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Here is a VID i made of what the right exhaust may look like if you dont take the decompression mechanism into consideration when adjusting... Here is the proper procedure, its also in my VID description..

THE CORRECT PROCEDURE TO ADJUST THE VALVES:

1. Remove the spark plug and both allen caps on left side of case.
2. Turn the motor counter-clockwise with a 17mm socket until the motor is at top dead center on the combustion stroke. (Right after the intake valves close) There is an indicator you can see through the smaller inspection cap, TDC is reached when the T mark is lined up with the notch you'll see.
3. Adjust the intake valves, and then the LEFT exhaust valve. Intake: 0.10mm / 0.004in & Exhaust: 0.12mm / 0.005in (this is for every year)
4. Turn the motor counter clockwise very slowly away from top dead center (at this time the right exhaust valve is barely opening up to let the compression out) until you hear a "click" (at this time it just closed). Then STOP immediately!
5. Now adjust the right exhaust valve to 0.12mm / 0.005in

Tighten the valve adjusting hole cap to 11ft-lb / 15n-m. If you don't have a torque wrench just be very careful not to over tighten.

 

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Here is a VID i made of what the right exhaust may look like if you dont take the decompression mechanism into consideration when adjusting... Here is the proper procedure, its also in my VID description..

THE CORRECT PROCEDURE TO ADJUST THE VALVES:

1. Remove the spark plug and both allen caps on left side of case.
2. Turn the motor counter-clockwise with a 17mm socket until the motor is at top dead center on the combustion stroke. (Right after the intake valves close) There is an indicator you can see through the smaller inspection cap, TDC is reached when the T mark is lined up with the notch you'll see.
3. Adjust the intake valves, and then the LEFT exhaust valve. Intake: 0.10mm / 0.004in & Exhaust: 0.12mm / 0.005in (this is for every year)
4. Turn the motor counter clockwise very slowly away from top dead center (at this time the right exhaust valve is barely opening up to let the compression out) until you hear a "click" (at this time it just closed). Then STOP immediately!
5. Now adjust the right exhaust valve to 0.12mm / 0.005in

Tighten the valve adjusting hole cap to 11ft-lb / 15n-m. If you don't have a torque wrench just be very careful not to over tighten.

400ex Tick PROPER VALVE ADJUSTMENT Tight Loose valve Exhaust valve in decompression when adjusting - YouTube
Thank you. This explains why it sends my right exhaust valve is a little off even though I just adjusted them.

"Fun Wheel Drive"
 

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Discussion Starter #3
your welcome... that may explain a lot of valve train noises that people claim is normal lol... mine is nice and quiet now...
 

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Experience matters

Why do you try to make a simple procedure complicated?

If you have to go past TDC to get the right exhaust valve to close, the auto decompressor is probably stuck. This happens on engines that don't get the oil changed regularly, has been worked on and not all the parts were reinstalled or the crankshaft was turned clockwise for whatever reason.

I will provide the text from the service manual following this advisement. If the camshaft has never been removed or you know without doubt that the spring and auto decompressor pin are installed in the head, then turning the engine counterclockwise to TDC is the only turning and alignment that is necessary. Note: engines with performance cams do not have decompressors and the spring and pin for the decompressor should have been removed.

Decompressor operation: (quoted from Clymer manual M454-4) (This information is not published in the Honda service manual)

"The decompressor system consists of two cam mechanisms. At engine startup, the decompressor cam holds the right exhaust valve slightly open to ease starting. After the engine starts, the decompressor cam disengages and the valve fully closes. During normal engine operation, the reverse decompressor cam and one-way clutch spin freely on the camshaft. If kickback occurs at startup, the one-way clutch locks up the reverse decompressor, which opens the right hand exhaust valve to stop the action.

If the decompressor is jammed, it will cause a steady ticking sound from the right exhaust valve when the engine is running. If all the valves are loose except the right exhaust valve, when the engine is at top dead center, this can indicate that the decompressor is not releasing properly. To release the decompressor, quickly pivot the wrench fitted to the crankshaft bolt back and forth. The quick changes in camshaft direction should release the decompressor from the valve. Replace the decompressor as described in this chapter."

The Honda manual (covering 2005 to 2009 EX and X models) simply states to turn the crankshaft counterclockwise till the TDC mark lines up in the inspection port, then adjust the valves. There is a side note in the Honda manual that states, "If the T mark is passed when trying to align it with the index notch, rotate the crankshaft counterclockwise again and align. This must be done to prevent the one-way decompressor system from functioning and obtain the correct valve clearance".

