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YZ250 kick start preventive fix summary

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I'm a big guy, and have been concerned that the broken kick starter may happen to me many miles from the truck. I read several older threads on this, thought I'd put the answers in one place, accessible with less reading. I'm not claiming to have come up with all this information, but I'm too lazy to go back and find the original post with each bit of information and assign credit. It all came from TT guys :lol:

Problem:

In 2002, the kick start shaft was reduced in diameter from 20mm to 18mm, and made hollow, matching the YZ250F. It's lighter now. It also has a tendency to break at the hole drilled through it for the spring. When it breaks, one end of the axle is unsupported, so the gear position is not controlled. There's also an 18mm hole in the side of the trans that oil will get sprayed out of and dirt will enter if you try to bump start it and ride. The engine side cover may or may not be cracked when the shaft breaks.

Facts:

The kick start shafts were all the same from 1989 to 2001. The shaft itself is listed as a standalone part from Yamaha for 1998 and earlier bikes. 1999-2001 parts guides list the entire assembly only, as do 2002 and newer.

The side cover supports the outer end of the shaft, so a 1999-2001 side cover and oil seal must be used with a 1989-2001 shaft. All inboard components are the same. The shaft's splined outboard end is larger, so the 2002+ kick knuckle won't fit.

The 1999-2001 kick lever knuckle is bigger, and so is the post. The screw and ball bearing are in different locations, so you can't just bore the 2002+ lever to go on the earlier knuckle. The earlier lever has a different bend and is also shorter. The end doesn't fit into the notches for the tip on desert tanks.

However, it was discovered by CaptDan that the YZ400F-426F-450F knuckle and lever will fit the 01 shaft, thus making the kickstart the same or similar to the original. (I assume this means the length and shape are the same as the 2002+ YZ250 knuckle, so it will mate up perfectly with the frame geometry, oversize tanks, etc.)

So, the preventive solution bolt-on parts combo is:

1989-2001 shaft only (all other bits can be reused, or the shaft can be sourced as an assembly including everything)

1999-2001 side cover and oil seal

YZ400F-426F-450F lever assembly with knuckle

The scope of this post is a bolt-on solution. I don't mean to get into possibilities of machining or repairing the side cover, modifying or machining earlier shafts to fit later kickers, etc. Basically, something that anyone with basic R&R skills and tools can successfully install in their garage.

It's possible I've misinterpreted or misremembered something I read, so anyone with information to correct this, please post. I'll edit this as many times and for as long as the site lets me in order to get it right, without people having to read through many pages of discussion, speculation, trial and error, and just gnashing of teeth about the problem.

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This is great information, thanks for putting it all in one place.

I haven't run into this issue yet, but It's good to know there's a solution if I do.

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I still think rather then going through all that crap the easy soution would be to take your original shaft and bore the center one even size and press a steel rod into it to beef up the original shaft. Any machienest should be able to something like that for cheap. There not breaking at the end there breaking right at the center were the spring hole. If you had a steel rod down the center theres no way it should break if you drill the spring hole just deep enoufgh. Just another way to fix this. Ive ran my oe shaft on my 300 110 olney and it kicks harder then my old yz426f did. Some times no matter how hard I kick if I dont start in the right spot the kicker will hit compression and stop dead. Ive yet to break my oe shaft and I have 300+ hours on the 300 kit. I have spare parts for when it does But I wouldnt worry too much as ive been hard on mine ad its yet to break.

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2006 yz295 original owner, broke the original kick shaft 3rd ride after 295 break-ink, April 2010. April 2011 broke the 2nd kick shaft

MAX!!!

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It's strange that some people break multiple shafts and some of us have multiple bikes with no issues at all. I have a 2002 and a 2010 with zero issues. My 2002 has hundreds (if not a thousand) hours on it with the same shaft.

