426 Valve Job...To lap or not to lap?


39 replies to this topic
  • grayracer513

Posted September 15, 2009 - 09:37 AM

#21

At only $16 I think I'll get a SS valve just for lapping and then check the fit of the Ti valve. I have a 20X optical micrometer that I use to check the contact width and placement and also surface condition.

That is one approach you can take. However, there are hazards.

First, you need two valves at minimum, so now we are at $32 for your throwaway lappers. Second, when lapping, as the seat begins to take on the perfect, ground shape of the valve face, the valve face begins to take on the worn, irregular shape of the seat. So, even though the SS valve is probably somewhat harder that the iron seats used in YZF's, when you lap your second valve, the valve you lap with is no longer the brand new, perfectly ground piece it was to begin with. Then, on the intakes, there are three.

Exhaust valves can be and in fact are smaller than intake valves since the gases are forced out. The intakes need to be as large as possible since the gases are simply drawn in by vacuum. But if they are too large, valve float becomes a problem at high RPM's with resulting valve damage.

Valve float is a non-issue once the right springs are in place, and no one has ever verified that the CRF, for example, ever suffered from it. Neither do the current R1/R6 models, which are also 4 valve, and operate reliably at engine speeds that makes the hair on the back of my neck bristle to even think about.

The real reason exhaust valves are smaller is because the the exhaust gases are less bulky than the intake mixture because the fuel has been burned out of them.

Using three intake valves allows a larger intake cross sectional area using smaller valves. The smaller valves reduces or eliminates float at higher RPM's thereby increasing reliability. Or perhaps longevity would be a better word.

The Genesis 5 valve head design was originally introduced in large displacement road bike engines, and the intake configuration was designed to improve mid-range power and fuel efficiency. It has a distinct tendency to stratify the intake charge somewhat in the manner of the Honda CVCC 3 valve engines, concentrating the bulk of the fuel at the center of the combustion chamber and surrounding it with a much less fuel-dense charge of air. It was never intended as a means of producing maximum top end power.

I do not understand how more top end power is achieved with two rather than three intake valves.

Continuing from the above point, charge stratification is a handicap from the standpoint of maximum power production, and short of placing 3 discrete injector nozzles in the ports, is unavoidable in the 3 valve intake. A much larger problem exists in getting the port to flow well. The additional port divider and valve stem become obstructive beyond any gains made by have larger valve area.

In fact, ideally one would choose to have one port each for the intake and exhaust, but the ideal combustion dome in the head is a relatively shallow concave shape. With that, there is a limit to how large a pair of valves can be made and still fit into the available space. The engine will normally be potentially capable of using a larger intake and exhaust area than can be had with two valves. By going to two of each, the port area can be greatly expanded. The additional valve stem, valve head, and port pocket on both sides, are an added liability, but their negative effect is out weighed by the added benefit of increased total area. Likewise, the port divider, an obstruction on the intake side, does not hurt more than the increase in area helps.

But when you compare 3 intake valves to 2 within the confines of the same combustion chamber, there is no significant gain in port area that can be made versus using two valves, and the additional flow restrictions hamper maximum performance.

Ron Hamp, one of the nation's premier engine builders in flat track competition, long ago produced CRF450's well beyond the 60 HP mark, but it took him until last year to do the same with a YZ450. The head is the limiting factor.

And if there is nothing harder than the coating on a titanium valve face, I do not understand why it would hurt to lap with the titanium valve. That said, I will certainly defer to Eric Gorr's advice on not lapping them.

I love it when people do that. I did not say "there is nothing harder", I said almost. Most abrasives used in lapping pastes are hard enough to damage the hard coating, hard as it is (off the top of the Rockwell scale), and the problem with that is that the coating is less than .001" thick. ANY damage to it would be intolerable, and reduce the life expectancy of the valve.

  • trailscout

Posted September 15, 2009 - 11:13 AM

#22

Thanks. I appreciate the information.

First, you need two valves at minimum, so now we are at $32 for your throwaway lappers.

Normally, yes. But the engine in question is very low miles. None of the valves have been re-shimmed and all are full spec except the center intake which closed completely plus a little. Being retired and recreating on a small fixed income, my intent, unless something else shows up on tear down, is to replace only the center intake. Don't know why it would fail and not the others except it's a little heavier.

Valve float is a non-issue once the right springs are in place.

On my old KLX I tried heavier springs from RDSprings in Hesperia. I tried SS valves. I tried a set of "Bee Hive" springs. I put in LR's cam. Nothing worked any better than stock. 5K miles was the maximum life and that's more than most got. If valve float was not the problem, I'd sure like to know what the heck it was.

