HEADS UP!!!

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Braaap04

Motor locked up

36 posts in this topic

2012 YZ 450F locked up on me last night. I went riding for about a half hour. I shut the bike off, to take a break. When I went to start it, motor was locked completely up. Kicker would not budge. When I put it in gear and tried rolling it, the bike made a bad grinding sound.. Valves are within spec.. Oil change with filter had about 2.5 hours MAX on it, with a freshely cleaned and oiled filter. Ruffley 20-30 hours ago I checked how many hours the bike had and it only had about 24ish hours on it. Wtf happened? Wasnt overheating. HELP!! 

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Cam timing is the most likely culprit.  Remove the cover and check. 

What could have made it change and what could it have broke?

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If it's the chain, you will probably find it has several tight, binding links.  If present, these can keep the cam chain tensioner from extending as far as it should.  Then, when the engine stops, if it happens to rebound off of the compression stroke, or kicks back slightly on the following startup, the kinks get yanked out of the chain going backwards, slack appears, and it skips time.

 

That being the case, the chain will be defective, the tensioner may be damaged, and you may have bent a couple of valves and possibly broke a valve guide as well.

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If it's the chain, you will probably find it has several tight, binding links.  If present, these can keep the cam chain tensioner from extending as far as it should.  Then, when the engine stops, if it happens to rebound off of the compression stroke, or kicks back slightly on the following startup, the kinks get yanked out of the chain going backwards, slack appears, and it skips time.

 

That being the case, the chain will be defective, the tensioner may be damaged, and you may have bent a couple of valves and possibly broke a valve guide as well.

Well I have the motor out so I will start tearing it down. Priced some stuff oil and this isnt gonna be cheap.

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Hope it's not too bad.

Me too. The year before this bike I bought an RMZ that blew from the tranny up. Spent all summer fixing it to only get rid of it. Rode that twice. Now this happened with my yzinger. Half a summer on it  :bonk:

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I found one missing circlip from my piston and found one broken cirlcip in my stator cover.. With no damage inside the cylinders what so ever

Edited by Braaap04

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Do u have the cylinder off? I wanna see a picture of this

Edited by Chris7280

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Do u have the cylinder off? I wanna see a picture of this

I will take a picture of it when I get done with work. I couldnt believe it either

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I found one missing circlip from my piston and found one broken cirlcip in my stator cover.. With no damage inside the cylinders what so ever

when you say this are you saying one of the circlip that holds the piston to the rod came out and you found it inside the stator cover, or did you find 2 different circlips? if it's just the one from the piston if it came out it could find its way to the stator cover quite easily. have you ever done a rebuild on the bike? sounds like whoever put the piston in didn't seat the clip all the way. however, this wouldn't have caused the symptoms you described, so had the timing jumped?

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when you say this are you saying one of the circlip that holds the piston to the rod came out and you found it inside the stator cover, or did you find 2 different circlips? if it's just the one from the piston if it came out it could find its way to the stator cover quite easily. have you ever done a rebuild on the bike? sounds like whoever put the piston in didn't seat the clip all the way. however, this wouldn't have caused the symptoms you described, so had the timing jumped?

No I only found one circlip. It was the one that holds the wrist pin in place in the piston and found it in the stator cover. When I bought the bike, it was freshly rebuilt by the previous owner. As far as the timing jumping, I honestly forgot to even check it before I took it apart.

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So great news! I over looked my piston. Idk if it was the oil covering the circlip mixed with bad lighting or me just going to fast. Anyways, both circlip are in the piston and it's not missing. So where could it be from? Tranny?

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Looks like a wrist pin clip to me.  Probably was dropped in during a previous piston change.  Nothing like that one in the transmission.

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I'm just confused and getting frustrated now. Without the head on, motor spins freely. Put the cylinder and head on it. When to time it and again. You can only turn it so far before it hits something. I can feel it hit the compression stroke, then it feels like it his a wall and won't budge. I don't get it. Bent valve..?

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Head on, plug out, no cam chain...will it turn over?

 

If it will, time it, then look at the lobe position from the right side.  They should be pointing up at roughly 25 degrees and toward each other.  If they don't either one of the sprockets slipped or you did something wrong.

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