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YZ450F transmission gear upgrade? (Close Ratios)

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I am starting a new thread to cover possible CLOSE RATIO transmission upgrades for the motocross crowd.

A lot of this info is from the various (and excellent) WR gear swap threads on the forum. I am not looking to do a WR upgrade, so I don't want to cause confusion in those threads. I still think you WR guys have the majority of experience with these transmissions and what may work.

My problem is the occasional detonation that happens with 4th gear in the YZs. The last time it happened to my 2002, I undercut the dogs slightly to take stress off of the shift forks, it has helped a ton, but I'm worried about still shattering teeth on the narrow 4th gear.

The solution I've been considering for a while is the wider gears from a 5 speed YZ450F. From what I can tell, the 450F gears are wider and have 4 engagement dogs instead of the 3 on the two stroke gears.

Another upgrade that appears to have come with the 2006 450F's new 5 speed trans is the sleeved 1st and 2nd countershaft gears. I'm making the assumption that those sleeved gears either improve shifting feel or increase longevity.

I have checked every part number from every year and looked at photos and diagrams for the YZ, YZ-F and WR-F. My conclusion is that there is a TON of crossover from year to year in many of the models but there is no solid trail of part number crossover that can guarantee that the gears will fit, or work with the YZ shift forks and shift drum, etc.

I decided to take a stab at it by measuring the parts. I purchased a 2007 YZ450F transmission from e-bay for $65. I'll take measurements to compare to a YZ250 transmission. $65 is worth it just to learn.

Has anyone done this swap, or tried to make it work? Is there anyone with a YZ250 transmission out of the engine who is willing to take some measurements so that we can all learn and compare?

I will have my 450 parts in a few weeks (shipping to Afghanistan is slow).

When they arrive I'll measure them and make a PDF diagram.

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With a bit of luck you'll be able to put the complete gears into the gear box. I don't really know but I exchanged the clutch plates of my YZ250 (2009) ones with the ones of the YZ450 year 2006. I'm about to open my 2007 engine due to the failure of the needle bearing or the spacer. Which measurements do you need?

I also have still the OEM gears with shafts after I changed the YZ gears 3-5 with the wrf426.

Edited by arnego2

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With a bit of luck you'll be able to put the complete gears into the gear box. I don't really know but I exchanged the clutch plates of my YZ250 (2009) ones with the ones of the YZ450 year 2006. I'm about to open my 2007 engine due to the failure of the needle bearing or the spacer. Which measurements do you need?

I also have still the OEM gears with shafts after I changed the YZ gears 3-5 with the wrf426.

The Basic measurements I plan to compare are:

-Lengths of each shaft and the distance to each critical feature (circlip grooves, splines, shoulders) from a good datum point like the shoulder behind the clutch hub on the mainshaft.

-Diameters at each critical feature along the shafts.

-Widths and distances of/to each critical feaure on each gear.

(including the shift for grooves and dogs)

-Overall width / diameter of the assembly at outermost gears.

(To compare for case clearance issues)

Obviously that's a lot of pretty involved/detailed measuring that needs to be done with a dial caliper or height gauge. I should have my gears in a few weeks. When I get the measurements from the 450F trans I'll post up a diagram.

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Due to a midseason case split, I won't be splitting them this winter. If I were, I would love to help see if we can get a beefier trans.

Hopefully someone helps.

How close are the gear ratio's between the yz and yzf?

I would think the yzf gears would be much taller, but if they had equal spacing to the yz, a sprocket change would bring it back to stock.

Cool project, keep us updated.

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Not that much taller IMO but I can´t really measure the m/h the bike runs. I like it but at the moment the people selling the complete set of wr400f and wrf426 have some funny ideas how much they should cost. 200+ is not what I would pay for it. You gain some 15m/h

So far I have measured only the diameter of the shafts, the gears all sitting still on them. 20mm on one side and 25mm on the other. Later I´ll have hopefully some time to get the rest of the data. I presume that most shafts and diameters are the same as Yamaha seems to like the interchangeability.

Someone here on the board has done a YZ450 gear set and wrote what he´s done and how´s done it. Way over my idea of mod for me.