The real reason exhaust valves are smaller is because the the exhaust gases are less bulky than the intake mixture because the fuel has been burned out of them.

If E=MCC, how much lighter could the exhaust gases be than the intake?

A much larger problem exists in getting the port to flow well. The additional port divider and valve stem become obstructive beyond any gains made by have larger valve area.

I wondered about that. Makes sense at higher RPM's.

  • pscook

Posted September 15, 2009 - 11:36 AM

#23

The real reason exhaust valves are smaller is because the the exhaust gases are less bulky than the intake mixture because the fuel has been burned out of them.


If E=MCC, how much lighter could the exhaust gases be than the intake?


Notice he said less bulky, not lighter. Gas takes up less space than a stoichiometric mixture of air and fuel, and therefore easier to compress and force through a smaller orifice. Fluids don't compress nearly as well as gases do.

  • psellers22

Posted September 15, 2009 - 11:38 AM

#24

i lapped my valves in 50 hrs ago no adjustments yet! i think its a myth but everybody here frowns upon me doing that! i did it in my race bike! didnt know at the time ..i just followed the manual!:busted:

  • grayracer513

Posted September 15, 2009 - 12:49 PM

#25

Trailscout,

The center intake does seem always to be the first to go. I believe it's related to the fact that the center port handles most of the fuel (note how clean the center one always is).

Your old KLX is not a modern, high performance 4-stroke, so it makes a poor comparison to any of the others.

Your energy equation leaves out the fact that the mass of the intake charge was reduced by the combustion process, so there is no parity between intake and exhaust.

  • TDW

Posted September 15, 2009 - 03:53 PM

#26

Trailscout,

The center intake does seem always to be the first to go. I believe it's related to the fact that the center port handles most of the fuel (note how clean the center one always is).

Your old KLX is not a modern, high performance 4-stroke, so it makes a poor comparison to any of the others.

Your energy equation leaves out the fact that the mass of the intake charge was reduced by the combustion process, so there is no parity between intake and exhaust.


I am not well versed on the yamaha's, but having seen and heard of many honda's having issues with an intake valve fail on one side, while the other one looks great, Im with you on the idea of unequal fuel distribution. Almost like a port bias in terms of delivering the fuel charge to the engine. Seems like kind of a tough thing to prove or verify, but in theory makes alot of sense to me.
I have tried adjusting or shimming the intake valves slightly different from side to side-between .001-.002- to see if this will help equalize(for lack of a better term) the fuel charge between the ports, does seem to make a difference but my little experiment is not scientific.

  • trailscout

Posted September 15, 2009 - 06:34 PM

#27

The center intake does seem always to be the first to go. I believe it's related to the fact that the center port handles most of the fuel (note how clean the center one always is).

The center intake almost certainly handles more fuel than either of the other two since it is larger. But I fail to see how the mere act of handling more fuel could cause a valve to wear out or fail earlier. But being heavier, I could see it floating more often since I just checked and the springs for the outer and center intakes are the same.

Your old KLX is not a modern, high performance 4-stroke, so it makes a poor comparison to any of the others.


My old '94KLX is dated for certain. But it was the first 250cc dirt bike on the planet with a bucket and shim valve train. Being bucket and shim, I fail to agree that is a poor comparison to later model bikes in terms of general valve problems. Were it a rocker arm train, I would agree. BTW, after around 60-70K miles, the smallish exhaust valves were never shimmed and are still in spec.

Your energy equation leaves out the fact that the mass of the intake charge was reduced by the combustion process, so there is no parity between intake and exhaust.

What I was trying to point out, in an admittedly somewhat smart alecky manner, was the precise fact that the mass of the intake and exhaust gases were NOT changed by the combustion process.

The EXACT same atoms that entered the intake went out the exhaust. In a different molecular configuration, yes, but the same atoms and therefore the same mass or weight.

The gases entered mostly in the form of a carbohydrate and air. When the carbohydrate was burned (oxidized-chemically combined with oxygen), water H20, and carbondioxide CO2 were formed from the combination of the burned chemicals. Plus impurities, additives, etc.

Although the same weight or mass, the volume of exhaust gases is actually greater than the volume of intake gases. That should dictate the exhaust valves to be larger. But the piston can force more gas out a small opening than it can "suck" in through a larger opening. As you most certainly are more aware than I, fourstroke intake is all about breathing.

