400EX valve mod

[MtnEX]

I had my 400EX way down and apart body-wise dealing with a bad fuel issue. So while I had access I decided to go ahead and check over my valve clearance again... as someone suggested to me when I was complaining about the clack noise returning after oil changes.

It had also been a year since I had, so I did. I did not really see any change in them at all.

Then while I was doing it, I started thinking about a conversation I had with a builder almost a year ago... and building on top of that I decided to do a little valve mod to see what happened.

What I did was go outside of spec.
I went down tighter on them.

Factory spec is
IN ~ 0.004
EX ~ 0.005

I set mine
IN ~ 0.003
EX ~ 0.004

The intake is not a real tight 0.003 but close and the exhaust is a snug 0.004.

I just wanted to see what it would do.

At this point I am still evaluating, but the throttle response seems much better and the engine seems to wind up a lot faster. Also, the general valvetrain noise is reduced.

My theory behind trying this was to open the valves a little bit earlier to see if I could tell a difference, and to see if the valve noise would hush a little.

I really did not expect to be able to tell a difference at all, but I can. As I put more time on it, I'll give more feedback.

[honda400ex2003]

Nice info, that is like running a longer lift and duration cam to a point. there will be more wear though too since it it is hitting the cam for that much longer and maybe that much harder. Keep us updated and thanks again for the info. steve

[F-16Guy]

The idea of valve lash is to provide a clearance so that when things heat up to operating temperature, the lash is reduced to as close to zero as safely possible. Too much lash is bad because it causes slop in the valvetrain, but too little is worse. Too little, and the valves (especially the exhaust) can fail to fully close and be burnt by combustion gasses. Setting the lash to less than the specs isn't a good way to achieve more duration, it's a good way to get a premature valve job.

[honda400ex2003]

Agreed, I did not think about it that way. thanks f-16. steve

[Wheelie]

Originally posted by F-16Guy
The idea of valve lash is to provide a clearance so that when things heat up to operating temperature, the lash is reduced to as close to zero as safely possible. Too much lash is bad because it causes slop in the valvetrain, but too little is worse. Too little, and the valves (especially the exhaust) can fail to fully close and be burnt by combustion gasses. Setting the lash to less than the specs isn't a good way to achieve more duration, it's a good way to get a premature valve job.

You hit the nail on the head.

[dariusld]

Originally posted by F-16Guy
Too little, and the valves (especially the exhaust) can fail to fully close and be burnt by combustion gasses.

When the valves don't seat, they don't have a chance to cool down because of heat transfer, to the cool valve seat.

[MtnEX]

I understand what you guys are saying here... in concept...


But I do not really see where it is going to hurt anything in an older 400EX. There is a lot of tolerance built into the engine for the heat of air cooling.

Nothing wrong with the loose rattles or anything. After tightening there is still enough tolerance that there is still noise. Just less because the travel distance is less before impact I guess.

I could be wrong, but I think all this is doing operational-wise is opening the valves sooner... and since nothing else is changed, the valves also close sooner.

And after much thought about trying to figure out how I can even tell a difference.... I'm thinking if this was going to hurt anything that a Sparks advance key would too.

I'm thinking that is how I can tell a difference.... I'm thinking it's sort of similar.... in that it changes the valve timing in relation to the spark timing.

But I could be wrong.
Many of you "know" more than me about these things.
I'm working with pretty much theory only.

[F-16Guy]

Like I was saying, at operating temps, in theory, there should be almost no clearance between the rocker and the cam lobe. The problem with this engine is that, because of the layout, you have rockers AND sub-rockers, which add to the clearance requirements. You can probably go a little tighter, depending on mods, riding style, and conditions, but just a hair loose is better, IMO, than too tight. If your valves are extremely loose, then yes, it can affect the actual duration of opening, but tightening the valve clearance can't give you more duration than the cam is physically able to supply. You're probably fine with what you have now, it's just probably not good advice for members to tighten their valve lash for extra power. Some people that aren't very mechanically inclined might think "If a little is good, then a lot is better" and end up doing some damage.

[Honda#4]

As much as I like your idea I would have to say in my opinion that I would'nt try something like that simply cuz when you go to throw money in a motor you expect things to be in spec and if you take them outta spec and run the motor for a given period of time well then you run the risk of something ruining your once nice motor which would give you a big day of headaches.

[MtnEX]

Yeah... I'm not giving advice here... just sharing something "in general" that I'm trying.


Also, to repeat, I don't thing it changes duration at all... you must change the cam for that. All I think it does is change the valve timing a hair. They open and close a little sooner than before.

I was just surprised I could even tell a difference. I did a blind test on my buddy who rides it often, and he asked me what I did to it. I played dumb at first and he describes what I do.

I like what it has done with throttle response and how much faster it winds up to power... and I also like how it starts much better (dunno why).

I won't swear this is a safe adjustment though... because I don't "know" for sure that it is.

[honda400ex2003]

I say leave it and see what happens. it may be worth doing if it doesnt hurt anything for a long time anyway. steve

[Honda#4]

I think the only way to call it safe is actually riding it for awhile then tear it apart and see if anything is wearing down faster than expected.

But props to ya for trying something different, I know that if I did something like that i'd for sure blow something up but whats another couple thousand:D

[zrpilot]

Another thing to think about is the different expansion rate of an aluminum head and steel valves. Is it possible the valve lash could get larger as an engine heats up because of the dis-similar metals and their different expansion rates? I don't know, but interesting to think about......

[quad2xtreme]

Originally posted by MtnEX
Also, to repeat, I don't thing it changes duration at all... you must change the cam for that. All I think it does is change the valve timing a hair. They open and close a little sooner than before.


If tighter clearance makes it open a little sooner then wouldn't it also make it close a little later?

[F-16Guy]

Originally posted by quad2xtreme
If tighter clearance makes it open a little sooner then wouldn't it also make it close a little later?
Yep. Which would effectively increase duration, but only to extent that the cam lobes allow.

[killer400ex]

doing this would actually cause the valves to open a hair more than before because it is the same principle as adding shims.
personally i would not screw with anything like this especially if you have an after market cam like i do, and when they sent me the cam they tell you to increase the lash if anything, manufacturers dont just make this stuff up or blow smoke at you when it comes to stuff like this, if it was not a factor they would tell you to just keep it the same but since its not they give you recommendations to HELP you motor not hurt it, tooling with this stuff is like using NOS, it might increase performance for a while but in the end you get nothing good out of it, id rather sacrifice a barely noticeable amount of power than blow my motor, but thats just my opinion, and if your running an after market piston with higher compression you shouldnt even consider doing this, an aftermarket piston expands more than a stock one, thats why when you bore up the specs leave more clearance between the cylinder and the piston than the stock one for expansion