300ex crank case

I don't suppose that any could tell me if there is a difference in a 250X and a 300EX crank case??? My 300 has a crack in the case, not bad just a minor oil leak, and I found a good deal on a 250X case but I don't want to buy it if I can't use it. As far as I know, the only diff. is the electric start but I think that goes in the out side case....What is the difference in these tow motors anyway??? Bore? Stroke?? Head???Compression????Valve sive????Any thoughts anyone??? Need to find out today hopefully. Thanx's a mill!!:devil

[330EXman]

hey man i can tell you that the bottom end and everything else except the Piston bore is exactly the same.

you can put a 300ex head on a 250x bottom end. or vice versa

[330EXman]

o ya i forgot to tell you that you will only have kick start but that will work cause the fly wheel the thing the starter turns is all hooked up to the timing chain any way so that will all work.

the only difference is the bore. the cam,valves, valve springs and everything is all the same.

later man Jay

[DEAL]

The 300ex and 250x bottom end are the same , so are the piston and rings, the only diffrence is the 300 has a longer stroke , which means it has a diffrent crank.

Thanx's for the info.....I did notice that the crank cases for a 250X and a 300EX have different part#'s. I'm hoping thats just to identify diff. years. We'll see though. What is everyone's suggestion to getting the biggest bang for your buck out af a 300EX? Minus the pipe and air box lid hole,and aircleaner swap. Is it worth the time and money to get a 330 kit? Is it possible for the 300(with some hot rod mods) to keep up with 400ex's and Raptors? Or should I just get another bike? I mean, I already have a 250R swingarm and front and rear suspension....all I need is some H.P. to go with it. I need to look into the Mickey Dunlop stuff and anyother 4 stroke tuners out there.
Again, thanx's for the info.
Ted :devil

[330EXman]

hey man LRD has some serious mods to help you out. i have just made a good thought on getting a four stroke tech 390cc stroker kit. this will wizz by all those wimppy raptors. lol

umm as for the 250x and 300ex the stroke has nothing to do with the difference. umm hhhmmmmm 250x means 250cc and 300ex means 300cc. i dont know how this isnt a difference i mean the 250x piston bore size is NOT the same size

any way there is the 330cc kit if you dont have the bug bucks this will help you keep up with slight modded 400exs but you might wanna get a good set up with port job and stuff.

later man

here's a list of builders,

four stroke tech
sparks racing
TC racing
CT racing
LRD performance
Denton racing
and some others
I WOULD GO WITH ONE OF THE ABOVE THEY HAVE SOME HIGH QUALITY PRODUCTS

Thanx's for the info on the aftermarket stuff 330EXman, I'll have to check them all out. But I still need to get a positive answer on the difference between the two motors though. Everyone had something different to say about it. Sounds like everyone is just guessing. I know a 250X is 250cc, approximatly and the 300EX is only like 290 something.... But is that determined by the size of the pistion? The size and the distance the piston travles in the sleave(hence a stroker motor)????
I still find it hard to believe that with any mod's that a 300 could possible even come close to a Raptor, 400EX, SeaDoo thingiemobob, or that new Suzuki 400.....Guess I'd have to see it in person.... Thanx's again everyone.:devil
Ted

:devil
The 300ex and 250x have the same bore diameter(74mm). The 250ex has a smaller bore (68.5mm).

Bore doesn't have to be smaller to have smaller CC's. Only stroke.

By the way CC's = Pi x R^2 x Stroke
eg. 300ex = 281.56cc = 3.14 x 37^2 x 65.5

R = One Half Bore Size
Pi = 3.14

You do the math.:D

Does anyone know the websites to any of the metioned aftermarket suppliers listed in this post? I'm looking for some info on kits for the 300EX.....330....or bigger....gotta keep up with the new machines...Thanx's:devil
Ted

[Dustybear300ex]

so if the motors are the same, couldn't i take the right side crank case cover from a 250x and put it on my 300ex and use the kick start instead of having electric start? that would be very nice and would loose weight also. thanks

[redrider ex]

they are close but not the same the cranks are different and the fly wheels and the fly wheel side of the case is made different on the inside.

[250xman]

ok if you need the left side case they arent hte same. the right one will fit but yes you will have a kicker if you put the gear and rachet in too. the bore on a 250X and a 300 ARE i repeat ARE the same. there are only 3 things that arnt the same on both, crank, flywheel, and left side case cover. the right will fit but you either have to put in a kicker or make a plug. hope i answerd all your ?'s

[danney f]

The oil pump is differant between the 2 so I don't think the 2 will match. Also the only thing that make a 300ex(284cc's) is the stroke of the crank, both of the jugs are 74mm bores.

[fender]

Ok, I've just acquired a 87 250X. At least I know this by the sticker on the frame. I looked up the serial number on the engine and it matched the motor that comes with the 250x only and not the 300ex according to some chart on the internet. Stamped right on the side of the case is '281cc'. The most confusing part in this is that it is electric start. I keep hearing that the 250x is supposed to be kick start. The engine was supposedly replaced however, but that doesn't change the fact that the engine serial numbers match that of a 250X. I seriously doubt it was converted since that would be very involved and the guy I bought it from just wasn't that bright. He actually told me it was a 300ex. I've just started to get into ATV's and I know what a 300ex looks like and I saw the 281cc on the engine so I thought it was too. I didn't notice the 250x sticker on the frame until I had the seat off back at the shop. I'm just trying to figure out the real difference between my quad and a 300ex other than the name and the engine serial code.

[bansheemorphine]

you had asked about weather you should buy a 400ex or something bigger or modify your bike well i was stuck with the same problem a while back and i decided to go with a 400ex tht was already somewhat modifyed and personally altho i love my 400 i kindof regret making that choice because simply you get more satisfaction out of beating someone when you are riding a way smaller quad and i have read that a 330ex will indeed beat a 400ex and keep up with a z you can find info on the big bore kits at www.fourstroketech.net if i were u i would keep your 300ex and get a 390 big bore kit as for putitng the 250x crank case cover onto your 300 i can't help yah there i know nothing of the 250x

[CDCHONDAS]

For a fact, the difference in displacement comes from a longer stroke on the 300EX than the 250X also the piston is different to accomodate this, the bore is the same, for example 330 kits use the same sleeve on either one, as far as someone saying the starter is run by the cam chain I have no idea, its driven by a set of gears to a one-way clutch bolted to the flywheel, i know the left case will be different to accomodate this but take note that you need to have the two bolt holes to hold the starter down in the right side case which i think (not postitive at the moment) that there are bosses on the case that could be drilled and tapped, i have never tryed to put the two together but I will tell you that unless your crack is really bad it can be welded some may not like to hear that but we have had a pile of them welded, a boy I used to work with does them for me, tig welded, he says they weld easy and i've never had one come back, find a good repair shop or someone good with a tig and it can be done normally alot cheaper than a new case and doesnt look goobered up, by the way if you want to weld it and cant find anyone to do it let me know