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Yamaha YZ450F (2007)


Owner: Yammy Rider
Added on November 29, 2016
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just bought a 11' yz450f project that's got symptoms of a "locked up kickstarter"...any help?


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29 replies to this topic
  • kxfreak

    TT Platinum Member

1,585 posts
Location: Maryland

Posted July 26, 2016 - 05:30 PM


hey everyone, I've been away for a LONG time. riding became more scarce in my area and haven't been in the MX scene for a while. anyways, as you all know you can never get rid of that itch for off road riding, the street just doesn't cut it. long story short, last night I bought/traded for a 2011 yz450f. supposedly the previous owner was riding, shut the bike off, went to kick it and the kickstarter seemed jammed up. I searched the forums and saw alot of post about this and read how alot of people have this happen and can rock the bike in gear to free it up. I did this, and sometimes it free up for almost a full rotation but locks up again. to me this screams valves and timing!!!? so when it's in gear and I rock it I can hear some noise inside the motor but it's hard to put my finger on it. I pulled my stethoscope out and gave it a listen and I seemed to "source the noise" from behind the Kickstart lever. my question is has anyone else had this issue and not have been able to free it up by rocking it and found something moved out of place in the Kickstart mechanism? does the timing jump that often on these bikes? I just picked it up last night and haven't had a chance to go over it yet, and probably won't until this weekened. of course I will be checking the timing, but if the timings spot on is there something I should look for before I pull the head off(can I gain access to the kickstarter gears through the clutch cover?) sorry for the dumb questions, I am a boat mechanic by trade, my memory of working on Mc bikes is just vague.

BTW, I did pretty good on the buy/trade, so I'm prepared for the worst, but hoping for the best. thanks again, I just can't wait to get back out on the dirt.

  • damnbiker94

    TT Member

58 posts
Location: Georgia

Posted July 26, 2016 - 05:42 PM


Not much if anything can get out of place on a kickstarter setup with the clutch cover in place. Could be many things causing the lockup. First and foremost, pull the valve cover and check valve clearance and valve timing. Note any issues and proceed from there. Pulling the head would be the next step after that. Then rotate the motor slowly to see if you get any lockup or binding. Also check crank/rod specs while you are there. Post up your findings.

  • kxfreak

    TT Platinum Member

1,585 posts
Location: Maryland

Posted July 26, 2016 - 07:31 PM


I definitely will, I forgot to ask in my OP but how often do these Cam chain tensioner go bad? I know when I jumped the timing on my r6 last year it was because the tensioner was failing and they were known to start failing every 16,000 miles so I replaced it with a manual CCT.

  • nucular

    TT Silver Member

636 posts
Location: Indiana
Garage View Garage

Posted July 26, 2016 - 08:02 PM


If the timing is good, I would think the rod bearing is the next likely culprit.

  • grayracer513
42,862 posts
Location: California
Garage View Garage

Posted July 27, 2016 - 06:20 AM


The tensioner is almost never at fault when the timing slips in a YZF using stock cams and valve springs.  Usually, it's the chain itself.  It can develop stiff, binding links that interfere with the correct operation of the tensioner.  IMO, it's caused by inferior oil maintenance, since that's been a common trait among the failures I have personally seen.



  • kxfreak

    TT Platinum Member

1,585 posts
Location: Maryland

Posted July 27, 2016 - 02:18 PM


okay, so I ended up getting off work a little earlier than planned today, gave the bike a wash down and decided to start tearing into it even though it's about 110°f in my garage, it's just been driving me crazy. so as planned, I went straight for the valve cover and plug on the crankcase to determine TDC. sure as sh!the, the timings off at least 1 tooth on the exhaust side, maybe even more. while doing the rotation of the crankshaft manually it's locking up right before, and I mean right before it hits TDC. so I'm keeping my fingers crossed that the timing has jumped enough so that it's catching the valve just enough to stop it up. i know that might soundshere's a picture although it's hard to tell how far off because it's a picture, and you have to compensate a tiny amount for it being just a hair off TDC. I'll keep you guys posted

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Edited by kxfreak, July 27, 2016 - 02:23 PM.


  • grayracer513
42,862 posts
Location: California
Garage View Garage

Posted July 27, 2016 - 03:09 PM


Well, from the picture, neither cam is more than a half tooth out, which suggests that the crank isn't positioned exactly on the mark (or that the chain is rather worn).  Remember that the cam in front is the intake on this engine.  Something most people don't know (and I don't know why it's like this) is that the timing mark on the EFI bikes is not located at TDC, but a bit ahaed of that, so be sure you use the mark itself and not actual top dead center for this job.  My best guess as to why is that the bore offset has something to do with it. 

