I would think the clearance is less because as the 2 metals being measured (top of valve and rocker) heat up, the gap between them has decreased because the 2 metals have expanded.
valves, tappet clearance
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tochi
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Temperature impact on valve lash?
Here is another thread that addresses this phenomenon (mostly) with air cooled Porsche engines: http://forums.pelicanparts.com/911-engine-rebuilding-forum/519852-temperature-effect-valve-adjustments.html Another with motorcycle engines: http://www.eng-tips.com/viewthread.cfm?qid=267592
As has been alluded to, metal expansion is a tricky business, especially when dealing with different metals in different physical configurations. Metals experience thermal expansion but not at the same rates or in the same directions. The first linked discussion mentions the concept of linear expansion. It may be that aluminum alloy rockers experience thermal expansion that vectors indirectly away from the hardened steel heel that follows each cam lobe. This might result in a greater lash when the metal is hot and expansion has occurred. (By analogy, some aluminum piston pin bosses are reinforced with steel that serves to prevent or limit unwanted thermal expansion. Different piston designs and materials have varying coefficients of thermal expansion whether hypereutectic alloys, cast aluminum and forged aluminum.)
Here is another thread that addresses this phenomenon (mostly) with air cooled Porsche engines: http://forums.pelicanparts.com/911-engine-rebuilding-forum/519852-temperature-effect-valve-adjustments.html Another with motorcycle engines: http://www.eng-tips.com/viewthread.cfm?qid=267592
As has been alluded to, metal expansion is a tricky business, especially when dealing with different metals in different physical configurations. Metals experience thermal expansion but not at the same rates or in the same directions. The first linked discussion mentions the concept of linear expansion. It may be that aluminum alloy rockers experience thermal expansion that vectors indirectly away from the hardened steel heel that follows each cam lobe. This might result in a greater lash when the metal is hot and expansion has occurred. (By analogy, some aluminum piston pin bosses are reinforced with steel that serves to prevent or limit unwanted thermal expansion. Different piston designs and materials have varying coefficients of thermal expansion whether hypereutectic alloys, cast aluminum and forged aluminum.)
Different materials expand different amounts when heated. The metals that are in the engine, aluminum and various steel alloys, plus the geometry of the build will make the change in clearance not obvious. Testing a warm engine vs. cold is the only way to know the net result of the different expansions.
Below is a bit from Wikipedia about compensating for thermal expansion in clocks where precision is important. If it was critical that valve clearance did not change with temperature, there are materials that would make that possible, but it would be at the cost of other more desirable features such as durability, cost or weight. Invar valves in a fused silica head?
Temperature compensation
One source of error in clocks is thermal expansion; the pendulum rod changes in length slightly with changes in temperature. An increase in temperature causes the rod to expand, making the pendulum longer, so its period increases and the clock loses time. Many older quality clocks used wooden pendulum rods to reduce this error, as wood expands less than metal.
The first pendulum to correct for this error was the mercury pendulum invented by George Graham in 1721, which was used in precision regulator clocks into the 20th century. These had a bob consisting of a container of the liquid metal mercury. An increase in temperature would cause the pendulum rod to expand, but the mercury in the container would also expand and its level would rise slightly in the container. With a correctly designed container, the centre of gravity of the pendulum remained at a constant height, and thus its period remained constant, despite changes in temperature.
The most widely used temperature-compensated pendulum was the gridiron pendulum invented by John Harrison in 1726. This consisted of a "grid" of parallel rods of high-thermal-expansion metal such as zinc or brass and low-thermal-expansion metal such as steel. If properly combined, the length change of the high-expansion rods compensated for the length change of the low-expansion rods, achieving zero length change of the pendulum with temperature changes. This type of pendulum became so associated with quality that decorative "fake" gridirons are often seen on pendulum clocks, that have no actual temperature compensation function.
A few of the highest precision scientific clocks, constructed around 1900, had "high tech" pendulums of ultra-low-expansion materials such as the nickel steel alloy Invar or fused silica.
Below is a bit from Wikipedia about compensating for thermal expansion in clocks where precision is important. If it was critical that valve clearance did not change with temperature, there are materials that would make that possible, but it would be at the cost of other more desirable features such as durability, cost or weight. Invar valves in a fused silica head?