Unless Yamaha has a QC issue in their heat treating department, there must be some difference in the way some of us kick the bikes. I tend to kick hard, jumping down on the lever with my weight (I'm a fit 165 lbs). My starters stop hard against the footpeg. This results in aluminum on the little stopper nub half-way up the lever getting dented/distorted and flaking off. It even results in slightly dented footpegs.

I would say I am merciless with my kickers, perhaps excessive and abusive. I have yet to break one or have any issue.

I see a lot of guys sort-of "half-kicking" their bikes. They stay sitting on the seat and just push down hard with their leg. I see these guys usually going two or three kicks to start a YZ250 because they aren't kicking it over as fast.

How are you guys kicking them over?

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Id guess one issue "may" be that some people just kick without engaging the gear first :lol: I like to get the kick starter engaged before I give THE kick.. :)

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I think that if you check it for cracks and wear, you will be fine. It will usually give you some kind of indicator that it is about to break.

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I have a few spare on my shelf just incase. If I actualy ever break one ill do as stated above.

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2006 yz285 (215# comp) with 180hrs (140+ w/ 285 jug) and still on my original, but I'm nervous about it.

I bumpstart at every opportunity and give it nice smooth kicks from TDC to minimize impact.

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Id guess one issue "may" be that some people just kick without engaging the gear first :lol: I like to get the kick starter engaged before I give THE kick.. :)

Good point. I didn't think about that. Some guys just slap the kicker without engaging it first. That may be the key here. I do check for engagement and maintain pressure on the engagement before I kick.

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Facts:

The kick start shafts were all the same from 1989 to 2001. The shaft itself is listed as a standalone part from Yamaha for 1998 and earlier bikes. 1999-2001 parts guides list the entire assembly only, as do 2002 and newer.

The side cover supports the outer end of the shaft, so a 1999-2001 side cover and oil seal must be used with a 1989-2001 shaft. All inboard components are the same. The shaft's splined outboard end is larger, so the 2002+ kick knuckle won't fit.

Been looking up parts, getting ready to do this on my '02.

2001 kicker looks like 2002, but with differences that make the outline above seem right.

2001 parts:

2001YZ250N1starterdiagram.gif

1998 kicker looks completely different than 1999-2001. You'd need to at least have #s 4, 5 and 6 along with #1, but I'm not really sold on the idea that the assemblies are the same. No part numbers are the same from 1998 to 2001. Has anyone actually verified interchangeability of the shafts?

I'm thinking the information I compiled above included a typo (in the original source post, not mine): Instead of the shafts all being the same from 1989-2001, they are all the same from 1999-2001. That would be an important correction. Also means the only chance of getting just the shaft is used, not from a dealer. If you go that route, get the spring guide #7 as well, because it is different (I assume to fit the larger diameter shaft).

I have access to a friendly machinist. I'm going to attempt to reverse engineer the dimensions from my old seal, shaft and side cover versus the new seal and shaft to determine what sizes to machine the cover to, rather than get a new cover. Even buying a couple reamers will probably cost less than a new cover.

1998 parts:

1998YZ250K1starterdiagram.gif

Edited by FRECNDY
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There were four kick shaft assemblies and side covers from 1999-2001 YZ250s on fleabay when I went looking tonight. The nicest ones are now headed my way. Looks like shaft assembly, cover and YZ450 lever are commonly available for about $50 each, so this problem is solvable, as of right now, for about $150 plus gaskets.

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Was about to pull the trigger on a 450 kick lever on fleabay, and did some more research on the Yamaha parts fiches on www.yamaha-motor.com. Glad I did!

BTW, I don't use TT Store or any other retailer listings for this kind of work, because I've ordered parts and gotten the wrong ones due to p/n being misassigned relative to the identifying numbers in the diagram.

Turns out not all YZ400-426-450 starters are the same.

I assume the following information makes YZ400 and YZ426 irrelevant.

In 2003, both WR450 and YZ450 used all the same part numbers in the starter group, including the 93102-18278-00 starter shaft oil seal. The bold, red 18 in the p/n indicates the shaft is 18mm.