 

Your diagnosis sounds plausible nevertheless if your getting a stop right as it gets to the top.



  • kxfreak

    TT Platinum Member

1,585 posts
Location: Maryland

Posted July 27, 2016 - 03:35 PM


yes, correct the intake is forward, it's to help with the gyroscopic effect while riding supposedly. the intake cam is pretty close if not damn near on, but like I said the exhaust cam is about 1 tooth off, the angle of the picture is just deceiving. when it cools down I'm going to go back out there and investigate more. as much as I'd like it to be something with the head, I just have a feeling it's going to be something in the bottom end. the PO stayed that he had a local mechanic, that use to work on my bikes when I was younger, just go over the bottom end and put new main bearings, new gasket/seal kit, and so on and so forth. which I can tell that the bottom end was recently split and reassembled. the noise I'm hearing just doesn't sound like valve interference. my next move is to remove the cams and see if I can get a full rotation, if not I'll have to dig deeper

  • grayracer513
42,862 posts
Location: California
Garage View Garage

Posted July 28, 2016 - 08:09 AM


... it's to help with the gyroscopic effect while riding supposedly.

 

 

Not actually, no.  But that's sidebar to the topic. 

 

http://www.thumperta...3#entry13091658

 

Besides, there is no gyro effect from the relatively tiny camshafts spinning at half crank speed, and where it is in relation to the exhaust cam or the rest of the head would make no difference if there was. 



  • kxfreak

    TT Platinum Member

1,585 posts
Location: Maryland

Posted July 28, 2016 - 09:06 AM


sorry, that's just what I had read in another topic on here, sorry for the mis information i should have looked into it a little more before stating it. like i said i havent looked into much about this bike or mx period for the past several years...my concern is what's going on with it currently but I'll check out that link you posted later tonight. anyways, as an update, i adjusted the timing, I was able to get the marks to line up pretty perfect but still no luck. I guess it's time to just pull the whole thing out of the bike and get it on the bench. I'm baffled because you can clearly hear whatever it is causing it to catch up; but it's coming from the area near/behind the kickstarter shaft. anyways I'll get some more pics when I actually find the problem....

  • grayracer513
42,862 posts
Location: California
Garage View Garage

Posted July 28, 2016 - 11:27 AM


If a valve was bent, and bent while it was far enough opened it can become jammed in the guide and hang out far enough to become a piston stop.  Much less likely but possible is a broken valve with the valve head laying on top of the piston.  I say less likely because 1) I haven't yet seen or heard of a valve failure in a four-valve YZF, and 2) such failures are usually extraordinarily dramatic and destructive to the point that the symptoms are much worse than what you have so far.



  • kxfreak

    TT Platinum Member

1,585 posts
Location: Maryland

Posted July 31, 2016 - 09:05 AM


okay, I didn't delve into the bike as far as I had hoped to yet....but I've come to the conclusion it's time to clean up my bench, pull it out, and start a major breakdown. so I took the valve cover off, removed the cams, pulled the buckets and inspected the valves from the topside. they all looked as if they were in good condition, nothing looked seriously out of place. even without the cams in, still couldn't get a full rotation. drained the oil, it looked good and clean. pulled the oil filter and I can definitely see remnants of a bearing failure(that's what it looks like to meel, very Fine metal dust/particles in the filter housing and gray/silver color when oil from filter is wiped on white rag). I didn't see any large metal chunks, just that real fine stuff the screams bearing failure to me. so after doing some looking around I'm curious if anyone here has, or knows of someone who has had experience with those wrench rabbit rebuild kits on ebay? they seem awfully convenient and come with everything for the lower end and the piston which would just leave me with having to purchase valves and valve components else where. Or is there something better out there? thanks for all the help guys

  • cpetz24

    TT Bronze Member

427 posts
Location: Missouri

Posted July 31, 2016 - 12:58 PM


Have you pulled the clutch cover and inner clutch cover off to look at the kickstart gear, idler gear, clutch basket and primary gear?  You can do all this with the motor still in the bike. If something is broke, like a gear tooth, you could save it a lot of work nit having to pull out the entire motor..  