Temperature compensation
One source of error in clocks is thermal expansion; the pendulum rod changes in length slightly with changes in temperature. An increase in temperature causes the rod to expand, making the pendulum longer, so its period increases and the clock loses time. Many older quality clocks used wooden pendulum rods to reduce this error, as wood expands less than metal.
The first pendulum to correct for this error was the mercury pendulum invented by George Graham in 1721, which was used in precision regulator clocks into the 20th century. These had a bob consisting of a container of the liquid metal mercury. An increase in temperature would cause the pendulum rod to expand, but the mercury in the container would also expand and its level would rise slightly in the container. With a correctly designed container, the centre of gravity of the pendulum remained at a constant height, and thus its period remained constant, despite changes in temperature.
The most widely used temperature-compensated pendulum was the gridiron pendulum invented by John Harrison in 1726. This consisted of a "grid" of parallel rods of high-thermal-expansion metal such as zinc or brass and low-thermal-expansion metal such as steel. If properly combined, the length change of the high-expansion rods compensated for the length change of the low-expansion rods, achieving zero length change of the pendulum with temperature changes. This type of pendulum became so associated with quality that decorative "fake" gridirons are often seen on pendulum clocks, that have no actual temperature compensation function.
A few of the highest precision scientific clocks, constructed around 1900, had "high tech" pendulums of ultra-low-expansion materials such as the nickel steel alloy Invar or fused silica.
I missed your point and was focusing more on lubrication and machined tolerances as an explanation for “more noise when hot.”
I am familiar with the phenomenon of tappet clearances varying with temperature you describe. I am also aware that temperature-related valve lash clearances can vary with engine design, be it overhead cam or pushrod-linked valve operation. I do not pretend to understand the situation fully yet I think Bwana is on to something when he mentions valve train geometry.
In a solid lifter arrangement, a mechanical linkage operates each valve. Depending upon the linkage routing/configuration, heat would cause the links to elongate and reduce any connection clearances. This is analogous to the simple linkage found in a ball point pen. However, the mechanical linkage that operates an M30 valve involves the transmission of mechanical force via many angles, so that thermal expansion may result in some of the linkage "deflecting" “bowing” or “arcing.” This may result in a linkage that is elongated due to thermal expansion, but the expanded (heated) and deflected linkage is also effectively looser than when cold.
One analogy may be the expanding garden hose that gets larger and longer when pressurized, but some of the effective length can be minimized due to deflection around bends and corners. A stiffer reinforced garden hose (or flexible heater hose or bowden cable
) might resist expansion, similar to metal, but some unavoidable deflection/malformation still occurs, especially at bends and angles, as exists in the M30 valve in head valve train geometry.Naturally, there are other dynamics involved including parts that might stretch when reciprocating, such as valves. (I hasten to add that the above oversimplified analogy might not explain greater tappet clearances (when hot) for valves that are operated directly by a cam lobe, without any intervening rocker, as found in other engine designs.)
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all this info sounds good, it seems that we are finally building the case
i know valve noise is a very relative term hence the difficulty to compare if you are not in front of the car
is good to know that you'd better set the gap in the lower part of the tolerance or range, in our case 0,25mm
i know valve noise is a very relative term hence the difficulty to compare if you are not in front of the car
is good to know that you'd better set the gap in the lower part of the tolerance or range, in our case 0,25mm
Here is what my engineers said about this discussion.
This guy does engine programming for professional race teams including a team that got third at LeMans a few years ago.
"My personal experience has been that the lash is reduced when valvetrain warms to operating temperature. I also would not ever call the valvetrain of an old BMW "complex" in any way - that part made me laugh.
Maybe the specific metallurgy of his valves causes them to shrink lengthwise - who knows".
And this guy is a machinist and builds some pretty cool motors. Mostly old school now.
"On the Robert Yates motor I just finished and raced at Road Atlanta, Elliot Sadler used to drive the car. The valves were set .004" intake and zero on the exhaust. Now, ask them what is going to happen when that tightens up, the exhaust will never close. I must be giving some horsepower away. That was aluminum heads and titanium valves but it is much the same though not as much on Cast iron heads.
