Reasoning over Bentley's figures on m30 valve clearance

[Rustam]

Bentley's manual tells the reader that greater valve clearance should be set to HOT engine - .35mm and lesser valve clearance should be set to COLD engine - .30mm...

I find strangeness in these figures for the reason that everything expands in size with greater temperature - the camshaft becomes a bit wider, so do the rockers, and the eccentrics, and the valves, and everything else in nature...

The reasoning tells that therefore, HOT engine must exhibit LESSER valve clearance for the reason of supplanted space by the mentioned parts since they are greater in size. That is:

HOT - .30mm
COLD - .35mm

[rob101]

http://member.rivernet.com.au/btaylor/BMWText/technical/SettingValvesM30E28.html
this should help you out, but i believe you are right smaller clearances when cold is just stupid

[SRR2]

Drill a hole in a plate of steel. Heat the plate. Is the hole larger or smaller when it's hot?

[Bill R.]

also state, .012 cold and .014 thousandths when the engine is warmed up...This motor also doesn't have tappets. It has rocker arms that ride directly on the cams...all this talk of cams expanding etc etc is wonderful except for the fact that the aluminum head that the rocker arm shafts,cams and valve are mounted in grows faster and more when heated than do the steel and cast components... so if you imagine the aluminum head expanding in all directions as it heats up that means the valve seat in the head is going to get closer to the the piston and the rocker shaft is going to get further away from the valve stem.... But rather than argue about what the factory determined a long time ago why don't you set the valves when cold as the factory specifies to .012 inches and then measure the clearance when the engine has warmed up... the factory spec states after the thermostat has opened.




no obviously someone hasn't had to seat a bearing before heat housing, housing gets bigger.
Actually its because the cam expands and is on the other side of the pivot (the rocker) thus the gap closes on the follower and tappet side. i am used to working on cars with different rocker setups where the cam is the same side of the pivot as the tappet.

[iNomis]

everything expands in size with greater temperature - the camshaft becomes a bit wider, so do the rockers, and the eccentrics, and the valves, and everything else in nature...



FWIW ... Not ice, one important exception.

[rob101]

also state, .012 cold and .014 thousandths when the engine is warmed up...This motor also doesn't have tappets. It has rocker arms that ride directly on the cams...all this talk of cams expanding etc etc is wonderful except for the fact that the aluminum head that the rocker arm shafts,cams and valve are mounted in grows faster and more when heated than do the steel and cast components... so if you imagine the aluminum head expanding in all directions as it heats up that means the valve seat in the head is going to get closer to the the piston and the rocker shaft is going to get further away from the valve stem.... But rather than argue about what the factory determined a long time ago why don't you set the valves when cold as the factory specifies to .012 inches and then measure the clearance when the engine has warmed up... the factory spec states after the thermostat has opened.
I meant to correct myself bill, this was after looking at haynes and realising that 2 workshop manuals can't be wrong, The justification I gave was wrong too, but thats life :p sometimes your brain just stops working. So no i don't think the BMW factory is full of idiots, if I did I wouldn't be driving one would I? There are cars that have hot clearances that are smaller then cold clearances aren't there? I swear i've seen that somewhere before.

PS: I have deleted that second post as it is a load of ****, I don't know what the hell was going on with my brain last night none of what i said makes sense lol.

[rob101]

Question Bill R., should i set my valve clearances when the engine (M30 that is) is cold? I've read in a few places that this is the best for an aluminium head otherwise you get all different clearances as the head cools down too quick

[Rustam]

FWIW ... Not ice, one important exception.

expansion of ice is not important in this topic. neither is it pertinent...

[Rustam]

Drill a hole in a plate of steel. Heat the plate. Is the hole larger or smaller when it's hot?

drilling a hole and heating is unnecessary - given that metal expands at higher temperature its quite obvious that the hole will be a bit smaller after heating...

[Rustam]

also state, .012 cold and .014 thousandths when the engine is warmed up...

At stake here is not quality of BMW engineers but the quality of Bentley's Mechanic reference for e34... I did find a couple of inconsistencies there.