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Due to a midseason case split, I won't be splitting them this winter. If I were, I would love to help see if we can get a beefier trans.

Hopefully someone helps.

How close are the gear ratio's between the yz and yzf?

I would think the yzf gears would be much taller, but if they had equal spacing to the yz, a sprocket change would bring it back to stock.

Cool project, keep us updated.

I will add to this thread and share as much as I can learn.

According to the tooth counts in the Yamaha parts diagrams, The 2006-2009 YZ450F share all gear ratios with the 2003-2012 YZ250.

Tooth counts for both 2T and 4T YZs are:

1st) 14:27

2nd) 15:23

3rd) 18:23

4th) 22:24

5th) 21:20

Keep in mind that the 2003-2005 YZ450F had a 4 speed.

Arnego, are you talking about the primary gear swap for top speed that was done recently? My project is to replace the actual transmission (10 gears and 2 shafts) in the centercases with the close ratio gears from a YZ450F. I am hoping they are a drop in fit, or can be slightly modded to work in the YZ250 cases. If someone has already made it work, or tried and failed, I'd love to learn from their experience.

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My notes from looking at the parts fiche. This is pretty raw and straight from my notepad document and could be riddled with Type-Os.

I was using fitment and crossover of parts (including the WR-F) to try to build a "logic bridge" of crossover between the '03-'12 YZ250 and the '06-'09 YZ450F. It's not conclusive, but it's a strong maybe.

YZ426F & WR426F vs YZ450F vs YZ250 transmission notes:

======================================================

Parts changed gradually year by year with lots of overlap from year to year.

This leads me to the conclusion that the overall dimensions of 5 speed boxes are

consistent enough to swap entire transmission assemblies from bike to bike.

Guys on ThumperTalk.com are already swapping 400 & 426 WR transmissions into YZ250 two strokes.

The 400 & 426 YZ models share some gears with the two stroke, and will swap over.

The two strokes have different bearings, but all the four strokes through 2003 are the same.

There is overlap between shafts and cases, shafts and bearings, gears and shafts.

This is very promising for a swap.

In 2006 for the YZF and 2007 for the WRF, the countershafts changed along with the 1st and 2nd gears on them... They have sleeves in those gears probably meant to reduce friction and ease shifts or increase longevity of the gears/shafts.

2006 was the introduction of the close ratio 5 speed in the YZ450F.

(2003-2005 YZ450F were 4 speed)

-2002 YZ426 & WR426 use the same shift drum (part # 5JG-18541-00-00)

-2003 YZ450F is 4 speed

-2003 WR450F is 5 speed

-2003 WR450F & YZ450F, 2002 WR426F & YZ426F (share all four transmission bearings)

-2002 YZ426F crank case assembly (Part # 5SF-15150-00-YX) YZF Gear set A (YZ250 compatible)

-2002 WR426F crank case assembly (Part # 5SF-15150-00-YX) WRF Gear set A (YZ250 compatible)

-2003 WR450F crank case assembly (part # 5TJ-15100-10-YX) WRF Gear set A-2

-2003 YZ450F crank case assembly (part # 5TA-15100-11-YX) 4 Speed Transmission

-2006 WR450F crank case assembly (part # 5TJ-15100-10-YX) WRF Gear set A-2

-2006 YZ450F crank case assembly (part # 2S2-15100-01-00) [sleeved countershaft 1st & 2nd gears]

-2007 WR450F crank case assembly (part # 2S2-15100-11-00) [sleeved countershaft 1st & 2nd gears]

-2009 WR450F crank case assembly (part # 2S2-15100-11-00) [sleeved countershaft 1st & 2nd gears]

-2009 YZ450F crank case assembly (part # 2S2-15100-21-00) [sleeved countershaft 1st & 2nd gears]

-2002 WR426F main shaft (part # 5BF-17411-10-00)

-2002 YZ426F main shaft (part # 5JG-17411-00-00)

-2003 WR450F main shaft (part # 5TJ-17411-10-00)

-2003 YZ450F main shaft (part # 5TA-17411-20-00)

