Is it possible to make a 02-07 YZ250 a six speed?


Dekester

Member
Jan 2, 2007
31
0
I would really love to have that extra gear when riding with 450's in the desert. I actually out pull the 450's I ride with. When I get pinned in 5th, they pass me. My bike has plenty of engine left and would have no problem pulling an additional gear.

I remember hearing back in the day that you could do something with a YZ125 to make a 6 speed YZ250. I can't remember if you put a 250 jug on the 125 engine or the 125 gearset in the 250 case (seems more likely to me).

Any thoughts or experiences would be appreciated.
 

adam728

Member
Aug 16, 2004
1,011
0
I don't know about a 6 speed, but you can swap in some parts from the WR426 transmission to make a wide ratio 5 speed. You can change all 5 gears, or just do 3rd, 4th, 5th (which I think most people do).

Sorry Adam, that is not allowed. Mully
 
Last edited by a moderator:

84cr125

Member
Apr 8, 2007
292
0
hey, i replyed a while ago but it was deleted...... again. so basically what adam said is what i said as well. change around your gear ratios and you could pump out some more power. But doing so remember that your bike is only meant to have 5 gears and if you supe it up to make it run like it has 6 gears you might have to re-jet.
 

76GMC1500

Uhhh...
Oct 19, 2006
2,142
1
The trouble with a 6-speed is that the gears would have to be cut narrower to fit them in the same case as the 5-speed. This would weaken the gears. The wide ratio transmission and a change of sprockets would be the way to go.
 

adam728

Member
Aug 16, 2004
1,011
0
Can we do it this way? I hate to leave a guy hanging when all this information is already available.

Absolutely. Contrary to another members' post, the WR426 mainshaft, countershaft, and tranny gears will all retrofit to the YZ250 (02-on).
You actually have two options for doing this. If you want a taller 5th and lower 1st, you can replace the entire tranny with the WR parts (m/s, c/s, and all 9 gears.) This is kind of expensive but cool if you ride super tight trails. The other option is to just replace 3rd, 4th, & 5th gears with the WR gears (6 gears total.) This is what I did to my YZ last summer and it works great. It buys the bike about 10mph more top speed with stock sprocket gearing. For the desert riding I do, 1st & 2nd are fine where they are.
The guys with large displacement thumpers I ride with don't check-out on me in the fast washes anymore.

I just picked up the parts today for my tranny. 3rd 4th 5th gears, '99 WR 450, all three shift forks and a crank shaft key were 321.00 Not too bad.. Now I just need odds and ends...
Here ya go friends

Gear, 3rd Wheel 5BF-17231-00
Gear,3rd Pinion 5BF-17131-00
Gear. 4th Wheel 5BF-17241-00
Gear, 4th Pinion 5BF-17141-00
Gear, 5th Wheel 5BF-17251-00
Gear, 5th Pinion 5BF-17151-00
 

Dekester

Member
Jan 2, 2007
31
0
Thanks Adam for taking the time to do the cut and paste.

If I can not find a way to do a 6 speed, I will look into the wr gears next. I wonder what the difference is in the primary reduction between the bikes. That would make a difference as well.
 

76GMC1500

Uhhh...
Oct 19, 2006
2,142
1
I don't think there is a difference. Dirt bikes seem to be pretty universally 3:1 on the primary. I think the 500's are the only exception.
 

BSWIFT

Sponsoring Member
N. Texas SP
LIFETIME SPONSOR
Nov 25, 1999
7,926
43
Thanks.
 

Dekester

Member
Jan 2, 2007
31
0
Primary reduction ratio per Yamaha's website:

YZ250
06-07 3.000
04-05 3.353
02-03 3.000

WR426f
02 2.952

I guess I answered my own question if the website info is to be trusted.

I do not completely trust the website because it shows secondary ratio (sprockets) as 48/13 for the 2005 yz250. I thought all the 2000+ model yz250's came with a 50 back and 14 front as the stock setup.

So I am still confused.

OK. I must sound really neurotic. As I was typing, I just dug up my factory manuals for 2001, 2003, 2004, and 2005. They all say primary is 3.000 (63/21) and secondary is 50/14 (3.571). It looks to me as if the website is wrong.

Does anyone have a factory manual for a 2002 wr426f (or other 100% positive answer) to verify the primary ratio?
 

76GMC1500

Uhhh...
Oct 19, 2006
2,142
1
The website probably is wrong. 3:1 is pretty much the universal standard. There is a a little fudge room in there, would you consider 2.952 anything but 3:1? That's like a 2% difference.
 


Top Bottom