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Thread: Broken crank

  1. #1
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    Broken crank

    So has anyone ever broken the pin on the crank that the con rod attaches to? Just rebuilt a 3.3 with some mild modding. I polished, and rounded sharp edges on the crank, and some minor polish, and smoothing on the sleeve. I got about 5 tanks after breaking, and this thing was running really good. Wheelies on command with a 54/20 gearing. Was running saturday and it just died, would not restart, and I could spin the flywheel with no resitance. Removed back plate and found the pin on the crank broken. Luckily no other damage. I am gonna clean up real good, and replace the crank, and try again. I have a losi 3.4 carb ready to install, I just wanted get a little ways past break in first.
    T-maxx 3.3
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    Summit VXL
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  2. #2
    RC Turnbuckle Jr. Nitronaught's Avatar
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    Actually I've never seen a pin break on any RC crank, usually the conrod but not the crank.... Take a GOOD look at the starter plate and make sure that is not causing the pin to wear....
    Crankshafts are made from really tough steel, the other parts are purposely not that hard so they would break prior too...

    Sorry to hear about that though... That would have me pretty ticked off...
    Founder of H.U.A.
    Hop Ups Anonymous

  3. #3
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    Yeah it was kinda upsetting. That crank had been run alot, that is why I modded it. I didn't want to mod a newer one and mess it up. I will look at my back plate also, I have a new starter shaft if I need it. It sure was running good though, and I had not even gotten into it hard yet. I am really curious as to what the carb does.
    T-maxx 3.3
    Rusty 2.5r
    Summit VXL
    Nitro 4-tec

  4. #4
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    I actually just bought a used 3.3 off eBay (that supposedly ran great) and upon inspection found that crank was also broke. The journal that the connecting rod rides on was intact, but the little (edited out asterisks) on the end that fits into the backplate/starter plate was busted off and had been bouncing around the crankcase. Luckily I was able to find a new crank for cheap, and ended up picking up a new rod/piston/sleeve set from the LHS.

    .Please review your posts once you've posted them, if the language filter replaced the word with asterisks you need to re-word things... DO not try to work around the language filter by using characters or mis-spellings, that too is against the rules...

    You have 45 minutes to edit your post, after that you can be given points for triggereing the language filter/abusive language, etc
    NN
    Last edited by Nitronaught; 01-22-2013 at 11:06 AM.

  5. #5
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    I have seen this happen before to other engines. Its not very common though and dont let it stray you away from trying to mod them either. I have done over 100 3.3 cranks never had a issue like that with this engine yet.

  6. #6
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    This is a picture of my work to the 3.3 crank and have never had any issues or had any customers come back with a problem. Just keep on trying though. As far as I know nobody else does this to the 3.3 crank

    http://www.flickr.com/photos/9251761...in/photostream
    Last edited by 3.3 tweaker; 01-22-2013 at 08:45 PM.

  7. #7
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    Really? Describing the end of the crankshaft as having a "edit" is an offense around here? I'm sorry, but ask any mature adult who has a background in nearly anything mechanical and they will tell you that is a widely accepted term used to describe something like that.
    Last edited by Double G; 01-23-2013 at 09:33 AM.

  8. #8
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    Wow, I did not get that aggressive, I polished the hollow part, smoothed the edges there, and the opening between the bearings. It helped alot. I also did the same thing on the sleeve and block around the ports. Not alot of material removal, just mostly smoothing out, and deburring. It was running really good. I got my replacement crank done last night. So back together and running by this weekend. After I get a couple more tanks of fuel, I am gonna replace the carb with a losi 3.4 carb and see what that does. I also drilled the stinger on the exhaust out, I went one bit from 1/4". That made some difference also.
    T-maxx 3.3
    Rusty 2.5r
    Summit VXL
    Nitro 4-tec

  9. #9
    Marshal Double G's Avatar
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    Quote Originally Posted by Dux View Post
    Really? Describing the end of the crankshaft as ....
    I do see your point, however, the forum owners and administrators have deemed that word as being inappropriate for other reasons. If you wish to have it changed by all means feel free to constructively discuss this issue with them. Until then, when you see ** replacing words you wrote, go back and edit them out. Intentionally writing words just to trip the filter is not allowed either.
    Many others have heard me say this: This is a privately-owned forum. There are no advertisers, we do not have to pay to join nor do we have to prove that we even bought/own a Traxxas product to be a poster here. Since it is private what can be said is limited, therefore, any argument about freedom of speech is null and void. Much like you determine the rules of your house and can do whatever you want to me should I step out of line. I have rights but cannot claim "Freedom of Speech" violations when you tell me I have to cease and desist of belittling you or family.
    The Super Derecho

  10. #10
    RC Champion
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    I've seen a 3.3 crank break like that, it's from running too lean. NN is right about the design and everything, but in millions of cranks there's bound to be some weak ones.
    erbe emaxx 26maxx s27revo 18tmrevo XXL platinum

  11. #11
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    It was for sure not running lean.But that crank had many,many gallons of fuel ran through it



    sent from my not so smart, smart phone
    T-maxx 3.3
    Rusty 2.5r
    Summit VXL
    Nitro 4-tec

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