Thread: RPM mods

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    RPM mods
    #1
    Senior Member whitedragon64's Avatar
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    Had an RPM box come in for rebuild last week

    Usual top input bearing kaput

    Found a wider roller bearing the same dimensions 25 x 52 but 3 mm wider than original so 18mm wide instead of the 15mm

    Looked at fitting up tapper rollers but I wasn't happy with setting up pre loads and the aluminium housing thing

    So Bored the housing 3mm deeper to take the wider bearing and also machined out the seal section to 45mm and machined up a new seal sleeve that's 32mm now so that a metric seal 32 x 45 x 7 can be fitted , As these are more readily available here in Oz

    RPM mods-p1020250-800x600-.jpg

    RPM mods-p1020251-800x600-.jpg


    RPM mods-p1020252-800x600-.jpg


    RPM mods-p1020253-800x600-.jpg

    RPM mods-p1020254-800x600-.jpg
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    Re: RPM mods
    #2
    Senior Member whitedragon64's Avatar
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    The housing after been bored

    RPM mods-p1020255-800x600-.jpg
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    Re: RPM mods
    #3
    Senior Member MongooseGSXR750's Avatar
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    Love your work !
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    Re: RPM mods
    #4
    Intense Moderator Rat4020's Avatar
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    The wider bearing is deff a plus .. That input bearing in my book is about the weakest link of the RPM box . Ive done mine like 3 times in seven years .
    Ive had very good luck with mine since I started freshing it up every two years . The first time I did mine the bearing looked like yours. Ya gotta learn what to listen & look for as far as indicators whats goin on with yer box
    1. seals staring to leak (esp the input)
    2.it wines more tha yer o'le lady.. or the normal RPM wine
    3. It starts pushing more oil than norm out yer vent tube
    4. accessive flakes on the plug or more than norm . You will always have a certain amount of filings on acount of the str cut gears . But look close at them if there shiny its a good chance there bearing flakes and thats bad
    And if yer runnin a CVT to your RPM dont be a moron and sit in the shop reving it up in "N" gear while drinkin a beer late at night ..It will fry the top bearings LOL.. BTDT
    The question is not if its gona roll. Its when ..

    That be some kind of church cruzzer or commuter bike thingy ?
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    Re: RPM mods
    #5
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    Chris,after the last Northam event,I checked on my RPM trans in the FL800Pilot because of scary,bang'n noises while corner braking.
    I found the front,bottom trans mount bolt had done a runner,just left a hole.Also noticed a bit of weepage down from the input shaft seal area.
    After reading this post,I thought I got Buckleys of getting the seal.
    But Statewide Bearings in Welshpool are the agents for CR-Chicago Rawhide.So the CR12363 seal is in stock there,get this,over 270 of them.
    I left a message on your house phone.
    Trying to wear out BEFORE I rust out!..........Now just trying to getouta Bed!

    I drink...........therefore I am!
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    Re: RPM mods
    #6
    Senior Member whitedragon64's Avatar
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    Hi Baz
    Yeah went to replay Ya message and deleted it instead

    The mods I did uses the wider bearing and bored out to take metric seals as they are more readily available over here
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    Re: RPM mods
    #7
    Senior Member whitedragon64's Avatar
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    FNR box has again destroyed the input shaft bearing
    So i have dropped a much larger bearing in there now including a block to house the bearing in there
    bearing is now 30mm x 72mm x 19mm along with a stainless steel beefer sleeve fitted
    44814334_1538084236293585_5018302782931730432_n.jpg
    DSC00362 (800x600).jpg
    DSC00363 (800x600).jpg
    DSC00364 (800x600).jpg
    44737078_1538083902960285_3653721076615086080_n.jpg
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    Re: RPM mods
    #8
    The Bob Ross of MBN Bullnerd's Avatar
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    Putting some miles on that thing!

    Looks beefy now!
    "Speed is time-time is speed"-Dennis Hopper

    Quote Originally Posted by TALON View Post
    did you use a special bigfoot camera or something ,you know all blurry could be a tree stump kinda thing .
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    Re: RPM mods
    #9
    The Wizard bdkw1's Avatar
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    The load capacity of that larger ball bearing is only slightly higher than the roller bearing. 29.6kn versus 28.6kn. I don't think the bearing itself is the issue, more likely lack of adequate lube or housing/shaft flex. The ball bearing might stand up to the flex better but lack of lube will still be an issue.
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    Re: RPM mods
    #10
    Millenium Member plkracer's Avatar
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    It is probably the shaft flexing, causing the bearing to absorb that moment. They are pretty weak in that direction.

    I've been running a support bearing for a few years without issues. First gear clutch dumps aren't a problem, and the bearings I pulled out this spring looked great.

    A lot of people were using the nj205 instead of the nj205e, which has much wider rollers, and almost double the capacity, but any bearing that has to take the moment won't last long. A radial ball bearing has a lot more forgiveness in this direction, so it may hold up, or the shaft will fatigue out.

    If you stick with the single sided setup, it should be closer to what one finds on the countershaft, with a substantial bushing providing rigidity, and there is a paired up angular contact bearing behind that seal to take a serious moment.
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