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  1. #1
    RC Racer
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    Help! Why do I keep stripping spur gears?

    I dont know if its a meshing problem or what but I have gone through 2 spur gears in the last day..the truck does have a axial .28 big block ..not sure if thats it or not... is metal spurs an option?

    Thanks

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  2. #2
    RC Turnbuckle Jr. Cameron's Avatar
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    Improper Mesh would be the most likely culprit. Unchecked if you swapped out to metal spur the breakage would potentially just go internal.

    Need to make sure your mesh is being set properly and that your chassis isn't bent.
    (RAH) (AH) + [ROMA (1+MA)] + (GA) + (OOH)(LA)

  3. #3
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    Recommend checking your mesh between the spur gear and the clutch bell. Also check that your transmission is running smoothly. How tight is your slipper clutch set. Might try loosing it up a bit to allow a little slippage.

    Bill

  4. #4
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    Quote Originally Posted by Riverbluff View Post
    Recommend checking your mesh between the spur gear and the clutch bell. Also check that your transmission is running smoothly. How tight is your slipper clutch set. Might try loosing it up a bit to allow a little slippage.

    Bill
    Actually it is better to run with the slipper fully locked. I have found that running a nitro with any slipper that is not locked makes it extremely hard to tune the engine, because it is not near as easy to see when you have more or less power.
    It also makes the engine get significantly hotter because of the increased rpm's.
    Yes having it locked will be harder on the internals, but you can offset the damage mostly by keeping your bearings smooth and the gears clean.
    As for stripping spurs make sure your chassis is not bent which is a common problem on revos. If it is bent you will see the clutchbell is at an angle to the spur and not lined up straight. That will cause you to strip spurs just like you're doing. If its bent you'll need to replace the chassis.
    "I like rc cars"....."WHAT? YOU'RE KIDDING!"

  5. #5
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    This is wjat keeps happening... the one edge stays raised while the other is grinding down



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  6. #6
    RC Turnbuckle Jr. Cameron's Avatar
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    Wear like that scream bent chassis.
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  7. #7
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    That's improper gear mesh its only touching the tips of the teeth


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  8. #8
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    Quote Originally Posted by mydudrevo View Post
    That's improper gear mesh its only touching the tips of the teeth
    I agree... mesh isn't nearly deep enough. As long as that is consistant strippage around the entire spur. If only on one side I would suspect a bent shaft. But if worn at an angle then bent chassis.
    Last edited by MagicDragon; 03-31-2013 at 03:43 AM.

  9. #9
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    Definitely looks like you need to tighten your mesh just like the two above me said
    "I like rc cars"....."WHAT? YOU'RE KIDDING!"

  10. #10
    RC Racer
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    whats the best way to check for a bent chassis? i am very careful when replacing my spurs.. usually takes me a while until i feel the perfect mesh between spur and pinion (ive replaced the spur on my mini revo many times with no problems.) Am i correct in saying that the spur should move back and forth VERY slightly when pinion is held in place? Ive heard of the paper trick also..just never tried it....really hope its not a bent chassis.. if so, i guess ill be going with the slightly longer 3.3 chassis (its on 2.5 now)

    however, i think i may have found the culprit... the rear arm seems to be hitting the back of the pull starter..i dremeled it but doesnt look like its enough.. therefore that could be pushing the motor upwards with load on the suspension..heres the pic:

    Last edited by Jawz121; 03-31-2013 at 10:27 AM.

  11. #11
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    maybe your engine is moving.. if you ever took the engine mount out did you make sure and put back those star washers
    you know.. i never had a sig.. but i do now...

  12. #12
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    Are u talking about the ones that go in from the bottom of the truck?

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  13. #13
    RC Turnbuckle Jr. fallonguy's Avatar
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    Check and see how much play you get if you try and move the engine the mount looks like you only have one bolt the front one holding the engine. It looks like the brace on top of the mount has a gap which may allow some flex.

    This is a picture of a big block mount I found on the net.
    I wanted to put a really cool signature but I ran

  14. #14
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    listen to Fallonguy... looks like you have that engine sitting wrong.... tats needs to be addressed..

    they are 2 washers that go on either side of the mount the side that moves up and down.. hard to describe but if you look at the exploded views you will see it.. but Fallonguy most definitely hit on something you should address..
    you know.. i never had a sig.. but i do now...

  15. #15
    RC Turnbuckle Jr. Nitronaught's Avatar
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    Here are the MAIN causes for spur gear stripping.

    1. Loose motor mount screws (check all 4 of them).. Use loctite and avoid detergents in that area when washing, detergents can and will break down loctite so you might want to double check...

    2. Loose tranny mount screws, allowing the tranny to move while under load would change your mesh and cause the gear to strip.

    3. Bad BC bearing, this will cause the mesh to be out of whack easy.

    4. Landing while having too much throttle and having your slipper a little tight. This will kill a spur on a regular basis.

    5. Chassis flex. Not really happening with the Revo but if it does then the mesh would be changing as the chassis flexed causing the spur gear to strip...

    6. The tranny input shaft is not evenly parallel to the crankshaft of the engine.. Meaning the spurs are not evenly mating due to the shafts they sit on are skewed.. Usually due to a loose or stripped motor or tranny mount, or the operator was not mating the two up properly...


    +1 looking at the spur it seems that the CB is not making full contact with the spur. Loosen your motor mounts and tranny mount push them closer to each other..... If this was a modified or aftermarket setup of any kind I would suggest shimming the CB out a little but not in this case.... Something's just not lined up right...
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  16. #16
    RC Racer
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    thanks for the help guys... turns out the 2 motor mount screws on the left side had completely vibrated out so the motor was able to pivot right and left.. had a couple good runs today with no problems so I think i got it..thanks

  17. #17
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    you might want to consider a chassis brace, I have a stock traxxas brace which braces the complete chassis around the motor mount area pic1, I also have a q concept engine support brace that supports the bottom of the engine on the near flywheel pc 2, Ive also seen other braces on ofer out there.. a few pics for yo to see.




  18. #18
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    check evry bolt on ur engine mount i had tha issue with the stock 3.3 because the long bolt under the chasis tha holds the mount together had gone and engine was moving tore up one spur evry 5 mins

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