Now on Overhead cam motors depending on aluminum or iron heads, the metal will grow with heat, valves and head. The best way to determine what you want, figure the desired lash hot, set your valve cold and check it after you run. That way you can calculate what cold setting you need which answers the question".
deQuincey,
I'm just going to stay with what I've been doing for 50 years. I recently sold an M30 powered 84 BMW 533i with 312000 miles. Engine never opened up.
Wasn't even running oil with ZDDP most of it's life. Always used the settings from a Bentley manual.
It smoked a little on acceleration because the valve guides were wearing out.
As far as engine noise goes I would say an M30 motor would be a 6 on a scale of 1-10. 10 being the loudest.
It does have a mechanical valve train and a chain driven cam and oil pump. All of this makes more noise than say a motor with a rubber timing belt.
Be glad to see if you can show us if the valve clearance actually increases in a warm M30 motor. If my motor was in my car and running I would do this test.
Actually I've never thought to measure it and one reason would be how much the temp can drop before you can even get the valve cover off.
The data given in the manuals is for setting a cold engine so if the setting does get larger with heat I'm sure the engineers knew it and knew what they were doing stating the specs.
If you find some more info please let us know.
Gary
This guy does engine programming for professional race teams including a team that got third at LeMans a few years ago.
"My personal experience has been that the lash is reduced when valvetrain warms to operating temperature. I also would not ever call the valvetrain of an old BMW "complex" in any way - that part made me laugh.
Maybe the specific metallurgy of his valves causes them to shrink lengthwise - who knows".
And this guy is a machinist and builds some pretty cool motors. Mostly old school now.
"On the Robert Yates motor I just finished and raced at Road Atlanta, Elliot Sadler used to drive the car. The valves were set .004" intake and zero on the exhaust. Now, ask them what is going to happen when that tightens up, the exhaust will never close. I must be giving some horsepower away. That was aluminum heads and titanium valves but it is much the same though not as much on Cast iron heads.
Now on Overhead cam motors depending on aluminum or iron heads, the metal will grow with heat, valves and head. The best way to determine what you want, figure the desired lash hot, set your valve cold and check it after you run. That way you can calculate what cold setting you need which answers the question".
deQuincey,
I'm just going to stay with what I've been doing for 50 years. I recently sold an M30 powered 84 BMW 533i with 312000 miles. Engine never opened up.
Wasn't even running oil with ZDDP most of it's life. Always used the settings from a Bentley manual.
It smoked a little on acceleration because the valve guides were wearing out.
As far as engine noise goes I would say an M30 motor would be a 6 on a scale of 1-10. 10 being the loudest.
It does have a mechanical valve train and a chain driven cam and oil pump. All of this makes more noise than say a motor with a rubber timing belt.
Be glad to see if you can show us if the valve clearance actually increases in a warm M30 motor. If my motor was in my car and running I would do this test.
Actually I've never thought to measure it and one reason would be how much the temp can drop before you can even get the valve cover off.
The data given in the manuals is for setting a cold engine so if the setting does get larger with heat I'm sure the engineers knew it and knew what they were doing stating the specs.
If you find some more info please let us know.
Gary
dear gary, thank you for your post,
interesting point, if i understood well one is against and other in favour, well they are not M30 experts, no problem, different engines different behaviours,...i wish we can interview a NASA engineer he will probably have something to tell us ;-)
we have already demonstrated that gap grows with heat in our M30 engines:
1- not only me but several pople running M30 engines witness that valve noise increases when engine is hot (maybe is a local thing, like coriolis but that is between hemispheres :-()
2- the manual clearly says that despite valve gap should be set when engine is cold, if you decide to set them in a warm engine you should set a bigger gap, (take a close look to the page in the blue manuals, bottom note for warm engines: "1 at operating temperature, thermostat open: 0,30 to 0,35mm")
Didn't curiosity kill the cat?