The Honda manual only details how to replace the decompressor system. The only reason to replace the decompressor is if it malfunctions and locks up. The engine will still run even with a failed decompressor system, but it will make noise.

The procedure you detail for getting correct clearance leads me to believe you either turned the engine clockwise (even just a little bit) to get on TDC, or your decompressor is stuck and needs to be replaced.

I only write this because I have never had a problem adjusting the valves of a TRX400EX or an XR400R (which has an identical top end) by just turning the engine to TDC and making the adjustments.
 

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Why do you try to make a simple procedure complicated?

If you have to go past TDC to get the right exhaust valve to close, the auto decompressor is probably stuck. This happens on engines that don't get the oil changed regularly, has been worked on and not all the parts were reinstalled or the crankshaft was turned clockwise for whatever reason.

I will provide the text from the service manual following this advisement. If the camshaft has never been removed or you know without doubt that the spring and auto decompressor pin are installed in the head, then turning the engine counterclockwise to TDC is the only turning and alignment that is necessary. Note: engines with performance cams do not have decompressors and the spring and pin for the decompressor should have been removed.

Decompressor operation: (quoted from Clymer manual M454-4) (This information is not published in the Honda service manual)

"The decompressor system consists of two cam mechanisms. At engine startup, the decompressor cam holds the right exhaust valve slightly open to ease starting. After the engine starts, the decompressor cam disengages and the valve fully closes. During normal engine operation, the reverse decompressor cam and one-way clutch spin freely on the camshaft. If kickback occurs at startup, the one-way clutch locks up the reverse decompressor, which opens the right hand exhaust valve to stop the action.

If the decompressor is jammed, it will cause a steady ticking sound from the right exhaust valve when the engine is running. If all the valves are loose except the right exhaust valve, when the engine is at top dead center, this can indicate that the decompressor is not releasing properly. To release the decompressor, quickly pivot the wrench fitted to the crankshaft bolt back and forth. The quick changes in camshaft direction should release the decompressor from the valve. Replace the decompressor as described in this chapter."

The Honda manual (covering 2005 to 2009 EX and X models) simply states to turn the crankshaft counterclockwise till the TDC mark lines up in the inspection port, then adjust the valves. There is a side note in the Honda manual that states, "If the T mark is passed when trying to align it with the index notch, rotate the crankshaft counterclockwise again and align. This must be done to prevent the one-way decompressor system from functioning and obtain the correct valve clearance".

The Honda manual only details how to replace the decompressor system. The only reason to replace the decompressor is if it malfunctions and locks up. The engine will still run even with a failed decompressor system, but it will make noise.

The procedure you detail for getting correct clearance leads me to believe you either turned the engine clockwise (even just a little bit) to get on TDC, or your decompressor is stuck and needs to be replaced.

I only write this because I have never had a problem adjusting the valves of a TRX400EX or an XR400R (which has an identical top end) by just turning the engine to TDC and making the adjustments.
Interesting points. When I got my 400ex, the engine was outside the quad and had just been rebuilt. It was already at TDC, and I didn't rotate it through CC another two revolutions to make certain. I just checked and adjusted the valves.

Oh well, they're easy enough to get to.

"Fun Wheel Drive"
 

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Discussion Starter #6
I am not trying to make a simple procedure more complicated. I am trying to shed some light on the subject. Im trying to give people a heads up on something to keep in mind while they're ADJUSTING THEIR VALVES.. Like you said, this will happen when the oil isnt changed regularly, has been worked on and not assembled correctly or missing parts, crank turned clockwise or whatever reason....
That is exactly why I brought this point up. So people are aware and will take notice of that right exhaust valve when performing a VALVE ADJUSTMENT. When you buy a used 400ex, you have no idea of the actual history - a lot of them are under maintained and have not gotten their oil changes when they should have. a lot of them have been apart and re assembled. a lot of them have mis adjusted valves. The average "do it yourselfer" wont consider the decompression mechanism while adjusting the valves. Thats why I made this post. If the decompression mechanism is in fact jammed, then thats a different issue to address. All im trying to say is to make sure the right exhaust valve is in the correct position when adjusting the valves at TDC. Sorry to upset you, im just trying to be here 2 help
 

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Point taken - but the only thing you are shedding light on is the fact that doing it wrong can yield the correct result, but that doesn't mean there may not be a more serious problem that needs to be corrected.

