250x and 300ex piston...interchangable?

[Blue250X]

Alright, I have always thought that you could not interchange the two because of the pin or something? But my freind takes his 250x to a local mechanic and he tells him that the pistons do interchange, I'm flabbergasted. And he even said he out a 300 piston in the 250. So now I am about crapping out my mouth, I am still in disbelief. Has anyone tryed, actually had the 300 piston in their hand and and tryed to put it in but it didn't work? Thanks.

[400eXr1d3rZ]

The only thing different between the 300ex and 250x is kickstart, some cosmetic stuff and the 300ex has a longer stroke. I don't see why it wouldn't work.

[Blue250X]

Originally posted by 400eXr1d3rZ
The only thing different between the 300ex and 250x is kickstart, some cosmetic stuff and the 300ex has a longer stroke. I don't see why it wouldn't work.

That's what also crossed my mind, but wouldn't the pin have to be in a different location?

[Kickstarts-suck]

yea and when you buy big bore kits they only sell one

not one for 300ex and one for 250x:confused:

maybe just wisecos cant be interchanged ?

[bwamos]

Longer stroke on the 300ex. Shorter Rod.

Same wristpin location for both.

[Blue250X]

Originally posted by bwamos
Longer stroke on the 300ex. Shorter Rod.

Same wristpin location for both.

So, are you saying that they do interchange?

[bwamos]

Honestly, I couldn't tell you with certianty. But, I can't think of a reason why not.

[250X_project]

wtf.....I want an answer to this too....if you can interchange them I'm going to look like an idiot for telling people that you can't since that is what I have heard....anyone want to give me an old 300 piston so I can find out? lol

Also if you put a 12:1 250X piston in a 300EX what would it be, 13?...:devil:

[250X_project]

After some, but not all research, I have found that the 250X and 300EX Wiseco pistons have different part #'s.
The more I think about it the more I doubt it...with the longer stroke on the 300EX must have the pin located higher on the piston or the piston would go to far into the combustion chamber....

I also found that I guess it is possible with some 250X parts and case machining you can put a kicker on the 300EX...also one person claimed to have put a 300EX crank into a 250X bottom end.:confused: ...this was all just from an old past back in '02......

Has anyone actually done any of these 3 swaps?

[Blue250X]

LOL, this is really starting to make me wonder... I might be helping a freind rebuild his 300ex around x-mas, and I have an old 250x piston in my bedroom from when i rebuilt my 250, I might just try to fit it in.

[250X_project]

Do it. I think it will probably fit the rod but go too far up the cyl. but who knows...

[250X_project]

Now I'm wondering..can you use a stock piston in a stroker then, or does it not come up farther with the shorter rod? on my 12.7stroker the rings line up with the cases at BDC but top seems the same as stock.....

[Blue250X]

Originally posted by 250X_project
Do it. I think it will probably fit the rod but go too far up the cyl. but who knows...

I def want to, just so i can come on here and tell everyone for sure if it works or not, ya kno?

[250X_project]

FN Right. I want to know.

[bwamos]

Originally posted by 250X_project
Also if you put a 12:1 250X piston in a 300EX what would it be, 13?...:devil:

It would be 13.7:1 static compression.

[elementryder]

no they dont inter change my friend (atvracer9m) tried to and it dosent work i forget why

[250X_project]

I knew it! lol get your friend in here. :D
Bwamos-what would make the compression 11:1 with a 70mm stroke, when stoke is 57.3mm? I believe 10.5, because on the Powroll big bore kit is labeled 10.5:1 by itself and 11 w/ the +12.7mm stroker combo. Thanks!

[elementryder]

ok ill see if i can

[Ripitupfilms]

no they are the same piston theres no difference,, u can swap them

[elementryder]

then its the crank yu cant swap right? shiz i was wrong

[250X_project]

Tell me ALL about this, was it a 250 piston in a 300 or vise verse? What brand? Did you actually run this?? Tell every detail you can think of please.

Doesn't the crank have different bearings? Someone in an old post claimed to have done the swap though:confused:

[dork]

you can't swap the cranks, the bearings are different diameters. the 300ex has a 123mm rod and the 250x is 127mm. since half the stroke difference is 4.1mm then the 300ex rod would need to be 122.9mm. so it looks like they use the same wrist pin height in the piston. but i thought i read they were different. atvracer are you sure they're the same?

