1986 250 Big Red Motor in a 1985 250sx Frame?

**almac16** · 01-21-2004, 12:01 PM

Hello,

I am wondering if this is possible or not. Will a 1986 big red motor fit directly into a 1985 250sx? I know the 1985 big red fits perfectly.

Thanks for the insight,

Alex

**atcmatt** · 01-21-2004, 06:05 PM

Yeah i Think it will fit, but isnt the gearing in the 250es motor lower than that of the 250sx? With this in mind maybe it wont........

Matt

**almac16** · 01-21-2004, 06:38 PM

Yes, I believe you are correct in that the internal gearings are definitely a little lower on the es. I am only conerned with the actual size of the motor. Externally are they the same? Like I said I know for a fact that the 85 es and 85 sx are interchangable. But for some reason over the years I've never owned a 86 so I am not sure on them.

Thanks,
Alex

**ScottZJ** · 01-21-2004, 07:13 PM

Well it should fit without any problems. It is basicly the same engine minus the gearing.

**Dirtcrasher** · 01-21-2004, 07:25 PM

In 86 the CDI got changed to a 2 plug setup which looks like 1 plug but it may run the 85 just fine. I believe it is all the same color wires.

As far as the gearing?? I'm still waiting for some "real" evidence. I have an 86 ES motor and an 85 SX and both are in 10 thousand pieces. They have the exact same teeth on every gear.

I can tell you that the Clymer manuals amount of teeth versus my SX and ES does not match and they may be why people have suggested that the gears are changed. But with a 1st gear that is super low and a top speed of about 50MPH - I just can't see the need to change the ES tranny to get an even lower speed??

I have found some where 5th gear has clips holding it on the countershaft and others with no clips so I'm confused as hell.

One is silver one is black - I found no other difference.

People talk about the tranny gears changing and the diff gears changing so I truly don't know whats up with it.

Maybe somebody can shed some light here??

**King44** · 01-21-2004, 07:34 PM

The gearing is the same in both, the rear axle gearing is what is lower in the 250es.

**atcmatt** · 01-21-2004, 10:27 PM

Thanks for clearign that up king44, ive always wondered if the es was really geared lower than the sx!

Thanks,

matt

**bentwrench** · 01-21-2004, 11:56 PM

I copied these numbers from the spec pages in the owners manuals of an '86 SX & also an '85 ES.

**250SX_rider** · 01-22-2004, 05:57 PM

cool info 8)

**Dirtcrasher** · 01-22-2004, 09:06 PM

I talked with HEEHAW who has owned countless 250SX trikes and he has found numerous different gear ratios and teeth counts on the SX.

Again - both my SX and ES are identical but not the same as the Clymer.

I'm assuming your information is from the Honda Service Manuals which I would believe to be much more accurate than Clymer. However, based on the cases I have split or spoke to others about there seem to be lots of crazy gearings.

But what would the end result in terms of speed?? Maybe the tranny gears are changed along with the final drive and or the rear diff??

I'm confused now..... I must digest a vicoden

**hondajas** · 01-23-2004, 03:24 PM

The SX has a hotter cam, that's why it's faster.

**Dirtcrasher** · 01-23-2004, 06:02 PM

Originally Posted by hondajas

The SX has a hotter cam, that's why it's faster.

Both my SX and ES have the same cam.

**ebecme01** · 12-10-2005, 10:31 PM

I have read many places that the engines are identical within the year. The difference isnt for speed or power, its for the tire size difference. The ES has 25 inch tires and lower gearing in the rear differential. The SX has 22 inch tires and higher gearing in the differential. The reason the SX is faster is weight and weight only. Although the SX isnt light by any means, the ES is a tank. On these 20HP bikes, 50 pounds make a huge difference.

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1986 250 Big Red Motor in a 1985 250sx Frame?