Now regarding various rates of expansion of aluminum and steel. The manual distinctly addresses the state of the engine as HOT it does not say "on the way of heating up". So the premise is of having an engine, warmed up to operational state - that is things are warm and expanded maximally. The issue of faster expansion of aluminum is irrelavant - its not what is addressed. Whats addressed now is the state of things after they have finished expanding - that is when the engine is hot.

[dacoyote]

expansion of ice is not important in this topic. neither is it pertinent...

It's a good worthless triva post...

[rob101]

drilling a hole and heating is unnecessary - given that metal expands at higher temperature its quite obvious that the hole will be a bit smaller after heating...
no actually holes get bigger after heating, its why you head the housing and cool the bearing if you are seating a bearing. Bill R is right in this case, it is because aluminium expands alot more than steel. slightly less than twice as much to be exact.

[SRR2]

Except that your opinion is exactly wrong, which was my point. The simplest thought experiment to prove this is to consider what happens to the plate without a hole. Imagine a circle drawn on the plate before you make the hole. Now heat the plate. The circle is larger because the entire plate expands uniformly. When it cools, remove the material inside the circle. Heat both pieces. The circular piece expands as does the piece with the hole, but when they're the same temperature, the circular piece will drop right into where it came from in the piece with the hole. Thus, the circular piece has expanded as has the hole it came from.

The same principle applies to valve gaps.

[Scott H]

warm/hot/whateveryouwanttocallit ??

Practicality takes over here....



Now regarding various rates of expansion of aluminum and steel. The manual distinctly addresses the state of the engine as HOT it does not say "on the way of heating up". So the premise is of having an engine, warmed up to operational state - that is things are warm and expanded maximally. The issue of faster expansion of aluminum is irrelavant - its not what is addressed. Whats addressed now is the state of things after they have finished expanding - that is when the engine is hot.

[rob101]

Except that your opinion is exactly wrong, which was my point. The simplest thought experiment to prove this is to consider what happens to the plate without a hole. Imagine a circle drawn on the plate before you make the hole. Now heat the plate. The circle is larger because the entire plate expands uniformly. When it cools, remove the material inside the circle. Heat both pieces. The circular piece expands as does the piece with the hole, but when they're the same temperature, the circular piece will drop right into where it came from in the piece with the hole. Thus, the circular piece has expanded as has the hole it came from.

The same principle applies to valve gaps.
who's opinion? there are engines that have hot clearances smaller than cold AFAIK

[SRR2]

But he's wrong. Once ice has formed it exhibits a positive thermal coefficient of linear expansion = 51x10^-6 until the temperature falls to approximately 80K at which point, for which there is no agreed-upon explanation, the coefficient passes through 0 and turns negative (i.e. it expands as it falls further in temperature toward absolute 0). The commonly observed expansion-on-cooling property of ice is only at the point of liquid-solid phase change where the solidified volume is higher than the liquid volume due to crystal-like ordering of the water molecules. Once it's frozen it behaves like most other solids with respect to thermal expansion -- as it cools, it shrinks -- until it hits the aforementioned 80K.

[dacoyote]

But he's wrong. Once ice has formed it exhibits a positive thermal coefficient of linear expansion = 51x10^-6 until the temperature falls to approximately 80K at which point, for which there is no agreed-upon explanation, the coefficient passes through 0 and turns negative (i.e. it expands as it falls further in temperature toward absolute 0). The commonly observed expansion-on-cooling property of ice is only at the point of liquid-solid phase change where the solidified volume is higher than the liquid volume due to crystal-like ordering of the water molecules. Once it's frozen it behaves like most other solids with respect to thermal expansion -- as it cools, it shrinks -- until it hits the aforementioned 80K.

Learn something new every day....

[rob101]

Now regarding various rates of expansion of aluminum and steel. The manual distinctly addresses the state of the engine as HOT it does not say "on the way of heating up". So the premise is of having an engine, warmed up to operational state - that is things are warm and expanded maximally. The issue of faster expansion of aluminum is irrelavant - its not what is addressed. Whats addressed now is the state of things after they have finished expanding - that is when the engine is hot.
perhaps you should read about the phenomenon of thermal expansion, if two materials expand at different rates, then at a higher temperature (which is constant) the one with the higher coeffecient of expansion will have expanded more, that is how this works, Bill R is right, perhaps you should admit defeat and go set your clearances. as the steel components (cam, rocker valve) expand less than the aluminium head they sit in just as bill said.

