I have decided to undertake the 350x to 250x conversion. I purchased a beat-up 350x for $400 and plan on using the engine and the swingarm on the 250x. I have herd that the transplant is fairly easy, but I have a few questions.

1. Should I cut the rear motor mount and replace it with a modified one, or cut the engine mount 1.75 in. and use spacers?
2. What is the best way to handle the oil screw on the head clearing the frame.
3. What is the best way to mount the oil cooler on the 250x?
4. What problems & solutions will I face on using the 350x swingarm on the 250x?

Thanks in advance for any help in these areas. I will post photos and a journal of the modifications when I complete it.

 

I just finished this project. I also updated the suspension to run the 250R a-arms and swingarm. So, I basically have a 250R thats about two inches shorter than a stock 250R frame. There are also some posts back a few months that have a lot of information. There is also an article in the ATV Sport Magazine June 2000 issue that went through the first steps of the motor transplant.
I decided not to do any cutting on the engine itself and made all the modifications to the frame. For the left upper rear motor mount I cut it off and had my dad make a piece that would fit (my dad is a fabricator/welder). We machined a spacer out of aluminum round bar to gap between the right upper rear motor mount and the engine mount. I built the same spacer for the lower front motor mounts.
For the oil screw on the head you can do it one of two ways. Some people just grind on the screw and take like 1/16" to an 1/8" off. I followed the article in ATV sport. I notched the frame and welded in a piece of tubing in the notch to keep the strength of the frame. I like this approach because all I need is a socket/wrench to take out the screw if I needed.
For mounting the oil cooler you have to decide which way you want to route the exhaust system you are using. the only company that makes an exhaust system is Powroll racing. Their pipe comes out and goes around the frame. this is what most people do. They mount the cooler out between the front shocks or up by the fender mounts. I bought a DG exhaust system for the 350X. It only cost me $155 through rocky mountain ATV. Powroll wants $400 for theirs. I took the head pipe and shortened it about 1 1/2" so it goes around the engine and in front of the frame. I then took a piece of flat bar and mounted the cooler in between the frame. in front of the engine. some have cut the oil cooler lines. Put on some High pressure hoses Which allowed the oil cooler to be moved around more freely for mounting.
For the 350X swingarm I am not sure here. I modified the frame to allow the 250R swingarm to be bolted up with the linkage setup. I do know that at Lordmotorsports web page he has done/or is doing the 350X swingarm. I know he can help you out there. He has done this conversion also
If your interested or have any further questions please email me at ttaylor@klune.com. I have pictures of my bike and the modifications that I have done to it. I will be glad to help in any way I can.
Over all the project isn't too bad. The biggest areas people run into are the pipe and oil cooler. Good Luck

 

I'm sorry i can't answer your questions but in ATVsport they took a 350x had it bored over and inded up having a 250x with a 450x engine that was to much for a 250x frame.

 

Ttaylor covered all the goodies for you. I have some pictures of his bike and it is a very nice conversion. I did a couple of things differently on my motor swap and I have pictures of it also. I was hoping to have the pictures that Ttaylor sent me and my own pics on my webpage by now, but I just haven't had the time.

The 350x swingarm almost bolts right in. The only problem spots are that spacers will need to be made on each side of the needle bearings because the swingarm is a little narrower than the original. Also the top shock bushing will have to be replaced. I have had the 350x swingarm installed on my 91 TRX350x for about two months now and I really like it a lot.

Here is the link to my webpage (which really needs to be updated)