-2006 WR450F main shaft (part # 5TJ-17411-10-00)

-2006 YZ450F main shaft (part # 2S2-17411-00-00) [sleeved countershaft 1st & 2nd gears]

-2007 WR450F main shaft (part # 5TJ-17411-20-00) [sleeved countershaft 1st & 2nd gears]

-2007 YZ450F main shaft (part # 2S2-17411-00-00) [sleeved countershaft 1st & 2nd gears]

-2009 WR450F main shaft (part # 5TJ-17411-20-00) [sleeved countershaft 1st & 2nd gears]

-2009 YZ450F main shaft (part # 2S2-17411-00-00) [sleeved countershaft 1st & 2nd gears]

-2002 WR426F counter shaft (part # 5BE-17402-00-00)

-2002 YZ426F counter shaft (part # 5BE-17402-00-00)

-2003 YZ450F counter shaft (part # 5TA-17402-10-00)

-2003 WR450F counter shaft (part # 5BE-17402-00-00)

-2006 WR450F counter shaft (part # 5BE-17402-00-00)

-2006 YZ450F counter shaft (part # 2S2-17402-00-00) [sleeved countershaft 1st & 2nd gears]

-2007 WR450F counter shaft (part # 2S2-17402-00-00) [sleeved countershaft 1st & 2nd gears]

-2007 YZ450F counter shaft (part # 2S2-17402-00-00) [sleeved countershaft 1st & 2nd gears]

-2009 WR450F counter shaft (part # 2S2-17402-00-00) [sleeved countershaft 1st & 2nd gears]

-2009 YZ450F counter shaft (part # 2S2-17402-00-00) [sleeved countershaft 1st & 2nd gears]

-2002 YZ250 clutch hub (part # 5NX-16371-00-00)

-2002 WR426F clutch hub (part # 5JG-16371-10-00)

-2002 YZ426F clutch hub (part # 5JG-16371-10-00)

-2003 YZ250 clutch hub (part # 5NX-16371-00-00)

-2003 WR450F clutch hub (part # 5TA-16371-02-00)

-2003 YZ450F clutch hub (part # 5TA-16371-02-00)

-2006 YZ250 clutch hub (part # 5NX-16371-00-00)

-2006 WR450F clutch hub (part # 5TA-16371-10-00)

-2006 YZ450F clutch hub (part # 5TA-16371-10-00)

-2007 WR450F clutch hub (part # 5TA-16371-10-00)

-2007 YZ450F clutch hub (part # 5TA-16371-10-00)

-2009 WR450F clutch hub (part # 5TA-16371-10-00)

-2009 YZ450F clutch hub (part # 5TA-16371-10-00)

-2010 YZ250 clutch hub (part # 5NX-16371-00-00)

Clutch Nuts:

===============================

90170-20255-00 02 YZ

90179-20001-00 02 WRF

90170-20327-00 02 YZF

90170-20327-00 03 WRF

90170-20327-00 06 YZF

90170-20327-00 06 WRF

90170-20255-00 10 YZ

Clutch Washers:

===============================

5CU-16154-00-00 02 YZ

2JN-16154-00-00 02 WRF

2JN-16154-00-00 02 YZF

5TA-16154-00-00 03 WRF

5TA-16154-00-00 03 YZF

5XD-16154-00-00 06 YZF

5XD-16154-00-00 06 WRF

5XD-16154-00-00 07 YZF

5XD-16154-00-00 07 WRF

5CU-16154-00-00 10 YZ

-2003 WR450F 1st and 5th countershaft gears and 2nd main shaft gear are 2002 WR426F parts

-2006 WR450F & 2003 WR450F use the same gears.

-2007 started sleeved 1st & 2nd countershaft gears for the WR450F (part # changes to gears & cases)

-2006 started sleeved 1st & 2nd countershaft gears for the YZ450F

-Sleeved countershaft gears have a new countershaft Part #

-2002 YZ426 & WR426 transmission can be swapped into a YZ250

-2006 - 2009 YZ450F & WR450F transmisions may swap into a YZ250

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I was trying to find the thread which explained what has to be done to make the YZ450F gears to make them fit. If I remmeber right he had to do some machining and use a clutch of the YZ450. But I could not find it so it is not sure it is correct.

