YZ 250 Kickstarter Axel "WARNING"


118 replies to this topic
  • mullet708

Posted March 17, 2009 - 05:04 PM

#1

After reading another post that I found in the general section on here of another rider with a YZ250 and a broken kick start axel, I started thinking that maybe we should be looking a replacing this part on our YZ’s at certain intervals as a preventative maintenance. It seems to be a very common problem I am starting to see, for me it’s the only problem I have ever had with my YZ250 that left me without a bike but it couldn’t have come at worse time, I was on a 2 day trip to a indoor track. So I had bit of money invested in the trip, hotel, fuel in the truck, meals out and first thing on the 2nd just after I signed and paid to ride pulled the bike out of the trailer and on the 3rd kick the kickstarter axel snapped, luckily I was there with a group so I just shared everyone else bike which was fun but not the same (06 KX125, brother’s 07 YZ250F, and a 08 KTM 250SX). I got off lucky too because I only had to replace the Axel I had no case damage but I have heard of a few guys needing to replace the outer case as well. It really has me thinking that we should maybe be replacing this part in some type of hourly schedule I would say around 80 to 100 mark maybe a bit more. But for some trail guys this breaking miles away from the truck would really cause some problems. I only ride mx but still its annoying and a outer case isn’t cheap. I was just wondering what other people are thinking on this issue. It seems to be a common issue on the YZ250’s lately and I also give it as warning to guys with YZ’s that have a few seasons of use on them.

  • love2strokes

Posted March 17, 2009 - 05:07 PM

#2

why didnt you just bump start your bike to ride?

  • travisn

Posted March 17, 2009 - 05:07 PM

#3

Couldnt you just pop start it?

  • mullet708

Posted March 17, 2009 - 05:10 PM

#4

Nope when the axel brakes its in side the engine, so the outer case is no longer holding the assembly in place as well there is 3/4" hole left by the missing axel, oil will spill out and dirt will get in

  • travisn

Posted March 17, 2009 - 05:17 PM

#5

I figured it had to be something like that. Ouch, I wonder if my yz400f has the same fate

  • Anravqsuh

Posted March 17, 2009 - 06:48 PM

#6

I'm one of those guys who broke the shaft and outer case. Pain in the arse to say the least. I saved the the old shaft assembly and actually thought about having one made from a piece of billet based on the broken one.

I don't know anything about metalurgy but I figured someone who works with metal could come up with something stronger.

The metal just seemed to have twisted. Believe me I'll think twice whenever I kickstart my bike.

The cost and down time sucks.

  • RCannon

Posted March 17, 2009 - 06:54 PM

#7

How much is the part minus the case? This has happened to enough people that it just might be worth replacing on a regular basis.

  • mullet708

Posted March 17, 2009 - 07:18 PM

#8

the part is around $100 i got it from yamahasportsplaza.com plus gaskets and seals, in the very least i think we should be inspecting it, it seems to be cracking around the area in the shaft where the hole is for the spring, As far as metals and types i am pretty good in this feild being a tool and die maker dealing with different steel types, and hardening them to different hardness to what is need in the application the part is going to be used for. to me the problem with shaft is that they are too hard, making them brittle. ideal mat'l for this shaft would be something like a 4140 steel, and case hardened, case hardned means just the outside is hard helping to prevent ware usally to a depth of .030" to .050" then the inside is left soft, this gives you a part that is ware resistant but the soft core makes it tought and less prone to breaking. i cant see yamaha going that far beacuse for case hardening it cost a bit more than reg hardening. for normal hardening the steel is put into a oven brought up to its critical temp which differs depending on steel type. left for a certain time which depends on mat'l and thickness, then taken out and quenched in either air, oil, or water depending on steel type, after cooled its but back into a oven to draw it back, this relives some of the strees, the temp for this is much lower than the first heating and it is dependant on the hardness req'd and the mat'l type. but then case hardening the part is heated to its critical temp in a case filled carbon and it takes much longer at the temp needed, it can need over 8 hours some times in the carbon where just normal heat treating can be done in less than a hour, then it still has to follow the same quenching and draw back as reg heat treat process, in the very least i think yamaha has made these shafts way harder than they need to be, they are too brittle, they dont see much wear at all they dont need to be very hard.
i will try to post pics of broken parts tomorrow, i still have them in a drawer somewhere,

  • shrubitup

Posted March 17, 2009 - 10:08 PM

#9

Mine took a crap on me when I had my '03 (a bike I got to save some money cause I spent too much on my '04 making it street legal :banghead: :)).

I had just done a top end on the bike because it was new to me. Did my heat cycles and then installed a GYTR replacement flywheel. The woodruff key snapped and then so did the spline and then next the outer case. It was $250 at least in parts for all the gaskets outer case and the starter assembly - add to that the normal three week wait for the parts. I was TORQUED and mad to say the least. :banghead:

Now, before I kick my bike when cold, I run a tight checklist to make sure NONE of my kicks are wasted and have to be repeated - because the more kickin' it gets the sooner it's gonna snap (again). :foul:

  • BRM

Posted March 18, 2009 - 12:32 AM

#10

I was just considering bring this topic up. As a few of you know I have an 01 engine in an 06 frame and I'm in the process of rebuilding the 01 bike up with an 03 engine.
I was considering swaping the side cases, kick start shaft and kick start arm over so my 06 hybrid would look aesthetically more like an 06.
The only drama is the 02 + shaft breaking. The 01 is a lot thicker where the splines are and I presume inside also.
May be I would be better of just cutting the kick start legs off and rewelding them or just leave it the way it is.


