Xr500 Topend bolting onto 350x

[cragster]

I remeber reading that a complete xr/xl 500 top end bolts on to the 350x bottom end. Is this true? If so i think im gonna be building me a 500x sometime soon?
Or was i realllly tired when i thought i saw this:beer ?
Thanks! Cragster

[mean350]

dont know if it works but that would be awesome!!!

[cragster]

yeah thats what i was thinkin! i coulda swore i read it though....

[dividebyzero]

I remeber reading that a complete xr/xl 500 top end bolts on to the 350x bottom end. Is this true?
Or was i realllly tired when i thought i saw this:beer ?

Yes,you were really tired.

[cragster]

You think so? So theres no way this will work?
WHat about a 400ex/450r/crf450 etc etc?
Im for real i swear i read it

[dividebyzero]

You think so? So theres no way this will work?
WHat about a 400ex/450r/crf450 etc etc?
Im for real i swear i read it
Give me a minute or 2,gonna send a pm

[Erics350x]

i read on another form it would work but only a couple of years. and the cases had to be modified. it also said that the gain wasnt worth the trouble. it stated that the big bore kit made alot more power.

[Billy Golightly]

It doesnt bolt up, I dismissed this myth a long long time ago. With extensive center case welding and machining yes it might be possible. The heads however do for the most part seem to bolt right in place of each other. THe difference being the rocker cover with the top head stay mount for the XR500 engine is near the front of the engine insteead of the back. It hits and rubs on that backbone of the frame where the airbox tube hooks to. More trouble then its worth IMO

[leprogle]

I was told that the xr 500 headpipe mounts up, however and is BIGGER. and everyone knows bigger is better. He said it made it work a hell of a lot better

[El'Capitan]

what about just swaping the 500XR engine for the 350X engine. Would it be a pretty easy swap?

[erectordale]

I had 1 of these xr500 conversions it was a cobbled mess with all the frame mods it takes too make the 500 fit

[nate b]

i remember reading about that in dirtwheels or something. They did a 500 big bore 350x and It seemed like it was a bolt on mod? of course that was probably 15 years ago when I read that.

[jason 32]

hi i dont know how -because of the cam timing!!! the cam sprockets the same?
maby your camsproket if cylinder fits

[Tecate performance]

its not worth the hassle, a bore kit and cam will get you more power. the only advantage is the 500 head has bigger valves and ports, but thats only an advantage on a bigger cc motor. the top end is oiled internally on the 500 and you have to do some drilling in the 350 cases to make it work. put in a 452 bore kit, cam, and fcr carb and you'll have plenty of power for a 350x.

[mean350]

where do *Edited* get a 452 bore kit, cam, and fcr carb at anyways?

[BigGreenMachine]

www.powroll.com

[dividebyzero]

IF my motor gets done in time for TF,i will shed some more light on this subject ;)

[NOS_350X]

None of the 500 400 600 or 650's woudl be an easy change it woudl be extremely difficult. As for the Headpipe test have shown that the stock pipe flows as good as anything, So in that case bigger isnt going to be any better. I took of a oversized bassani headpipe for a stock 400ex pipe.

[greenhuman]

The head for the conversion is an FT500 head. With a bit of work, the 350X rocker box fits to the FT head and that takes care of the oiling and head mount. Sleeve the 350X cylinder to accept an FT500 92mm big bore piston, a Powroll +6mm stroker with a rod shortened an extra 3mm so you don't have to mod the piston and you get serious HP. Been there, done that. No ammount of of big valves or port work on a 350X head works as well as a stock FT500 head.

[deathman53]

I know some builders used to use a certain type of xr 500 head on 350x's. They said the conersion was well worth it, as the valves are bigger and ports are a better design.

[Tecate performance]

Four Stroke Tech has a 452 bore only kit, along with some smaller sizes. la sleeve used to make a kit for 452cc(they may still have it) too. i used the FST kit and cam with a 41 fcr and powroll exhaust in a 300ex frame and it runs very strong, right there with piped banshees no problem. for the carb, get a fcr kit for the 400ex and it will bolt right up. just use a 300ex manifold as it has a bigger spigot. FST used to do the 500 topend, greenhuman what exactly has to be done to the rocker box to fit?

[greenhuman]

If you sit the 350X rocker box on the FT500 head, you will see most of the rocker box bolt holes line up OK. From what I can remember, it is the front and rear that dont line up. You have to build up with weld along these areas on the FT head , mill or file it level, then drill and tap the new holes. When you first put the rocker box on, it is really easy to see what has to be done.