Here where someone tried to put the gears into the gear box but it was too small. He said> they fit on the YZ250 shafts they did not have sufficient clearance< I think maybe a 4 gears tranny could fit.

Changed the 3-5 gears of the wrf426 on the YZ250 engine year 2007 and it is nice but the price tag of the sellers on ebay so far over 200 so for me that is too much. Shipping I pay US$ 50. so with 250 no thanks.

I put the 3-5 gears onto the stock YZ250 shaft as I have 14 on the primary gear and the WRF426 has 13. If riding alone I do not need it. But sometime I ride with the KTM group and all have enduro bikes so their top speed is highr as the MX bike. With the 3-5 gear I am as fast as them at least.

No races for me, so alone the YZ250 is enough and fast enough too. I did the change of the gears because I had the 4 gear breaking. Locked up the gears.

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arnego, thanks for the link.

For reference, this is the last post from that thread:

motojason07-15-2011, 04:31 PM

I experimented with some transmission parts I had. YZF 450 gears from 06-08 are wider and although they fit on the YZ250 shafts they did not have sufficient clearance in the 2-stroke cases. The 450 gears have four gear dogs while the 250's only have three. From what I have seen the 3-4-5 426 gear swap is the best set up for off road.

So if that's the situation, I'll try the measurements anyway to see if clearancing the gears or the cases is possible to make the YZ450F Gears fit.

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Not a problem I was today trying to get the data you need, but got a bit crazy.

So I started from the side where no threads sat on the shaft to make it easier. One downpoint is the I own a few calipers one of Starrett co ltd which goes to 30mm. The other is a digital truper caliper but won't go further than 155mm.

Starting at the main shaft with the 2.nd gear which is 18.05mm wide and 48.36mm tall and sits 3.35mm behind those 12mm of nacked surface. Followed by forth gear being 55.84mm tall and 13.15mm wide. Than comes the first circlip groove at a distance of 32mm (plus 12mm nacked or the end of the shaft). Third gear 24.60mm on its slimmest and 29.15 at its thickest area. 51.75mm tall followed by the fifth gear 10.90mm wide and 59.70mm tall. The shaft is 184.79 long once I added those point I could measure. No guarantee unfortunately.

Just the first shaft, the main one. I think that the 4gears YZ450f could fit, 4 gears are small than the 5 ones.

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Do you guys remember the thread (I think by JesseChop?) from the guy who wanted to put the mainshaft I think it was in his yz250 since the primary gear reduction ratio was slightly different and it allowed him to get higher top speeds?

I could be way off and not remembered it correctly however if not that thread may have some useful info because he talks about where/how he needs to shave down certain parts to make it all fit.

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Subscribed! Ive always wanted to see if there is a way I can get a little more reliable gear set for my 426, since every time I open the case the teeth look worn and I end up replacing parts. If something would fit in the yz 250 it would make sense that is fits into the 426 then too, right?

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I think it was someone else who actually did it. The primary gear swap tread was more a talk about what could be done to raise speed. I could not find the thread about the yz450F gears and I looked through some 10 to 15 pages. So if someone remembers ...

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Yeah, I searched a bunch too. I was hoping to find a difinitive answer with photos or a description of what the differences really are when you try to assemble it. All I found were the threads discussing WR gears. Those WR threads to provide some useful cross reference info, but not 100% answers.

I got an e-mail that my '07 YZ450F gears were "marked as shipped" today. It will probably be about 2 or 3 weeks before I have them in hand to take measurements.

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I find it strange how people think the YZ gears are weak because some people bust them when we do not know haw they operate the machine.

When you consider that a YZ gear box were used in Yamaha Australia's Supermotard championship winning YZ 450 back in 04 to convert it to a 5 speed. (04 YZF 450 being a 4 speed.)

That was a highly tuned 450 running the YZ gears on the bitumen without a gear being broken.

