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    Reverse gearbox concept
    #1
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    I have a concept for a reverse box:
    I have done a rough concept drawing (looks like gibrish otherwise I would have posted it) and I think I can make it work dimensions wise.

    Here is the rough idea:

    Chain drive from engine to input shaft. Shaft will have interchangeable outer sprockets (as in the one that connects it to the bike engine).
    Needs about a 2:1 reduction but would be adjustable

    Input shaft:
    Using PTO shaft, probably 1-3/4". Leave the splines in the middle of the shaft, and machine down each side to take a bearing surface. On one side will be the reverse sprocket (chain drive), on the other the fwd sprocket (chain drive), both on bearings. These will sit inside the casing.

    The input shaft will extend outside the casing and I will machine splines on the end to fit a standard motorcycle sprocket.

    A splined coupler will be machined to match the sprockets with hardened pins in it. These pins will align with holes on the fwd/reverse sprockets, and can slide side to side to engage F/N/R

    Output 'shaft'
    The output shaft will be an LSD from a FWD car. They have a ring gear that is a helical gear cut so that the two shafts run parallel (not at 90 deg like a RWD diff). I will use the existing ring gears as the reverse drive.
    (similar to this ring gear http://www.ebay.com/itm/MFACTORY-4-5...-/251722623877)

    FWD drive:
    the fwd drive sprocket on the input shaft will be a direct chain drive to a sprocket bolted to the LSD. When engaged, the engine will run purely on chain drive, with no gears utilized. should get around 2:1 reduction (total fwd gear around 4:1 reduction from bike output shaft... similar to what my buggy runs now)

    REVERSE:
    Reverse will go from the input shaft (acting as a layshaft) to the gear shaft that drives reverse. These gears will come from a car and are the final drive gears so should be very strong (overcomes the problem lots of people have had with gears destroying themselves.) Probably around 4:1 reduction... so total for reverse is going to be about 8:1 or so but depends on the gearing of the chain sprockets. Probably best to drop the buggy straight into second for reverse.



    Only issues I see with this are the following
    1: You fry an internal chain and destroy the box.
    I was planning on using 630 drag chain for the internal chains, or alternatively two chains internally for fwd gear, with a single chain for reverse.

    2: the bearings on the main shaft
    Reverse gear so low means that the reverse sprocket will hit 10,000 rpm regularly, not sure if that's going to cause issues with heat build up

    3: Input shaft
    PTO shaft is the only thing I can think of using. I'm OK on a mill/lathe, but no expert. I can happily machine as I described above. I feel that it may be the weak link, which is why I would go for the 1-3/4" shaft. I don't really want to go down the road of custom machining splines and hardening shafts, I have seen that go wrong and I don't have the budget to make a few different version before it starts working.


    Hope that made sense...

    What do you think, see huge problems that I haven't thought about?
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    Re: Reverse gearbox concept
    #2
    Senior Member JD66's Avatar
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    Ham,

    Are you thinking the case will be enclosed with oil inside? If so, I'd go with a silent chain like they use in transfer cases. I was looking at the Ramsey chain website a while back for ideas.

    In my setup, I think the o-ring chain is the weak link and hope to avoid them in the future. I'm running an RPM, but plan to build an oil enclosed silent chain between the m/c countershaft and the rpm input shaft.
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    Re: Reverse gearbox concept
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    Quote Originally Posted by justindutton66 View Post
    Ham,

    Are you thinking the case will be enclosed with oil inside? If so, I'd go with a silent chain like they use in transfer cases. I was looking at the Ramsey chain website a while back for ideas.

    In my setup, I think the o-ring chain is the weak link and hope to avoid them in the future. I'm running an RPM, but plan to build an oil enclosed silent chain between the m/c countershaft and the rpm input shaft.
    Opps, should have mentioned that. I was going to put it all in a case with oil, hoping splash lubrication would be enough so that I don't have to worry about an oil pump or an oil pump failure.

    I'll look into the silent chain, I hadn't heard of them before so its great to learn about!
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    Re: Reverse gearbox concept
    #4
    Millenium Member plkracer's Avatar
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    Even the silent chain has its limits. I know they were a weak link in the np203 transfer cases, and they were only driving the front wheels before the axle reduction.

    It's a huge chain oto, like 2.5" wide if I remember correctly.
    Proud owner of a two seat pucker-mobile. Funco inspired mini buggy powered by a Busa. Giving out free rides to anyone brave enough.
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    Re: Reverse gearbox concept
    #5
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    I was originally thinking ek630ms drag bike chain. Rated to 11,000 lbs breaking stress and 500 hp. I figue the weak link will be the drive chain connecting the engine to the box so if something is going to break, thays the best part to go.

    should add ill be running a gsxr1000, about 150hp. Nothing insane
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    Re: Reverse gearbox concept
    #6
    Millenium Member plkracer's Avatar
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    Quote Originally Posted by Hambam View Post
    I was originally thinking ek630ms drag bike chain. Rated to 11,000 lbs breaking stress and 500 hp. I figue the weak link will be the drive chain connecting the engine to the box so if something is going to break, thays the best part to go.

    should add ill be running a gsxr1000, about 150hp. Nothing insane
    The 500hp figure is misleading, as you can have nearly infinite torque from nearly zero hp.

    That figure probably refers to a drag bike, which only has a limited amount of traction. It won't fly in a buggy with triple the weight and shock loading.

    I put an excel sheet up here a while ago explaining why chains really only work when they are the first in the series. Once you go through your 2:1, your stress on your chain doubles, to the point that 11,000 lbs isnt enough strength, unless you are running 20+ tooth sprocket. Bugpac tried this years ago and broke/twisted every chain made.

    Double chain s would probably work, it is going to get expensive though.
    Last edited by plkracer; 06-04-2015 at 11:53 PM.
    Proud owner of a two seat pucker-mobile. Funco inspired mini buggy powered by a Busa. Giving out free rides to anyone brave enough.
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    Re: Reverse gearbox concept
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    Senior Member JD66's Avatar
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    I gave some initial specs to an engineer at Ramsey Chain, he was suggesting a 2" wide silent chain. Note sure how a silent chain would compare to an o-ring chain for shock loading though.
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    Re: Reverse gearbox concept
    #8
    The Wizard bdkw1's Avatar
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    Chain from a 70's Eldorado transmission. Big block, big car. They even put those tranys in motorhomes.
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    Re: Reverse gearbox concept
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    Had a look. The problem with the silent chain is the width. 2" wide is not going to work for me. The Diff I want to use is from a honda civic, and with a diff that narrow, 2" wide won't leave enough room for the ring gear, bearing housings, etc...
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    Re: Reverse gearbox concept
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    Your chains will be very short and doing some work because your pinion and gear won't have a very big center distance.

    I've done something similar, but I used "of the shelf" gears and 2 x 530 chains side by side. I had to use an idle shaft though.

    Still untested, so I'm not entirely convinced it will work.
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