[rob101]

But he's wrong. Once ice has formed it exhibits a positive thermal coefficient of linear expansion = 51x10^-6 until the temperature falls to approximately 80K at which point, for which there is no agreed-upon explanation, the coefficient passes through 0 and turns negative (i.e. it expands as it falls further in temperature toward absolute 0). The commonly observed expansion-on-cooling property of ice is only at the point of liquid-solid phase change where the solidified volume is higher than the liquid volume due to crystal-like ordering of the water molecules. Once it's frozen it behaves like most other solids with respect to thermal expansion -- as it cools, it shrinks -- until it hits the aforementioned 80K.
I am throwing in the towel, Bill R's post should have been the end of this arguement. bye bye :)

[Bill R.]

cold. I knew i had seen this a few times in the past myself. Most auto manufacturers don't give you specs hot and cold. Most give you one or the other depending on how they want them set.. A quick look through some of my old books shows a opel 1966 1100cc engine having a gap that shrinks as it heats up. I know that some of my datsun factory manuals also gave specs hot and cold but i'm not going to dig them all out. Off the top of my head i would venture to say that any that get smaller as they warm up are going to be iron block,iron head pushrod motors, not overhead cam motor.I seem to recall a number of american engines that meet those specs that have ironblock,ironhead, aluminum pushrods with steel ends and the pushrods expand more than the block/head so the clearances tighten up as they warm up.




I meant to correct myself bill, this was after looking at haynes and realising that 2 workshop manuals can't be wrong, The justification I gave was wrong too, but thats life :p sometimes your brain just stops working. So no i don't think the BMW factory is full of idiots, if I did I wouldn't be driving one would I? There are cars that have hot clearances that are smaller then cold clearances aren't there? I swear i've seen that somewhere before.

PS: I have deleted that second post as it is a load of ****, I don't know what the hell was going on with my brain last night none of what i said makes sense lol.

[632 Regal]

remember it too, there will be a test on this Friday.
Learn something new every day....

[Rustam]

The circular piece expands as does the piece with the hole, but when they're the same temperature, the circular piece will drop right into where it came from in the piece with the hole. Thus, the circular piece has expanded as has the hole it came from.

you're concluding that the hole expands based on the argument that circular piece becomes bigger as does the piece with the hole - that is shown by the fact that the circular piece cannot pass through the opening after heating. Well, that tells that the hole acquires smaller radius - correct word for what happens with the hole would be "shrinking" not "expanding"...

the circular piece has expanded albeit not as the hole has... the hole has shrunk.

in fact, if the hole expands, using the experiement that you have provided in the argumentation becomes very hard if not irrelevant...

[Rustam]

perhaps you should read about the phenomenon of thermal expansion, if two materials expand at different rates, then at a higher temperature (which is constant) the one with the higher coeffecient of expansion will have expanded more, that is how this works, Bill R is right, perhaps you should admit defeat and go set your clearances. as the steel components (cam, rocker valve) expand less than the aluminium head they sit in just as bill said.

I never said that the material with higher coefficient of expansion should not have expanded more. Its quite obvious in fact, that X that grows faster in size will grow to greater extent than Y which does not grow as fast in given amount of time under same heating conditions. That said - I don't see the basis for a conclusion that I should read about the phenomenon of thermal expansion. How I succeded in showing to you that I don't understand this phenomenon totally alludes me.

But what I did mention was that the issue of rate of expansion is irrelevant at the end result which is simple observation of the fact that things in total had become bigger... I never mentioned what happened on the way to heating but mentioned what happens after things have heated - that was my concern...

What defeat are you talking about? I never made statements but inferences which I brought out for a discussion.



