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Valve issues explained?

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Hi Guys,

I've recently had issues starting my 450, and although I haven't used my bike very much lately (actually twice max last year) the symptoms are suggesting I have an issue with my valves.

The task doesn't look too bad, so once the nice weather gets here I'm gunna pull the 450 out and double check the clearances.

There are lots of articles (thanks TT!) on how to check them, what I'm looking for and even how to shim them. The only thing I don't see a lot of information on is an actual explanation of the issue.

I know some people say causes could be bouncing off the rev limited (which I have never done) or dirt getting past the filter, but I'm looking for a more detailed explanation of what is happening to the valves, how exactly they work, and what damage can be done. The only bike I had before this (dirtbike anyways) was an old XR and I never had any issues.

If someone can point me to some information for a curious mind, that would be greatly appreciated!

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Hi Guys,

I've recently had issues starting my 450, and although I haven't used my bike very much lately (actually twice max last year) the symptoms are suggesting I have an issue with my valves.

The task doesn't look too bad, so once the nice weather gets here I'm gunna pull the 450 out and double check the clearances.

There are lots of articles (thanks TT!) on how to check them, what I'm looking for and even how to shim them. The only thing I don't see a lot of information on is an actual explanation of the issue.

I know some people say causes could be bouncing off the rev limited (which I have never done) or dirt getting past the filter, but I'm looking for a more detailed explanation of what is happening to the valves, how exactly they work, and what damage can be done. The only bike I had before this (dirtbike anyways) was an old XR and I never had any issues.

If someone can point me to some information for a curious mind, that would be greatly appreciated!

You will probably get lots of responses to this question. Modern 4 strokes use the 'bucket and shim' method of setting valve clearances. It is very precise, and very direct contact, unlike the old screw adjustment rocker arms.

I believe there are several issues working at once that cause Honda valves to 'mushroom' at there contact point against the seat. I know the Titanium coating that is supposed to keep the valve contact area nice and hard is one of the main issues: it goes bad, and the valve's contact area with the seat becomes soft. Now the valve/valve stem sits higher in the head causing it to become 'tight': less gap between the bucket/shim and the cam.

I'm not sure what the primary issue for the Titanium coating to go bad, but I believe it is a combination of jetting (lean condition), contaminants (creating abrasive action on the coating, and burning hotter in spots), and mechanical (floating valves that 'bang' against the seat instead of being 'set' down by valve spring tension).

That' my best guess.

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You will probably get lots of responses to this question. Modern 4 strokes use the 'bucket and shim' method of setting valve clearances. It is very precise, and very direct contact, unlike the old screw adjustment rocker arms.

I believe there are several issues working at once that cause Honda valves to 'mushroom' at there contact point against the seat. I know the Titanium coating that is supposed to keep the valve contact area nice and hard is one of the main issues: it goes bad, and the valve's contact area with the seat becomes soft. Now the valve/valve stem sits higher in the head causing it to become 'tight': less gap between the bucket/shim and the cam.

I'm not sure what the primary issue for the Titanium coating to go bad, but I believe it is a combination of jetting (lean condition), contaminants (creating abrasive action on the coating, and burning hotter in spots), and mechanical (floating valves that 'bang' against the seat instead of being 'set' down by valve spring tension).

That' my best guess.

thanks i learned something new.

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i thought that the honda 450X had adjustment screws like on the xrs, where you use a fealer gage to set clearence. don't you have a manual for your bike?

I can't believe I'm going to say this... but, KTM has what your speaking of. Super easy. Husky might too... I never had mine long enough to adjust the valves however :)

Shim under bucket isn't so friendly if your caught needing a shim, and out camping somewhere.

And Kran... I was explained at one time, that the valve will give before the seat for a reason. So as to not have a major expense and catastrophic failure if the seat is worn before the valve. Seems reasonable to me. Somethings gotta give. What-cha-think about that?

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I can't believe I'm going to say this... but, KTM has what your speaking of. Super easy. Husky might too... I never had mine long enough to adjust the valves however :)

Shim under bucket isn't so friendly if your caught needing a shim, and out camping somewhere.

And Kran... I was explained at one time, that the valve will give before the seat for a reason. So as to not have a major expense and catastrophic failure if the seat is worn before the valve. Seems reasonable to me. Somethings gotta give. What-cha-think about that?

:banghead: I think you are a wise beyond my years.

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:) I think you are a wise beyond my years.

True, I agree, but are you suggesting that the route people are taking with the SS valves is possibly not the best route to take due to the possible risk of seat damage?

If the springs are good enough, and the clearances remain proper dont u think SS would suffice?

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thanks for the info guys.

Ive been trying to start my bike and there is jsut no way it would go. Weather was nice today to I checked the valve clearances. These are the digits I came up with.

Left intake: .008 (manual says .006 +/- .001)

Right intake: .006 (manual says .006 +/- .001)

Left exhaust: .009 (manual says .011 +/- .001)

Right exhaust: .009 (manaul says .011 +/- .001)

So clearly they are out, but at least they haven't completely sealed up or anything.

Where do you guys suggest I go from here? Just a shim kit for the intakes? I'm not sure what size shim is currently on the exaust though. Looks like they are starting to tighten up a bit.

