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View Full Version : 99-05 rs50 upside down fork conversion 125 front end!! The Write Up!



newnut
03-07-2014, 02:15 PM
It's taken a lot more work than I initially thought to do this conversion. The documentation on line from previous people trying is very vague and incomplete so I'll try and remember everything and I'm happy to answer any questions.


Pics will follow when I get more time to upload them

THIS HAS NOW BEEN COMPLETED! READ ENTIRE THREAD AS MORE ISSUES AROSE!


To start off I will say you need to be very handy with an angle grinder. you need to modify the bottom yoke, ignition barrel and frame, so it's not a simple swap. you'll obviously need the complete front end from the 125, yokes, forks,wheel, speedo drive, caliper and disc and of course spindle. you dont need the bars as its easier to just put yours on. on top of all that you'll also need 2 new nuts for your steering stem. (you'll see why later in the post)

I ran into quite a few issues doing this swap, mainly clearance issues. The top yoke of the rs125 has the ignition barrel closer to the stem, so this is why you have to shape your existing barrel. In doing this I'm afraid you loose the use of the steering lock. you also have to shave back the mounting points on the underside of the top yoke to help gain clearance of the frame. This wont be enough so you also have to remove the top nut and bolt from the frame, file the protruding edges and replace the nut and bolt with something flat headed. I put a sleeve in, tapped it and inserted a flat head bolt from each side, hopefully its clear in the pics below... I couldn't find a pic of the barrel after, so to give you an idea, first cut straight across, removing the lock and leaving about 3mm from the mount holes, then grind out in a semi circle where i've tried to draw a red line.
http://i1104.photobucket.com/albums/h339/newnut/WP_20140223_003_zps2a2d46b8.jpg (http://s1104.photobucket.com/user/newnut/media/WP_20140223_003_zps2a2d46b8.jpg.html)

Now to save you all the trial and error which I had to go through. The only way this swap will work keeping your fairings that I am aware of, without having to modify your fairings and/or fairing brackets etc, is to have the top yoke as low as you can get it. The 50's top yoke has a downward drop before it gets to the bar mounts, these again have a downward slope. The 125's top yoke is flat, then the bar mounts slope downwards. so this means you have to do away with the big disco biscuit retaining nut that sat above your bearing washer, replace it with a 2mm washer. then place your top yoke on top of that, now you need something to secure it all down. you need 2 nuts. the size is M25x1.00 I recommend not getting anything with an outer diameter more than an inch and a half or it will look odd above your top yoke. The top hat nut I have used has a hole in the middle, yours doesn't have to, but I thought it would look good to have the radiator overflow hose going through.

Your not done yet! lol. The steering lock set up is completely different. at this point you'll be lucky if you can push the bike in a full circle within a mile! its best to have 2 people for this part as it takes a lot of time. taking the front end on and off repeatedly. you have to take a tiny amount off the stops on the bottom yoke at a time at an angle. (see pic below) I mean a small amount!!! about 2mm transfers to about an inch at the end of the bars! Take off too much and your bars will hit the tank, In the UK this is an MOT failure and you'll need a new bottom yoke and try again. Take it off too straight and you will miss the frame also causing the same problem. When this is done make sure you clean out the bearings and race in the frame, re grease.
First pic is of the stops untouched. second is how they should look after your adjustment...
http://i1104.photobucket.com/albums/h339/newnut/DSCF6662_zps6c33634d.jpg (http://s1104.photobucket.com/user/newnut/media/DSCF6662_zps6c33634d.jpg.html)
http://i1104.photobucket.com/albums/h339/newnut/WP_20140307_006_zps19df05bf.jpg (http://s1104.photobucket.com/user/newnut/media/WP_20140307_006_zps19df05bf.jpg.html)

