RMX250 halfway build

Discussion in '2 smokers' started by 81cr450, Apr 7, 2013.

  1. 81cr450

    81cr450 Been here awhile

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    I'm pretty good with motors , but the shiney stuff is not my thing. So this is only halfway. I may powdercoat eventually but so far it's just to get it running & riding
    What I bought was a 93 rmx250. I like the wide ratio trans of the RMX & Guy Coopers' whip in the early 90's Dirtrider always had me wanting an RM. I'm more of a big bore 2-stroke guy so the motor really needed to be breathed on a bit. I ended up just using the 93 trans & clutch. The jug is from a 91 RM which has the biggest exhaust port of the series. The case & crank are 1995 because they started using crank stuffing in the later motors. The head is a 95 rm because it actually has a squish band. I'm using VF3 reeds because they reduce crankcase volume too. I would have done some stuffing but I am lazy.

    Here I gotta say thanks to Bix & Mike Wier. Mike runs OEM-CYCLE.COM Bix', place is called motoxman.com , these 2 gave me a smoking deal on the crank & jug. Both parts were to me in 3 days.

    I had others supply parts but these guys stood out.

    I'm also using a new PSI pipe I found on ebay for $125 shipped, talk about SCORE.

    I intend to dual-sport this for a bit , but as with anything I build its always for sale. As part of the dual sporting I went with a KTM LC4 tank & grafted it to the bike. I figure I need the extra range of more fuel. I really wanted a 6.6 gallon 2003 yz250/450f tank but couldnt find one so I took what was cheap.

    My photos will start with the motor & I'll kinda go from there as I complete the build. The handle bars on these are way far back & I have a trick for that. The plastic & seat cover colors that are available now dont match the old suzuki yellow & I have a few tips on that.

    I do have a question though , have any of you used permatex anti-sieze on your powervalves. I've been using it on my last 3 powervalve motors & it takes a few rides to really loosen up but once it does it works quite nice. It kinda helps keep you from beating on a fresh motor because the powervalves dont react as fast as normal so you kinda ride a DOG till the lube melts in .

    Sorry for the long post but I'm kind of a Blatherer

    Pics to come
    #1
  2. 81cr450

    81cr450 Been here awhile

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    On the piston I windowed it & dropped the boysen port before the replate. On a kx500 it equals 2.5 hp in the mid range. The reason I think it works like that is if you think of swinging a bucket to keep the water in the bottom the highest point of pressure is in the very bottom so a window relieves this hgih pressure point.

    [​IMG]

    The piston is also skirt coated with an antifriction coating & ceramic on top
    Here's the boysen port drop

    [​IMG]
    #2
  3. 81cr450

    81cr450 Been here awhile

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    Powerseal does beautiful work as well.

    Heres where the bike is at

    [​IMG]

    Yes it's in my kitchen & yes its a work in progress. You can see the tank on it at this point but the shrouds still need to be attached.

    The 91 jug needed some port work to smooth out the powervalve area & the powervalves had to be relieved as I went 2mm overbore

    [​IMG]

    You can see the rechambered head above as well & below here you can see how the everthing is flush when the valves are open, they were 1/4 inch deep before the work.

    [​IMG]

    The RMX is know for having excellent fuel economy due to such a small exhaust window, you can kind of see it here when the powervalves arent open

    [​IMG]
    #3
  4. 81cr450

    81cr450 Been here awhile

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    The crankcase stuffing I was refering to I lost the pic to but you can kind of see it in these 2 photos here. The aluminum insert on the second pic is where it's at.

    [​IMG]

    [​IMG]

    Veshrah Japanese rods are the good stuff, no wiseco China junk

    [​IMG]
    #4
  5. 81cr450

    81cr450 Been here awhile

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    This may be a bunch of crap no one cares about but it might also help someone understand what theyre paying for so...

    Heres an illustration of the head with no squish band off the RMX vs the RM head with squish. The clay is there to illustrate what I'm talking about.

    [​IMG]

    The bar mounts are off of a honda ascot 500 & they put the bars forward a 1/2 inch at least. I had to turn a spacer to on the lathe to use them though & the retaining nut is small enough I worry a little that it wont be strong enough

    [​IMG]

    [​IMG]
    #5
  6. 81cr450

    81cr450 Been here awhile

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    The little details are what pay the dividends. Intake matching helps a bit too.

    [​IMG]

    [​IMG]
    #6
  7. third eye

    third eye back road loon

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    :lurk
    very cool, looks like part of the return of two strokes
    #7
  8. Foot dragger

    Foot dragger singletracker

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    That should be a runner,I sold an RMX PSI pipe a while ago on ebay,,could it be?
    I found 8 RM/RMX's all in parts in a pile for so cheap I couldnt pass it up.
    Also one with a current CA plate in complete bike form but it's gone now.
    Ive got a few odds and ends left but most has sold off.

