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Thread: Undoing metal welds

  1. #1
    Flashaholic* Fallingwater's Avatar
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    Default Undoing metal welds

    I'm trying to unrestrict my two stroke 50cc scooter's exhaust pipe. To do this I need to remove a small metal cone that restricts the gas flow. The cone is placed at the start of the exhaust, right after the gases exit the cylinder, and is held in place with two welds. I need to break these welds to remove the cone, but this is proving harder than at first foreseen. I tried whacking one with a screwdriver and hammer, but only managed to slightly dent it.

    Here are two piccies:



    How do I get the bloody thing off?

    Thanks.
    Eat, drink and be merry, for tomorrow you may die.

  2. #2

    Default Re: Undoing metal welds

    Hand grinder, like a Dremel tool. Weld penetration between the two parts may be minimal. Weld bead could be the only thing holding the parts together. Remove the weld bead and beat on it again.

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    Default Re: Undoing metal welds

    Die grinder.

    Got Biodiesel?

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    Flashaholic* RA40's Avatar
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    Default Re: Undoing metal welds

    Agreed, a smallish grinder in this case. Even your cordless drill with an small abrasive wheel/cone may work.
    Mike

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    *Flashaholic* PlayboyJoeShmoe's Avatar
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    Default Re: Undoing metal welds

    I've had to remove weld a lot of times. I have an electric die grinder that rocks!

    How about just drilling to open it up a bit. The thing might fall on it's face without the cone.....
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  6. #6
    Flashaholic* Fallingwater's Avatar
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    Default Re: Undoing metal welds

    No, the cone is just tacked on.
    Italian laws mandate that all 50cc scooters and mopeds sold can't go faster than 45 km/h, which is not only dangerous for the user but actually damaging to the engine.

    Of course, the law is universally ignored and people unrestrict the things as a matter of course. Unrestricting is widely tolerated by the police and insurance companies, and so common that the dealerships themselves usually do it at the first maintenance check.
    The manufacturers know this and build the engines with two restrictors (usually one on the exhaust and one on the CVT transmission) which are designed to make the scooters technically legal when sold but very easy to unrestrict... for any competent mechanic.

    Not being a mechanic, however, I'm lacking proper tools for the job. I'll try shrinking a Dremel cutting disk and using that.
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    *Flashaholic* LuxLuthor's Avatar
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    Default Re: Undoing metal welds

    Not sure how hard the metal/weld is, but one of my favorite set of Dremel bits are their "High Speed Cutting Tips" or sometimes I have used their "Tungsten High Speed Cutters" for harder metals.

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    Flashaholic* dulridge's Avatar
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    Default Re: Undoing metal welds

    Similar nonsense in the UK except the cops and insurers do not tolerate that sort of mod. Piece of wood of the right diameter and a large hammer will often do the trick.

    The Aprilia 125s sold here are equally horribly restricted to 12bhp even if you aren't a learner and are not restricted to 12bhp (As the rules used to be. It is a very long time since I passed by bike test so no longer care about the details)

  9. #9
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    Default Re: Undoing metal welds

    Quote Originally Posted by Fallingwater View Post
    No, the cone is just tacked on.
    Italian laws mandate that all 50cc scooters and mopeds sold can't go faster than 45 km/h, which is not only dangerous for the user but actually damaging to the engine.
    Are you sure unrestricting the exhaust will accomplish the desired goal of a faster top end? I'm asking because a restricted exhaust may decrease power output, but it doesn't necessarily restrict top speed in all cases. A tailwind or a light rider will still result in a higher speed than a heavy rider, for example. Most top speed limiters measure speed somehow, and cut off fuel when that speed is exceeded. If that's the case here, what you're doing won't work. As to determining if that's the case, does the scooter accelerate sharply all up to 45 km/h, and then the acceleration immediately dies at that speed? If so, then the scooter is using some sort of power cutoff determined by speed. If the scooter's acceleration dies off long before 45 km/h, and it gradually creeps up to that speed, then top speed is engine power limited, and what you're doing may work. Sorry about the long-winded analysis, but I just don't want you to go through a lot of work, and find you didn't accomplish your desired goal (which I assume is increasing the maximum speed). As for 45+ km/h being dangerous to the user, I think that depends upon the scooter design and the user. Some designs are great and can handle twice that speed. Others don't seem safe even at 30 km/h. (Note for US readers: 45 km/h = 28 mph)

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    Flashaholic* turbodog's Avatar
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    Default Re: Undoing metal welds

    Quote Originally Posted by jtr1962 View Post
    Are you sure unrestricting the exhaust will accomplish the desired goal of a faster top end? I'm asking because a restricted exhaust may decrease power output, but it doesn't necessarily restrict top speed in all cases. A tailwind or a light rider will still result in a higher speed than a heavy rider, for example. Most top speed limiters measure speed somehow, and cut off fuel when that speed is exceeded. If that's the case here, what you're doing won't work. As to determining if that's the case, does the scooter accelerate sharply all up to 45 km/h, and then the acceleration immediately dies at that speed? If so, then the scooter is using some sort of power cutoff determined by speed. If the scooter's acceleration dies off long before 45 km/h, and it gradually creeps up to that speed, then top speed is engine power limited, and what you're doing may work. Sorry about the long-winded analysis, but I just don't want you to go through a lot of work, and find you didn't accomplish your desired goal (which I assume is increasing the maximum speed). As for 45+ km/h being dangerous to the user, I think that depends upon the scooter design and the user. Some designs are great and can handle twice that speed. Others don't seem safe even at 30 km/h. (Note for US readers: 45 km/h = 28 mph)