As DQ mentions, the manual's spec sheet includes a footnote for setting valve clearances when hot that is larger than when cold. .014" versus .012. Although the manual is hardly infallible, there should be an obvious reason for this recommendation. Presumably, the hot setting is in the manual as advice for professional mechanics, working on an hourly rate, who may not care to charge for the time it takes an engine to cool. A quick look at the owners manual and the relevant Autobooks guide only mentions setting valve clearances when cold (below 95 degrees Farenheit). (From long ago personal experience, I have measured valve clearances on M10 and M30 engines when hot when dealing with reground cams. For the most part, I found negligible variations between cold and hot settings. This was not for the direct purpose of measuring any thermal impact on valve clearances as opposed to making sure that everything was operating within acceptable limits.)
For those dubious of DQ's observation and the shop manual's recommendation, perform your own careful test by simply measuring cold versus hot. In the large scheme of things, the differences are negligible. especially since the vast majority of us DIY'ers adjust our valves when cold.
I tried to offer a lay-explanation by focusing on the various angles involved in the mechanical linkage that controls each valve. Per the illustrations, assuming that normal thermodynamic principals apply, the metal expands with heat although some of it expands at different rates and in different directions, allowing for deflection with expansion. (See bowden cable illustration ^^^^.) But there was an equally plausible explanation in one of the linked sources mentioned in this thread: "As the aluminum gets hotter it expands and moves the rocker arm away from the valve."
The design of the aluminum alloy M10 and M30 cylinder heads suspends and supports the cam and rocker shafts securing the rockers. From the illustration below, the aluminum bosses would likely expand upward and away from the heat source (combustion chamber), thus causing a slightly increased valve lash clearance when hot. Being steel, the cam and rocker shafts will not expand at the same rate as the aluminum and this might explain why, all things being equal, all of the heated metal parts do not result in a decreased valve lash clearance. Additionally, the rockers are isolated from the cylinder head and therefore the cylinder head's heat and are therefore less likely to expand at the same rate as the cylinder head material. (Someone handy with a pyrometer and a spare head could measure the expansion of the bosses that carry the cam and rocker shafts to confirm this theory.)
As DQ mentions, the manual's spec sheet includes a footnote for setting valve clearances when hot that is larger than when cold. .014" versus .012. Although the manual is hardly infallible, there should be an obvious reason for this recommendation. Presumably, the hot setting is in the manual as advice for professional mechanics, working on an hourly rate, who may not care to charge for the time it takes an engine to cool. A quick look at the owners manual and the relevant Autobooks guide only mentions setting valve clearances when cold (below 95 degrees Farenheit). (From long ago personal experience, I have measured valve clearances on M10 and M30 engines when hot when dealing with reground cams. For the most part, I found negligible variations between cold and hot settings. This was not for the direct purpose of measuring any thermal impact on valve clearances as opposed to making sure that everything was operating within acceptable limits.)
For those dubious of DQ's observation and the shop manual's recommendation, perform your own careful test by simply measuring cold versus hot. In the large scheme of things, the differences are negligible. especially since the vast majority of us DIY'ers adjust our valves when cold.
I tried to offer a lay-explanation by focusing on the various angles involved in the mechanical linkage that controls each valve. Per the illustrations, assuming that normal thermodynamic principals apply, the metal expands with heat although some of it expands at different rates and in different directions, allowing for deflection with expansion. (See bowden cable illustration ^^^^.) But there was an equally plausible explanation in one of the linked sources mentioned in this thread: "As the aluminum gets hotter it expands and moves the rocker arm away from the valve."
The design of the aluminum alloy M10 and M30 cylinder heads suspends and supports the cam and rocker shafts securing the rockers. From the illustration below, the aluminum bosses would likely expand upward and away from the heat source (combustion chamber), thus causing a slightly increased valve lash clearance when hot. Being steel, the cam and rocker shafts will not expand at the same rate as the aluminum and this might explain why, all things being equal, all of the heated metal parts do not result in a decreased valve lash clearance. Additionally, the rockers are isolated from the cylinder head and therefore the cylinder head's heat and are therefore less likely to expand at the same rate as the cylinder head material. (Someone handy with a pyrometer and a spare head could measure the expansion of the bosses that carry the cam and rocker shafts to confirm this theory.)
