what's the did between an 86 and 85 250sx

[TecateDan]

I have this thought that someone said an 85 has a prob the 86 doesn't

[fabiodriven]

The 85's differential is more susceptible to water damage than the 86-87's. I'm pretty sure that's the only major difference.

[atc007]

That's the major one^^, Carb,starter,starter reduction gears,stator,cdi,oil pump,complete rear,axle,hubs,controls,choke and cable,rims,helmet lock,colors ,decals,seat, exhaust heat shield,,,,,,,other than that ,,they're about the same. Seriously! They run and drive almost identical,,if you haven't been in the water on the 85,,good to go.

[Flyingw]

Thats not the only differance Fabio. Although the diffs are basically the same, there is a depression in the diff casting where the axle tubes set in to seal the axle tube to the diff. On the 85, the depressions are shallow whereas the 86 has deeper depressions. With that said, an 86 diff will bolt up to the 85 axle tubes but the 85 diffs do not allow the 86 axle tubes to seat all the way in. Honda did seal the axle tubes with orings but the axle tubes leak on both years. The diffs are pretty tight but when assembling the axle tubes to the diff, always seal up those joints with silicone.

In addition to that, the 85/86 ES/SX starter gears (under the oval cover) the double gears likes to grenage. This was redesigned in 87 and thats why the 87 starter gear cover is teardrop shaped.

Both 85/86 ES/SX carbs have cold start problems. This mainly effected trikes in very cold places. The 86/87 carbs have a different jet stack and a larger startup jet.

There are subtle differences in the motor on both models between 85 and 86 and despite what people say, the motors are very different between the ES/SX.

The same goes for the carbs. ES and SX carbs internally are exactly the same but they have different vent tube configurations so that drives a different part number otherwise they will interchange.

The ES has a larger output stator but electrically they aren't much different.

As I mentioned, there are differances in the motors. Mainly the transmissions are geared different along with the diff. The ring gear in the diff has one more tooth than the SX diff. Almost every gear in the tranny is typically larger in the ES than the SX.

[Flyingw]

Double O Seven mentioned the oil pump. The oil pump on both models in 85 were the same pump but Honda changed the oil pump and crank for both models in 86-87. They put a larger gear on the oil pump and changed the mating gear on the crank to accomodate the oil pump change so the cranks are different between years. The ES transmission main shaft is also different and will not work in the SX tranny case.


The stator, flywheel, and one way starter clutch is different between models and between years.

I learned all this with my Army trike build. I had seven ES and SX motors completely disassembled and they were mixed between 85 and 86 years. When I started to put together a motor for the Army trike. I thought they were basically the same but boy did I go through some pains learning that the motors are in fact very different. I was trying to stuff SX gears stacked up on an ES main shaft and I couldn't get the tranny to rotate when I pinned the cases together. When I researched the part numbers I concluded they are machined different. I swapped out the main shaft and it all went together fine.

I tried putting an 86 oil pump in an 85 case with an 85 crank, the oil pump wouldn't mate up. I did a 1 for 1 comparison of the tranny gears and the gears are all different.

The top ends are identical.

What I eneded up with is an 85 SX chassis with an 86 rear end being driven by an 85 ES motor.

[Dirtcrasher]

Really, all that crap didn't have many advantages.

Bottom line: The 86/87 brake drum is enclosed, so just a small axle seal has to hold up. The 85 had this whole 8" or whatever drum constantly turning and a leak always developed. Then it made it's way to the diff bearings and things got bad. They tried to fix them by punching an "X" into the ones that came back as recalls.

The 86/87 SX came with a keihin QA08 carb (or however it's spelled) which eliminated the cold start issue. The other was a QA3 or QA5, I forget; It merely needs a larger starter jet and from there it runs just as well.....

And they tried to beef up the swinger as well as add o rings at each connection which I would also silicone.

I always meant to make a guard for the universal joint boot as I ripped a couple by using riding boots.

Yes, there were many other changes but the didn't have the impact these did.

And don't jump any year or you will bend the pieces bolted to the swinger. Or, I'm just too fat or jump too much

It's an awesome utility/sport vehicle for what it is........

[Flyingw]

The odd number carbs are ES and even are SX
QA01A =85 ES
QA07A = 86/87 ES
QA02A = 85 SX
QA08A = 86/87 SX

[Flyingw]

Oh, and I agree with dirt, dont do allot of jumping with the SX. They weren't designed for that. You WILL mess stuff up if you jump those things.

[Dave Little]

but the 85 diffs do not allow the 86 axle tubes to seat all the way in.

*raised eyebrows* Ahhh I see.

[dustrunner]

so if you take a 250es engine and install it in a 250sx will it go faster than the 250sx engine ?

[Flyingw]

No, slower by just a bit but you gain some bottom end. I have a small trail with a short hill behind my house. Its only about 20 feet long but its moderatly steep and my Army trike goes up it at idle. Remember, the ES was geared far lower than the SX but that's with a lower geared tranny, larger ring gear in the diff, and larger rear wheels. I like my SX with the ES motor. its a tank. The ES nor the SX were any kind of speed machine but they can hold their own and take you damn near anywhere you want to go. My ES motor is connected to an SX wire harness with an SX CDI. It runs like a sewing machine.

[Dave Little]

Thought I'd resurrect this thread, it has the best potential of becoming a reference going forward. Found another 85-86 difference tonight:

When this part breaks away, you can no longer downshift...you can only go up:

[Dirtcrasher]

Maybe your manual clutch adjustment is off just a hair. They usually don't break there..............