Now, Bill's comment did not provide much explanation but did provide further grounds for questioning. Having mentioned what happens at bottom end of the head Bill R misses to mention what happens at top end of the head. Top end of the head expands also, tending to counteract the effect of bottom expansion thereby pushing the valve up towards the rocker, minimizing the space... What Bill R's "explanation" misses to account for is the fact that bottom end of the head being in combustion chamber accepts more heat and expands more than the top end of the head - that being under PCV. Both ends pull the valve, however bottom end of the head now having expanded more tends to pull more - net effect being displacement of the valve down, further away from the rocker...

This serves as an explanation for me.

[88m53453]

seems backwards ,but Bentley is right on this one. .010-.012 on cold and add .002 for a hot engine, in thousandths here of course

[rob101]

I never said that the material with higher coefficient of expansion should not have expanded more. Its quite obvious in fact, that X that grows faster in size will grow to greater extent than Y which does not grow as fast in given amount of time under same heating conditions. That said - I don't see the basis for a conclusion that I should read about the phenomenon of thermal expansion. How I succeded in showing to you that I don't understand this phenomenon totally alludes me.

But what I did mention was that the issue of rate of expansion is irrelevant at the end result which is simple observation of the fact that things in total had become bigger... I never mentioned what happened on the way to heating but mentioned what happens after things have heated - that was my concern...

What defeat are you talking about? I never made statements but inferences which I brought out for a discussion.



Now, Bill's comment did not provide much explanation but did provide further grounds for questioning. Having mentioned what happens at bottom end of the head Bill R misses to mention what happens at top end of the head. Top end of the head expands also, tending to counteract the effect of bottom expansion thereby pushing the valve up towards the rocker, minimizing the space... What Bill R's "explanation" misses to account for is the fact that bottom end of the head being in combustion chamber accepts more heat and expands more than the top end of the head - that being under PCV. Both ends pull the valve, however bottom end of the head now having expanded more tends to pull more - net effect being displacement of the valve down, further away from the rocker...

This serves as an explanation for me.
no it doesn't miss that fact, it doesn't really matter because ultimately a hot head will expand more than a cold one, since the rocker assembly are mounted on the topside of the head and the valve seat is mounted on the bottom side expansion = increased distance.

Just go set your clearances already.

[Rustam]

no it doesn't miss that fact, it doesn't really matter because ultimately a hot head will expand more than a cold one, since the rocker assembly are mounted on the topside of the head and the valve seat is mounted on the bottom side expansion = increased distance.

Yes it does miss that fact - in his message he never differentiates for the variation in temperature between top part of the head and the bottom part of the head. What he does differentiate between is variation in speeds of expansions and extents of expansions of metals involved.

He never mentions the fact that the head expands to different extents at top and bottom.




ultimately a hot head will expand more than a cold one

Pardon me, but cold head doesn't "expand" - it is taken as the datum in this discussion...

Overall I fail to see logic in your message - especially at the arrival to the conclusion.




Just go set your clearances already.
I was not seeking to set the clearances.

[632 Regal]

you get more displacement with a HOT engine than a cold one.

[Rustam]

you get more displacement with a HOT engine than a cold one.

How so? If the metal expands in heat it supplants space making available less of it.

I would say that one gets greater compression ratio with HOT engine...

This message wasn't really meant to be serious was it?

[rob101]

so if you imagine the aluminum head expanding in all directions as it heats up that means the valve seat in the head is going to get closer to the the piston and the rocker shaft is going to get further away from the valve stem
so there you go since the rocker assembly is mounted on the top of the head, and the valve seat is on the bottom of the head an expanding head causes these to move further away. since the ALUMINIUM head expands more than the steel components when you increase the temperature, then the friggin' clearances increase.

I am sorry your logic is so bad newbie, Bill R. said it the right way first time. sorry that you didn't realise the valve seat is on the lower surface of the head and the rocker assembly is on the top.

[632 Regal]

I said displacement not compression...and yes it's a serious post.

How so? If the metal expands in heat it supplants space making available less of it.

I would say that one gets greater compression ratio with HOT engine...

This message wasn't really meant to be serious was it?