[bwamos]

Originally posted by 250X_project
I knew it! lol get your friend in here. :D
Bwamos-what would make the compression 11:1 with a 70mm stroke, when stoke is 57.3mm? I believe 10.5, because on the Powroll big bore kit is labeled 10.5:1 by itself and 11 w/ the +12.7mm stroker combo. Thanks!

I'm sure they just use a shallower dome on the piston for the stroker.

It's a 22% increase in displacement/stroke compressing into the same space. You'd have to have a shallower dome to keep the static compression around 11:1.

Stock bore: you'd have to have a ~9:1 (stock stroke) piston to get 11:1 at a 70mm stroke.

[250X_project]

Yea I talked to an administrator at Powroll who told me the pistons were the same.

bwamos- As far as the compression I have about 65% more displacement with an 86mm piston....Is it possible to achieve 12:1 even with the stock 9.4 compression?

[bwamos]

The very basic math is really simple.

If you have a 74mm piston w/ a 57.3mm stroke at 9:1 your 246.3 cm^3 compressed down to 27.4 cm^3.

Increasing that stroke to 70mm increases the displacement to 300.9 cm^3.

The top of the piston is going to stop in the exact same spot if done correctly, leaving the same final volume. So your 300.9 cm^3 will be compressing down to 27.4 cm^3. 300.9 / 27.4 = 10.98:1 ratio.

This isn't exact.. as I don't account for added volumes.. but the results will be within +/- 2%. Close enough to ballpark without having the motor and doing fluid tests or going into extensive calculations based off of micrometer/caliper measurments..

[250X_project]

I apologize if I am a burden, but I greatly appreciate this.
Does this mean with the now 406cc divided by the same 27.4...as the 9:1 gave, I would then have about 14.8:1?and 7.3:1 (stock) to get the desired 12:1. Is this even possible?

But yet on Powroll they show the 80mm piston as 10.5 w/ stock stroke but 11 with the 70mm...my calculations give me (288/10.5=27.43..352/27.43=12.8:1) ...I must be very lost :confused:

I'm sorry.
Thank you once again.

[bwamos]

Originally posted by 250X_project
I apologize if I am a burden, but I greatly appreciate this.
Does this mean with the now 406cc divided by the same 27.4...as the 9:1 gave, I would then have about 14.8:1?and 7.3:1 (stock) to get the desired 12:1. Is this even possible?

But yet on Powroll they show the 80mm piston as 10.5 w/ stock stroke but 11 with the 70mm...my calculations give me (288/10.5=27.43..352/27.43=12.8:1) ...I must be very lost :confused:

I'm sorry.
Thank you once again.

No. You're correct. The 10.5:1 with an additional 12.7mm stroke and the same piston dome height will add much more compression than an 0.5:1 increase.

But on yours, you have a larger bore, so your compressed area will be larger as well.

If your piston (80mm) is supposed to be 10.5:1 at stock stroke you'd be compressing 287.9cc into 27.4cc (very close to the displacment you'd have with a 300ex w/ 74mm x 65.5mm stroke @ 11:1).

Adding your stroke in you get up to 351.7 cc compressing into 27.4cc. 351.7/27.4 = 12.8:1 compression.

If you want 12:1 take 351.7cc /12 = 29.3cc compressed.
At stock stroke 287.9cc compressed to 29.3cc = 9.8:1 compression.

However, it's easier to jsut order a 12:1 piston at 70mm stroke and let them figure it out.. lol. If you want to run pump you may want 11:1. 12:1 usually requires mixing race fuel in.

[2muchquad]

Dude just put the motor together and worry about the specifics later...:D

[250X_project]

bwamos- That's great info, only my piston is an 86mm :devil: yet I get the same 9.8 for the 12:1. And 11stroked gets me 9stock?

You said "But on yours, you have a larger bore, so your compressed area will be larger as well.", this means since the bore is obviously bigger on the top and bottom both it doesn't need to be formulated in?


2muchquad- I'm gettin' to it....LMAO but I don't want to run 87oct. in a 15:1 (exaggeration) lol...I also need to put reverse back into it, since the last owner of this bottom end removed it, along with the decom. It's a long-term project and I'm okay with that.