Re: Help me explain hot/cold valve lash to someone!
[Re: mikemotorhead]
#576556
01/08/10 12:40 PM
01/08/10 12:40 PM
|
Joined: Mar 2006
Posts: 9,910
Eighty Four, PA
B G Racing
master
|
master
Joined: Mar 2006
Posts: 9,910
Eighty Four, PA
|
Quote:
I always set my valves cold and set them .002-.004 tighter than spec for when the motor heats up and the lash increases but to explain to someone that metal expands when it heats up and contracts when it cools seems to contradict what I am doing. Can anyone simplify the explanation so that I can at least sound like I know what I am talking about?
Thanks Mike
Couldn't say it any simpler,Mike.Hot expands,Cold shrinks(contracts)different metals different rates of expansion and contractions.Iron engine componants expand aprox. .004 at temp,aluminum engines .012/.018 aprox.  Most valve setting is for hot,expanded engine componants.If your hot setting is .020 and you set your lash at .016 cold it will be looser at running temperture,closer to your desired .020 setting.The mass (head) is usually a porous metal such as cast iron and grows the most as does your rocker arms,your valves and pushrods are a more dense material,usually stainless steel and chrome moly and is less effected.
Last edited by B G Racing; 01/08/10 12:50 PM.
|
|
|
Re: Help me explain hot/cold valve lash to someone!
[Re: B G Racing]
#576557
01/08/10 12:57 PM
01/08/10 12:57 PM
|
Joined: Nov 2003
Posts: 6,293
Rock Springs
Bob_Coomer
master
|
master
Joined: Nov 2003
Posts: 6,293
Rock Springs
|
I think I understand what you mean. Your thinking that when the motor heats up, the pushrods expands, and this would make the adjustment tighter correct? Well..everything expands and grows not just the pushrods, the rocker arms, the heads, the pistons, the bores, the rings..everything. The heat excites the molecules causeing them to move. Just like airing up a tire..You add molucules they bump into each other, they have now where to go, they expand the tire..It heats the tire up also....
When pressure goes up so does temp they are proportional. As pressure goes down so does temp. This is why those old Deodorant cans get real could when you use them for a few seconds. This is actually the basic principle of how a A/C unit works.
[color:"red"]65 Hemi Belvedere coming soon [/color]
[color:"#00FF00"]557" Indy engine 1.07 60ft 144mph in the 8th 2100 lbs package [/color]
|
|
|
Re: Help me explain hot/cold valve lash to someone!
[Re: Bob_Coomer]
#576559
01/08/10 01:17 PM
01/08/10 01:17 PM
|
Joined: Mar 2006
Posts: 9,910
Eighty Four, PA
B G Racing
master
|
master
Joined: Mar 2006
Posts: 9,910
Eighty Four, PA
|
Quote:
I think I understand what you mean. Your thinking that when the motor heats up, the pushrods expands, and this would make the adjustment tighter correct? Well..everything expands and grows not just the pushrods, the rocker arms, the heads, the pistons, the bores, the rings..everything. The heat excites the molecules causeing them to move. Just like airing up a tire..You add molucules they bump into each other, they have now where to go, they expand the tire..It heats the tire up also....
When pressure goes up so does temp they are proportional. As pressure goes down so does temp. This is why those old Deodorant cans get real could when you use them for a few seconds. This is actually the basic principle of how a A/C unit works.
No Bob,the pushrods and valves are a denser(tighter grained)material and are less effected by heat.Combustion tempertures have the greatest effect on a pourous cast material such as the head,combustion tempertures are transferred through out the mass casting causing the growth, conversly the rockers,iron or aluminum conduct the heat from the head mass also,but to a lesser degree than the head mass.Valves are the lest effected since they(exhaust) are designed and made of material that would only be effected by extreme heat that you will not see in an engine.The main growth to be concerned with here are blocks and heads or "mass,pourous metals"
|
|
|
Re: Help me explain hot/cold valve lash to someone!
[Re: B G Racing]
#576560
01/08/10 01:44 PM
01/08/10 01:44 PM
|
Joined: Nov 2003
Posts: 6,293
Rock Springs
Bob_Coomer
master
|
master
Joined: Nov 2003
Posts: 6,293
Rock Springs
|
Quote:
Quote:
I think I understand what you mean. Your thinking that when the motor heats up, the pushrods expands, and this would make the adjustment tighter correct? Well..everything expands and grows not just the pushrods, the rocker arms, the heads, the pistons, the bores, the rings..everything. The heat excites the molecules causeing them to move. Just like airing up a tire..You add molucules they bump into each other, they have now where to go, they expand the tire..It heats the tire up also....
When pressure goes up so does temp they are proportional. As pressure goes down so does temp. This is why those old Deodorant cans get real could when you use them for a few seconds. This is actually the basic principle of how a A/C unit works.
