ATC 250ES Big Red Gear Reduction?

[Stonewall]

So I've looked all over the net trying to find some information on gear reductions, because I'm running 30's and they're hell on my clutch. I've seen where some of the guys that run Fourtrax 300's have 18% and 54% gear reductions, but I can't find any info on who sells/makes them or how exactly they're done. I know it involves different gears on the clutch basket and primary, but that's all I know. Does anybody know anything about a gear reduction that might be available for the 250 engines? I know they're very similar to the 300's in alot of aspects. Any help would be much appreciated.

[Dezlemke]

The 300ex gears are the 18% gear reduction for the fourtrax 300.

[Stonewall]

Do they just bolt on or does it require machining? I can't even find a set of those gears on ebay.

[ps2fixer]

I don't think the 300ex gear set would work anyway, the 250es is clutched off the crank, and the clutch basket is for between gears, while all clutching demans are though the clutch basket on the 300ex.

Closest machine I know of to the 250es bottom end wise would be the trx350D, even though it is 4x4, the bottom end is very similar to the big reds.

TRX350D http://www.partzilla.com/parts/searc...TCH/parts.html
85 250ES http://www.partzilla.com/parts/searc...TCH/parts.html

If you click the part number, the bottom of that page will say the interchange purely based on part number. The 350d parts work for some models up to 2004, so I suspect the bell of the clutch is standardized a bit. Sadly the part descriptions didn't give a number of teeth to see if it is geared the same or not.

I don't really know any other models I'd feel is the same, but there are probably plenty. I do know the primary gear and secondary gear (clutch basket) will need to be swapped as a pair, larger the clutch basket, the lower the gearing will be. I don't think there would be a 50% reduction option since the case would probably cause problems going that much larger in the clutch basket, but maybe swapping the gears and looking for an alternative for the rear diff can net you that much.

For finding the gear sets on ebay, I'd say look for the keyword clutch with the model of machine... ex: 250es clutch.

Quick search shows there are several machines with the same gearing in the engine clutch basket area, 250sx, trx250, and trx300(fw). Possible machines to research for gear reduction kits as well since they use the same main drive gear. http://www.partzilla.com/parts/detai...0-HC4-750.html

[TheRealFatShady]

I can post pics for ya tomorrow.

For a 54% you need some expensive gears, and it's harder to machine. For the 18% for the trx300 (same for 250 or close) you need a 300ex or 250x primary gear and the clutch basket gear. Drill out the stock basket's rivets and rivet or tap and bolt on the ex clutch basket gear. The primary is harder to do, you use the original atc 250 primary but cut off and turn down the gear end (this gear meshes with the clutch basket) and then you must bore out the ex primary to fit the turned down 250 primary and press it on then tig weld.

I have some partially made but haven't had access to a TIG welder. And I only have one basket done because it required special bolts that were a shallow head that wouldn't hit the clutch plates.

It's been done a lot on the trx300 and the 250 engines are basically the same minus the longer stroke of the 300 crank, wrist pin, and the output shaft.

[Stonewall]

Pictures would be awesome! I have access to a machine shop and TIG welder, so I should be able to make it myself no problem. How much difference do you think the 18% would make for turning 30's? Also, do you know the specific gears needed for the 54%?

[Stonewall]

So from what I've found after a couple hours scouring the web is that information on the 54% Fourtrax 300 reduction is evidently a big secret, known to maybe half a dozen people. Apparently it's a 74 tooth clutch basket gear and a 20 tooth primary gear, but the big mystery is where they come from. I've seen a few claims that they come from a couple different Suzuki 4 wheelers, but no confirmation on what works.

[ps2fixer]

Pictures would be awesome! I have access to a machine shop and TIG welder, so I should be able to make it myself no problem. How much difference do you think the 18% would make for turning 30's? Also, do you know the specific gears needed for the 54%?

If the tires are a true 30 inches tall, then the 18% reduction would make it feel as if they were 24.6 inchs... just slightly smaller than factory. Of course this doesn't account for the extra weight assuming they are heavier than factory, but it should be similar to factory sized performance with +2.5 inchs of ground clearance and better grip =).

[DohcBikes]

Why no consideration for re-gearing the differential?

Serious question coming from a non machinist.

[TheRealFatShady]

Best bet for that is to get a whole rearend from another quad or trike and weld it to the factory setup, I've seen a kawasaki 300 (?) rear end welded on and it had lower gearing, not a problem on 2WD, would be a problem on the trx 300 4x4 because the front ratio would be different.

To change the rear end gearing would require a new ring and pinion gear, I'm not sure if there's anything else that'll fit that isn't the same amount of teeth.



Pics - shows the new finished product with the three bolts holding the basket gear on, and the original gear is compared. Then there's the trx300/250es primary with the bored out 350x/300ex primary made to a press fit. Not fully seated in that one picture, it was just to show how much gets taken off the 350x primary.


Edit - If you want, I'll send you mine to finish the tig welding and you're welcome to use the second one while you acquire one of your own or build a 54% or I can pay for the welding. Running behind today, but it's an LTZ400 i think around 2003 2004, and then there's 3 options for the 20 tooth primary, xr250, and a few others the XR one is not the most common. I'll have to check my notes later tonight, but I'll have those pics up by tomorrow. Btw, I believe the 350x gears are the same as the 300ex and 250x.

Edit 2 - I haven't looked into it too much but I did just send out a trx350d case to be machined to fit so I can run an oil cooler, and then also the inside is being machined out a little to fit a 450 one-way clutch. Figured the clutches are cheap enough, I'd give it a shot. But I believe there's a gear on the back of it that needs to get cut off so it matches the 250es/trx300 specs. (not the clutch basket mentioned above for the gear reduction)

[ps2fixer]

Cool photos, helps makes things so much visualized =D.

As for the comment above about the ring/pinion swap, pretty sure the 250sx and trx250 are interchangeable, but sadly the 250es is the lowest geared if I remember correctly. Not sure if anything else would fit w\o mods. If the gears their self isn't interchangeable, I know as a whole unit they are. My cousin's 250sx has a 250es rear in it and that tiny bit lower gearing made it into a fun wheelie machine with factory sized tires. It is crazy how such a little change in gearing can effect things.

[Stonewall]

PM me about those gear reductions Shady. This is much appreciated info, those gears match the speculation I've seen for the 54%. If you can check your notes to confirm I'll get right on trying to source them. I actually just picked up a 350D side cover on ebay myself for the same reason, should be interesting to see how well that works.

[Stonewall]

Shady your PM box is full haha.