250R 300EX or 400EX Conversion???

[Merge_88]

I have an 86' 200X, 85' 350X, and now an 85' 250R. After riding the 200X and 350X, I love four strokes for trail riding and lugging up hills, but now the R has me spoiled with it's handling, braking, and suspension. I 've been kicking around the idea of finding another 85/86 250R rolling chassis and putting in a 300EX or 400EX (electric start and reverse) engine for possibly the ultimate trail trike. I was wondering if anyone has something similar to this or possibly this exact swap? Maybe it's just me, but I think it would make one helluva trail machine. Originally I thought this would work on my 200X until I rode the 250R! To me the 250R is like a cross between the 200X and 350X when it comes to size, it seems to fit me the best. What are your thoughts, tips, etc. on this conversion?

[RedRider_AK]

The biggest problem with putting a thumper engine into a 250R chassis is the engine size. It has to be an exceedingly small 4-stroke engine to fit in the frame without extensive modifications.

[super90]

Hows that? People have been putting 450 engines in there?

[Merge_88]

I have been using the search quite a bit and I have found that the engine cradle needs to be made taller to fit the 450R engine. I dint find any other thumper engine that has been converted though. Im going to line up my 96' 300EX and 85'250R and start measuring.

[SYKO]

Hows that? People have been putting 450 engines in there?


just 250Rfan has, but he completly modded the frame for this, most of the other 450 conversions have been in 350x chassis or a tri-z, wich becouse of the design can accomadate a 450 easier

[RedRider_AK]

Syko explained it pretty well.

[Merge_88]

I was reading about how the larger frames of the 350X work well with the thumper engines BUT the 350X I have just feels so darn bulky compared to my 85' R. I am trying get the best of both worlds for a trail machine.

[SYKO]

you will have to do something simialar to 250rfans 450 conversion, with is quite an undertaking, but I guess you wouldnt have to go to that extent that he did.

[Merge_88]

I'm not afraid to tackle the frame work, I just want to be sure that I will have a better machine than a 400EX engine in a 350X chassis. (which I feel I will have)

Looks like the 200X and 350X will be looking for new homes so I can fund the build of this bike.

[RedRider_AK]

Why don't you put a big-bore 250R engine into it, with some carb and exhaust work to make the power better for low-end.

Reed spacers, gnarly/bottom end pipe, and a big bore engine will all help provide plenty of torque.

[Aka_am]

What would a big bore be compared to? you still could put could you? I have riden a 400ex and I want something faster of course, but with that same torquey feeling.

Can a 250 bigbore do that? and what do you suggest

[Dirtcrasher]

BRAPP did it too kids......

My goal oneday is to build a completely nasty 86 200X motor and drop it in a 250R chassis. DEATHMAN has mentioned it also. The lightweight motor with 6 speeds and gobs of power would be NASTY in an 86 250R chassis.....

I am looking for an 86 chassis if anyone has one........

[saleen_n_around]

Keep me in mind for the 200x stuff when you go to sell.

[Trike Dude]

Part of the reason your R feels so nimble in comparision is due to the fact the engine weighs half as much as the X engine. Put a 450 or what ever in there and your weight will increase dramatically and make the R frame seem "clunky" as well.

Just my $.02

[SeaBass8]

I think the idea of putting an 86 200x motor in an 85/6 250r chassis is very interesting. Kinda the best of both worlds for the trails.

Has anyone ever done an auto-r? That would be a cool trail bike too but not sure if any of the auto motors would have enough power/speed. What motor would you use?

[300rman]

i agree. the R motor is fairly light compared to a 300 04 400ex engine.......
a 2 stroke will never have low-end torque like a thumper, but after you get used to the 2 stroke powerband, you will be able to move out on the trails faster than with a thumper.

[200x Basket]

i would rework the 350x front suspension and then mate the 250r pro link rear suspension to the 350x chassis before i tried to put a 400ex engine in a 250r frame.

basically make the 350x suspension mock the 250r set up.

[The Goat]

wait a minute...the difference in the 200x engine and the 350x engine weightwise is like 18 pounds or so.

[BigGreenMachine]

Say it with me, KTM 300cc EXC. Wide ratio transmission and a powerful twostroke.

In reality the liquid R motor is more then capable of woods riding. Barry Hawk proved this to no end.