Your new forks will sit approx 30mm above the top yoke, this is to keep geometry the same as original. see pic below. this was an early pic so ignore the nut on the stem.
http://i1104.photobucket.com/albums/h339/newnut/DSCF6742_zpsa959bb4b.jpg (http://s1104.photobucket.com/user/newnut/media/DSCF6742_zpsa959bb4b.jpg.html)
I think thats it! I'll add any more info if I remember. feel free to ask any questions. Keep checking back for pics, I'll add more when I have more time.
http://i1104.photobucket.com/albums/h339/newnut/DSCF6762_zps57ea2561.jpg (http://s1104.photobucket.com/user/newnut/media/DSCF6762_zps57ea2561.jpg.html)

Stem nuts I've found with the same thread pattern so far are Kawasaki ZR-7 (ZR750) 99-04, Kawasaki ZX636 B1-B2 Ninja 03-04 Kawasaki ZX7R P1-P7 Ninja 95+, Kawasaki ZXR750 J-K 91-92 Kawasaki ZXR750 M 94 Triumph Daytona 675 06-08 Triumph Daytona 675 09+, Triumph Street Triple 675 07-1 Honda CR85 r 2003-07, Honda CRF150 2007-12

mattology
03-07-2014, 04:25 PM
how much bigger is the 125 frnot wheel?

newnut
03-07-2014, 05:03 PM
how much bigger is the 125 frnot wheel?

its a 110/70/17, i'm yet to play with tyre sizes, im planning on trying a 100/80/17 on it with a 130 or 120/70/17 on the rear.
original 50's size is 90/80/17 front 110/80/17 rear.

newnut
03-07-2014, 05:15 PM
just seen what your running with! lol. exact same set up i'm hoping will work on this bike. clean bike by the way mattology. It's getting the 100/80 on the 3.00 rim I'm unsure of, I'll let you know. does the backend feel sqidgy runnin the 130? I was leaning more towards the 120

mattology
03-07-2014, 05:43 PM
newnut: it felt great on the track. it felt every bit as confident riding it as i did riding my rs250. the sava mc50's are only available in the 100/130 so that's what i went with on it.

newnut
03-07-2014, 06:07 PM
newnut: it felt great on the track. it felt every bit as confident riding it as i did riding my rs250. the sava mc50's are only available in the 100/130 so that's what i went with on it.

due to the 3.00 front rim, I may have to go with 110/70/17, and just up the rear to the 130 like yours to balance it out as best as i can.

mattology
03-08-2014, 08:21 PM
yeah true, i am trying to find a way to use the traditional rs50 wheels but with upside down forks. Or possibly switching to honda rs125 wheels front and rear.. that might also work.

Zav
03-09-2014, 05:50 AM
yeah true, i am trying to find a way to use the traditional rs50 wheels but with upside down forks. Or possibly switching to honda rs125 wheels front and rear.. that might also work.

Get your self derbi gpr front forks preferable a full font end from a gpr125 and just use the rs 50 wheels as the gpr forks are same as new shape rs forks what are same as rs4 forks what has same frame as your rs

simple and I can see 2 for sale in use on eBay

newnut
03-09-2014, 07:07 AM
have you done that swap Zav, or seen it done?

Zav
03-09-2014, 10:44 AM
I'm doing it now with 3 other conversions

putting my06 rims on a rx
my06forks on am6 frame
and rx wheels and shock on my06 rs

newnut
03-09-2014, 11:25 AM
I'm doing it now with 3 other conversions

putting my06 rims on a rx
my06forks on am6 frame
and rx wheels and shock on my06 rs

oh nice! put some pics on here when its done. I'd like to see the difference it makes.