Are the valves off enough to cause probems starting or could the issue be elsewhere? I'm going to pull the carb out and clean it up next nice day I get. Such a bitch to get at on the X's. Went through it once when I was installing a quickshot.

What do you guys think?

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thanks for the info guys.

Ive been trying to start my bike and there is jsut no way it would go. Weather was nice today to I checked the valve clearances. These are the digits I came up with.

Left intake: .008 (manual says .006 +/- .001)

Right intake: .006 (manual says .006 +/- .001)

Left exhaust: .009 (manual says .011 +/- .001)

Right exhaust: .009 (manaul says .011 +/- .001)

So clearly they are out, but at least they haven't completely sealed up or anything.

Where do you guys suggest I go from here? Just a shim kit for the intakes? I'm not sure what size shim is currently on the exaust though. Looks like they are starting to tighten up a bit.

Are the valves off enough to cause probems starting or could the issue be elsewhere? I'm going to pull the carb out and clean it up next nice day I get. Such a bitch to get at on the X's. Went through it once when I was installing a quickshot.

What do you guys think?

Valves are definitely enough to cause problems starting. They are most certainly off like you said, so re shim... Then you take that variable out of the equation. If you have problems from there, cold be spark plug/jetting/etc... So re shim and see how she starts, then go from there.

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if the size is not on the shim (wore off) you will need a micrometer to measure its thickness. Even if the size is on it, you should measure anyways to account for wear. Verniers aren't really accurate enough, unless you have a good one.

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thanks for the info guys.

Ive been trying to start my bike and there is jsut no way it would go. Weather was nice today to I checked the valve clearances. These are the digits I came up with.

Left intake: .008 (manual says .006 +/- .001)

Right intake: .006 (manual says .006 +/- .001)

Left exhaust: .009 (manual says .011 +/- .001)

Right exhaust: .009 (manaul says .011 +/- .001)

So clearly they are out, but at least they haven't completely sealed up or anything.

Where do you guys suggest I go from here? Just a shim kit for the intakes? I'm not sure what size shim is currently on the exaust though. Looks like they are starting to tighten up a bit.

Are the valves off enough to cause probems starting or could the issue be elsewhere? I'm going to pull the carb out and clean it up next nice day I get. Such a bitch to get at on the X's. Went through it once when I was installing a quickshot.

What do you guys think?

your valves are not your problem. My 450X exhaust were at .009 from day one, and your intakes would tend to tighten not loosen, so I dont think your valves are on the move at all. i would replace the spark plug, put some fresh gas in it, clean the carb as you were stating and make sure that all your jets are not plugged up!

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It doesn't look like the valves are the culprit.

You might try the usual suspects:

- loose ground near coil under tank

- loose battery connections

- plugged jets, usually pilot

- bad kill button: wire it out to test

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thanks for the info guys. I will start from the top and try everything listed. It's not the repairs that drive me crazy, its the troubleshooting! ARGH!

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your valves are not your problem. My 450X exhaust were at .009 from day one, and your intakes would tend to tighten not loosen, so I dont think your valves are on the move at all. i would replace the spark plug, put some fresh gas in it, clean the carb as you were stating and make sure that all your jets are not plugged up!

I agree. :)

The OP valves specs don't sound like the cause of the starting problem. All thought those exhaust valve do seem a little tight I don't know if that would cause the starting problem.

Sounds like a case of lack of use:naughty:

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"your intakes would tend to tighten not loosen"

That's what happens. The valves deteriorate become deformed and sink into the valve seats. Once it starts it's downhill from there. Prepare for the never ending round of reshimming till the valves become worthless and can't be shimmed again. Then it's off to head shop for about $800-$1500 worth of new parts and labor. Or sell it to some sucker(like me) and tell them I just checked the valves and they are in spec.(Yea, for about 1/2 ride they are in spec).

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I does not sound like your valves are you problem at all. Sure the valves are not in spec pefectly but as mentioned when the valves go out the cleances tighten up not loosen up...They dont start due the the valve never fully closing causing a loss of compression. By how much you ride your bike I would start by putting new gas in the tank and draining the fuel from the float bowl.....there is a screw that you turn and allows the fuel to drain right from it...That is a common problem on bikes that sit alot....The next thing you do if that doesnt work. Is to verify spark and if ok remove and clean the carburator...I am betting that new fuel will go a long way though. Good luck

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The valves may not be your problem... but you should not let it go too long without reshimming. The loose intakes wont really hurt anything... But tight exhuasts (or any vavle) aren't good. Yours are not excessivley tight but you wouldn't want them to get tighter. The metal will expand when the bike warms up so they'll be even tighter. You should try to get them in spec.

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"your intakes would tend to tighten not loosen"

That's what happens. The valves deteriorate become deformed and sink into the valve seats. Once it starts it's downhill from there. Prepare for the never ending round of reshimming till the valves become worthless and can't be shimmed again. Then it's off to head shop for about $800-$1500 worth of new parts and labor. Or sell it to some sucker(like me) and tell them I just checked the valves and they are in spec.(Yea, for about 1/2 ride they are in spec).

That sucks! Keep in mind my 450 is a 2005 (its now 2009) and my valves have never been adjusted...so I don't think these hondas are quite as bad as you make it out to be!

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