In 2004, both WR450 and YZ450 changed to the 5XD-15620-00-00 kick lever assembly. All components in the starter group are the same between WR and YZ, including the 93102-20108-00 oil seal (part number indicates 20mm diameter). That seal p/n is used in all WR450 up to 2011 and YZ450 through 2012.

In 2006, the YZ450 changed the lever assembly to p/n 2S2-15620-01-00. All sub-components of the lever assembly are the same, including the 5XD-15621-00-00 kick crank boss, except the lever itself, which is a beefier part (and only listed as a complete assembly, not standalone). The WR450 didn't adopt the 2S2-15620-01-00 assembly until 2008. The kick lever p/n remain the same for both bikes until the last available data called out above.

It would be great if a moderator could clean up the incorrect reporting in the first thread (summarizing reading in other threads, rather than original research), or at least add some big notes telling people to read the whole thread for correct information. Thanks.

The YZ kick lever is completely different after the 2010 YZ450 changeover, and the kick crank boss (splined part that mates to the shaft) is a different p/n. However, the kick shaft assembly is the same 2S2-15601-00-00 used from 2006, so the lever assembly may also work if the shape is right.

Short version:

You need a 2004-2011 WR450F or 2004-2009 YZ450F lever assembly. Within that group, later ones are beefier, but heavier. They should all bolt onto the shaft the same. Forget anything 2003 or earlier, because they used the same 18mm shaft diameter we are trying to get away from.

Off I go to the Intarwebz to buy one and verify that it actually fits the bike right.

Edited by FRECNDY

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It's strange that some people break multiple shafts and some of us have multiple bikes with no issues at all. I have a 2002 and a 2010 with zero issues. My 2002 has hundreds (if not a thousand) hours on it with the same shaft.

Unless Yamaha has a QC issue in their heat treating department, there must be some difference in the way some of us kick the bikes. I tend to kick hard, jumping down on the lever with my weight (I'm a fit 165 lbs). My starters stop hard against the footpeg. This results in aluminum on the little stopper nub half-way up the lever getting dented/distorted and flaking off. It even results in slightly dented footpegs.

I would say I am merciless with my kickers, perhaps excessive and abusive. I have yet to break one or have any issue.

I see a lot of guys sort-of "half-kicking" their bikes. They stay sitting on the seat and just push down hard with their leg. I see these guys usually going two or three kicks to start a YZ250 because they aren't kicking it over as fast.

How are you guys kicking them over?

I always push slowly down on the kick lever with my foot until i feel it click into top dead center, then i bring it back up and kick it. Itll light first kick just about every time. Also doing it this way reduces the amount of energy you spend kicking, and reduces stress on your bike, as your using momentum from the crankshaft to throw the piston through the next compression stroke, instead of your kick starter.

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Some people seem to think that because they haven't had the problem, it doesn't exist or has to be user error. Quality problems usually aren't all or none. They're caused by variation. Maybe an entire production run of a part will have something wrong that goes undetected, and by the time all the parts are installed and the final assemblies distributed, it appears random to end users. Maybe there's normal part-to-part variation within specified process limits, but the limits were not well specified by the engineers and when two or three steps are all toward one end of the limit, the result is poor. Maybe some element of the production process is not controlled sufficiently and drifts in and out of spec without being recorded or noticed.

In the case of a shaft cracking, it could be the quality of machining (sharp(dull)ness of tool leaving a burr, notch or other stress riser, etc.) on the hole, one operator's deburring technique versus another operator's deburring technique, could be the heat treat on the shaft, could be a material lot, or it could be some combination of those plus other factors.

Making stuff well is damn hard!

