Atc250es engine/rear diff into Atc250sx frame?

[ShaftDrive225dx]

I searched the old threads but couldn't find the answer, I have 85 atc bigred 250es that I got for free from a friend. The frame was in rough shape and missing all the plastics! The bike runs very well; I got my hands on a 85 Atc250sx frame and front end, well my 250es engine/differential, swap right over?


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[ShaftDrive225dx]

Here's a pic of what she's like so far, I just don't like the 2 piece fender option for the big red! I like the sportier look of the sx


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[dustrunner]

does you sx have the swing arm on it ? if so take your rear diff. off the big red and bolt it in and everything should be fine..

[ShaftDrive225dx]

does you sx have the swing arm on it ? if so take your rear diff. off the big red and bolt it in and everything should be fine..

I don't it's just the frame; Is the swing arm different than the big red? It's an 85 sx frame as well...


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[Dirtcrasher]

There are year and models that shared a swinger or same piece, but my record keeping records are amiss.

ES is just an SX motor with electric start, that's enough to know it's swaps into another models cradle....

[fabiodriven]

There are year and models that shared a swinger or same piece, but my record keeping records are amiss.

ES is just an SX motor with electric start, that's enough to know it's swaps into another models cradle....

[fabiodriven]

Engines are identical. Direct swap, yes.

[ShaftDrive225dx]

Engines are identical. Direct swap, yes.

Thankyou, for your response lol I didn't know exactly how to respond to the comment before yours! I was a little lost I seen the threads speaking on just the engine swap; but my question is will my swing arm/differential from the es bolt right up and work on sx frame along with es engine?


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[fabiodriven]

The swing arms are interchangeable but the ES has lower (higher numerically) gears than the SX to make up for the 25" tires. So SX rear is your highway gears, ES rear are your tractor gears.

[ShaftDrive225dx]

The swing arms are interchangeable but the ES has lower (higher numerically) gears than the SX to make up for the 25" tires. So SX rear is your highway gears, ES rear are your tractor gears.

Ok sweet thank you very much for your help tractor gears are good with me!


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[Name Brand]

I don't belive the swingarms will swap over. The SX has inboard pivots to meet the frame and I really think the ES pivots are outboard.

The engines are dimensionally the same and will swap between frames but the gearing in the transmission is different. ES has some lower gears. I use to have a little chart that showed this but can't find it now.

Since all your parts are '85, I would use the ES engine in the SX frame with SX swingarm. The ES rear diff had lower gears also. You could use either but I'd stick with the SX rear diff to keep the speed up. You'd have a torquey machine with the 22" tires. It would be geared really low with the ES diff and would need a 25" or so tire. Course that large won't likely fit a stock swingarm.

There's a link by the SX in my signature to make the gears in your head turn more. My SX; SX engine, TRX250 swingarm and rear diff with 25" tires.

[ShaftDrive225dx]

I don't belive the swingarms will swap over. The SX has inboard pivots to meet the frame and I really think the ES pivots are outboard.

The engines are dimensionally the same and will swap between frames but the gearing in the transmission is different. ES has some lower gears. I use to have a little chart that showed this but can't find it now.

Since all your parts are '85, I would use the ES engine in the SX frame with SX swingarm. The ES rear diff had lower gears also. You could use either but I'd stick with the SX rear diff to keep the speed up. You'd have a torquey machine with the 22" tires. It would be geared really low with the ES diff and would need a 25" or so tire. Course that large won't likely fit a stock swingarm.

There's a link by the SX in my signature to make the gears in your head turn more. My SX; SX engine, TRX250 swingarm and rear diff with 25" tires.

Wow! Dang a I was hoping it would; but sounds like I better look into a sx swing arm... Thankyou for the help!


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[fabiodriven]

I apologize if I was mistaken! Thought I knew all of that for fact...

[fabiodriven]

Engines are identical. Direct swap, yes.

[Dirtcrasher]

Hey , I may be just like the others. I'm so far away from the SX/ES, but I use to know that model very well.....

Your ES transmission is also a bit different than the 250SX, but yes, it bolts in.

As far as the right angle gearbox output, I'm not sure if it's exactly the same (I gave away my ES motor just a mere week ago).

And the swingarm, take a look on EBAY, pictures of the Big Red swinger appear to be far different than the 85 or 86/87 250SX.

Sometimes these guys can't get an answer at all which is why I chose to say "something", although not very informative at this point..... But I digress, I can't recall all of it but I do keep records in a book (which is buried somewhere), but I can't find it at the moment.

Anyhow, as I said along with others, the 250ES (although it does have some differences) does fit right into the SX cradle. But, I don't think the Big Red swingarms fit. Search for more posts, they are here at 3WW somewhere....

I am positive there is a thread somewhere about these swaps. I recall an upgraded 300cc motor that has a few changes that need to be done to get it all together.

As soon as I can find a 30' long shipping container, I can get back into all of it. My 20' x 16' shop can only do so much; Which is why some ATC's are in my basement.

Anyhoo, keep looking and posting, the answer is here at 3WW somewhere and I bet Ryan Dailey knows exactly whats up. I'm not sure what his board name is, but I will figure it out and try to send you in the right direction.

The sad frog says it all, pretty accurate picture.....