How to: Replace valve stem seals?

[quad2xtreme]

Both of my 400ex quads smoke when letting off the throttle if you don't pull in the clutch. I can't remember if this is a sign of bad rings or valve stem seals. I vaguely remember that smoking when accelerating is rings and when decelerating it is valves or valve stem seals.

So, what is involved in just trying to replace the valve stem seals? Does the head need to come off. Any special tools required?

Thanks,

[HondaRaceReady]

Valve stems are the things that come out of the tire that you use to fill the tire. They have nothing to do with the bike smoking. Not sure what you should do though.

[quad2xtreme]

you have valve stem seals inside the head too. Part #12209-KL4-005. They actually sit inside the valve springs.

I just don't know if you can replace them without special tools and without taking the head off.

[hornetgod13]

You will need to pull the cylinder head. Basic hand tools, new seals/gaskets, maintnance manual, and a valve spring compression tool is what you'll need.

[AtvMxRider]

Originally posted by HondaRaceReady
Valve stems are the things that come out of the tire that you use to fill the tire. They have nothing to do with the bike smoking. Not sure what you should do though.

[Ruby Soho]

No special tools. You should buy/borrow a valve spring compressor though. The seal itself needs no special tool though, its quite easy.

[quad2xtreme]

Originally posted by hornetgod13
You will need to pull the cylinder head. Basic hand tools, new seals/gaskets, maintnance manual, and a valve spring compression tool is what you'll need.

Thanks for the info. I will take to the shop then and let the guy do a full diagnostic including compression, etc. I was hoping for a cheap and dirty $24 solution for the 4 seals. I don't want to pull the head off and then discover this didn't fix it only to start over again.

[86 Quad R]

actually with the 400ex head geometry you can replace the stem seals with the head remaining on the engine. the procass takes two people. using the service manual to get access to the cam train and to remove the cam. the rest should be accomplished by someone with experience and a small dia. section of rope.

Originally posted by HondaRaceReady
Valve stems are the things that come out of the tire that you use to fill the tire. They have nothing to do with the bike smoking. Not sure what you should do though.

***He's on drugs***

[MtnEX]

Ummm... I'm new to my 400EX, but have been around them since they first hit the trails... and I have yet to see the first one that doesn't smoke some. To be honest with you, this and the lack of reverse turned me off for the 400EX... and only years of proven reliabilty won me back over.

So what are the characteristics of the smoke you are getting and how much?

Also, what kind of oil are you using, and are you making double sure not to over-fill them?


I'm not saying that you don't have a mechanical problem, because you might. I'm just pointing out that these are big-bore air cooled engines that get very hot... and if everything were so tight nothing got by they wouldn't be living this long... and there are several things that can make them smoke enough to make you think there is a mechanical problem.

Just my 2 cents....
And yes, for internal stuff I lean toward letting someone experienced/certified do the work. I'd at least get it checked, diagnosed and QUOTED. Might not be worth the trouble of doing it yourself.