro 4-tec

  10. #10
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    This just happened to me today. Out of the 5 Traxxas nitro motors I have had over the past 8 years, this is a first for me. Not sure how it happened or why. It was a fairly new motor too. Not quite a gallon through it. Oh well, I've heard of this happening more than it should. Guess I've got a little project to do now. Glad I had a spare on hand!

    If you can't beat it....destroy it!

  11. #11
    RC Turnbuckle Jr. Nitronaught's Avatar
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    Quote Originally Posted by jpsny108 View Post
    I would get some pics but I already swaped the engine into traxxas on they're replacment plan they have I think I'm goin to order the davis rod for the new 3.3 I got .... when I first got it I was haveing problems tunning it and it would run around 280 290 and thats probly were the problem had started for that engine... then I got it tunned it ran around 210, 220 degrees and was running good with loads of power right up to it's time of failure so deff. goin to take my time with this engine
    Tuning is an acquired skill. I would say I could not agree with your statement more. In many many cases it's the end user who is learning to tune that creates weakness's on the internals of the engine. Then they learn to tune but the damage is already basically done. Then it let's go.

    Cooling heads do no replace tuning skills. They often throw your tuning out of whack because they can cool too much, forcing the operator to lean up the engine to get the temps up, but then there is not enough fuel/lubrication flowing through the engine..

    I would venture as far out to say that most everyone who has never had a Nitro RC, will have a short engine life on their first engine, or shorter than others as they get experienced. It's the nature of the beast....
    All Lives Matter
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  12. #12
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    Quote Originally Posted by Nitronaught View Post
    I would venture as far out to say that most everyone who has never had a Nitro RC, will have a short engine life on their first engine, or shorter than others as they get experienced. It's the nature of the beast....
    This is so true. My first engine was the 2.5r and that thing was nice then it wouldn't run for more then 10 mins without stopping and having to cool down. Replace that with the 3.3 and I have ran almost 10 tanks (not including break in) through it and most of them were just stopping long enough to clean a filter or refuel.
    I have no stress because I am the best!

  13. #13
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    Would a chipped piston skirt effect the engine?

  14. #14
    RC Turnbuckle Jr. Snook Man's Avatar
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    Quote Originally Posted by stallion 63 View Post
    Would a chipped piston skirt effect the engine?
    It could absolutely affect the engine. Depends on how big the chip and where it’s located on the skirt as to how much it will effect it. A chipped skirt is never a good thing.
    No slipper/tall gearing/power = broken parts.

  15. #15
    RC Turnbuckle Jr. Nitronaught's Avatar
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    Quote Originally Posted by stallion 63 View Post
    Would a chipped piston skirt effect the engine?
    I have torn down well over 20 blown TRX engines with split conrods... I've only seen 1 split conrod that did not have a chipped piece from the piston skirt as well. Also signs of very high temps...

    Now It's just theory as far as what came first the piston skirt or the split rod.... It's my opinion that the temps get high from lean conditions (tune, leak) causes the piston to get hot, the thinnest part of the piston is the skirt, it has the least amount of material so it will get hotter faster than the rest. This causes it to become brittle and break off.

    Picture this, pieces of metal flying around inside a housing with parts spinning at 36,000 times per minute and they have no where to go.... This then starts increasing the friction of the pistons movement which puts huge strain on the conrod at the wrist pin. This then causes te rod to split...

    Many people feel it's the conrod that let's loose and then the piston gets damaged. I believe it's the opposite... That's in these particular cases. Others, the conrod is probably splitting cause it is ran at high rpms with the engine not running warm enough to expand properly... The lack of expansion would create higher than normal friction and stress on the conrod, especially at higher rpms...
    All Lives Matter
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  16. #16
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    Actually the fairly new 2.5r engine was running fine.I had opened it up to replace the 2.5 cs and put in a new 3.3 cs when I mistakenly pushed the piston skirt instead of the sleeve with a plastic tool to remove the sleeve.So a piece at the cs relieve cut out of abt 1x2mm broke off.I sanded it and now the cs cut out on the skirt is wider to 1 side.I started the engine after that and sit seems ok.But I'm concerned if it would lead to some major issues.

    By the way,the skirt doesn't seem to be the working part on the piston.Or is it?

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