When an engine won't start unless you push start it, push starting it does not fix the problem although it may run fine after it is push started. The problem needs to be corrected before a more serious problem occurs.

Question is; why does your engine have to be turned past TDC till you hear a click before you adjust the valve? The decompressor should have released already - sounds to me like the kickback decompressor one-way clutch has engaged and is stuck. The decompressor holds the right exhaust valve open about .005in till about 90 to 100 degrees before TDC, then closes. If you are seeing the exhaust valve opening after TDC and snapping closed and the engine is being turned the right direction, you have a problem that needs fixing.
 

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Discussion Starter #8
Your right... it can be considered a "trick" to get around an issue with the decompression, but at least your valves will be adjusted within spec.. I can see why you say its doing it wrong.. but in another perspective its a way to get a proper valve adjustment under this condition.
Your question raises a good point!! This had happened to me with 2 different 400ex's with stock cams and all... The thing they had in common was silicone for a jug gasket, thin cometic head gasket, and a machined head...without an adjustable cam gear. The shorter deck caused the cam timing to retard a bit, in turn causing the decompression mechanism to be delayed....holding the exhaust valve open later that TDC.. An adjustable cam sprocket will be the solution. What are your thoughts?
 

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Silicone is not a gasket - it's a disaster waiting to happen - it is not oil or gas resistant. Hopefully there was a paper gasket also, Honda engineered the thickness of the gasket for proper deck height and piston to head clearance.

I ran into cam timing and deck height problems back in 1972 when I decided to build a high performance, big bore XL125 pre-decompressor technology.

An adjustable cam gear will correct valve timing, but it will not affect the decompressor more than a few degrees and the valve should be closed at TDC regardless of the wear (or length) of the cam chain. The cam naturally retards timing as the chain wears. Honda allowed for this. The cam timing can be off by almost a full tooth and the valve will still close before TDC.
 

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The point of using silicone in place of a jug gasket is to lower the deck height a bit to gain a little more compression.. many 400ex racers do this.. i use hondabond and its indeed oil resistant. disaster waiting to happen? then ive been waiting 6 years of abusing my personal motor and have yet to experience any disaster. honda designed their motor to their spec.. the aftermarket offers tons of products to change factory spec to how you want it.. if your altering any of this its normal practice to check the piston to valve and piston to head clearance..
so your opinion is that the little change in cam timing from a shorter deck height will not have anything to do with the decompression hanging onto the exhaust valve at TDC. I disagree. I believe it will affect it and can absolutely be the reason the valve will hang open at TDC. Think about it. the piston is at TDC and the cam is slightly retarted - therefore the cam is not at TDC and has not finished its cycle, in turn the decompression is still holding the valve open a bit. By turning the crank a bit more to bring the cam to TDC the decompression will then release. The decompression wont release at TDC if the cam is off one tooth.
This is a controversial subject, its okay to disagree or agree with me, but not cool to have an arrogant attitude about it.
 

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The point of using silicone in place of a jug gasket is to lower the deck height a bit to gain a little more compression.. many 400ex racers do this.. i use hondabond and its indeed oil resistant. disaster waiting to happen? then ive been waiting 6 years of abusing my personal motor and have yet to experience any disaster. honda designed their motor to their spec.. the aftermarket offers tons of products to change factory spec to how you want it.. if your altering any of this its normal practice to check the piston to valve and piston to head clearance..
so your opinion is that the little change in cam timing from a shorter deck height will not have anything to do with the decompression hanging onto the exhaust valve at TDC. I disagree. I believe it will affect it and can absolutely be the reason the valve will hang open at TDC. Think about it. the piston is at TDC and the cam is slightly retarted - therefore the cam is not at TDC and has not finished its cycle, in turn the decompression is still holding the valve open a bit. By turning the crank a bit more to bring the cam to TDC the decompression will then release. The decompression wont release at TDC if the cam is off one tooth.
This is a controversial subject, its okay to disagree or agree with me, but not cool to have an arrogant attitude about it.
I think it's important to note that hondabond is not silicone. Silicone wouldn't hold up for that use, but HB is good stuff.

"Fun Wheel Drive"
 

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Damn! After 40 years of working on Honda (and other) engines I now find out I've been doing it all wrong. But then I do not have a degree in engine building, just experience.

Please explain what the advantage of eliminating the base gasket to raise compression is. What does raising compression do? How does the change in compression change the horsepower and torque output? At what rpm is the change the greatest and is peak rpm increased or decreased? Does it require a change in fuel octane and why or why not? And on the subject of octane; which burns faster - low octane or high octane?

