XR motor in a CRF/CR frame?

[UFS207]

I was wondering if anyone here thinks there would be a market for a bike with a full-on MX frame/suspension/geometery with a big, old-school, aircooled thumper motor from something like an XR400, 500, 600/650 or TTR600? I was looking at some of the new fourstroke offroad bikes and it seems ridiculous that these companies are simply modifying race bikes with mini-F1 motors for use offroad.

Why exactly does a dedicated offroad mount need a 250cc 4-stroke motor that needs 21st century technology and a 12,000 rpm redline to make a decent amount of usable power? I understand the need to form displacement classes for racing purposes and developing new technology but if all joe average (Like me and everyone of the 20+ people I know with a dirtbike!) does with his bike is trail-ride at good clip and run practice laps at the local MX track why bother? The 450 class bikes are nearly too much bike for most people even though they seem to be more durable than the 250's. 30-40 hp is more than most casual offroaders will ever need, admit it! 45+ is just insane on a tight trail.

I think what I would LOVE to see is a something like a modern CRF250R or CR125/250R rolling frame with an old wet-sump XR500R motor from the early 80's crammed in it. That would be the ultimate bike for me and alot of others as well. Handling/suspension of a modern motocross bike with the stump-pulling torque and damn-near indestructibility of an old aircooled XR motor. You could go years on a topend and 10's of thousands of miles as long as you keep fresh oil and filters in them.

I have pretty much made up my mind that my next bike is going to be a home-built frankenstein bike. I would like to try and find an early 90's and up steel MX bike frame and shoehorn an XR/XL 500/600 motor into it. As soon as I get a place of my own with a decent garage I plan on getting started.

Anyways I'm not really ranting, honest....just curious is to how other everyday joe riders feel about the current crop of 4 stroke offroad bikes. I'm also not bashing current owners of CRF250/450X's WR's and such....it is just that these bikes aren't for alot of riders. Also has anyone ever heard of someone building a bike like I describe? I have seen some of the BBR bikes but I'm taking about using an existing production MX frame.

 

[James]

I agree.

See if you can put and XR400 engine in a steel YZ450 Chassis...then tell me how to do it ECONOMICALLY.

BBR did Xr250s, an XR400, and a DRz400 using production CR250 frames...it can/has been done.

The problem with dumping that kind of work and money into a frankenstein bike is that for a LOT less effort, you could buy a new WR450 and have some money left over for rebuilds, valve jobs, and probably a radiator or two.

 

[highmileage]

When Honda puts an XR250 big bore (300???) in a CRF250X chassis, I will be the first in-line to buy one. I would even take a new generation CRF230 big bore (like 10.5:1 251cc with more aggressive cam and carburation) in a CRF250X chassis.

The only true fault of the XR line (ever) was the failure of Honda to do minor motor/performance mods and major chassis/suspension mods, instead of BNG. They would still be rolling out the stealership doors full tilt boogie, if they had given them half the update attention they deserved.

Honestly, tell me that if Honda would have placed a slightly revamped XR250 motor (10.5:1 piston with more aggressive cam, ala Hot Cams Stage 1 or HRC cam, and a proper sized pumper carb) in a CRF250X chassis that they wouldn't be selling like hot cakes, especially since the next best selling bike to the CRF450R is probably the CRF230F. The radiator area could be utilized for aluminum spacers with small dual oil coolers.

Oh Honda...wake up and smell the marketplace.

 

[Okiewan]

especially since the next best selling bike to the CRF450R is probably the CRF230F.

I believe the CRF50 is the #1 selling Honda dirtbike.

How about going the other direction? A CRF250 in an 80 frame? :p

 

[honduki]

I love my hybrid.With 19 hps Im faster than most of the gumby riders with 50 hp on the mx track

 

[kamchuka]

i think my next bike will also be a frankenbike. i know my wifes will be.she loves her crf230, but its too heavy. im on the lookout for a cr85 expert at a reasonable price, and i will tro a xr1,2,whatever in i can find in there. i've seen that excact setup and it was real usable and looked kicka$$. myself i think i will use an older xr400 powerplant and probably use my rm frame.......we'll see. i sure would like to keep all my goodies on that frame though. it probably wont look cool, but trees dont care :nener:

 

[UFS207]

highmileage:

I personally would like to see something a good bit bigger than even a punched out XR250 motor. I was thinking at least in the 400 range. Something that can effortlessly put out 35 or so horse without the need for crazy cam grinds, ultra-high compression or lots of RPM's. Something with that tractor-like torque and featureless/linear powerband that the big XR's are famous for.

james:

If money where no object I'd have no problem dumping the cash for a couple of new WR450's and a whole decade of WR-rebuilds in a project like this.

