Motor swap suggestions-whats best?

[dawnchris]

Got a complete LSR 250R, Axis, etc. I'de like a newer 4 stroke quad built like my 250R, but don't want to spend $15-20000 to do so. I'm thinking of doing a motor swap. I'de want something elec. start, so the CRF motor is kinda out of the pic. I'm thinking KTM520/525 or WR450 or possibly YZF motor if I could find one. Any suggestions as to what would work best in this chassis? Any and all input is appreciated, Thanks-CHRIS

[TC426EX]

I would do the CRF as my first choice, but you said you didnt want to do that. My second choice would be the YFZ motor since it is probably the second most popular swap for that bike behind the CRF. I dont know what kind of riding or racing you do. If you race I would do one of those two. If you just screw around and ride for fun I would go with the KTM and talk to Walsh Racecraft on how to do it. Mike Walsh is currently running that motor in the open class. The WR motor would be good too for play riding but its gearing would probably be a little too tall for racing (hence why its's called WR.......Wide Ratio tranny). You shouldnt have a problem with the YFZ motor. I dont know if you would have an easy time finding one, but I KNOW you could find a YFZ426 motor pretty easy and have it bored. The motor is the same shape and size as far as I know just with a larger bore and people have been doing yz426 conversions for YEARS now so I know it would work. I still say get the CRF......

[roostin_dale]

the KTM would probably take alot more work..

I would try a YZF or a CRF if i were to do something like that...

[dawnchris]

The CRF motor isn't out of the question, it's just that my first choice would be an elec. start motor. I race desert in So. Cal. and Nevada. If I HAD to go with a kickstart motor, then the CRF would be first choice. Is this a "fairly" straight forward swap? Since the bike's already watercooled, I would think that it wouldn't be overly difficult. I'm wondering about F to R balance, going with the heavier motor.

[dawnchris]

One more thing.....Is this a worthwhile project? I know that replacing a 400EX motor with a CRF motor would bring about big gains without much weight penalty, but what about replacing a 250R motor? I've got 2 motors now, a 265, and 310. I don't know that I'de gain much max power, though I know I'de gain alot of "grunt". I could sell both motors for what a 4 stroke would cost, and I'm thinking it may be more reliable over time. INPUT??

[pnut420]

Hey I see you are in Cali, I am currently doing a YZ conversion and got a good deal on it. If you are going to do desert racing the YZ would actually be a good motor to do, high Revs and pulls to about 11,600 RPM.

One average a CRF motor is going to cost about $600 more than the YZ motor.

I know someone that is selling a PRP frame, +1 1/4 swingarm, flip top subframe, PRP LT a-arms and a LT PEP rear shock with YZ426 linkage for about $3500

[dawnchris]

Definetly don't want to start with another quad.
Whats with the "YZ linkage"? You don't have to change anything on the rear suspension to do the motor swap do you?

[K_Fulk]

Get some measure ments to make sure the motors will fit in your frame. Remember the 4 strokes are taller the nthe 2 strokers.
The good is if you get another after market frame most of them use 250r parts as compared to 400ex.

[dawnchris]

...good point. Anybody out there put a CRF/YZF motor into a 250R chassis?

[pnut420]

Originally posted by dawnchris
...good point. Anybody out there put a CRF/YZF motor into a 250R chassis?

I havent, but if you need I have a frame sitting outside in my garage setup for a Yz426, I would take some measurements and pics if you would like.

The cool thing is thay you have the radiator already. Also there are several companies that have done conversions on EX frames to get the CRF and YZ to work, so Im sure they cold make some mounts for the R frame.

