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Joe846

2012 YZ450 loose exhaust valve

24 posts in this topic

I checked my valves today and ran into a small issue: a big movement towards loose on one exhaust valve. Last time I checked them, at 20 they hadn't moved at all, which I was hoping would mean little to no movement up into the 50+ hour range. That held pretty true through 3 of 4 valves until I hit the last exhaust valve and to my shock could just fit a .28 feeler gauge through! I check my math, checked again and then decided to the turn the motor over a few more times and press on the bucket to be sure it hadn't been locked in place by oil friction. After that the .28 wouldn't fit any longer, but to my displeasure I could still fit a .26 gauge. Granted, this is only .01 out of spec, but the last two readings were .23 on the dot, so I'm a little perplexed as to how the other three valves are in spec and this one has jumped to loose by such a large margin.

I'm guessing carbon build up, especially since the reading changed slightly after turning the motor over, but I'd love to here any other theories. A slightly bent valve is possible I guess, but I ride off road and don't ring it out on the limiter. Just confused as after years of checking valves I've never had them get looser, or had a spring wear out, bucket wear through, etc. Especially after so few hours.

And, if you agree it's carbon build up, any thoughts around what I can do to loosen them from the valve/seat (fuel additive, high heat, etc.)? I can take it all apart if need be, but I'm hoping that won't be necessary as I hadn't planned on cracking it open until 50-75 based on compression and how the motor felt/started.

Oh, and FYI the fuel has been rich-end at the bottom and the ignition has been retarded a bit to help ease the hit at first crack of the throttle.

Come on Grey, give me some love on this one.

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The easiest way to check for carbon affecting the clearances is to roll the engine around to where the valves are closed, the tap the lifters a few times lightly to bounce them off their seats and slam them shut a couple times, then check them again.

If this tightens things back up, you can try some commercial automotive injector cleaner additive (read the label for mixture ratios).

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The easiest way to check for carbon affecting the clearances is to roll the engine around to where the valves are closed, the tap the lifters a few times lightly to bounce them off their seats and slam them shut a couple times, then check them again.

If this tightens things back up, you can try some commercial automotive injector cleaner additive (read the label for mixture ratios).

Thanks Grey. I tapped the valve lightly, but all I had around was a brass shock punch and I didn't have the cams out so I didn't get a good whack. I know that doesn't always work, so if I don't tighten them back up with a few hard taps, should I just take the head off to see what the deal is? Oh, and I need an aluminum drift, huh?

Is there anything else that would happen to loosen them up that I'm missing other than wear on the bucket/cam or a bent valve stem?

Edited by Joe846

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I would pull the cams and check the tip of the valve. Mine wore down till the keepers let the valve drop. On mine it looked like the hard coating wore off, and then the valve wore down quickly after that. It was also exhaust valves on mine. One valve still looked perfect but I replaced both exhaust valves anyway.

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Thanks Grey. I tapped the valve lightly, but all I had around was a brass shock punch and I didn't have the cams out so I didn't get a good whack. I know that doesn't always work, so if I don't tighten them back up with a few hard taps, should I just take the head off to see what the deal is? Oh, and I need an aluminum drift, huh?

Is there anything else that would happen to loosen them up that I'm missing other than wear on the bucket/cam or a bent valve stem?

We aren't talking about smacking the lifters hard enough to worry over whether the punch is steel or wood, really. All you're trying to accomplish is to lift the valves of their seat an have them slam closed as hard as possible. It takes very little pressure to raise the valve (in fact, you can lift them off their seats by using too big a feeler gauge), and if you smack them too hard, you can potentially disengage the keepers.

As far as anything else that might make the valve looser, there have been a couple instances of the hard cap coming off the top of the valve stem as was mentioned above, and wear in the cam bore can also cause it. Check the camshaft clearance in the head if you suspect that.

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Great feedback, thanks guys. Going back to tap on the bucket again to see if anything loosens around the valve seat. If it's still overly loose I'll be pulling the cam to get a closer look.

Bummer to hear about the valves wearing down around the retainers... Good to know though!

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Yeah you may want to lift that cam and have a look. I just found my right ex valve loose and after lifting the buckets i found the top of the valve has flaten...

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I ordered gaskits, ex valve along with new keepers and such today. Hey luckyguy how is your new valve holding up? i am hoping this will be one time issue. But i have noticed that it seems to be the right side acting up if you have this issue that is.

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Mine's the left side exhaust valve. I doubt it's a side dependent issue, if it's an issue at all as that would mean there were some issues in the head, cylinder or cam lobe on one side only. Sounds more like it maybe a semi-consistent issue with the valve coating, fusing or make up.

I'm going to leave mine for now as it's barely out of spec and check it again soon. If it's moved again, I'll let you guys know what the top near the retainers looks like when I pull the cam's. Hopefully it's just some carbon on mine, and heating it up at the end of a ride will clean it out.

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yeah if your gap is becoming looser i would check that valve before launching off and double or tripple. unless your burning large amounts of oil i just dont see how fuel combustion carbon can build up on the matting surface of a valve without the valve working it off the direct seating surface...

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unless your burning large amounts of oil i just dont see how fuel combustion carbon can build up on the matting surface of a valve without the valve working it off the direct seating surface...

It doesn't build up on the seat itself. When carbon is at fault, it's usually a ridge that forms on the stem where it meets the guide, or just inboard of the actual face of the valve where it seats. It's also quite a bit more common on intakes than exhausts.

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Same deal. Although that type of carbon build up on an intake valve I have only seen on motors with EGR valves and PCV systems running into the intake and these motors do not have that… I wouldnt ride it without looking it over but thats just me. This post made me look mines over because i trust this bike as well of my others to cover 95 plus feet gaps in the air. Good luck.

Edited by Modmotoman

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I've only got a few hours on the bike since I got the new crank in. Seems to be running great. After about 10 hours I'll check the valve clearances again. I bought a YZ125 around the same time that this happened and have been spending most of my time on that. Braap.

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Thats good, I sold my backup 2007 YZ250 smoker because i keep breaking everything on it. My brother had the same issue with his, if you ride them hard they like to blow 3rd gear every 6 months and crack pistons when ever it feels like.

Too bad cause i sure miss that bike but i was tired of working on it.

I tend to put 4 hours a week on the meter of my YZ450f so i will keep you updated as to how it holds up in a month or so.

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Update. I checked the valves again after probably 5 more hours and the exhaust valve in question moved from .26 to .36! So, the bike is parked obviously, and I'll be pulling the cams if I have time this weekend.

At this point I'm guessing it has to be an issue with the valve wearing down at the top of the step and the bucket dropping as I can't imagine that much more carbon has built up on the one valve in such a short period of time. Also, you can see the bucket sitting lower than the other exhaust valve.

I'll let you all know what ends up happening and if I got away without any scuffing on the piston. Really disappointing that there seem to be some exhaust valve issues on some of the newer YZF's as reliability is one of the two main reasons I bought the bike. Oh well, that's the way it goes.

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Ok, I had my problem on the right side. Honestly I'd rather see people having problems with both valves rather than just one side. Better a valve problem then a head casting or heat build up problem.

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