The E=MCC is Einstein's formula for the conversion of mass to energy. So the exhaust gases would ACTUALLY be a little lighter. But only a fraction of the weight of one single electron in the full combustion charge. So for all practical purposes the intake and exhaust gas can be considered equal. Take the energy output of one firing, divide it by the square of the speed of light and you get a decimal with about 30 or so zeros before there is a one.

Intake/exhaust don't have good enough glasses to see that difference:)

  • grayracer513

Posted September 15, 2009 - 09:01 PM

#28

The center intake almost certainly handles more fuel than either of the other two since it is larger. But I fail to see how the mere act of handling more fuel could cause a valve to wear out or fail earlier. But being heavier, I could see it floating more often since I just checked and the springs for the outer and center intakes are the same.

The center valve is the same size as the other three, 27mm. The reason the center port handle more fuel is a simple matter of inertia. As the air fuel mix travels down the port, the air diverges laterally to the side ports, while the heavier fuel molecules continue straight down the center. Since pump gasoline is loaded with valve and fuel system cleaners ("techroline" or other trade equivalents) the extra fuel then washes the center valve cleaner than the other two. The gummy, tar-like combustion residue that becomes a carbon deposit on most valves is removed almost completely from the center valve. On the one hand, this is nice, since the valve is always clean, but the down side is that that same combustion residue acts as a kind of cushion to the intake valves as they close, and acts as a de facto lubricant.

Regarding the exhaust gases, without flogging the matter any further than this, there are two things you haven't taken into consideration: The bulk of long chain hydrocarbon radicals such as most of the components of gasoline vs. the relatively compact molecules created by burning them, and the fact that not everything that enters the intake port leaves the combustion chamber by way of the exhaust. Some is blown past the rings, and some remains as the aforementioned goo.

  • trailscout

Posted September 16, 2009 - 05:48 AM

#29

The center valve is the same size as the other three, 27mm. The reason the center port handle more fuel is a simple matter of inertia. As the air fuel mix travels down the port, the air diverges laterally to the side ports, while the heavier fuel molecules continue straight down the center. Since pump gasoline is loaded with valve and fuel system cleaners ("techroline" or other trade equivalents) the extra fuel then washes the center valve cleaner than the other two. The gummy, tar-like combustion residue that becomes a carbon deposit on most valves is removed almost completely from the center valve. On the one hand, this is nice, since the valve is always clean, but the down side is that that same combustion residue acts as a kind of cushion to the intake valves as they close, and acts as a de facto lubricant.

Your explanation certainly sounds plausible. Being new to the WR, I was not aware of the history of the center valve.

BikeBandit shows a cost of $85.51 for the outer intake and $92.92 for the center. Are you sure the center is not heavier even though the same diameter? Longer shaft or some other difference? I don't have the engine torn down or I'd weigh and otherwise compare them. There's gotta be some difference to account for the price difference. If it includes weight which I suspect it does, I'd go back to concluding the center would float first, notwithstanding your plausible theory.

Regarding the exhaust gases, without flogging the matter any further than this, there are two things you haven't taken into consideration: The bulk of long chain hydrocarbon radicals such as most of the components of gasoline vs. the relatively compact molecules created by burning them, and the fact that not everything that enters the intake port leaves the combustion chamber by way of the exhaust. Some is blown past the rings, and some remains as the aforementioned goo.

Well yeah. We could also talk about the molecules of wear from the piston, valves etc that exit the exhaust that were not part of the intake combustion charge.

The important point not to be overlooked is that for all practical purposes, the mass/weight of the exhaust gasses is the same as the mass/weight of the intake gasses.

If a log is burned in a fireplace, it appears a lot smaller and lighter than before it was burned. But if the CO2 and H2O that went up the chimney were weighed along with the flyash and residue remaining in the fireplace, the weight would be the same as the original log.

  • grayracer513

Posted September 16, 2009 - 08:43 AM

#30

BikeBandit shows a cost of $85.51 for the outer intake and $92.92 for the center. Are you sure the center is not heavier even though the same diameter? Longer shaft or some other difference? There's gotta be some difference to account for the price difference.

If I'm not recalling it backward, the center intake has a shorter stem because it sits in the head at a different angle to the same camshaft as the other two. The price difference is more likely the result of production volume and unit pricing, but I doubt there's really that much pure logic applied to the process, frankly. In any case, you need to forget valve float. None of the valves in that engine will float at 1000 rpm beyond the rev limit with 3 year-old springs. They have that thoroughly covered.


The important point not to be overlooked is that for all practical purposes, the mass/weight of the exhaust gasses is the same as the mass/weight of the intake gasses.