Didn't curiosity kill the cat?
As DQ mentions, the manual's spec sheet includes a footnote for setting valve clearances when hot that is larger than when cold. .014" versus .012. Although the manual is hardly infallible, there should be an obvious reason for this recommendation. Presumably, the hot setting is in the manual as advice for professional mechanics, working on an hourly rate, who may not care to charge for the time it takes an engine to cool. A quick look at the owners manual and the relevant Autobooks guide only mentions setting valve clearances when cold (below 95 degrees Farenheit). (From long ago personal experience, I have measured valve clearances on M10 and M30 engines when hot when dealing with reground cams. For the most part, I found negligible variations between cold and hot settings. This was not for the direct purpose of measuring any thermal impact on valve clearances as opposed to making sure that everything was operating within acceptable limits.)
For those dubious of DQ's observation and the shop manual's recommendation, perform your own careful test by simply measuring cold versus hot. In the large scheme of things, the differences are negligible. especially since the vast majority of us DIY'ers adjust our valves when cold.
I tried to offer a lay-explanation by focusing on the various angles involved in the mechanical linkage that controls each valve. Per the illustrations, assuming that normal thermodynamic principals apply, the metal expands with heat although some of it expands at different rates and in different directions, allowing for deflection with expansion. (See bowden cable illustration ^^^^.) But there was an equally plausible explanation in one of the linked sources mentioned in this thread: "As the aluminum gets hotter it expands and moves the rocker arm away from the valve."
The design of the aluminum alloy M10 and M30 cylinder heads suspends and supports the cam and rocker shafts securing the rockers. From the illustration below, the aluminum bosses would likely expand upward and away from the heat source (combustion chamber), thus causing a slightly increased valve lash clearance when hot. Being steel, the cam and rocker shafts will not expand at the same rate as the aluminum and this might explain why, all things being equal, all of the heated metal parts do not result in a decreased valve lash clearance. Additionally, the rockers are isolated from the cylinder head and therefore the cylinder head's heat and are therefore less likely to expand at the same rate as the cylinder head material. (Someone handy with a pyrometer and a spare head could measure the expansion of the bosses that carry the cam and rocker shafts to confirm this theory.)
dear sir you took the words out of my mouth, i fully agree, moving the rocker arm away is plausible
tgank you for your digression
I think you're not understanding what the second engineer said correctly.
He built an engine for a Nascar type car only to find that they were setting the exhaust valve at 0.0 which would probably because of heat expansion, not let the valve close thereby degrading the performance of the engine.
So both of these gentlemen are saying that expansion would decrease the valve lash when hot.
I like the idea of rocker arm growing but unless some parts are contained somehow it is going to grow in every direction. Not just away from the valve.
He built an engine for a Nascar type car only to find that they were setting the exhaust valve at 0.0 which would probably because of heat expansion, not let the valve close thereby degrading the performance of the engine.
So both of these gentlemen are saying that expansion would decrease the valve lash when hot.
I like the idea of rocker arm growing but unless some parts are contained somehow it is going to grow in every direction. Not just away from the valve.
Maybe we are saying the same thing, but from a different vantage point.
I start with the presumption that the factory had superior knowledge with what worked best in terms of optimum valve clearance, i.e., .012" cold . (They may not be correct, as another setting may be more advantageous for performance and engine longevity, but that is not the premise of my thinking.) This presumption also sets aside any hypothetical desire to have zero valve lash. So, as DQ has observed, if the factory recommends a .012" setting when cold, what is the explanation for an even larger setting when hot. i.e., .014"?
Both engineers' comments make sense to me, as it applies to most situations, including their own. I made a similar observation at the beginning of the thread. However, neither comment explains why the factory recommends a larger valve clearance setting when hot. Again, for the purpose of DQ's argument, accept the premise that .012" cold is the optimal target clearance. If we also accept the fact that metal expands when hot, common sense dictates that the factory would have recommended a smaller valve clearance setting when hot, to achieve a larger clearance when cold. If, on the other hand, you are assuming that setting valve clearance is always the most accurate when the engine is at operating temperature, you would also need to establish that hot setting as the base line and a cold setting - when the metal contracts - would still be larger.