 

I've had a gear tooth break on the clutch basket and just fold over which would then lock the kick starter up as it came around.  It would rotate but then lock up.  



  • kxfreak

    TT Platinum Member

1,585 posts
Location: Maryland

Posted July 31, 2016 - 01:28 PM


no I haven't as of yet, but I was planning to before I pulled the motor out. I'm still having my fingers crossed that the problem is something as simple as that, like I said before the symptom I'm getting from the motor, and the way it's locking up does not seem/sound like a bearing but as a broken gear because it's so smooth and quiet through the partial rotation I can get, than all the sudden it catches, in the same exact spot everything. I also used my stethoscope to try to help pinpoint where the noise was coming from and it's behind the Kickstart lever area. the temp/humidity here is still unbearable so I'm favoring being anywhere but in my garage (with no a/c) at the moment. hopefully your right CPETZ24, and as soon as I do find the problem I'll be snapping some pics

  • kxfreak

    TT Platinum Member

1,585 posts
Location: Maryland

Posted August 01, 2016 - 07:41 PM


So today it was finally somewhat moderate Temps. I got off work cam home and jumped right into ripping the clutch out to gain access to all those trinkets behind the basket. I was hoping to find a broken/chipped gear in there, but nothing. On a positive note ever spun super smooth, was nice and tight, and looked to be in excellent condition. Looking in the hole that would be the clutch cover with the basket and stuff removed, I could see the piston and rod through a small gap. I had my handy dandy assistant(my fiance) turn the crank while I studied it's movement, and to my delight it seems it has a spun rod bearing. On the bright side though, things could be much worse.

so if I'm going to have to tear the cases open, I'd like to do a rebuild while I'm in there even though it might just be the rod bearing. as far as the wrench rabbit kit goes, it comes with a hot rods crank which I've heard mixed reviews about. Have any of you used one before? I know I'm jumping the gun, because if I get in there and the OEM cranks not scored I'd like to keep it original. I might price out just buying everything seperate and see how much it will cost if I shop around. anyways, just would like to thank all of you guys for the help, especially you GRAYRACER.

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  • billygildark5007

    TT Silver Member

503 posts
Location: California

Posted August 01, 2016 - 08:48 PM


I'm pretty sure it's not just my opinion but I would stay away from anything hot rods if your planning on keeping the bike...
Especially the crank and head/base gaskets....

  • grayracer513
42,862 posts
Location: California
Garage View Garage

Posted August 02, 2016 - 06:26 AM


Haven't taken the head off yet?



  • kxfreak

    TT Platinum Member

1,585 posts
Location: Maryland

Posted August 02, 2016 - 05:09 PM


I had not taken the head off at the time of my last post. I had a half day today and used some of the time for just that. as for an update, it's not so good, lol. so after noticing something was ajar yesterday with the rod/crankshaft, I finished removing the head. what I found wasn't too, good. The valves are ok, but the head is is scored. Most of the marks in the picture are metal fragments smashed, so I won't be able to tell the full extent of the damage until it's cleaned but the future of it is uncertain at this point. To me the metal fragments appear to be portions of a main bearings, anyone else see that or what's your opinion? from what I can see in the cylinder it doesn't look scored up but I can only get access to the top half. so now the question is what's the rest of the bottom end look like? try find a new motor or go forth with bring this one back to life.

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Edited by kxfreak, August 02, 2016 - 05:12 PM.


  • grayracer513
42,862 posts
Location: California
Garage View Garage

Posted August 03, 2016 - 05:59 AM


Main bearings? Explain how main bearing frags would get on top of the piston without a hole in the piston, or a huge gash in the bore. 

 

The piston has been hitting the head, so either the cylinder shrank, which as far as I know has never happened, or the crank has failed.  Leak check the valves by filling the ports with solvent.  Odds are you'll need to replace them anyway and have the seats finished, but you might get lucky.  If there's no damage to the cylinder and it measures within spec, a new crank and a valve job should get you out of trouble. 



  • kxfreak

    TT Platinum Member

1,585 posts
Location: Maryland

Posted August 03, 2016 - 06:29 AM


I was wondering the same thing, but what piece of the motor would you think that looks like? I don't understand where those fragments came from or how they got up there, I can't explain it I was just staying that that looks like a piece of a main bearing, the round fragment, that is. as for the other piece I haven't the slightest clue. I was going to do a leak test this evening, but I'm staying optimistic.





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