If a log is burned in a fireplace, it appears a lot smaller and lighter than before it was burned. But if the CO2 and H2O that went up the chimney were weighed along with the flyash and residue remaining in the fireplace, the weight would be the same as the original log.

While the mass is reduced to an extent, as I stated, "bulk" would be a technically more correct term to have used. Since you can easily reduce a 6x18" oak log into a grapefruit sized ball of fluffy ash, I'm sure you'll agree that fitting out through a smaller hole than the intake is no difficult trick.

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  • trailscout

Posted September 16, 2009 - 01:33 PM

#31

If I'm not recalling it backward, the center intake has a shorter stem because it sits in the head at a different angle to the same camshaft as the other two.


I'll be tearing mine down within a month or less. I'll check your recall at that time.

While the mass is reduced to an extent, as I stated, "bulk" would be a technically more correct term to have used. Since you can easily reduce a 6x18" oak log into a grapefruit sized ball of fluffy ash, I'm sure you'll agree that fitting out through a smaller hole than the intake is no difficult trick.

The grapesized ball of fluffy ash you speak of is only a very small fraction of the products of combustion of the log. If all of the products of combustion that went up the chimney (exhaust) are captured and weighed, there is not a scale in the universe capable of measuring the difference in weight of the unburned log and the products of combustion. The difference in weight that actually does exist is, again, the mass/energy conversion that Einstein discovered which in the example being discussed, is near non-existent.

Combustion does NOT result in reduced mass. This is something that is covered clearly in high school chemistry and physics. I have taught both.

The only technical meaning that bulk has would refer to density. Combustion does reduce the density of the log by returning it from carbohydrates to H2O and CO2 gases. (This is also discussed in high school Biology under Photosynthesis) When density is reduced, volume is increased. Going back to the valves, that should dictate the exhaust valve to be larger. Which is of course erroneous. They can be smaller because the piston forces the exhaust out rather than using vacuum to draw it in as I said.

I quit

  • grayracer513

Posted September 16, 2009 - 02:51 PM

#32

... using vacuum to draw it in ...

If you were a physics teacher, give yourself points off for that one. :busted: The intake air is pushed in from outside by atmospheric pressure. I know you knew better. :thumbsup:

  • trailscout

Posted September 16, 2009 - 05:26 PM

#33

If you were a physics teacher, give yourself points off for that one. :busted: The intake air is pushed in from outside by atmospheric pressure. I know you knew better. :thumbsup:

Ok. I lied. I didn't quit.

Actually, if ya wanna get really technical about it, which I don't think you do, describing the intake as being pushed in by atmospheric pressure or being drawn in by vacuum are neither entirely quite correct.

However, since I was trying to convince someone that the intake was the same in mass as the exhaust, I didn't think it wise to get any more technical than necessary. :banana:

  • trailscout

Posted September 17, 2009 - 04:00 PM

#34

If you were a physics teacher, give yourself points off for that one. The intake air is pushed in from outside by atmospheric pressure. I know you knew better.


Since it now appears misconceptions about the relative weight/mass of the intake and exhaust gasses have now been cleared up, it is now time to clear up remaining misconceptions about the means by which the intake gases enter the combustion chamber.

Are they pushed in by atmospheric pressure? Or drawn in by vacuum? Or some of both? Or neither?

Please visualize a large box closed on all sides with a partition in the middle. Now imagine one side/compartment filled with ping pong balls that are bouncing in all directions.

Now visualize what would happen if the partition were magically removed. The ping pong balls that were about to strike the partition at various angles and then bounce back would instead go flying into the newly opened compartment.

So I ask, " Were they drawn in by vacuum or pushed in by pressure?". Neither. There was nothing to bounce off of so they simply kept going in the same direction until there was something to bounce off of.

The most technically correct word for the actual action that does occur would probably be diffusion or dispersion.

Ahem. "YOU REALLY SHOULD HAVE KNOWN! :busted:

  • grayracer513

Posted September 17, 2009 - 05:16 PM

#35

Now visualize what would happen if the partition were magically removed. The ping pong balls that were about to strike the partition at various angles and then bounce back would instead go flying into the newly opened compartment.

Fine, except that isn't what happens.

Piston at TDC, intake valve open, air pressure on both sides of the intake valve are in equilibrium. The piston then moves down the bore, expanding the volume of the combustion chamber/cylinder, reducing the air pressure therein, and the relatively higher air pressure on the intake side pushes into the depression created by the piston. They can diffuse or disperse if they choose, but the force driving them to do so is the pressure differential; the higher pushing toward the lower.