In 1970 we could double the power of most motors. Advancement in technology and manufacturing techniques limits what the garage builder can do to improve performance today. Most performance improvements are in the mind of the owner.

I watched the video of the 400 "owning" the 450, but I did not see the riders swapping rides to measure the ability of the pilot. Most of the time it's not the machine, but the skill of the operator. My 250 had 400's for lunch because it was lighter and more agile. It would not win a drag race, but it was almost unbeatable on a track. The only time it got beat on a track was when I was on the 400 and the 400 pilot was on my 250. He tried to rely on the grunt power that he was used to and I simply adjusted to the extra power that the 400 offered.
 

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Damn! After 40 years of working on Honda (and other) engines I now find out I've been doing it all wrong. But then I do not have a degree in engine building, just experience.

Please explain what the advantage of eliminating the base gasket to raise compression is. What does raising compression do? How does the change in compression change the horsepower and torque output? At what rpm is the change the greatest and is peak rpm increased or decreased? Does it require a change in fuel octane and why or why not? And on the subject of octane; which burns faster - low octane or high octane?

In 1970 we could double the power of most motors. Advancement in technology and manufacturing techniques limits what the garage builder can do to improve performance today. Most performance improvements are in the mind of the owner.

I watched the video of the 400 "owning" the 450, but I did not see the riders swapping rides to measure the ability of the pilot. Most of the time it's not the machine, but the skill of the operator. My 250 had 400's for lunch because it was lighter and more agile. It would not win a drag race, but it was almost unbeatable on a track. The only time it got beat on a track was when I was on the 400 and the 400 pilot was on my 250. He tried to rely on the grunt power that he was used to and I simply adjusted to the extra power that the 400 offered.
I don't think anyone said you were doing it all wrong. I'm just an at home wrencher, but I've heard about eliminating/thinning the base gasket to add a little compression from lots of guys in bikes and auto shops. It's just a little compression bump, what's the big deal? Yes, you do your due diligence, make sure your jetting is good, your octane is sufficient and it's not pinging, but hey - it's tuning. Comes with the territory.

"Fun Wheel Drive"
 

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Damn! After 40 years of working on Honda (and other) engines I now find out I've been doing it all wrong. But then I do not have a degree in engine building, just experience.

Please explain what the advantage of eliminating the base gasket to raise compression is. What does raising compression do? How does the change in compression change the horsepower and torque output? At what rpm is the change the greatest and is peak rpm increased or decreased? Does it require a change in fuel octane and why or why not? And on the subject of octane; which burns faster - low octane or high octane?

In 1970 we could double the power of most motors. Advancement in technology and manufacturing techniques limits what the garage builder can do to improve performance today. Most performance improvements are in the mind of the owner.

I watched the video of the 400 "owning" the 450, but I did not see the riders swapping rides to measure the ability of the pilot. Most of the time it's not the machine, but the skill of the operator. My 250 had 400's for lunch because it was lighter and more agile. It would not win a drag race, but it was almost unbeatable on a track. The only time it got beat on a track was when I was on the 400 and the 400 pilot was on my 250. He tried to rely on the grunt power that he was used to and I simply adjusted to the extra power that the 400 offered.
lol... im done with you. thank you for your input on this post.
 

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Yeah, I'm done too - you can make the changes, but you can't explain what the modifications accomplish, how the changes accomplish it or where the gains (or losses) occur.

Increasing the bore, stroke or compression boost low end power at the expense of high end power. A high lift cam improves top end power at the cost of low end power. Changing the exhaust scavenges back some low end lost when changing the cam. If you are trying to improve top end power, you need to reduce compression, shorten stroke, put in larger valves, open the ports, put on a larger carb and reduce the restriction of the intake and exhaust. If you only want a boost in low end power, increase the bore, lengthen the stroke and compression.

You remind me of the guy who bored his old 72 550 Honda to 600cc's and left everything else stock. What he got was a 550 that would accelerate better for a short distance, used more fuel and topped out at a lower speed than it did before spending $1000. He could have put that $1000 on a CBR600 that will accelerated harder longer, get better fuel mileage and run almost twice as fast on top end as the old bike he had.

I have a "miracle" carb that allows you to run pure alcohol and gives you a 100% increase in horsepower. I also have a bridge for sale if you are interested.

Yeah, I'm an a**hole - at 65 years of age I've earned the right,
 
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