[dawnchris]

I'm sure I could cut off the 250R mounts, and fab new 4 stroke mounts, and weld them on. I'm just concerned with weight bias and such. I'de hate to go to all the trouble, and have the bike end up handling like a turd. I have a 400ex as well, that I'm going to take some comparative measurements from, since I know that the YFZ and CRF motors fit in that bike. I might like some pics of your frame pnut420, I'll let you know, Thanks-CHRIS

[pnut420]

Originally posted by dawnchris
I'm sure I could cut off the 250R mounts, and fab new 4 stroke mounts, and weld them on. I'm just concerned with weight bias and such. I'de hate to go to all the trouble, and have the bike end up handling like a turd. I have a 400ex as well, that I'm going to take some comparative measurements from, since I know that the YFZ and CRF motors fit in that bike. I might like some pics of your frame pnut420, I'll let you know, Thanks-CHRIS `
I think it might work better to use the 400ex frame.

As far as weight and it handling like a turd, I could weigh my engine when it gets here, but it shouldnt weigh a whole lot motre than a 250r motor.

Also CRF's and YZ's are lighter than the EX motor and they handle great in the EX chasis.

I would just rather waste a ex than an R. :D

[R3Concepts]

A crf motor weighs like 2 lbs more than a 250r motor. Also for a YZF motor I almost positive you have to cut the top rails for the motor so fit, If I remember right its quite a bit taller then a crf motor. I dont know if the rails on LSR mx frame are the same as a stock chassis. Make sure you do your homework on this becuase there are things you have to take into consideration like motor angle, rear motor/swingarm pickups and mounts. I think the angle used on most crf motors is like 17 degrees. Also a yz426 motor will not pick up the swingarm bolt so it would flex alot without the motor acting as a big spacer.

[dawnchris]

Thats the kind of info I'm looking for. Especially stuff like motor angle and such. 250R chassis don't use the motor to mount the swingarm to. You can pull the motor without touching the swingarm. Thats part of my concern, though when you buy a LSR CRF chassis, I don't believe it uses the motor as a mount either.
As far as using the 400EX, won't happen-it's the wifes bike, I'm not allowed to mess with it.

[pnut420]

Originally posted by dawnchris
Thats the kind of info I'm looking for. Especially stuff like motor angle and such. 250R chassis don't use the motor to mount the swingarm to. You can pull the motor without touching the swingarm. Thats part of my concern, though when you buy a LSR CRF chassis, I don't believe it uses the motor as a mount either.
As far as using the 400EX, won't happen-it's the wifes bike, I'm not allowed to mess with it.

Not sure about the CRF, but my LSR YZ frame uses the swingarm bolt and is a true 4 point setup. I will go ahead and take a pic and show you how it is....

[pnut420]

Im trying to get those pics up, might take awhile

[K_Fulk]

here are some for pnut.
http://www.imagestation.com/picture/sraid118/p4448db4c2f3ff396b4b03cdd23f50bb8/f8911ca6.jpg http://www.imagestation.com/picture/sraid118/p2efc968ef16406dad7ba6ace8fdf6b2f/f8911db9.jpg http://www.imagestation.com/picture/sraid118/p8d2913589e3423f1f9a38585baec1556/f8911ee3.jpg http://www.imagestation.com/picture/sraid118/pe47e67cd8ecdbb46f0e4cb695c681877/f8912162.jpg http://www.imagestation.com/picture/sraid118/p5f949e4c41e3b9d6f64bf6b36b681139/f891220a.jpg http://www.imagestation.com/picture/sraid118/p9ebfb8a8fc97df1c7e77e3f8dfa42367/f89122da.jpg

[airheadedduner]

If you are dessert racing you will have to come up with some sort of oil tank setup for the CRF if possible.

[pnut420]

Originally posted by airheadedduner
If you are dessert racing you will have to come up with some sort of oil tank setup for the CRF if possible.

Thats why Im thinking the YZ might be the way to go. It just uses a stock 400ex oil tank, alse I dont think the YZ is much taller than a 250r motor, but I could be wrong

[airheadedduner]

I will measure one at work...............if I remember:p

[pnut420]

Ok the YZ motor is alot taller. I really think alot of work would need to be done to make it possible. For $1500 you can get a brand new Arens frame and most the 250r stuff should bolt up. I have a LSR and Im so happy with the way everything bolts up, they did a great job, I also like how the footpegs sit back another 3 inches or so.