    Ive still got a FMF 91/92 RMX pipe on there for sale but nobody wants it even for cheap.
    #8
  9. 81cr450

    81cr450 Been here awhile

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    The PSI pipe I got is new old stock. The guy had a few when I got mine.

    On to a place to put my :kat:

    The seat has been some work. Mating it to a non stock tank & the sukiest seat cover ever. The seat cover has been the biggest problem on multiple levels. Its the worst fitting one I've ever replaced, even with using new undamaged foam.

    The other problem was the color didnt match the 90s rmx color at all. Its like neon lime yellow & the older plastics are a orangish yellow & it just clashed :puke2. I could have gotten a black one instead which I would recommend , but the easy way isnt my way.

    Plastic for early 90's rm's is hard to find let alone multiple colors & I wanted the newer yellow to match the seat. I could have gotten the the factory fit tank in black but no black shrouds. So I tried to get a natural colored 6.6 yamaha, the only color they still make is blue. Which just left me randomly hunting for a large tank with shrouds. I lucked out & picked up a new lc4 tank for $80 on ebay.

    Mounting it was pretty slick. I had to cut off the original seat catch, represented by the cardboard in the pic, then weld in a new tank hold down there.
    [​IMG]

    The next step was the inner front mount, it's kind of an aluminum handle, with a rubber hose over to keep from wearing on the tank. Bolts right into the factory tank mounts

    [​IMG]

    These tank ears just slip right on

    [​IMG]

    For the rear mount I turned down a piece of derilin on the lathe. Figured it would wear decent against the tank.

    [​IMG]

    Feels snug no slop when mounted. I still nee to attach to the radiators, but they have some nice loops that will make it easy enough.

    [​IMG]

    To hook the seat to the frame / tank area I used an old cutting board of my Wife's cause it seemed like it wouldnt hurt the tank at all. It worked out to where the airbox now draws air from the front of the seat. You can see where the derelin bushing goes under the silver washer.

    [​IMG]

    The middle layer hooks the seat to prevent side to side movement but also alows for an air chanel
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    I also used an old milk jug to create a dust shield from the rear. I'd of liked it to seal up closer to the vents but you gotta be able to take the seat on & off
    #9
  10. 81cr450

    81cr450 Been here awhile

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    [​IMG]

    [​IMG]

    Real easy to attach just used my trusty stapler

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    The seat pan needed the old attaching points removed & a new one riveted in. I had a old cr250 seat to rob the front catch out of.

    [​IMG]

    [​IMG]

    You can see the gap here under the front of the seat for the air channel . It's decent sized under there I just couldnt get a better pic. & no my fat :kat doesnt smoosh it down to where it cant breathe.

    [​IMG]
    #10
  11. 81cr450

    81cr450 Been here awhile

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    From a couple feet back the gap doesnt look too horrible.

    [​IMG]


    Yea my picture skills need help.
    #11
  12. Foot dragger

    Foot dragger singletracker

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    Holey Moley,youve got some time on your hands,and some skills as well.
    I tend to buy what works and ride it till it dont.

    Looking good though. Ive got some 90's RMX/RM wheels around if your needing spares
    #12
  13. 81cr450

    81cr450 Been here awhile

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    I have some sort of mental disease that wont let me just buy something & leave it alone. Theres only 3 bike's I could even consider buying new right now, ktm/Husaberg 300, Hayabusa or Ninja 1400. Those would even need some tweaks from the factory. I dont have buckets of cash though so I kinda gotta build what I want. The time on this hasnt been to bad though , not compared to an aluminum framed bike.
    I already have a spare rear wheel though , thanks. They are factory excell's on the rmx you should strip the rims & sell them as such & sell the hubs separate.
    #13
  14. bobfab

    bobfab Long timer

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    Nice build, its the litttle things. Is that a DRZ400 IMS tank on there?

    Im looking at buying a RMX this summer for next winters rebuild needless to say im following along :lurk
    #14
  15. PSchrauber

    PSchrauber Long timer

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    Summer: Kemiƶ, Finland; Winter: North Germany
    Kitchen is this your kitchen holy cow what a mess :eek1
    #15
  16. 81cr450

    81cr450 Been here awhile

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    You do realize this is ADV not better homes & gardens right?
    When I was a about 5 I watched a guy build a harley trike in his front room. Getting it out was another story. You cant really call yourself a wrench if you've never washed parts in the tub either.