Engineer no 2 suggested that if valve lash is set to zero when cold, as soon as the engine reaches operating temperature and the metal expands, the result would be a negative lash and a valve so tight that it would not seat, in turn leading to compression loss and a burnt valve. This make perfect sense for most engines, assuming that metal expands with heat, and that the effective measured valve lash would decrease. This may be true for most engines. Conversely, based upon the factory recommendation, if the lash is set to zero when cold, the clearance would increase to ~.002" when hot. Again, set your lash to .012" cold and then measure the same clearance when hot. If it is a the same or slightly larger .012"-.014", your own observation will bear out DQ's position. And, assuming this is true, the explanation for this phenomenon remains elusive.
I don't think the rocker arm expansion theory is necessarily the best theory. Look at the cylinder head pictures again. Note those thick aluminum protrusions that carry the cam and rocker shafts above the combustion chambers. If the head expands, then those protrusions expand too. The expansion that is not constrained or saddled by other adjoining metal - is primarily upward. This expansion might "carry" the cam and/or rocker shafts upward too. The themselves may be less prone to the same expansion as the cylinder head. They are certainly exposed to heat, but not the same as conducted through out the cylinder head. The rockers are physically isolated from the aluminum cylinder head by the intervening steel components (rocker shafts and cam), the rocker heels are steel which also conducts heat differently and expands differently that aluminum, they are not in constant contact with either hot valve stems or cam lobes, and the rockers are cooled by a constant heat absorbing oil bath.
I start with the presumption that the factory had superior knowledge with what worked best in terms of optimum valve clearance, i.e., .012" cold . (They may not be correct, as another setting may be more advantageous for performance and engine longevity, but that is not the premise of my thinking.) This presumption also sets aside any hypothetical desire to have zero valve lash. So, as DQ has observed, if the factory recommends a .012" setting when cold, what is the explanation for an even larger setting when hot. i.e., .014"?
Both engineers' comments make sense to me, as it applies to most situations, including their own. I made a similar observation at the beginning of the thread. However, neither comment explains why the factory recommends a larger valve clearance setting when hot. Again, for the purpose of DQ's argument, accept the premise that .012" cold is the optimal target clearance. If we also accept the fact that metal expands when hot, common sense dictates that the factory would have recommended a smaller valve clearance setting when hot, to achieve a larger clearance when cold. If, on the other hand, you are assuming that setting valve clearance is always the most accurate when the engine is at operating temperature, you would also need to establish that hot setting as the base line and a cold setting - when the metal contracts - would still be larger.
Engineer no 2 suggested that if valve lash is set to zero when cold, as soon as the engine reaches operating temperature and the metal expands, the result would be a negative lash and a valve so tight that it would not seat, in turn leading to compression loss and a burnt valve. This make perfect sense for most engines, assuming that metal expands with heat, and that the effective measured valve lash would decrease. This may be true for most engines. Conversely, based upon the factory recommendation, if the lash is set to zero when cold, the clearance would increase to ~.002" when hot. Again, set your lash to .012" cold and then measure the same clearance when hot. If it is a the same or slightly larger .012"-.014", your own observation will bear out DQ's position. And, assuming this is true, the explanation for this phenomenon remains elusive.
I don't think the rocker arm expansion theory is necessarily the best theory. Look at the cylinder head pictures again. Note those thick aluminum protrusions that carry the cam and rocker shafts above the combustion chambers. If the head expands, then those protrusions expand too. The expansion that is not constrained or saddled by other adjoining metal - is primarily upward. This expansion might "carry" the cam and/or rocker shafts upward too. The themselves may be less prone to the same expansion as the cylinder head. They are certainly exposed to heat, but not the same as conducted through out the cylinder head. The rockers are physically isolated from the aluminum cylinder head by the intervening steel components (rocker shafts and cam), the rocker heels are steel which also conducts heat differently and expands differently that aluminum, they are not in constant contact with either hot valve stems or cam lobes, and the rockers are cooled by a constant heat absorbing oil bath.
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.and then there is a change in oil viscosity with temperature to add to the noise.
my belief is always SET the gap when the engine is cold.