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Engine jammed two times yesterday on YZF -03?

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Yesterday my engine jammed two times. Yes two times and yes you can call me stupid :):)

First time it jammed on a little jump but started immediately after I landed. I stopped to look what was wrong. I tought that something jammed the rear brake and when I landed it came free. Well I continued about 3 or 4 laps and all was good. Then I went for a break for about ten minutes and thought to go rideing again. I started the bike and a after about five seconds it jammed again. It made a metal to metal kind of sound both times.

I drained the oil and there was no sign of metal or anything else. I also took the valve cover of and didn´t find anything wrong there. The engine rotates like everything is okay. Next I´m going to inspect the top end and if needed piston, clutch and waterpump. I hope I don´t have to split the cases.

My bike is YZF -03 and has about 70 hours to it now. I have changed the oil after every 4 hours.

Any guesses what could be wrong. Piston, bearing...???

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This happened to me on my 2003. It locked up once coming into a corner, I thought I may have stalled it with the rear brake. It started after that and i kept going. after another 15 seconds stalled again, this time the kick starter had some drag on it, so i pushed it back. The bike had just been re-shimmed so i thought it may not have been assembled right, so i took it back to the mechanic. He pulled the top end apart first. could not find anything worng with it. He then split the cases, everything was sweet so he split the crank. There was nothing wrong with the big end bearing, but he put a new rod kit it anyway. He put the whole bike back together and it runs fine. He said it may have something to do with the kickstarter gear being jammed.

hope your bike turns out the same and is nothing too major.

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Oh Shit, look out.

I just put my '03 back together from a blown 4th gear. My symptoms were I did a a long practice moto with everything OK. 2nd time out went to kickstart and the bike was locked up feeling like kickstart gear was the problem. I put in gear and rolled it backward and bike started w/o incident. Rode 2 moto's w/o incident. Next start had same problem so I did the same as above and it started. When riding this time I heard what sounded like chain chatter but only in 4th gear. Guess what? 4th was in multiple pieces floating around my oil sump. The lockup was caused by some chunks wedging between the flywheel (magnetic)and the stator. Rolling it backward dislodged it.

To check for this put bike on the stand and roll the wheel backwards. Go through the gears (spark plug out) and listen. If it's not smooth you'll notice a big diff in the sound and smoothness.

03's and 04's are bad about blowing 4th.

I hope this isn't your problem.

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My bike is YZF -03 and has about 70 hours to it now. I have changed the oil after every 4 hours.

QUOTE]

The 1st blown 4th I got was 69 hrs (hourmeter) and this last was 122 hrs.

Do the transmission check and you can also just pull in the clutch in gear and reverse.

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I found out what happened. Yesterday I started to remove the cams and thought to adjust the timing marks first. I rotated the crank to align the rotor mark. The punch mark on the exhaust cam was on the cylinder head surface but the punch marks on the intake cam were not :)??? I rotated the crank few times to check again but no. The intake cam didn`t´t align right. So there it was. The intake cam had jammed and the chain had jumped. Alltough there is no sign of that on the intake cams teeth.

The damage doesn´t look bad. I hope the slide bearing surfaces can be polished or reworked, machined or something. My biggest concern is that the cylinder head is non repairable. The intake cam looks okay and valves hasn´t hit the piston :) .

So what do you think. What was the reason for this to happen? Oil channels on the head are not blocked. Well at least not now when I checked them. I haven´t looked at the oil pump yet.

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Maybe the cam cap bolts were over-torqued from the last valve adjustment? They only call for 90 in/lbs. Just a thought.

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I don´t believe that they were overtorqued. I have adjusted the valves once and that was 13:48 hours ago. I replaced every shim to 0,05mm smaller but to the middle intake valve I had to change 0,2mm smaller shim?? I took valves of but didn´t find anything wrong with them.

One other thing that has bothered me is that I just installed new used radiators to my bike. This was second time that I was riding after installing them. They didn´t leak and I checked many times that there was coolant.

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The damage doesn´t look bad. I hope the slide bearing surfaces can be polished or reworked, machined or something. My biggest concern is that the cylinder head is non repairable. The intake cam looks okay and valves hasn´t hit the piston.

call these guys --> http://www.enginedynamics.com/

see

http://www.enginedynamics.com/services.shtml

jim aka the wrooster

'01 wr250f

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Thanks Wrooster but I live in Finland. I work at airplane engine workshop so first I´m gonna ask what can be done here. I´m not a machine specialist but I know that they can do allmost anything here if only they have right tools. Now it looks like that slide bearing surfaces need only polishing. I´ll give it to guys here who do this kind of repairs daily. I´ll let you know how it goes.

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Since you so recently were inside the engine, my guess is that the cam chain tensioner was re-installed improperly or is not working, allowing the cam chain to jump time. Make sure it's working properly, and carefully read the manual for the installation procedure.

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I found out what happened. Yesterday I started to remove the cams and thought to adjust the timing marks first. I rotated the crank to align the rotor mark. The punch mark on the exhaust cam was on the cylinder head surface but the punch marks on the intake cam were not :)??? I rotated the crank few times to check again but no. The intake cam didn`t´t align right. So there it was. The intake cam had jammed and the chain had jumped. Alltough there is no sign of that on the intake cams teeth.

