300sx questions

[beastybaconman]

I'm planing on trading my 86 rm 250 for a 85 250sx this weekend. The guy selling the sx says it has the head, cam, and piston from a 300ex, a full cobra exhaust, barnett clutch, and a 350x front end. The guy owns a small engine repair shop so I figure it should be a decent running rig. I was just wondering if anyone else has tried the 300 top end conversion and does it really make much of a difference?

[jakep53]

ohh look at the bike in the background it's one of them 2wd rokon's very cool!!

[beastybaconman]

Just picked it up and took her for a spin. She's not perfect but she loves life. The 350x front end is a little weird cause it sits up so high, I can pick up the front end in every gear real easy, and it keeps up with my neighbor's crf 230 no problem. I took a look at the identification tag thing on the front and it says 1/85 on it does that mean it's the first one made in 85 or something? Also there is some fluid leaking out of the top of the forks, anyone know what could be causing this?

[jakep53]

1/85 is the first month of 85

[beastybaconman]

Ok thanks, I figured it was something like that

[jb2wheels]

... Also there is some fluid leaking out of the top of the forks, anyone know what could be causing this?

The bashed schrader valve on the fork cap.

[beastybaconman]

I thought it looked a little rough, I just wanted to make sure it wasnt something else, are those valves pretty easy to replace?

[redsox]

your forks look a bit bent. also, i'm no 350x expert, but i think its supposed to be a leading front axel. i think. not sure. i think your forks are backwards. your wheelbase is weird... any help from someone that knows??

[beastybaconman]

Thanks for mentioning that I looked at some pictures of 350x's and it looks like my forks are on backwards. Thats probably why it's so easy to wheelie

[beastybaconman]

Just turned the forks around rides a lot better, they are bent a little is there any easy way to straighten them up or am I better off just getting new ones?

[Xfile]

Just turned the forks around rides a lot better, they are bent a little is there any easy way to straighten them up or am I better off just getting new ones?
Bring them to a machine shop with a good press...a shop in my area straightens them for $30 a pair.

[beastybaconman]

Alright I'll try one of the machine shops around here, thanks for the reply

[beastybaconman]

I was just messing with my front wheel to get it centered more and I found that the axle bolt has different threads than the threads on the fork. Because of this, where it threads into the fork it's a little beat up. From what I can tell it is the front wheel from a 350x so I don't know why it isn't fitting, anyone know what could be going on? Maybe the previous owners used an axle bolt off a different rig or something?

[YTZ drew]

Just to let you know, a 300ex top end is identical to a 250x top end, except it has 282cc cast into it instead. The 300 gets it extra cc's from the stroke. I actually didn't realize that 300ex tops fit onto 250 Sx cases, but if that's what you have, I think you're still only at 250cc.

[beastybaconman]

I don't know if it is the whole top end off the 300, the way the guy was talking it was just the head and cam but not the cylinder. And if it did have the cylinder off the 300 with the longer stroke wouldn't that make it have less power?

[beastybaconman]

Just found out why my front axle bolt has different threads than the ones in the forks. The forks aren't even from a 350x. On a 350x the axle is on the front and the mounts for the brake caliper are on the back, but the one I have has everything on the front. Can anyone tell me what these forks came off from?

[beastybaconman]

Did a little looking on the internet and it looks like they are 200x forks. What do you guys think would be the easiest thing for me to do? Could I just get a 200x front axle, or am I gonna have to get the whole 200x hub and everything?

[YTZ drew]

You'd only loose power if the 300 jug was taller, and if it was taller by any significant amount, the compression would be so low it probably wouldn't even run. The 300ex cylinder, piston pin height, and head are all identical to the 250x, same bore, and same overall jug height. All the difference in the 300 engine comes from the crank and rod, Honda stroked the crank and shortened the rod to make the original cylinder height work, and keep the overall engine height the same so no frame changes were needed. One neat trick, however, is to put the stock 250X piston in a 300ex, the 250 is domed and the 300 is a flat top. Cheap high compression upgrade!

[beastybaconman]

Did some looking and I found that all 200x forks are 33mm (1.299in) in diameter but I just measured mine and they're 35mm (1.377in). Then I did some more looking and found that 83-84 250r forks are 35mm and look just like the 1st gen 200x forks. So I think I have 2nd gen 250r forks with a 2nd gen 200x or 350x hub. Does anyone know the diameter of the 350x forks?

[rdonald1979]

They are 1.75".

[beastybaconman]

Are you sure? I looked around on some other forums and most of them said that 350x and 83-84 250r forks are both 35mm, so I just ordered a set of 350x forks.

[beastybaconman]

I've seen a lot of people say that the 83-84 250r fork internals in the 350x forks is a good set up, so I figured I'd give it a shot. How hard is it to do this swap and what parts exactly need to be changed?

[beastybaconman]

Just got the 350 forks today, they fit good but and are less bent than the forks I had, but I'm pretty sure they don't have any fluid in them at all. The have some bounce to them if you just push down on the front end, but when I got on they just went down and didn't move until I pulled up the front. Can someone tell me what kind of fluid I should use for them and how much?