[njam22]

i had just noticed that the cylinder head on my 92.250x read 281cc which in the manual says its a 300ex? is this possible to mount the head on a 250x engine? or did the 300ex come in kick start at some point? They guy who traded it to me for my rm125 said it was a 300ex can anyone help thanks...
would this change my bore x stroke, compression and oil capacity?

Also can anyone tell me where i can find all the serial numbers on this?

Thanks:icon_ rasta:

 

[Helmut]

I believe the cylinders are the same, the 300EX just has a longer stroke. They never made a 300EX with a kick starter.

The following is from a 300EX service manual, but the 250X should be the same.

 

[FOXRIDER3361]

Thats weird?????

 

[TRX2fiveO]

Yes the heads are Identical. the rocker covers are different though the 300EX didn't have the decompression lever since it was electric start. but it will work also you would just have to kick it harder. lol

 

[94300ex]

it sounds like someone put a 300ex crank and top end on the 250x bottom end.

 

[TRX2fiveO]

it sounds like someone put a 300ex crank and top end on the 250x bottom end.

Crank will not work it's too wide because the flywheel is set-up for a starter. the 300ex carries the same topend, same piston bore ect. a 300ex head will work on a 250X or vise versa

 

[TRX2fiveO]

your bore and stroke will not change due to you having a 300ex head by the way

 

[Helmut]

Yes, the 250X and 300EX cylinders are exactly the same. The only difference is the 300EX cylinder will say 281cc, but it's still the same size as the 250X cylinder. The longer stroke of the 300EX is what makes the CCs higher, not the cylinder.

 

[FOXRIDER3361]

ok so I have a dumb question the Cubic Centimeters come from the volume of intake for the cylinder right?

 

[TRX2fiveO]

bore x bore x stroke x .7854 = total CCs the 250x is 246 CCs and the 300ex is 282 CCs only because the 250 has a 57.3mm crank and the 300ex has a 65.5mm crank that is the only internal difference aside from the crankcase being a tad wider on the 300 to accomodate the toothed flywheel for the electric start. does that help? they both carry a 74mm piston. to do the above formula the mm have to be converted to centimeters by moving the decimal left one number...for example.....74mm piston is 7.4 so.... 7.4 x 7.4 x 5.73 x .7854 = 246.4 CCs

 

[94300ex]

it sounds like someone put a 300ex crank and top end on the 250x bottom end.

Crank will not work it's too wide because the flywheel is set-up for a starter. the 300ex carries the same topend, same piston bore ect. a 300ex head will work on a 250X or vise versa

man i feel kinda stupid now, i totally forgot that the 250x had a kick start instead of electric lol. sorry guys

 

[87_250ex]

which head runs better on a 250x? are the port sizes the same? i could deal with the hard kicking if the ex head ran better i need more low/midrange power

 

[yamahasucks]

which head runs better on a 250x? are the port sizes the same? i could deal with the hard kicking if the ex head ran better i need more low/midrange power

either one will work the same just like moose said the rocker cover has the compression release is the only difference that will effect it

 

[TRX2fiveO]

the head is totally identical the rocker cover on a 300ex does not have a decompression set-up the indention is there but thats it. the 300 right case cover also has the indention where the 250x kick starter goes...lol

 

[400exbuilt]

yeah i used 300ex motor parts on a 250x but a crank will not fit... i know for sure crank is diff, so piston should be too... but cylinder and head are the same other than decompression lever... moose got it all covered...

 

[TRX2fiveO]

same piston too. also look in the end of your muffler and see if the opening is the size of a quarter. if it is remove the end and take it out. lol I have the same muffler I did it to mine and what a power difference.