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jgas 11-25-2012 12:26 AM

Yamaha RD 400 in a KDX frame?
I have always been a RD fan, although I've never owned one. I have had an idea to stuff an RD motor in an old 82 KDX 250 I have layihg around. For 2 yrs only, Kawi made the 200 and 250 KDX with different frames, and the 250 is MUCH more roomy in the engine compartment. My first idea was to use an old 4t air cooled single motor of some kind, but a buddy mentioned using a Yamaha Banshee 350 twin 2 stroke quad motor. Then I looked at the layout of the 2 Banshee pipes and quickly gave that up. I also want to use an aircooled motor for the nostalgia factor, and prefer to stick to a 2 stroke. But then I remembered that an RD had small diameter pipes routed under the frame like a Rally bike sort of has, and had a Eureka moment. I think I could make an RD motor work with enough fabrication to the frame.

Were all RDs kickstart only? I seem to remember that the last time I rode one it was kick only, or do they have the button? Is there a points to CDI conversion, or were some RDs already CDI?

stainlesscycle 11-27-2012 11:56 AM

not sure what you're trying to accomplish? - are you building a street bike out of this, or a dirt bike?

all rd's (aside from rd200) are kickstart only

there are many ignition conversions available.

earling 11-27-2012 03:02 PM

I have an RD350. I have a feeling that engine would feel massively heavy in a KDX frame, also too wide. No doubt it would rip, though. The RD's would probably be a little peaky for offroad work. They come with a 6 speed, and you need all six to stay on the pipe if it's at all modified. Stock they're a little tamer. You'd have to rig up an oil injection tank, or go to premix. The pipes on an RD and low slung and would be totally hopeless offroad. Any available expansion chambers would make it even worse.

Seems like a gigantic waste of time, honestly.

You can spend as much as you want on a CDI for an RD--There are a couple that I'm aware of, though I can't remember what they're called. Check out USA Two Strokers. One is made is from India, one is from Germany (MZ I think). Both expensive ($600+). Both are programmable, though.

RodT 11-27-2012 08:14 PM

TDR250 Yamaha
That's almost what this bike is

stainlesscycle 11-28-2012 02:11 PM


Originally Posted by RodT (Post 20131637)

kinda, but the tdr is a long stroke motor. the rd400 is close to square.

that's kinda why i asked what he was trying to attempt...

rd400 in a kdx frame would be pretty useless in the woods. could make a competitive flat tracker though... would take some work... would make a goofy street bike too. flat tracker would work..

pdxjim 11-28-2012 10:06 PM


Originally Posted by stainlesscycle (Post 20136557)
kinda, but the tdr is a long stroke motor. .

Nope. The TDR is 56.5x50 undersquare short stroker.

It sucks in the dirt and isn't even really all that well suited for supermoto either.

It wants to rev and only makes (much) power over 5000 rpm.

Once you get it spinning it is unbeatable and is a perfect twisty road weapon, but if you let the revs drop or miss a shift, you might as well get off and push.

stainlesscycle 11-29-2012 05:12 AM


Originally Posted by pdxjim (Post 20139511)
Nope. The TDR is 56.5x50 undersquare short stroker.

It sucks in the dirt and isn't even really all that well suited for supermoto either.

It wants to rev and only makes (much) power over 5000 rpm.

Once you get it spinning it is unbeatable and is a perfect twisty road weapon, but if you let the revs drop or miss a shift, you might as well get off and push.

my bad - i knew it was 56x50. typed long insted of short . doh!

jgas 11-30-2012 08:04 PM

I know I'm an idiot, but I have so much fun! I've ridden a KLR 650 to an Enduro and finished long course twice. Different events. I was slow but I had a blast. At the last one I had a nice fun 100 mile mostly dirt road trip to the event, camped, and even got lucky and hitched a ride home. I was prepared to ride home after the race but I didn't turn down a ride in a heated truck! I used to hillclimb on a KZ 650. I just do weird stuff. I have this old KDX in pretty good shape except for the motor and I want to do something different with it. Not going to race it, maybe ride it in some AHRMA events, maybe an ADV ride or two, or just play on the street. I know it's gonna suck, but it's an 82 KDX, it would suck if kept stock, or if I put in a new enduro motor. Drum brakes, funky ergos, crappy suspension no matter what I do to it. If it was really nice, ran, had good plastic, etc I'd just leave it stock but it's just rough enough that I don't want to restore it, and not rare enough to even get an even return on any investment, so why not do something different? No one else will have one. I'd like to use something with e start though due to a bum right leg and foot. I can kickstart bikes but it sure does hurt starting a big motor.

I will probably end up looking for an XR 650 L motor or something like that, but if I found a really good deal on something stranger, like an RD, I'd try using it. Another thought has been a Kawi EX 500 motor. It would still be funky but more practical than an RD motor. Or maybe an old air cooled twin 4 stroker from any manufacturer? I will likely use whatever motor I can find cheap that runs good. I prefer to stay with air cooled just for nostalgia, but if I use a big 4 stroke it'll have to be e start.

Thing is, this old bike has a huge frame. It's different and quite a bit bigger all over than a KDX 200 of the same year. Not even exactly the same as the MX frame from 82. It looks to me like they planned to build a frame that could hold a big 4 stroke motor. Kawi had a 4 stroke off roader back then, so maybe the plan was to make one frame for both? If you saw it in person you'd realize what I mean. Even pics wouldn't really show it, but the old 2 stroke motor is pretty big and there is a ton of room all around it. I even have it figured out how I can use a modern KTM linkless shock if I decide to, it has a blown Uni-trak shock now, which can be rebuilt but not cheaply. The old Uni-traks were'nt all that good until about 84 so why mess with it? I might even use 2 old school long travel shocks just to make it look even older. I have some from an 84 Husky WR 400 Ohlins that would be pretty cool.

I saw a bumper sticker that said: YBNormal? That should be my personalized license plate.

SOS 12-15-2012 11:30 PM

I like it
I say go ahead and build it. :clap It makes good use of an old frame that will most likely never be used again and it can't hurt to get something new out there. I have a similar project going and most of the guys around my shop don't get it, but it is fun to build and I think it will be a blast to ride.

1979 XS650 Special:

1987 YZ125:

And mixing the 2 together:

Shocktower 12-16-2012 09:16 PM

Find a KTM 2 stroke motor, it wil suite your fantasy

UngaWunga 12-17-2012 07:52 AM

I've seen the opposite, a more modern single cylinder 2stroke engine in a RD frame. Works well. A KTM 360exc motor would be neat in a RD or RZ frame.

Whale Rider 12-17-2012 03:48 PM

Have a look at this Post 109 & 206 & 251


tHEtREV 12-19-2012 04:47 PM

Or see this thread for how that bike came about.

Whale Rider 12-20-2012 11:03 PM


Originally Posted by tHEtREV (Post 20287582)
Or see this thread for how that bike came about.

Trev good build. What did it go like? I assumed it had been made for the scrap heap challenge.
Did the TDR250 ever make it to aussie?

tHEtREV 12-22-2012 03:37 AM

Every now and then a TDR does pop up for sale, but they are pretty rare.

The RZ beast thingy went surprisingly well, but all the power was in the upper rev range, and it was just going to fast before it started being very responsive.

The seating position was terrible and it would have taken to much work to fix.

Fun little project, but really unusable as a dirt bike, but it would have been great on gravel roads...:D

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