I feel like I am in a good position to attempt this though, at least from a financial perspective. I'm a machinist and my employer is ultra-cool about us bringing personal stuff in on our off-time. I've made all sorts of oddball stuff in my freetime and we have piles of scrap 6160 aluminum, 304/316 stainless and tons of steel that just gets thrown out anyhow. So....any mounts/spacers/welding I would need would basically cost me nothing more than time.

My only real costs would be acquiring bikes to hack up. I figure I could find a well-used 93-99 or so MX bike with a ratty motor for a few hundred and an old XR/XL for maybe a grand or so. Maybe another 1-1.5K freshening up the motor, suspension and replacing the consumables (tires/sprockets/chain/misc non-engine bearings).

Anyways, I probably shouldn't have thrown the part about wanting to build one in there. I'm not even sure I have the intelligence and/or willpower to actually see a project like this from start to finish. I mainly was wondering why manufacturers don't offer such a bike.

An XR400R was probably the closest anyone got but even a slightly agressive novice will be doing suspension mods on the bike in short order and no matter what you do it will never be as good as a true motocross bike.

 

[James]

If you have the resources and time to do it, then I'd say go for it if that is what you want. If I had a friend in a situation like yourself, we'd be building some frankenbikes. Problem is, I can't weld yet and don't have access to machinery anymore...so I'd have to pay. I had looked into the BBR route back when I had my first XR400 and it cost 10-15 thousand dollars per bike if I remember correctly. I was particularly disappointed in the suspension and fragile frame. Needless to say, XRs aren't entirely "bulletproof" if you ride them hard...the engine is tough but the rest of it could use some improvement. Luckily, BBR had quit offering XR400 conversions at that point and I don't think I could have justified the cost anyway.

Let us know what you come up with.

 

[BadgerMan]

It would be much easier to acquire a YZ/WR250F and install a set of SS valves. An XR400 engine would produce less HP, it would weigh twice as much, and it would not be much more reliable, after the YZF’s valve job.

A hybrid type bike would be a ball to build but I would rather spend my time and money on something like an XR100 engine in a CR85 BW frame. Or, a KLX125 engine in a KX100 frame. Or, a CR500 street legal super motard. Or, a CRF450 powered Odyssey. Or……….

 

[highmileage]

highmileage:

I personally would like to see something a good bit bigger than even a punched out XR250 motor. I was thinking at least in the 400 range. Something that can effortlessly put out 35 or so horse without the need for crazy cam grinds, ultra-high compression or lots of RPM's. Something with that tractor-like torque and featureless/linear powerband that the big XR's are famous for.

I agree that crazy compression or crazy cam grinds have no place in an XR because its changes the very nature of the old school great 4 stk power.

That is why a XR250 motor at 10.5:1 78mm (284cc) and a good cam like the stage 1 is perfect is great being that the stock compression was at 9.0:1 and didn't take advantage of an opportunity. An honest 28-30 hp motor with the right exhaust, like Thunder Alley, and carb.

With the 400, a 426 cc build at 10.5:1, along with a similar cam, and pumper carb is a really good and reliable 35-36 hp motor with excellent torque characteristics. I think it is probably close to a 38 hp motor with a hand made exhaust like a Thunder Alley.

Neither motor needs anything except clean synthetic oil and super pump gas to run with the reliability of an off the floor XR250/400.

Well I guess there is always a XR400 motor in a CRF450 roller project. If you look, you should be able to find a CRF450 roller for around $1000-1200. I saw an 02-03' not to long back that they wanted 1200.00 for. It was actually in very nice condition. I think an 02 roller is probably the best otion because of the less compact and more upright 450 motor of that vintage. I think the key would be to keep the stock shroud configuration with either of 2 options:

1) Oil cooler taking up the width of the rad on one side and a spacer on the other

or

2) preferred for me; spacer and smaller width oil cooler on each side. No frame oil capacity like the XR frame so the oil coolers would take the place of the frame capacity.

 

[kamchuka]

the new 4's produce alot of power, yes, but i just dont think IMHO, they are as reliable. all i would need to do is loose 10-15lbs off my a$$ and the weight issue wouldnt be a prob ;) i think i will look for a claped out 90's cr 125 and go from there. i have a welder and some free time, so im going for it this winter. i had the perfect donor but i eb@yed it to generate some cash for another project :bang:

 

[Vic]

the new 4's produce alot of power, yes, but i just dont think IMHO, they are as reliable.