Zav
03-09-2014, 12:24 PM
Which one ???
Ive semi done the my06 and the sumo but haven't started on the am6 rs yet

newnut
03-09-2014, 01:21 PM
Which one ???
Ive semi done the my06 and the sumo but haven't started on the am6 rs yet

the 06 on am6 mainly.

mattology
03-09-2014, 07:12 PM
Yeah I might be interested in that also. Do they make spring kits or anything for the upside down fork? The fact that my front end is reworked and much stiffer than stock along with dual damping makes these traditional forks a lot better than bog standard am6 marzocchis

Zav
03-10-2014, 03:01 AM
Nope they do not do any forks spring sets as they use same forks on there 50 cc 125cc road bikes and same forks on there 80cc 90cc 125cc race bikes but only use the 125 caliper as it has more pistons and more power (look up toras brake thread as he's done a lot of work with brakes) so they have to be good as aprilia don't even use there 50 forks on the 125

but out that's only for Tora shape gpr aka the honda crashed one the old shape one he's got they do not use in any race bike and never will

and I'll post some pics in summer time as I need to sell 2 bikes first as I have no room left in my garage even tho it's a double ones I've filled it with bikes and parts

newnut
03-10-2014, 06:09 PM
This conversion cant be completed dur to another issue I just discovered. the stem has a very very small taper so the top bearing is loose causing movement like worn bearings. a sleeve wont work as it tapers inwards as you go down. a smaller inner diameter bearing wont fit past the top, the only solution I can think of is to get the stem thickened. I dont know the measurements yet, I'll get back to you all.

mattology
03-10-2014, 06:11 PM
Can you get some photos of this ?

Zav
03-10-2014, 06:13 PM
This conversion cant be completed dur to another issue I just discovered. the stem has a very very small taper so the top bearing is loose causing movement like worn bearings. a sleeve wont work as it tapers inwards as you go down. a smaller inner diameter bearing wont fit past the top, the only solution I can think of is to get the stem thickened. I dont know the measurements yet, I'll get back to you all.

Never heard of this problem nor have I seen it got any pics ??

Zav
03-10-2014, 06:25 PM
Just to show it's been down
http://www.apriliaforum.com/forums/showthread.php?39527-RS50-Upside-Down-Front-Forks
http://www.apriliaforum.com/forums/showthread.php?75507-RS50-s-one-powered-by-a-rotax-123-and-the-other-by-a-mito-engine
http://www.apriliaforum.com/forums/showthread.php?162159-RS50-CR85-conversion

I know they don't say how it's done but gives you few looks at how they did it

newnut
03-10-2014, 07:08 PM
yeah i saw those. Don't know if somethings diff in the states, but its definitely an issue with what i have. I'll try and get a pic tomorrow. Its only a very slight bit of movement, maybe they just lived with it.
]

Zav
03-10-2014, 07:10 PM
yeah i saw those. Don't know if somethings diff in the states, but its definitely an issue with what i have. I'll try and get a pic tomorrow. Its only a very slight bit of movement, maybe they just lived with it.
]

Not sure how a mot guy would fair with it tho as I got a advisory as mine was slightly loose but didn't move never mind moving

newnut
03-10-2014, 09:28 PM
whats the diff between the 93-98 forks and the 98-2005? 125s
just wondering if I have or if they used the early/later model triple tree

Zav
03-11-2014, 02:44 AM
whats the diff between the 93-98 forks and the 98-2005? 125s
just wondering if I have or if they used the early/later model triple tree

There the same

they use same frame forks swing arm from 93 all way too now

newnut
03-12-2014, 09:07 AM
woohoo! it's done! got it all sorted. The solution was to fit an old cbr600 headrace bearing below the rs50 top bearing. the reason for this is because the cbr bearing has a thinner profile, allowing the rs50 bearing to sit a little higher. The other way round it was to press out the stems and swap them round. I may still do that at some point. I'll add pics of the stem and issue further down the post!
http://i1104.photobucket.com/albums/h339/newnut/DSCF6773_zpsfbceae8f.jpg (http://s1104.photobucket.com/user/newnut/media/DSCF6773_zpsfbceae8f.jpg.html)http://i1104.photobucket.com/albums/h339/newnut/DSCF6777_zpsf4a0e69e.jpghttp://i1104.photobucket.com/albums/h339/newnut/DSCF6775_zps5d380c34.jpg (http://s1104.photobucket.com/user/newnut/media/DSCF6775_zps5d380c34.jpg.html)
http://i1104.photobucket.com/albums/h339/newnut/DSCF6778_zps95d86b1c.jpg (http://s1104.photobucket.com/user/newnut/media/DSCF6778_zps95d86b1c.jpg.html)