The damage doesn´t look bad. I hope the slide bearing surfaces can be polished or reworked, machined or something. My biggest concern is that the cylinder head is non repairable. The intake cam looks okay and valves hasn´t hit the piston :p .

So what do you think. What was the reason for this to happen? Oil channels on the head are not blocked. Well at least not now when I checked them. I haven´t looked at the oil pump yet.

This is what I would of guessed. My yz400 did the exact same thing. If you overtorqued the cam cap bolts that will cause this. I learned the hard way. Make sure that the cam sprocket hasn't spun on the cam. The cam sprockets are only pressed on. When you sieze a cam you may have spun the cam sprocket and not jumped timing. Took me forever to figure this one out. This dosn't happen very often but it has happened to some of us.

If you have a good maching shop they can press the sprocket off and reinstall it in the correct orientation (whatever that is) and then weld the cam sprockets in place. Or but a new intake cam (what I did)

Replace the timing chain while you are in there. They are cheep. :)

Reset your cam timing marks and look at the cam lobes they should look like this

good_cam.jpg

If they look like this you have troubles with the cam gear

bad_cam.jpg

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Well it wasn´t so recently when the tensioner was touched last time. It was 13:48 hours ago. My bike has now 71:46 hours. Last time I checked the valve adjustment was at 69:40 and they were ok. It´s nice to have an hour meter :p . I write everything down to excel-file so I have a full history. Alltough I bought it used, but it was from someone I knew so I knew also the history approximately before I bought it.

Now the cylinder head intake cam´s slidebearing surface is fixed (I hope). It only needed some honing (is that the right word?). The dimension raised about 0,02mm. The camshaft-to-cap clearance is 0,08 max and it is now about 0,06-0,07mm so it should be OK. :):)

Now I wish I find the problem that caused this.

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Make sure that the cam sprocket hasn't spun on the cam. The cam sprockets are only pressed on. When you sieze a cam you may have spun the cam sprocket and not jumped timing. Took me forever to figure this one out. This dosn't happen very often but it has happened to some of us.

Yes first I thought of that too, but the chain must have jumped because when the marks on crank and exhaust cam were on spot the intake cam was somewhere else.

Of course I can´t tell exactly if it hasn´t spun but I compared my cam to pictures in this site: http://dirtrider.com/tech/141_0412_yz250f_top and it looked to be same.

Are you really sure that cam sprocket can spin on the cam?

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Are you really sure that cam sprocket can spin on the cam?

if the cam bearing surfaces are galling, and the cam becomes difficult to turn -- yes, the cam sprocket (which is simply pressed on to the end of the cam) will spin in relation to the cam.

or put another way, the power and inertia of the piston, crank, and flywheel are driving the timing chain. if the cam is binding or stops in it's tracks, something has to give. either the timing chain breaks, the teeth come off one or both of the crankshaft and cam gears, or the cam sprocket slips in it's mount.

jim aka the wrooster

'01 wr250f

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Yes first I thought of that too, but the chain must have jumped because when the marks on crank and exhaust cam were on spot the intake cam was somewhere else.

Of course I can´t tell exactly if it hasn´t spun but I compared my cam to pictures in this site: http://dirtrider.com/tech/141_0412_yz250f_top and it looked to be same.

Are you really sure that cam sprocket can spin on the cam?

I am positive the cam sprocket can spin. I have one on my shelf right now that has spun. There is no splines or key ways on the cam/sprocket connection. Its just a round shaft on the cam and a round hole on the sprocket pressed together with an interferance fit. Thats it.

Like I said. It dosn't happen very often but it can happen. Just dont overlook it. It took me months to figure out why it wouldn't run right. Even the Yamaha dealer couldn't figure out that one.

From what I understand the Cam lobe centerlines are 105 degrees from Max lift. Asuming that max lift is when the cam lobes are pointed straight down then that would mean that the cam lobes should be pointed up at 15 degrees from horizontal (the valve cover surface) This is a rough guess mind you but should get ya close enough for diagnosis purposes.

If you think about it. When the intake cam siezes it stalls out the motor. There is a lot of force involved in this. Something has to give. Asuming that the tensioner dosn't back off there should be no way for it to jump timing (as long as the chain isn't worn out past what the tensioner can take up) So the next thing to go is the cam sprockets. The cam sprocket would have spun counter clockwise.

But the more I think about what you described it does sound like yours jumped timing cause the marks are off. If it spun the marks would still be on but the lobes would be out of time.

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jim,

the timing chain can also JUMP teeth on the cams as well, when a cam siezes.

hopefully it jumps enough to where it dies instantly, won't restart and does NOT hurt any parts.

yzman400,

you are most correct in that the gear can spin on the shaft. i know of one incident of this. happend back in '00 on a 400f of my friends. before any of the 250f's were out yet.

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Thanks for the info. Just another question. How can I tell if the intake cam sprocket has spun? If it has it has spun so little that I can´t tell it directly just comparing to pictures of a good cam. Does anyone know any accurate measuring techniques and measures?

yzman400, I didn´t quite understand what you meant. You said: Asuming that max lift is when the cam lobes are pointed straight down then that would mean that the cam lobes should be pointed up at 15 degrees from horizontal.

How can the cam lobes point to two directions at the same time? Am I missing something here? :)

And yes Rockyracer, I am definitely going to check the chain tensioner thoroughly.

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