Valve clearances

I have a 2013 YZ450F and after riding it quite hard a few weeks ago I realized a noise in the motor most mechanics sugested its a piston slap or main bearings so i replaced the piston rings gudging pin timing chain and barrel was renicled I did a race this weekend and that same noise came back its in the top end so I checked valve clearances today and found that some sizes where out by .05 mm would this cause the noise I hear??

Ordinarily, valve clearances should grow progressively smaller, not larger.  This is because the normal point of wear is at the valve seat and the valve sealing face, and loss of material at that point causes the valves to move up into the head, closer to the cams.

 

YZ450's have a long reputation as one of the noisiest engines around, and the Gen3 ('10-'13) is no different.  Be sure it doesn't just sound like all the rest.

 

One unusual thing that does happen in some of the Gen3's is that the valve stem tops will shed their hardened cap, either breaking off a good sized bit of it, or just mushrooming themselves, making the valves shorter and increasing clearance.  That would be what I'd look at first in this case. Pull the cams, buckets, and shims and have a look.

Ordinarily, valve clearances should grow progressively smaller, not larger. This is because the normal point of wear is at the valve seat and the valve sealing face, and loss of material at that point causes the valves to move up into the head, closer to the cams.

YZ450's have a long reputation as one of the noisiest engines around, and the Gen3 ('10-'13) is no different. Be sure it doesn't just sound like all the rest.

One unusual thing that does happen in some of the Gen3's is that the valve stem tops will shed their hardened cap, either breaking off a good sized bit of it, or just mushrooming themselves, making the valves shorter and increasing clearance. That would be what I'd look at first in this case. Pull the cams, buckets, and shims and have a look.

Hey gray,

iI just adjusted my valves and within a few rides an intake valve is back to .08 (out of spec) would it be safe to say the tita I'm coating is wearing? Or why would it move so quickly?

Let me guess that it's the middle one....

 

Yes.  Almost all the mistakes you could have made would have resulted in more clearance, not less.  If it tightened up that quickly, it's probably time to replace it. 

Let me guess that it's the middle one....

Yes. Almost all the mistakes you could have made would have resulted in more clearance, not less. If it tightened up that quickly, it's probably time to replace it.

I think you thought I was the original poster. Lol well mine is a 2010 and there is only 4 valves. It is the left intake if you are sitting on the bike. Should they be replaced in pairs or is it ok to just do one. And stupid auto correct messed up titanium but glad you got it anyway. Thx!

I think you thought I was the original poster. Lol well mine is a 2010 and there is only 4 valves.

Reflex.

You can replace one if the others are OK. The very little used valve will have some wear in a narrow band around the sealing face, where it contacts the seat, but there will be areas within that band that are still the same dark gray that the rest of the valve is.  As it wears further, that band will "fill in" so as to look a lighter gray, then begin to turn bright, "polished".  If you see it worn bright, it's only a matter of time. 

 

 

... stupid auto correct messed up titanium but glad you got it anyway. Thx!

Once, I responded to a message that had been "corrected", then followed by a correction to the "correction". I intended to type "danged autocorrect". What I got was "fanged". :excuseme:

No worries I know your knowledge far exceeds mine. I can only hope to know as much as you one day. That's the Beauty of these forums. Thx again

I can only hope to know as much as you one day.

 

You might set your sights a little higher ;)

Ordinarily, valve clearances should grow progressively smaller, not larger.  This is because the normal point of wear is at the valve seat and the valve sealing face, and loss of material at that point causes the valves to move up into the head, closer to the cams.

 

YZ450's have a long reputation as one of the noisiest engines around, and the Gen3 ('10-'13) is no different.  Be sure it doesn't just sound like all the rest.

 

One unusual thing that does happen in some of the Gen3's is that the valve stem tops will shed their hardened cap, either breaking off a good sized bit of it, or just mushrooming themselves, making the valves shorter and increasing clearance.  That would be what I'd look at first in this case. Pull the cams, buckets, and shims and have a look.

 

 

Hi Grayracer,

 

I'm doing my first top end on my 2012 YZ250F @ 59hrs (piston+rings+gaskets). It's mostly back together now and I'm checking the valve clearances before I close everything up.

 

Intake spec: .12-.17mm

.23, .18, .25 (170 shims)

Exhaust spec: .17-.22mm

.21, .23  (176 & 180 shims)

 

You can see they're all on the high side of the spec. Is what you mentioned before (valve stem mushrooming) likely to occur on all valves? What else could cause all of the clearances to grow instead of shrinking as you say is the norm? Also, I don't think it matters, but the cam chain isn't on and the head+cylinder are not bolted on - is there anything I need to consider when measuring these clearances apart from having the cam caps correctly torqued?

 

P.s. apologies for hijacking your thread Adrian but I figured this was fairly on-topic.

I figured this was fairly on-topic.

That's not even a YZ450.

The head not being on torqued on the engine can make more difference than you think.

When I get a a new valve do I need to prep the seat in anyway? I wouldn't think it would seal the same as the one that comes out...is that logical thinking?

Ordinarily, valve clearances should grow progressively smaller, not larger.  This is because the normal point of wear is at the valve seat and the valve sealing face, and loss of material at that point causes the valves to move up into the head, closer to the cams.

 

YZ450's have a long reputation as one of the noisiest engines around, and the Gen3 ('10-'13) is no different.  Be sure it doesn't just sound like all the rest.

 

One unusual thing that does happen in some of the Gen3's is that the valve stem tops will shed their hardened cap, either breaking off a good sized bit of it, or just mushrooming themselves, making the valves shorter and increasing clearance.  That would be what I'd look at first in this case. Pull the cams, buckets, and shims and have a look.

This happened to my 2013. Top end became very noisy at first, then as I continued to ride it I began loosing power, until finally the bike would barely start and run. Tore the top end apart and...

Valvebad.jpg

Both intake valves looked like this. I would tear the head apart and have a look before riding much more!

When I get a a new valve do I need to prep the seat in anyway? I wouldn't think it would seal the same as the one that comes out...is that logical thinking?

 

Yes.  The seats need to be professionally refinished, either by cutting or grinding with tools specially made for the purpose.  NEVER lap a titanium valve under any circumstance.

This happened to my 2013. Top end became very noisy at first, then as I continued to ride it I began loosing power, until finally the bike would barely start and run. Tore the top end apart and...

attachicon.gifValvebad.jpg

Both intake valves looked like this. I would tear the head apart and have a look before riding much more!

Do you have a pic of the other intake?

I'd really be interested in someone more knowledgeable explaining why it looks like there's 3 retainer clips... My 11 only has 2...

Do you have a pic of the other intake?

I'd really be interested in someone more knowledgeable explaining why it looks like there's 3 retainer clips... My 11 only has 2...

No, I just took a pic of the worst side. The other side was just mushroomed badly. I'm not sure where your seeing 3 retainers? There are only 2, one is just badly damaged.

Valvebad.jpg

F.Y.I. this pic was from a brand new GYTR Head that came pre assembled. Less then 2 hours on it!! Replaced the intake valves with Faction MX stainless steel valves and springs and it has ran like a dream since :excuseme:

Edited by WYO522

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