That's the static model, of course, and at speed, the air pressure within the intake is complex and dynamic, and changes a lot depending on when and where along the air path it's measured. Directly on the atmosphere side of the intake valve, the pressure can be well above atmospheric between the time the valve closes and the moment when it reopens as a result of the inertia of the moving column of air as it comes up against the closed intake. That sets up the pressure wave behavior used to "tune" the length of intake tracts (what a velocity stack does if it's made right), which, if done correctly can cause a returning pressure wave to arrive at the intake valve in the last third of it's opening, increasing manifold absolute pressure further.

  • trailscout

Posted September 17, 2009 - 06:11 PM

#36

Fine, except that isn't what happens.


Hate to be so contrary, but yes, that is what happens. Instead of magically removing the partition, this time magically cause the partition to move toward the end that contains no ping pong balls. This can represent a moving piston. Same thing, the balls continue in a straight line until they hit something. Nothing pushed them, nothing pulled them.

Or you can magically make a hole appear in the partition. This could be a valve opening. Same thing. The balls that would have hit that spot now continue in a straight line until they hit something. Same thing. Nothing pushes or pulls them. They just keep doing their thing until they hit something. (kinda like i ride)

And sure, this example is simplified to illustrate a point or principle. There's things like the Brownian movement and all kinds of stuff going on that I don't think either of us are versed enough to get into.

Hey, I think talking about pressure and vacuum makes more sense in normal day to day conversation rather than dispersion, just as long as assertions are not made that one is right and the other is wrong when they are both wrong. But even if both are wrong, everyone knows what is being said or meant, and that's really what's more important anyhow.

BTW, did an awsome single track loop Southwest of Pocatello, Idaho today. Center valve continues to hold enough clearance for a first kick start every time. Cross my fingers until I get to Norcal for a teardown.

Take Care

  • grayracer513

Posted September 17, 2009 - 08:05 PM

#37

Hate to be so contrary, but yes, that is what happens. Instead of magically removing the partition, this time magically cause the partition to move toward the end that contains no ping pong balls. This can represent a moving piston. Same thing, the balls continue in a straight line until they hit something. Nothing pushed them, nothing pulled them.

Dispersion describes movement of gases or fluids within or among one or more still volumes, absent any impelling force. If you are going to suggest that that has anything to do with the movement of the intake charge into the combustion chamber, or that the downstroke of the piston does not create a pressure differential that results in atmospheric pressure filling the cylinder, then you are at odds not only with me, but with 130 years of gasoline engine design technology. Please excuse me if I don't continue the discussion?

Thanks.

  • trailscout

Posted September 18, 2009 - 04:10 AM

#38

Yeah, I agree. We've "carried on" long enough. On my way out I'll mention that I'm not referring to a static situation and that I'm aware of all the waves passing through gasses in movement etc. Especially expansion chambers in two strokes.

But as complex as the movements appear, the particles, or molecules in this case, still travel only in straight lines. The waves and other motions of gasses can only be clearly analyzed and understood by analyzing and understanding the travels of a singly particle within the whole.

  • ckr427

Posted October 21, 2009 - 05:21 PM

#39

I know you guys signed off on this a while back but have to agree with greyracer. I've studied gas engines for a long time now. Find a gas engine that doesn't use smaller exhaust valve sizes than intake. There's a reason for that. Also, to prove greyracer's sayings on atmoshperic pressure, Engines run better at sea level for this exact reason-longer column of air pushing into the engine than say at 10,000ft.

  • trailscout

Posted October 21, 2009 - 06:22 PM

#40

oh crap here we go again. yes, exhaust valves are smaller. did you read everything? the disagreement was on why they are smaller

pressure. high pressure, low pressure. air conditioning. high side, low side. high pressure/low pressure are relative to each other. one can't exist without the other. same for vacuum. can't exist without pressure. using pressure to push or vacuum to suck/draw/vacuum. same thing. both terms are for talking about what happens in simple terms.

the disagreement is when one decides that one term is right and one is wrong when neither actually gets into the nitty gritty of what's going on. you can talk about a pressure differential in terms of one side being high and one side being low. or you can speak in terms of a vacuum. sometimes one is less clumsy sometimes the other.

but if someone wants to tell someone that pressure is right and vacuum is wrong, then that person doesn't know or understand what is really happening.

there is just a bunch of gas molecules bouncing around off of things. if the thing they were gonna bounce off of is moved they keep going until they bounce off of whatever they reach. ain't no pressure or vacuum involved at that level of analysis.

i would suggest cracking a couple of books before deciding upon an opinion. this is science not opinion.

Edited by trailscout, October 21, 2009 - 06:24 PM.
copy/paste left out first sentence





 
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