De-tune them to the power level of the old air cooled motors and they would be more reliable.

 

[xsnrg]

Get a petition going and a list of 'committed' buyers and perhaps Mr Wagoner (sp?) will build one @ Service Honda for you?

 

[junkjeeps]

I've been wanting to combine a 300EX 4-wheeler motor into a current model aluminum framed CR125. You'd have the XR reliability with electric start on a lighter more agile frame with good suspension. I think that would make a nice woods bike.

 

[john stu]

xr400 engine in a crf450 frame .....air cooled no expansion chamber to smash no radators to smash..easy to handle power sounds great to me

 

[Matt Fisher]

I've been wanting to combine a 300EX 4-wheeler motor into a current model aluminum framed CR125. You'd have the XR reliability with electric start on a lighter more agile frame with good suspension. I think that would make a nice woods bike.

Plus it would have reverse! Think of all the jealous looks you'd get backing your bike out of a tight spot...

Actually that motor's a bit of a turd. The valves were undersized even back when it was the TRX250X, and the overall size would make mounting it in a dirtbike frame difficult.

Of course, with the counterbalancer, it would be a very smooth motor.

 

[babalu]

Street Legal?

I've been thinking of doing the same thing. XR motor --> MX chassis --> Baja Designs kit. Does anyone know if I could get plates for a bike like that. I know you can get modern XRs and even CRFs plated but what about a mid-90's CR, KX or YZ frame?

 

[XRpredator]

Get a petition going and a list of 'committed' buyers and perhaps Mr Wagoner (sp?) will build one @ Service Honda for you?

I believe AJ has a few e-start 400 engines out of TRX400s that he uses to build the Service TRX250R machines.

I'd love an e-start XR400 in a CR250 aluminum frame. There are times I miss the ol' Earth Pig XR400 since I swapped it out for my 525EXC.

Until I come to a big hill and twist the throttle, anyway. ;)

 

[john stu]

aj are you seeing this...............

 

[James]

I bought another XR400 after being off of one for 3 years or more. At this point, I'd rather have a 250F in a 250F frame than an XR400. Good bike, but once you get used to riding with some power, it is hard to go back.

 

[2 strokes for life]

I would not mind something like what you guys are talking about. I know that my name says 2 strokes for life but it more so means older style engines. The XR400 in a 250 frame would make a nice hill climber. If you guys have acces to it then do it. I am in the process of making my own creaction in metals works and automitive class. What would go good with a 1992 CR80 frame.

 

[junkjeeps]

I'd love an e-start XR400 in a CR250 aluminum frame.QUOTE]


Put me down for one. Estimate a price so I can start allocating funds!!

 

[cujet]

The air cooled engine is OK as a play bike powerplant. In theory there really is no reason an air cooled mill cannot be as light as a water pumper. Might be down on power by cc but probably not down on power too much by weight. Otherwise the XR motor should be a good choice.

One other way to look at a project like this is to modify a Yam WR or CRFX 250 to achieve the power curve you desire. A big bore'd and stroked two fifty with a proper exhaust could be made to behave in a similar manner.

Chris

 

[Matt Fisher]

I think Yamaha is the only one with most of the pieces still in production. WR250 chassis, TTR250 motor with a larger crank and cylinder to make around 350-400cc's; use the WR's FCR carb. Add an oil cooler to one side of the tank, enlarge the tank on the other side for more capacity. There's an air cooled medium+ displacement bike with good suspension, easy to build, maintain, and it'd still have 6 gears.

 

[Rich Rohrich]

I think Yamaha is the only one with most of the pieces still in production. WR250 chassis, TTR250 motor with a larger crank and cylinder to make around 350-400cc's; use the WR's FCR carb. Add an oil cooler to one side of the tank, enlarge the tank on the other side for more capacity. There's an air cooled medium+ displacement bike with good suspension, easy to build, maintain, and it'd still have 6 gears.

The TTR250 cylinder head is horrible and even with lots of work it will never flow enough air to adequately feed an engine that size. A $500 FCR carb won't change that. Cam selection is also fairly poor so you'd end up with a heavy bike fitted with an underpowered engine that stops making power way too early.

As cujet pointed out, building a WR290F or a WR305F is relatively cheap these days with the availability of new cast cylinders from Athena (290) and stroker cranks from Hot Cranks. You wouldn't have the simplicity of air cooling, but in all other respects you would have a vastly superior bike.