Edited by FRECNDY

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Some people seem to think that because they haven't had the problem, it doesn't exist or has to be user error. Quality problems usually aren't all or none. They're caused by variation. Maybe an entire production run of a part will have something wrong that goes undetected, and by the time all the parts are installed and the final assemblies distributed, it appears random to end users. Maybe there's normal part-to-part variation within specified process limits, but the limits were not well specified by the engineers and when two or three steps are all toward one end of the limit, the result is poor. Maybe some element of the production process is not controlled sufficiently and drifts in and out of spec without being recorded or noticed.

In the case of a shaft cracking, it could be the quality of machining (sharp(dull)ness of tool leaving a burr, notch or other stress riser, etc.) on the hole, one operator's deburring technique versus another operator's deburring technique, could be the heat treat on the shaft, could be a material lot, or it could be some combination of those plus other factors.

Making stuff well is damn hard!

I think you're taking my comments about kicking technique the wrong way. I think these kick shafts are just like the broken 4th gears in these YZs. Some of us seem to have the issue while others don't. I have broken the 4th gear in my 2002 YZ250 twice, and I've had it sustain non-catasrophic damage a 3rd time. Other guys are like "What 4th gear problem?".

Just because I don't have any broken kick shafts doesn't mean the problem doesn't exist, or won't effect me or anyone else. I agree 100% with your statements about de-burring, stress risers, quality control, etc. When you design a part on the edge of material strengths, quality and consistency are that much more important.

Still, that weak part can be stressed harder by the way some people use it. I'm not saying it's their fault. Is it my fault that I trash 4th gears riding MX?

I think your thread and info is great, I'll keep it in my back pocket and if or when I break a shaft in the future I'll know the way to solve the problem.

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...Turns out not all YZ400-426-450 starters are the same.

I assume the following information makes YZ400 and YZ426 irrelevant.

In 2003, both WR450 and YZ450 used all the same part numbers in the starter group, including the 93102-18278-00 starter shaft oil seal. The bold, red 18 in the p/n indicates the shaft is 18mm.

In 2004, both WR450 and YZ450 changed to the 5XD-15620-00-00 kick lever assembly. All components in the starter group are the same between WR and YZ, including the 93102-20108-00 oil seal (part number indicates 20mm diameter). That seal p/n is used in all WR450 up to 2011 and YZ450 through 2012.

The YZ kick lever is completely different after the 2010 YZ450 changeover, and the kick crank boss (splined part that mates to the shaft) is a different p/n. However, the kick shaft assembly is the same 2S2-15601-00-00 used from 2006, so the lever assembly may also work if the shape is right.

Short version:

You need a 2004-2011 WR450F or 2004-2009 YZ450F lever assembly. Within that group, later ones are beefier, but heavier. They should all bolt onto the shaft the same. Forget anything 2003 or earlier, because they used the same 18mm shaft diameter we are trying to get away from.

Wow! Awesome detective work, FRECNDY. :bonk:

I thought I had already dug through all those 400/426/450 kick shaft part numbers and was sure what would work, but I'm glad you provided a "second set of eyes" to verify.

Hard to believe Yamaha used an 18mm kick shaft on a 450! :smirk:

EDIT:

I went back and looked at seal part numbers, and pretty much found everything as FRECNDY did, except for one thing...

Year Model Part P/N

1981-98 YZ250 OIL SEAL 93102-20309-00

1999-01 YZ250 OIL SEAL 93102-20484-00

2002-12 YZ250 OIL SEAL 93102-18278-00

1998-9 YZ/WR400F OIL SEAL 93102-20108-00

2000-2 YZ/WR426F OIL SEAL 93102-20108-00

2003 YZ/WR450F OIL SEAL 93102-18278-00 SHAFT 5TA-15601-10-00

2004-12 YZ/WR450F OIL SEAL 93102-20108-00 SHAFT 5XD-15601-10-00

1998-2002 YZ/WR400-426 kick levers will work; it appears only the 2003 YZ & WR 450s have the undersized 18mm kick shaft & lever.

Again, great research FRECNDY!

Edited by CaptDan

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I need to cut and paste this to my PC info.

Good stuff.

Edited by BRM

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