Zav
03-12-2014, 02:25 PM
woohoo! it's done! got it all sorted. The solution was to fit an old cbr600 headrace bearing below the rs50 top bearing. the reason for this is because the cbr bearing has a thinner profile, allowing the rs50 bearing to sit a little higher. The other way round it was to press out the stems and swap them round. I may still do that at some point. I'll add pics of the stem and issue further down the post!
http://i1104.photobucket.com/albums/h339/newnut/DSCF6773_zpsfbceae8f.jpg (http://s1104.photobucket.com/user/newnut/media/DSCF6773_zpsfbceae8f.jpg.html)http://i1104.photobucket.com/albums/h339/newnut/DSCF6777_zpsf4a0e69e.jpghttp://i1104.photobucket.com/albums/h339/newnut/DSCF6775_zps5d380c34.jpg (http://s1104.photobucket.com/user/newnut/media/DSCF6775_zps5d380c34.jpg.html)
http://i1104.photobucket.com/albums/h339/newnut/DSCF6778_zps95d86b1c.jpg (http://s1104.photobucket.com/user/newnut/media/DSCF6778_zps95d86b1c.jpg.html)

Looks so wrong with the size of front wheel compared to rear but looks good everywhere else

get your self a new shape top yoke, clean up the fairings (looks like a Mansfield town football club rep ahaa google it if dunno what I mean) maybe a rs4 swinger or my06 swinger to top of the uniqueness of the bike

newnut
03-12-2014, 02:43 PM
It wasn't supposed to be such a project as it turned out to be. the front doesn't really look odd in the flesh, looks a million times better than the original. just gonna add a 130 rear tire when I get some more time, and a "camel" decal kit and sponsor decals. The different swing arm may be something I do in a month or two. after the decals are added I'm gonna leave it a while before the wife gets the hump! (back to hunting down a zx10r for me now!)

newnut
03-12-2014, 02:51 PM
oh damn I hate you ZAV! LOL! :bangwall: whats the score putting the rsv4 50 swinger on, I've just seen it!

Zav
03-12-2014, 03:00 PM
If you get all the right spacers from a rs4 should be a straight fit bit tried it yet as I'm going to do it my self and I think you may have to make a new top mount for shock I'm not sure as I haven't seen a rs4 subframe to compare to a am6 subframe as there different the only same his on both bikes are the main frame even cradles different (yes that's the best way to fit a d50b0 into a am6 bike

newnut
03-12-2014, 03:05 PM
when you looking on starting that? you'll have to keep us posted. I guess I'll start looking in to it. lol

Zav
03-12-2014, 03:06 PM
It's not a rsv 4 that's a 1000 cc bike it's the rs4 50 or 125 both frames same just different cradles (you can also fit a 125 4 stroke easily this way into am6 frame)

Zav
03-12-2014, 03:10 PM
when you looking on starting that? you'll have to keep us posted. I guess I'll start looking in to it. lol
Summer time ish ahaa I'm not sure yet my old shape rs is still upside down in my garage and I need to source a swinger and I need to sell some more of my06 bike as I still have a lot of it left I'm keeping the wheels, forks, brakes, engine, brakes rest has to go to pay for a new spray gun and compressor I want

mattology
03-12-2014, 07:38 PM
I've been trying to get an rs4 swingarm for a while off eBay

Zav
03-12-2014, 07:58 PM
I've been trying to get an rs4 swingarm for a while off eBay