    Anyway its coming along , I've thought of a couple points on the motor I forgot to mention. The 1995 & up bottom end has 8 ball main bearings , the same used in the CR500. I replaced the mains with factory honda parts . The 1993 has the same main on one side but the other side got a smaller less beefy piece. Seems like a good deal for longevity.
    The case also has a pocket in it that can hold a little more oil if you ditch the gasket & drill 2 holes. The bike only holds 650ml so I think its worthwhile to get some more fluid in there. I did have to run my crank side clearance on the minimum to make up for the .010 gasket thickness. The trans still was good on clearance.

    You can see the largish pocket here

    [​IMG]

    On this side you can see where the oil will come out of the trans into the clutch , then theres a built in scraper that will put the oil back in the transmission. I'm hoping this will generate circulation through the pocket. I also went kinda small on the holes so the trans couldnt be over scavenged

    [​IMG]

    I also heard that the latter RMX powervalves could fall into the motor if a spring broke, this motor is not like that. There are 2 springs that should be replaced, but if the do go bad all that will happen is the second stage of the powervalve will flutter.

    [​IMG]

    I also read that the powervalve rod clips break when you take them appart but mine were good so I just used them over

    [​IMG]

    I also changed the carb from a keihin pk that "barely" idles off the choke, to a mikuni 36mm tmx which fits the 92 rm boot perfect. I figure if a cr500 can make 65 hp off of 38mm a 250 should be fine with 36mm & have better throttle response. Alot of people think tmx mikuni's suck, the problem in my opinion is the jetting table out of the oem manuals. This carb calls for a 35 pilot from honda, but from experience the thing takes 4 sizes leaner down to a 25 , some even say a 20 is the ticket. I like em I had a bored out 38mm tmx on my kx550af & they work. Scared me leaning it down that far but...

    [​IMG]

    I need to mention how tight the head is to the top of the powervalves, I had to clearance a bit & I will have to build a new mount but it's worth the squish, trust me.

    [​IMG]

    You can also see the $8 a foot 500 degree silicone hose, it should be leak proof I hope. Which reminds me ... I need to flush the radiators.
    #16
  17. PSchrauber

    PSchrauber Long timer

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    I know that this is NOT a thread about home building or how to clean up your home when in need.

    But as it is so obvious that the refubisjed parts are really sanitary the mess in the background doesn't fit. There are certainly important things and less important in live, ... which comes first depending the kitchen I will not discuss here.
    :evil
    #17
  18. 81cr450

    81cr450 Been here awhile

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    Thanks for your concern for my well being, & the positive input
    " the refubisjed parts are really sanitary "

    I'd like to say thanks for some of the idea's I've gleaned from this & other sites. I was putting on my sprocket today & greased the splines, a trick I learned from the guys on the xr650l thread. It is really nice to be able to share idea's & technique's , as everybody has their own way of doing things.

    I believe it's a Ben Franklin saying I'm gonna slaughter here but it goes something like "No matter a mans social standing, walk of life, or intelligence there's always something to be learned from him." I know some of the best lessons I've learned have been from people of diminished capacities.

    I hope in taking the time to post this up I can return some of the positive energy I've received from others who've done the same & helped me by sharing what they've learned .

    This pic kinda illustrates an idea I stole / improved on from E-Gorr. The crankcase vent on these motors comes out from the powervalve area & is the vent for the entire motor. He recommends just plugging it off. I know on a v-8 if you plug it all off it will blow seals & gaskets so I assume the same would hold true for a dirt bike engine. If I hadnt read his page on how that vent will suck a bit of dirt into the motor I would have just run it straight down like the factory did & suck up trail dust, with the cheap 3/8 fuel filter it can breathe fresh clean air

    [​IMG]

    I used some aluminum duct tape under the tank as a heat shield where the exhaust runs by. I hope it sticks as nice when the fuel is in there. I might oughta put a bunch of pin holes in it so it can breathe, like they do on tank stickers.

    [​IMG]
    #18
  19. Foot dragger

    Foot dragger singletracker

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    I can appreciate working in the kitchen,I dis-mantled and rebuilt a rubber cow(1976 R75/6 BMW) in the backroom,engine torn to bits,changed frame and forks out due to bent issues. Spent a minimum of 3 hours a day for months on it.

    Then rode it and realized what I had done,cripeola what a tank,ill handling sloth of a pig.
    Traded it for an 05 650 Strom,but lessons were learned and I moved on with my life.
    ---------------------------------------------------------------------*

    Still got those spare RMX wheels sitting here.
    ---------------------------------------------------------------------------------------------------------------------------------
    A Keihin carb fits into the RMX intake rubbers with no changes Ive been told,supposed to work well.
    (refubisjed is in the "new" dictionary.
    #19
  20. Spikester300

    Spikester300 Roll Tide!

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    They usually vent a little smoke out the vent hose so check the filter after running it to see if it clogs up.
    #20