honda 250sx engine change

[191145guy]

does the honda big red 250 engine fit a 250sx exactly

[350for350]

I'm no expert on this, but I believe that they do.

[fabiodriven]

I think they do as well. There's a difference in the final drive gearing I think, but that's in the rear end. I think it's a direct swap but I'm not positive.

[191145guy]

Is 200 for a running engine a good deal

[fabiodriven]

Tough to say without being there but generally speaking, yes.

[ps2fixer]

Just wanted to set things right, both the 250es and 250sx internal transmissions AND the rear axle gear ratio are different. Most of the gear ratio change is in the engine. Both have the same final gear ratio (engine rpm vs tire rpm), atleast from what I've read here I've never did the math to validate, but the 250sx came with 22in tires and the 250es came with 25in tires.

Besides the gear ratio, I know the engine psychically interchanges in the frame just fine. I'm not 100% sure if the engine connectors are exactly the same, but I suspect they are since I've never heard of anyone swapping the harness with the engine.

$200 for the engine seems pretty reasonable to me assuming it's a strong runner, not a smoker. Carb and starter would be a nice bonus since most engines are sold without them on say ebay.

Basically, 250sx in an es frame will give you a bit higher gearing, as long as you're not hauling big loads with it and such, it probably won't be super noticeable. The rear axle is only like 1 ring gear tooth different. My cousin's 250sx has a 250es rear diff and his machine performs about the same as my stock one. We both top out very similar max speeds on gravel roads too. My sx goes 52mph based on a Honda Rincon speedometer.

Here's the gear ratios to compare from the service manuals. Looks like I'm off on the 1 tooth difference thing, rear diffs are a bit over 10% off from each other. Engine gear ratios (I picked 4th or highest gear) is around 7% difference.

ATC250SX
https://i.gyazo.com/fed19d1963584e9d8a017a45d8f05fb9.png

ATC250ES
https://i.gyazo.com/491f5bff3d0f7a4cb10ca454ea670c6d.png

[fabiodriven]

I had that rattling around in my head but I wasn't sure. Thanks for clarifying.

[ps2fixer]

Not a problem, I like posting values from the service manuals instead of trying to remember things, my memory isn't perfect and the manuals don't normally change lol.