No Bob,the pushrods and valves are a denser(tighter grained)material and are less effected by heat.Combustion tempertures have the greatest effect on a pourous cast material such as the head,combustion tempertures are transferred through out the mass casting causing the growth, conversly the rockers,iron or aluminum conduct the heat from the head mass also,but to a lesser degree than the head mass.Valves are the lest effected since they(exhaust) are designed and made of material that would only be effected by extreme heat that you will not see in an engine.The main growth to be concerned with here are blocks and heads or "mass,pourous metals"
I agree with that Bob...I was actually trying to think like his friend in the first paragraph LOL, where the contradiction occured LOL.
Let me ask you this...
Looking at those old KB Hyper style pistons. They always call for a much larger top ring gap like .0065-.007 per inch of cylinder Vs standard forged pistons were .004-.0045 is usually a good target for end gap/per inch of bore.
Looking at the piston I noticed how much the the top ring is moved up toward top of the piston.
This made me think for a second. I know the material used is diff and has a diff expansion rate, and even requires diff piston wall clearance also.
Here is what I first thought. The ring being much closer to the top of the piston would be exposed to much more of the combustion temp and heat.
Also I thought about the ring placement in the bore compared to the water jacket. Id imagine that the top of the cylinder runs generally a bunch hotter than the bottom portion. Which this is the point were all the combustion process works. maybe this is why the cylinder mostly wears at the top.
Anyways
From a engineering stand point, or from a veiw of guys smarter than me. Why? Why have the top ring so high on the piston? Why not have the ring were it suppose to and have a normal ring gap?
[color:"red"]65 Hemi Belvedere coming soon [/color]
[color:"#00FF00"]557" Indy engine 1.07 60ft 144mph in the 8th 2100 lbs package [/color]
|
|
|
Re: Help me explain hot/cold valve lash to someone!
[Re: B G Racing]
#576561
01/08/10 01:58 PM
01/08/10 01:58 PM
|
Joined: Jan 2003
Posts: 732
mikemotorhead
OP
super street
|
OP
super street
Joined: Jan 2003
Posts: 732
|
"I think I understand what you mean. Your thinking that when the motor heats up, the pushrods expands, and this would make the adjustment tighter correct? Well..everything expands and grows not just the pushrods, the rocker arms, the heads, the pistons, the bores, the rings..everything. The heat excites the molecules causeing them to move. Just like airing up a tire..You add molucules they bump into each other, they have now where to go, they expand the tire..It heats the tire up also...." See this is where I get into trouble explaining it. They say "Well if the pushrod is expanding and getting larger and the roller tip is expanding then the lash will become smaller(tighter) as the two metals "grow' towards one another as they expand!!!  Mike
|
|
|
Re: Help me explain hot/cold valve lash to someone!
[Re: mikemotorhead]
#576564
01/08/10 03:09 PM
01/08/10 03:09 PM
|
Joined: Aug 2003
Posts: 43,204
Bend,OR USA
Cab_Burge
I Win
|
I Win
Joined: Aug 2003
Posts: 43,204
Bend,OR USA
|
Quote:
"
See this is where I get into trouble explaining it. They say "Well if the pushrod is expanding and getting larger and the roller tip is expanding then the lash will become smaller(tighter) as the two metals "grow' towards one another as they expand!!!
Mike
Your not keeping in mind that the block, crankshaft, heads, piston, pushrods, lifters and every thing metal expands when heated up, BGR is saying that the different metals expand at different rates, alumlinum more than cast iron, steel less than cast iron. I will set the valves cold and then run the motor up to operating temps and drive it for ten or more minutes to make sure the complete motor is warmed up evenly.I then recheck the valve lash hot to see how much THAT motor has tighten up and correct as needed. If there is a lrge correction I try that process several times until the changes settle down to a consistent change and use that as the correction factor for that motor. I have one motor with Eddy RPM heads and a 400 block(cast iron) that changes .002 hot to cold  That is setting it cold and rechecking it hot and again after letting it sit overnight and rechecking it cold the next morning  I know, I have way to much time on my hands  
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
|
|
|
Re: Help me explain hot/cold valve lash to someone!
[Re: Bob_Coomer]
#576565
01/08/10 05:31 PM
01/08/10 05:31 PM
|
Joined: Dec 2008
Posts: 1,200
UK
602heavy
pro stock
|
pro stock
Joined: Dec 2008
Posts: 1,200
UK
|
Quote:
Anyways
Why have the top ring so high on the piston? Why not have the ring were it suppose to and have a normal ring gap?
Emission control is one of the reasons , the high placement of ring land minimises any 'build up' of fuel between top of piston & ring , just wish us nitrous guys could run with this high placement setup , piston companies would go out of buisness. 
|
|
|
Re: Help me explain hot/cold valve lash to someone!
