YZF 250 Gearbox mods

[flameboy]

Hi all, 2nd attempt at my first post ...fingers crossed!

A couple of weeks back I destroyed 5th gear on my 05 yzf 250.

I was competing in the NZ national enduro series and had it pinned to the rev limiter on the firebreak sections.

Deciding I needed a better top end speed I have ordered the WR 4th and 5th gears and hope the shop has it finished in a day or so. Has any one else done this? My thinking was I would keep 1st 2nd and 3rd standard which will give good grunt around the MX tracks and the 4th and 5th WR gears will give me the higher speed I need for the Enduro events. I would be keen to hear from anyone who knows about this.

Cheers

[Blutarsky]

The YZ 3rd to WR 4th jump might be a little large....

Stock YZF Gearing

1st 30 14

2nd 28 16

3rd 29 20

4th 27 22

5th 25 24

Stock WR Gearing

1st 31 13

2nd 28 16

3rd 28 21

4th 25 24

5th 22 27

24/25 from 20/29 = 40% jump. +35% is about the max that will work unless you put a bore/stroke kit in to broaden the powerband.

Here is my ideal all around tranny to go with my YZF315....

1st-WR 31 13

2nd-YZF/WR 28 16 +36%

3rd-YZF 29 20 +20%

4th-YZF 27 22 +18%

5th-Custom 22 24 +33%

The idea is to have a trail usable first. 2nd through 4th are tight...because thats where you are most of the time. 4th to 5th is a big jump for motoring along. I'll let you know how my custom 5th project goes....

[flameboy]

Cheers

The works should be done inthe next couple of days and if the jump is too big maybe I could use the WR's 3rd as well?

[av]

Let us know if it works out. I wanted to have the WR's 4th & 5th gears also but remember that the WR's rear sprocket is 52T vs. 48T for the YZF so that will also add into your equation. You might consider running a 50T rear with the taller WR's gears... ?

[flameboy]

Hi Thanks for the advice, I have decided to go ahead with the transplant of the WR 4th and 5th and see what happens I guess. I was running a 49 tooth on the rear and I will try that as a starting point and play around from there. I have got to say it has stirred up a bit of interest from some upper end enduro riders who are keen to see how it works, all the new parts are with the bike shop now after a small delay ordering from Japan, so hopefully a couple more days! Cheers

[tranqwhl]

man, that's a cool idea. If I was going to build the "ultimate" bike, I would probably do the same. 5th is a little short for wide open sections when you ride with 450s.

way cool

[celfon]

Please let us know how it turns out for you. I am definitely interested in doing something like that also.

[Rockyracer]

I have swapped gears on the yamaha two stroke 250. What you have done I have considered. But I would have only changed the 5th gear. I know my 06 has enough torque and horsepower to pull the giant gap between the YZ 4 and the WR 5th. 1st through 4th are your raceing gears 5th is a overdrive. The only problem I see with what I have sugested is probably in the whoops,where you may have to scream 4th.

[Dirtriding4life]

I'm really looking foward to your results! Please don't hold out on us and not tell us about how well it worked!

[flameboy]

Hi hows it going, All work is now completed I had to replace half the crankshaft web,(the side the timing chain drive is), the middle selector fork, 4th gear pinion and gear and 5th gear pinion and gear.I did the big end bearing while it was apart and a new set of rings as well. I have had it running but have not ridden it yet.

This weekend there is a 2hour enduro just north of here and I am going to ride there after I have run it in. I am running it in with mineral oil, probably about 30 minutes or so then dump the oil clean the filter (stainless) and replace with synthetic Then it will be death by rpm for the rest of the day. I'm really looking forward to it and can't wait, it sounds crisp and angry (pro circuit). I'll post a report as to how it goes, who knows it could be a dog, in which case I'll put it back to standard but I don,t think so. There are two other rider I have spoken to who are going to do the same thing to theirs if mine works Am I the first one in the world to do this????

I'd love to hear from anyone else who has it.

Cheers.

[Dirtriding4life]

I'm kind of wondering how much it costed you to do all this and how long? I hope you don't mind me asking that. What gearing are you running? You can't forget about that.

[flameboy]

Hi no problem,

Parts were just over $900 (all NZ $) and $460 for labour and bits and pieces.

I actually went down to the shop and helped put the motor back in the bike and conect it all up, They are very good mechanics and cool guys, there you are a little plug for the boys at Spectrum Motorcycles of Barrys Point Road Takapuna Auckland city, they even let me buy the parts through a contact I have at Yamaha to save a couple of bucks, great guys!!

Cheers

[flameboy]

Oh and the rear sprocket is a 49T, up 1 from standard but I find it gives a better launch out of corners, for the Enduro I used the standard 48T to give me more top end but it was still way short of what I needed hense the blown 5th gear.

I'll play around untill Ive got it about right.

Cheers

(Live every day as if it's your last because one day you,ll be right)

[flameboy]

OK, Just completed a club day enduro, quite tight and technical and only one decent piece of track to use the new gears.

Yes there is a gap from 3rd to 4th and it can catch you out if you are short changing up a hill or the ruts get a bit deeper. It wasn't the perfect terrain for the new gearing as it was a bit gnarly and not very flowing. To be honest in this particular event standard gearing would probably have been an advantage, but... I think in the normal round of events that I ride this new gearing set up is going to be great!

The step is not too big and the bike has more than enough power to pick up the revs except in the real snotty places.The new gearing is going to shine on the trail rides and the bigger enduro events and I'm sure won't be to much of a problem on the MX tracks.i am running a 49T on the rear and the front is standard.

Would I do it again... Yes I think I would, but, it's early days yet and i need to spend more time riding to make sure. I'll let you know

Cheers

[Dirtriding4life]

That sounds really good for my type of riding out in the desert. What is the exchange rate to American? I'm just wondering how much it would be in American money.

[flameboy]

New Zealand $1400.00 equates to US $924.00

I doubt you would need to do all the work I did so it would probably run you about US $700 to change the 4th and 5th gear only.

[flameboy]

Just an update from NZ, I have now had the opportunity to run the YZF in four meetings since my last post.

In all but one of the meetings I felt the bike performed better with the new gearing. The only motocross meet where I felt the old gearing would have been better had a knarly uphill section which peaked out just a little bit more than "pinned in third" and just a bit steep and rough for the new fourth.

In all the other meetings (2 x motocross 1 x 2 hour enduro ) the new gearing was great The best improvement is in the wet and sloppy conditions where you can hardly tell the difference between the old and new but on the straights you gain a much longer continuous push.

I run a 49 tooth rear and all in all I,m pretty happy I did it really!

Cheers ?