But all good info being sourced by OP:thumbsup:

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I had a broken gear because of a small tiny waterpump bearing failure. That happens and I bet that any other stronger gear box would have done the same to me. Actually it was a chain reaction. The little ball dropped between primery and waterpump sprocket, the waterpump sproket borke off 2 teeth and those found their way into the gear box.

Now I run a wrf426 3-5 gear set which otherwise I'd never had tried out.

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YZs have weake transmission, it is pretty well known. Its not even like the dogs get worn out or anything. The teeth just bust. Even horrible shift wont cause it, that would round the dogs. I had constant problems on my 04 125 and i am having problems on my 426 also

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I find it strange how people think the YZ gears are weak because some people bust them when we do not know haw they operate the machine.

When you consider that a YZ gear box were used in Yamaha Australia's Supermotard championship winning YZ 450 back in 04 to convert it to a 5 speed. (04 YZF 450 being a 4 speed.)

That was a highly tuned 450 running the YZ gears on the bitumen without a gear being broken.

But all good info being sourced by OP

Thanks, I hope my info is helpful. I have learned a lot of from this forum. It's the friendly (sometimes heated) sharing of ideas, tips, tech, and a laugh or two that keep me coming back.

Supermoto at the pro level probably doesn't involve the same number of hours that our play/race bikes do as low-buck amateurs. I don't follow Super-Moto, but do they blitz whoops and hammer the bike with on/off traction situations like we MX guys do? Also,

Yamaha updated the 5 speed with gears that appear to be wider/stronger when they put it in the 450. Clearly they didn't think the YZ250/400/426 transmission was overbuilt by any means. Perhaps they had seen failures, or know the design was already close to or at it's limits.

A couple of guys are having this problem and it seems to keep coming back for the same guys. At first I didn't think much of it, but over the course of a few years, there have been enough guys on here with teeth busting off of that 4th gear after a year or two. It just seems to be that the gear is right on the engineering edge with regards to fatigue life. The teeth just shatter right off of the gear.

YZs have weake transmission, it is pretty well known. Its not even like the dogs get worn out or anything. The teeth just bust. Even horrible shift wont cause it, that would round the dogs. I had constant problems on my 04 125 and i am having problems on my 426 also

I think some failures are due to metal fatigue and others are due to abuse. I have had teeth crack off of a couple 4th gears in my 2002. It takes some time, but they seem to fatigue and eventually crack off.

I have also had failures due (probably) to crashing/abuse as well. My theory about that is when you crash hard and the shifter hits the ground in the wrong gear, it can tweak a shift fork. Eventually, with full power shifting, blitzing whoops and a slightly bent shift fork the dogs are going to skip out of mesh and finish off that shift fork and completely round off the dogs. That still doesn't explain the 4th gear tooth failures when the dogs and forks come out looking like new.

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I think some failures are due to metal fatigue and others are due to abuse. I have had teeth crack off of a couple 4th gears in my 2002. It takes some time, but they seem to fatigue and eventually crack off.

I have also had failures due (probably) to crashing/abuse as well. My theory about that is when you crash hard and the shifter hits the ground in the wrong gear, it can tweak a shift fork. Eventually, with full power shifting, blitzing whoops and a slightly bent shift fork the dogs are going to skip out of mesh and finish off that shift fork and completely round off the dogs. That still doesn't explain the 4th gear tooth failures when the dogs and forks come out looking like new.

I would say a majority of failures are due to fatigue because of the loading and unloading gear teeth undergo.

I had a nasty crash one weekend, bike landed hard on it's side from about ten feet in the air. Needless to say I called it quits for the day.

The next weekend I went out and after one lap, I couldn't shift out of second very well at all.

Bent shift fork and shift shaft.

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It is quite curious that the 4rth gear is the one which takes the hit. In my case I had a pin break (governor) A bearing failure with subsequent waterpump sprocket breakage but only the sprocket part was the only time it made it to the 4rth.

I have seen a lot of people not willing to maintain their bikes and simply ignore small bearing failures, I had on guy who still rode his 4 stroke with a burst head gasket. It made 90 min.

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