Theres 2 on ebay at moment

my only concern with the mod is rs4 50 and 125 have same swinger so I dunno if the chain will line up well or how the stock am6 brakes will fit you might have to get a complete rear end eg rear brake, swinger, wheel, brake bracket and so on so I dunno how well the am6 wheel will fit you may have to use the rs4 wheel/my06 wheel

if found this on my Rx I'm having to make a custom bracket to hold rear brake and going to have to skim the wheel to try get sprocket closer so chain lines up as the wheel is a tad too big ahaa there 1cm each side of room

mattology
03-12-2014, 09:26 PM
Link me it zav

Zav
03-13-2014, 06:18 AM
Link me it zav

Theres no brakes on or spacers or bushes but there's these
http://www.ebay.co.uk/itm/Aprilia-RS4-RS-4-125-12-Rear-Swinging-Arm-Read-Description-/181063051898?pt=UK_Motorcycle_Parts_13&hash=item2a2832ea7a
http://www.ebay.co.uk/itm/Aprilia-RS4-125-10-11-12-Swingarm-Swing-Arm-/181249787065?pt=UK_Motorcycle_Parts_13&hash=item2a335444b9

newnut
03-13-2014, 06:22 PM
hmmm, i'll look into it when I get a chance. keep us updated with your findings guys. the RS is in for its MOT tomorrow! fingers crossed! lol

mattology
03-13-2014, 11:54 PM
Zav Neither one of them will ship to the USA. Would you ship it for me ? If I buy it for you, and you try it out and see if the rear brake, rear brake plate, and rear wheel from an AM6 bike will work, would you send it ?

newnut
03-14-2014, 11:39 AM
Zav Neither one of them will ship to the USA. Would you ship it for me ? If I buy it for you, and you try it out and see if the rear brake, rear brake plate, and rear wheel from an AM6 bike will work, would you send it ?

thats a big ask mattology! you'd be better off waiting for one in the states. shipping rates here in the UK have just gone through the roof. seriously expensive, It just cost me 20 to send a wheel 30 miles. thats over $33!!! then then there's the time and work getting it to fit, I doubt it's just a straight case of bolting it on.

hold ya horses a little while, It will be tried soon enough by one of us and I'm sure the workings will be posted.

mattology
03-14-2014, 07:26 PM
I bought two sets of forks already from the UK. I don't have the time to wait three years. Can I send you the money and you see if it fits? And if so send it on?

mattology
03-14-2014, 07:27 PM
By the way the RS4 never came to the USA, I already contact AF1 to see if I could just order one brand new like almost two years ago

mattology
03-15-2014, 03:38 AM
You know, I think it's possible to install some fork emulators into the stock forks to get a lot better damping out of these things..

I'm going to try and order up a set and see what happens. I'll keep errbody updated.

ryanpetrolhead
03-15-2014, 04:46 AM
woohoo! it's done! got it all sorted. The solution was to fit an old cbr600 headrace bearing below the rs50 top bearing. the reason for this is because the cbr bearing has a thinner profile, allowing the rs50 bearing to sit a little higher. The other way round it was to press out the stems and swap them round. I may still do that at some point. I'll add pics of the stem and issue further down the post!
http://i1104.photobucket.com/albums/h339/newnut/DSCF6773_zpsfbceae8f.jpg (http://s1104.photobucket.com/user/newnut/media/DSCF6773_zpsfbceae8f.jpg.html)http://i1104.photobucket.com/albums/h339/newnut/DSCF6777_zpsf4a0e69e.jpghttp://i1104.photobucket.com/albums/h339/newnut/DSCF6775_zps5d380c34.jpg (http://s1104.photobucket.com/user/newnut/media/DSCF6775_zps5d380c34.jpg.html)
http://i1104.photobucket.com/albums/h339/newnut/DSCF6778_zps95d86b1c.jpg (http://s1104.photobucket.com/user/newnut/media/DSCF6778_zps95d86b1c.jpg.html)
That looks awesome! I like the unique paint style as well.