Gear Change - CraigW, anybody else?

How hard was it to change the gears? Did you need any special tools. You have to split the cases? right? How long did it take you?

I run desert and MX, I don't see 5th on an MX track, at least not on the SX style tracks around here and 1st isn't used much either. So I had though about changing 1st and 5th to give me sort of a WR gear box...


Chris in the Mojave

'98 YZ400F

When deciding to change the gear ratios on my bike (I only race offroads and enduros), I compared the WR and YZ gearing with the view of replacing the minimum number of gears (cost considerations).

The ratios were as follows:


1st 1.846 2.417

2nd 1.500 1.733

3rd 1.278 1.313

4th 1.091 1.050

5th 0.952 0.840

When you graph the above ratios it becomes obvious that only changing 1st gear will create too big a jump to 2nd gear . Therefore I believe both gear sets must be replaced together. My next decision was wether to replace 5th gear or not. I was torn between replacing the gear set or just using sprockets to tune top speed - a lot easier once 1st and 2nd gears are replaced as now 1st is not nearly as long as before. Finally I decided on a new 5th gear set as the difference in ratio (4th-5th) is now 0.251 as compared to 0.210 for a standard WR. I'm still to run the bike with the new ratios so I dont know how the box will now 'feel'. I'll keep you posted.

As to the job of changing the gear ratios myself, I opted to have a good Bike Shop do the job. They charged 4hrs labour for the work (converts to $66.00 in dollars - our lousy South African exchange rate). I'm not too experienced on gear boxes but I figured I could do more damage than $66.00 if I got it wrong.I had to remove the engine and supply it to the shop. Incidently the 3 gear sets and circlips needed cost $240.00 from the Yamaha agents.

I'm sure it will work as I know others in this country have done it with positive results.

Do keep us posted. I'll be interested to hear what you think after you get a race or two on the beast with the new gear set!


Chris in the Mojave

'98 YZ400F

Update So Far

I installed the motor and all the rest of the gear - oil pipes, radiators , cables etc.

Then I decided to start the bike. Only one problem, the motor's got no compression. The mechanic who reassembled the motor has obviously made some sort of a #@*!@#$% mistake. To say I'm @#$%^&* pissed off is an understatement.

I've dropped the bike off at the shop this morning to them to fix the fault (????) and hopefully I get it back this evening.

The moral of the story. "If you want something done properly, do it yourself!"

Amen, Brother.


Chris in the Mojave

'98 YZ400F

[This message has been edited by Chris in the Mojave (edited 05-19-2000).]

Ok, this has nothing to do with swapping gears, but after reading a few suggestions on the WR side, I bought a 13/50 sprocket combo with a new chain. For anyone out there who finds the stock gearing too tall for woods riding and technical climbs, this set-up is a blast! Wheel placement is also a snap with the added torque down low.

When I'm on the MX course, I pop on the 14t front sprocket and leave the 50t rear. It works well for me, and front sprockets sure are cheap.

Hey Chris, why don't you save your $ and wait until you get that YZ440 :) !

[This message has been edited by alexjoz (edited 05-20-2000).]

If I do the gear change it'll be on the new bike....I'll be leaving the motor stock on this bike, easier to sell when the 440 show's up!

I'll depend on what Yamaha does with the gearing this year.


Chris in the Mojave

'98 YZ400F

Well I found the zero compression problem. It seems a shim under the tappet bucket had shifted skew off its seat thereby effectively increasing its size and keeping one of the valves slightly open. With the shim reseated, all the compression is back.

I pitched up during the final assembly to watch and good thing too. The problem with the 'short' camchain appeared, and luckily having read the solution on this web site I was able to offer advice.

On my first ride though, things didnt go too smoothly. When I stoped after 5km to check the oil level, I noticed a lot of oil on my bash plate and no level reading on the @#$!% dipstick. I isolated the problem to the flywheel side cover and on removing, it in the middle of the bush, found the gasket had missed one of the locating bolts. Once rectified the leak was over. Unfortunately I had to limp home, not knowing exactly how much oil I had remaining in the bike. A big gamble, but one that the Bike shop was going to pick up if I toasted the motor. Fortunately, on topping up the system I found it to be only 300ml short. Phewww!!!

The gear change works great. Riding technical terrain in the mountains (1600m above sea level) and a 15 front (vs 14 standard), I was able to ride real slow rock climbs and still rip on the dirt roads (145km/h approx). This conversion is definitely worth it if you dont use your bike exclusively for motocross.

I went with 1st, 2nd, and 5th also. I wanted a high 5th gear with stock sprockets for desert racing and a low 1st for mountain trails.

Added a Steahly flywheel weight, Terry Cable remote Hotstart button, and an IMS 3.2 gallon tank.

Now I have a WR or YZ. Just depends on what I put on or take off!!


I had to replace a broken 3rd gear on my YZ 250. I was absolutely petrified to split the cases. I could just see all the gears falling out! I removed the engine from the frame and removed the cylinder head from the engine. I brought the engine to a dealer and asked them if they could split the cases quick. The mechanic did (for free). I then asked if he would mind taking a peak to see if he could see any more problems. He pulled the case apart and did not see anything else other than 3rd gear. I took the split engine home and studied how everything worked. The shift drum was definitely the most unique part of the engine. I would split the cases myself in the future if need be. The thing to know is to not remove the engine from the frame until you remove the clutch, flywheel-if need be, and countershaft sprocket. With the engine on the frame, you can use your rear brake to lock up the engine while removing the aforementioned parts. I would never do this without a case splitter.


99 WR, all YZ mods, de-octopused, OEM YZ tank and seat, jetting by Clark.

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