[iNomis]

But he's wrong. Once ice has formed it exhibits a positive thermal coefficient of linear expansion = 51x10^-6 until the temperature falls to approximately 80K at which point, for which there is no agreed-upon explanation, the coefficient passes through 0 and turns negative (i.e. it expands as it falls further in temperature toward absolute 0). The commonly observed expansion-on-cooling property of ice is only at the point of liquid-solid phase change where the solidified volume is higher than the liquid volume due to crystal-like ordering of the water molecules. Once it's frozen it behaves like most other solids with respect to thermal expansion -- as it cools, it shrinks -- until it hits the aforementioned 80K.

Sorry for the slight off topic. I was just referring to the solid-liquid phase change decrease in volume on heating in reference to the "everything in nature expanding when heated" part of the original post. I'm glad we could also examine the areas beyond my knowledge. Thanks!:)

[Rustam]

so there you go since the rocker assembly is mounted on the top of the head, and the valve seat is on the bottom of the head an expanding head causes these to move further away. since the ALUMINIUM head expands more than the steel components when you increase the temperature, then the friggin' clearances increase.

I am sorry your logic is so bad newbie, Bill R. said it the right way first time. sorry that you didn't realise the valve seat is on the lower surface of the head and the rocker assembly is on the top.

This quote does not account for the difference in the expansion between the top of the head and the bottom of the head... You've failed to show how Bill R accounts for that effect even though you said that he did...

Perhaps sometime you may wish to carefully reread what I put together earlier in the critique of his comment.

and what makes you think that I didn't realize that seat is on the lower surface of the head and the rocker assembly is on the top??? how did I show that? another baseless inference...

[Rustam]

I said displacement not compression...and yes it's a serious post.

well, if this is a serious post you may want to consider answering my question - "How so"? which I put ahead of everything else...

I don't see a reason to be reminded that you said "displacement" and not "compression". it is exactly this fact that made me ask the question "how so?" to begin with... Unfortunately I got nothing for the answer.

Now, I wouldn't have asked the question if you said "compression" - that was the point of the statement that followed.

[Rustam]

Once it's frozen it behaves like most other solids with respect to thermal expansion -- as it cools, it shrinks -- until it hits the aforementioned 80K.

This actually makes a lot of sense, and simple sense at that. Of course, the ice gets to expand at turning into solid state because of the hydrogen bonding that makes rigid "mesh" structure. Certainly, at this point, having become a solid it should exhibit srinking properties of a solid with cooling.

Now I imagine it tends to shrink very slowly doesn't it?

It may not be possible to shrink all along the cooling process for the ice since molecular forces involved are not due to covalent bonding but dispersion forces. So the compresion of ice is essentially a compression of multitude of dipoles. The space between electrons in Oxygen provides probability for distribution closer or farther from the nucleus - that may provide decrease in volume, but what does one do with dispersion link between two Hydrogens from neighboring molecules?

[Rustam]

Sorry for the slight off topic. I was just referring to the solid-liquid phase change decrease in volume on heating in reference to the "everything in nature expanding when heated" part of the original post. I'm glad we could also examine the areas beyond my knowledge. Thanks!:)

Well, iNomis I did not account for possible presence of scientifically inclined here, and the effect of volumetric expansion of water due to cooling is something of a rarity in daily life whereas common experience provides effects otherwise.

This is actually interesting thing to mention to someone who says "well now that we have global warming, all these waters from icebergs are going to flood us"... how much of an iceberg gets exposed above water level? 5% or so?

[rob101]

This quote does not account for the difference in the expansion between the top of the head and the bottom of the head... You've failed to show how Bill R accounts for that effect even though you said that he did...

Perhaps sometime you may wish to carefully reread what I put together earlier in the critique of his comment.

and what makes you think that I didn't realize that seat is on the lower surface of the head and the rocker assembly is on the top??? how did I show that? another baseless inference...
lol:D make another critique, do whatever you want you're way smarter than everyone else here aren't you? and you're doing us all a favour by correcting our flawed thinking you're a real hero rectum.

[Rustam]

lol:D make another critique, do whatever you want you're way smarter than everyone else here aren't you? and you're doing us all a favour by correcting our flawed thinking you're a real hero rectum.

It's obvious that you have nothing to add to support any one of your points in this thread. Particularly for this ridiculous, childish comment...