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Old 04-07-2013, 07:33 PM   #1
81cr450 OP
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Joined: Jul 2011
Location: Piute ATV trails Utah , Dreaming of Baja
Oddometer: 93
RMX250 halfway build

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

81cr450 screwed with this post 04-21-2013 at 10:25 PM
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Old 04-07-2013, 07:42 PM   #2
81cr450 OP
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Joined: Jul 2011
Location: Piute ATV trails Utah , Dreaming of Baja
Oddometer: 93
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.



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


81cr450 screwed with this post 04-07-2013 at 07:52 PM
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Old 04-07-2013, 07:51 PM   #3
81cr450 OP
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Location: Piute ATV trails Utah , Dreaming of Baja
Oddometer: 93
Powerseal does beautiful work as well.

Heres where the bike is at



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



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.



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

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Old 04-07-2013, 08:00 PM   #4
81cr450 OP
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Location: Piute ATV trails Utah , Dreaming of Baja
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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.





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

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Old 04-07-2013, 08:23 PM   #5
81cr450 OP
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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.



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



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Old 04-07-2013, 08:41 PM   #6
81cr450 OP
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Location: Piute ATV trails Utah , Dreaming of Baja
Oddometer: 93
The little details are what pay the dividends. Intake matching helps a bit too.



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Old 04-18-2013, 01:52 PM   #7
PSchrauber
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Quote:
Originally Posted by 81cr450 View Post
Powerseal does beautiful work as well.

Heres where the bike is at



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.
Kitchen is this your kitchen holy cow what a mess
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Old 04-18-2013, 07:07 PM   #8
81cr450 OP
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Location: Piute ATV trails Utah , Dreaming of Baja
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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



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



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.



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



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...



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.



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.
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Old 04-19-2013, 12:00 PM   #9
PSchrauber
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Quote:
Originally Posted by 81cr450 View Post
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.

...
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.
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Old 04-18-2013, 10:12 AM   #10
bobfab
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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
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