    The CVT transmission can usually be modified by changing springs/wedges/cams/rollers/etc to allow a better gear ratio for high speed. This is common in the atv world also as more and more of them are using a CVT tranny versus a geared one.
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  11. #11
    Retired Administrator Norm's Avatar
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    Default Re: Undoing metal welds

    If you decide to drill it be careful it going to grab
    Norm

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    *Flashaholic* Marduke's Avatar
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    Default Re: Undoing metal welds

    I suspect that the cone has more to do with maintaining the proper back pressure for the engine and less to do with limiting how fast you go.

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    Default Re: Undoing metal welds

    I wouldn't play with the tuning of a two-stroke exhaust. Two stroke engines need specific back pressure to operate properly, adn screwing with the back pressure may cause issues.
    There's more to a light than its output.

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    Default Re: Undoing metal welds

    I suspect that if you "mess" with/remove that cone, you'll turn that sedate 2 stroke into a loud dog with no power.

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    *Flashaholic* PlayboyJoeShmoe's Avatar
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    Default Re: Undoing metal welds

    Yeah, I never thought of it in those terms.

    A 2 stroke race bike with a cracked exhaust pipe don't go as good as an un-cracked pipe!
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  16. #16
    Flashaholic* Fallingwater's Avatar
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    Default Re: Undoing metal welds

    Quote Originally Posted by jtr1962 View Post
    Are you sure unrestricting the exhaust will accomplish the desired goal of a faster top end?
    Yes.
    The modification I'm talking about is very common around here. That cone is confirmed as one of the limiters. It is not part of the unrestricted exhaust, and it does not provide needed backpressure. It just smothers the engine so it can't gain too much power. That, combined with a metal ring that prevents the CVT from fully extending, is enough to crudely limit the speed to about 45/50 km/h. Remove the cone and the ring and you can floor it to about 80/85 km/h with no other modifications (on two strokes; unmodified unrestricted four-strokes usually top out at 60/65).

    Modern 50cc scooters, especially if four-stroke, usually have another limiter in the form of either an undersized carb needle or programming in the ECU. Mine has the normal needle and, being a nine year old model, doesn't have an ECU, and thus can't be limited in this fashion.

    As to determining if that's the case, does the scooter accelerate sharply all up to 45 km/h, and then the acceleration immediately dies at that speed? If so, then the scooter is using some sort of power cutoff determined by speed. If the scooter's acceleration dies off long before 45 km/h, and it gradually creeps up to that speed, then top speed is engine power limited, and what you're doing may work.
    It does everything slowly. I've used it restricted for seven years thanks to my dad's paranoia. I wanted to sell it after getting the bike, but then I decided to keep it at my mom's place so I can use it there when I go back by train.
    Since the scooter officially belongs to me now, I'm free to get it back to the state it should always have been in.

    As for 45+ km/h being dangerous to the user, I think that depends upon the scooter design and the user. Some designs are great and can handle twice that speed. Others don't seem safe even at 30 km/h. (Note for US readers: 45 km/h = 28 mph)
    That speed is generally unsafe, because scooters around here are commonly used in very heavy traffic. Not being able to go as fast as the rest of the cars on the road means you're being constantly overtaken, sometimes by large trucks which tend to move a lot of air. This is dangerous in and of itself; when you add the complete inability of restricted scooters to accelerate fast enough to get you out of tight spots, and the additional wear and general unreliability of restricted engines, it makes it clear why Italians never accepted the law and broke it from day one.

    Fortunately, most cops are aware of this and don't give you trouble, and most insurance policies for mopeds have a clause that basically says they will pay even if the vehicle is not technically road legal. Which is good, because close to 100% of 50cc scooters and mopeds aren't.

    I'd love to get whoever thought up this law and put them on a restricted scooter in a city tunnel during rush hour. Then, maybe, they'd understand how idiotic the restriction is.
    Do the same to all the paranoid parents who think that slower speed is always a good thing and perhaps there would be no need for the whole restriction shenanigans.

    Quote Originally Posted by turbodog View Post
    The CVT transmission can usually be modified by changing springs/wedges/cams/rollers/etc to allow a better gear ratio for high speed. This is common in the atv world also as more and more of them are using a CVT tranny versus a geared one.
    Many young boys not old enough to legally drive 125cc vehicles (you need to be 14 to drive 50cc, 16 for 125cc) apply further modifications to their scooters to make them even faster. They usually replace the carb, exhaust and CVT transmission, which by itself can get a scooter up to 100 km/h or more. And then there are the nutcases who go so far as to remove the whole cylinder and piston and replace them with 70/80cc ones, which gets the top speed up to 130/140 km/h.

    I never wanted to do any of that, because a) it's dangerous, b) I have no need for such speeds in what is basically a tiny utility vehicle, and c) police have much less tolerance for scooters that are modified in ways other than simple unrestriction.

    I just want the thing to go at normal traffic speed.
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