Suggestions??

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  • Matt_W

Posted March 18, 2009 - 07:08 AM

#11

Add me to the long list of victims :) Happened to my 2005 in the fall of 2007. I was one of the unlucky SOBs who cracked the case in the process

Here is the thread I started about it. Included in the thread is a complete parts list with prices > > > http://www.thumperta...ad.php?t=563506

  • mullet708

Posted March 18, 2009 - 08:02 PM

#12

i was really really lucky to not have cracked my case, i think because i have read on here of so many fellow YZ 250 owners having this happen its always in the back of my find when starting my YZ, so when i was about half way through my kick something didnt feel right and pulled my foot off as quickly as i could and just let the kick start fall, im pretty sure thats what saved me from causing any damge to the case, but after making this post and seeing how many guys have had this happen, and think about all the ppl that have YZ 250's and dont come on here that are out there thats this has probably happened to it makes me think that its almost of question when is it going to break, then will it break?

  • rusky

Posted March 18, 2009 - 11:30 PM

#13

Big bore two strokes have a big problem with this. If you want to stay on the safe side then start your bike like you would a cr/kx 500:

1. Slowly kick the bike over, just by putting your foot on the kick starter and using its dead weight.

2. Then once you have gotten to TDC give it a good kick.

Most of the time kick start shafts break is we kick the bike when its not at TDC which causes a high build in pressure, especially when there is a lot of fuel in the cylinder which might even cause a hydro lock. Once that happens it puts extra strain on the shaft which after a couple hundred times will cause it to break (happens much more often on 500's).

  • RCannon

Posted March 19, 2009 - 04:03 AM

#14

I was just considering bring this topic up. As a few of you know I have an 01 engine in an 06 frame and I'm in the process of rebuilding the 01 bike up with an 03 engine.
I was considering swaping the side cases, kick start shaft and kick start arm over so my 06 hybrid would look aesthetically more like an 06.
The only drama is the 02 + shaft breaking. The 01 is a lot thicker where the splines are and I presume inside also.
May be I would be better of just cutting the kick start legs off and rewelding them or just leave it the way it is.


Suggestions??


I dont think anyone has broken an older model. I believe I would stick with what works.

  • BRM

Posted March 19, 2009 - 02:19 PM

#15

I dont think anyone has broken an older model. I believe I would stick with what works.


I was thinking the same, reliability ia a major factor to me, saves a lot of time also.
Thanks RC

  • RCannon

Posted March 19, 2009 - 03:43 PM

#16

I am not going to kick start mine again. Bump start only or I am moving to a house on a hill.

I wonder if we might have any action available? Remember when the factories could deny problems like this? Things like the XS 1100 having a flexible frame. It was chalked up to "bad paint" Oddly enough this occurred at the swingarm pivot. I was lucky in tha tthe death wobble only sent me 140 feet, broke three ribs, punctured my lung, etc.

Yamaha said back then, "No, yours is an isolated incident."

  • mullet708

Posted March 19, 2009 - 04:18 PM

#17

i have thought about contacting yamaha, i just dont really know how to go about it, and im not saying i think i will get or want to get something from them i just think this problem should be brought to their attention, so they can improve on it and maybe make an update kit or something

  • bryawn

Posted March 19, 2009 - 04:31 PM

#18

You are not lucky that it didn't break your case. The reason the shaft breaks is because it doesn't get enough support from the case and then gets bent down through normal use, causing it to fail. I'm speaking from experience.

The shaft on my 02 broke so all I did was replace the kick starter shaft. Thought I was "lucky" that the case was OK. It worked fine for a few weeks and then it broke again. I have to say that I really don't like that feeling. The second time, it did break the case, which as it turned, out was the source of the problem. The tolerances around the shaft were a bit much.

If I were you, I would stop using the kickstarter and get a new case ASAP. That way you won't have to buy two shafts. You're on borrowed time right now.

  • mullet708

Posted March 19, 2009 - 06:16 PM

#19

i acutally thought that may have been the case with mine, so i checked the fit of my new axel with my case it was snug no play, and the hole was not out of round, i really do think yamaha's heat treat process for these is not right and they are using way to hard of steel that is just brittle and has not be tempered right, some last longer than others, if you read the link MATT W left there is a guy in his post that had it happen twice with in a few months and the case went the first time for him and the 2nd time it didnt.

  • harjp1959

Posted March 19, 2009 - 09:42 PM

#20

Here's a fiche of the kick start on the '03 model. Which part is the one that is breaking??

http://www.phoenixpo...=2003&fveh=1174





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