[Re: 602heavy]
#576566
01/08/10 05:57 PM
01/08/10 05:57 PM
|
Joined: Jan 2005
Posts: 3,635
Oakland, MI
dizuster
master
|
master
Joined: Jan 2005
Posts: 3,635
Oakland, MI
|
Few comments... First steel and cast iron grow at almost the same rate (actually if anything cast iron grows slightly less per degree F then steel does). Aluminum definately grows more per Degree F then steel. This is why you'll see on an aluminum headed motor, that they will have a bigger cold/hot change, then an iron headed motor. Iron block/iron head will have almost no change at all in hot/cold lash (maybe .002") Also, I think the reason that you see a hot change at all is because the head itself sees more heat then the rest of the parts do. The pushrod certainly doesn't see the combustion flame front that the head does. More heat=more expansion. Here is a chart for some comparison... http://www.engineeringtoolbox.com/linear-expansion-coefficients-d_95.htmlAs for the hypereutectic piston question. The KB hypereutectic pistons are made of a special material. That material has a slower thermal expansion, along with a lower heat transfer. That means if the piston is seeing (absorbing) less heat, all of the other components take more heat (especially the top ring). Because the top ring sees more heat, it needs more gap. As commented on before, moving the top ring up helps keep the combustion gasses in the chamber. Also, KB likes to keep the 1st/2nd ring as far apart from each other as possible. Their theory is that pressure build up between the two rings can cause ring flutter. They like big gaps, and big volume between the two...
|
|
|
Re: Help me explain hot/cold valve lash to someone!
[Re: TS3303]
#576567
01/08/10 06:05 PM
01/08/10 06:05 PM
|
Joined: Mar 2006
Posts: 9,910
Eighty Four, PA
B G Racing
master
|
master
Joined: Mar 2006
Posts: 9,910
Eighty Four, PA
|
Quote:
Quote:
See this is where I get into trouble explaining it. They say "Well if the pushrod is expanding and getting larger and the roller tip is expanding then the lash will become smaller(tighter) as the two metals "grow' towards one another as they expand!!!
Mike
The pushrod is expanding at a smaller rate per material and it only see ambient temperature inside the valley. The block and heads see a much higher temp from combustion and higher thermal expansion rates. The roller tip expansion is almost nil.
Edit: short answer the block/heads are expanding at a greater rate than the cam/pushrods/roller tip.
ask someone who has an aluminum block and aluminum head Hemi about setting lash cold.
Our all Aluminum Hemis expand aprox .018 at operating temperture.We set inital valve setting at the minimum .005 cold.
|
|
|
Re: Help me explain hot/cold valve lash to someone!
[Re: moparniac]
#576569
01/08/10 06:21 PM
01/08/10 06:21 PM
|
Joined: Mar 2003
Posts: 15,491
the boonies
aarcuda
I Live Here
|
I Live Here
Joined: Mar 2003
Posts: 15,491
the boonies
|
hence the reason to adjust the lash with a HOT engine..... cause adjusting them cold might get you close but not exactly where they want it
also, since the head is hotter in the center because the exhaust ports are closer together, the head probably grows slightly more in the middle vs the ends when its hot
It's got a cop motor, a 440 cubic inch plant, it's got cop tires, cop suspensions, cop shocks. It's a model made before catalytic converters so it'll run good on regular gas.
|
|
|
Re: Help me explain hot/cold valve lash to someone!
[Re: moparniac]
#576570
01/08/10 06:36 PM
01/08/10 06:36 PM
|
Joined: Mar 2006
Posts: 9,910
Eighty Four, PA
B G Racing
master
|
master
Joined: Mar 2006
Posts: 9,910
Eighty Four, PA
|
Quote:
My cam lash on my bullet cam is .020 on both sides... and yes it all aluminum.... so cold settings at .005 on both sides cause I thought you didnt wanna go any tighter than that... anyways after setting cold lash at .005 and then check lash after engine is hot and then youll know what to actual set cold lash at to match cam makers lash spec hot... right 
That may get you close,we would rather set them hot when ever possible..005 is to get you fired up never set them any closer.Cams with larger lash can be set between .005 and .010.cold.We like the engine to be aprox,180 degrees for lash settings. 
|
|
|
Re: Help me explain hot/cold valve lash to someone!
[Re: dizuster]
#576571
01/10/10 08:55 PM
01/10/10 08:55 PM
|
Joined: Oct 2007
Posts: 4,206
New York
polyspheric
master
|
master
Joined: Oct 2007
Posts: 4,206
New York
|
True, but it's even more complex.
Different materials exposed to the same heat source will experience different temperature changes.
At around 212°F, 1 gram of aluminum takes almost double the amount of heat (193%) to increase by 1° than 1 gram of iron.
This is one reason why the apparent expansion is not as close as the comparison between materials suggests.
This is counter-intuitive, because this factor (specific heat) is not related to heat transfer properties. Silver conducts heat even better than aluminum, but increases in temperature almost 5 times faster for the same heat input.
Don't try to calculate.
Boffin Emeritus
|
|
|
Re: Help me explain hot/cold valve lash to someone!
[Re: polyspheric]
#576572
01/11/10 12:32 PM
01/11/10 12:32 PM
|
Joined: Jan 2005
Posts: 3,635
Oakland, MI
dizuster
master
|
master
Joined: Jan 2005
Posts: 3,635
Oakland, MI
|
Quote:
Don't try to calculate.
LOL...
You know though, everything up to temp should be close to steady state. The heat transfer rate shouldn't really come into play?
It's not like you're lashing valves during the run, a warmed up motor should be pretty temperature stable...
|
|
|
|
|
