Thermodynamics - Expansion of Motor Parts

[kd]

I believe that's what started the discussion. It was based on the understanding that lifters with limiters set one flat off the bottom would increase the lower chamber as the cylinders got hot.  The growth in the barrels was thrown around from Ken's number of .018 to previously mentioned growth out to .040 or more.  This thread is an effort to come up with some sort of consensus on what is reasonable.

[Admiral Akbar]

The cylinder studs will not limit how much the cylinders and heads expand.

Actually it will.  It's the stress vs strain stuff.. Youngs modulus.. It likely won't be much tho.

OK, perhaps my understanding of physics is metallurgy is out of date. When (certain) metals are heated, the atoms they are made of vibrate more, forcing their relative distances to each other apart. So yes, when aluminum is heated, it will expand, in length, surface area, and volume. Note that I said 'cylinders and heads will expand', not grow in one dimension only. If you attempt to constrain that growth in one dimension, it will cause the metal to expand more in other dimensions. Like an inflating balloon trapped between to fixed surfaces. I agree, we are talking only thousandths of an inch, but still...

Back to cylinder studs. They are made of steel, which has a lower coefficient of expansion than aluminum. And thus why when the engine gets hot, the clamping force between the heads/cylinders/block increases. Yes, the studs will expand also when heated, but not nearly as much. They will indeed get longer, though, due to force on them from the expanding aluminum parts. This is by intended design, and why the (stock) studs neck down between the threaded ends. If the studs constrain the growth in length of the heads/cylinders, that then turns into distortion of the cylinder walls. That aluminum has to expand somewhere, right?

So correct me if I'm wrong, but I believe the stud's job is to clamp the heads/cylinders/block together without causing the cylinders to distort, not limit the length of them. Yes? No?

-JW

While you are correct on expansion, I think you need to look at it differently. The metals you are discussing grow at some rate in all directions when heated.  Add a force from another source like studs and the shape will change. While the expansion from heat increases the stress, it's really the tension on the stud that creates the distortion.  A balloon might be a bit of a poor analogy as atoms really aren't moving but are changing spacing based on loads. I would guess the could increase the diameter some. Might be worth stand a short round in a press, put a lot of pressure on it and see if the diameter changes. Bet it does some.

Over temp, like you mention, the tension on the studs will increase as temp increases. Setting the diameter of the stud helps to keep the tension from becoming too great as you say.  I'm sure there is a science to this to ensure sufficient clamping pressure coupled with distortion.

I suspect that cylinder studs are selected to not stop distortion but to limit it with other factors like headgasket seal, metals changing young's modulus under tension and different expansion rates of other materials. 

[Admiral Akbar]

I believe that's what started the discussion. It was based on the understanding that lifters with limiters set one flat off the bottom would increase the lower chamber as the cylinders got hot.  The growth in the barrels was thrown around from Ken's number of .018 to previously mentioned growth out to .040 or more.  This thread is an effort to come up with some sort of consensus on what is reasonable.

Well, I think that we can all agree that the depth of the plunger in the lifter decreases some with increase in temperature due to the different expansion rates of the material involved. Not sure why the calculation is important. One time, Larry told me, "You'll know when you got the pushrods too tight cuz the bike won't start".. 

[Ohio HD]

Couple things. 

1. The round numbers you are using for coeffects of expansion are for degrees C and Not F.

2. It's not really thermal dynamics. It's really thermal statics or at least the numbers you are using re-static. You do mention as the motor heats which is dynamic but assume everything is the same temp.

Appreciate your jumping in.

I just took a look, you're right about the values being for C° and not F°.

I was using the simple example to only show difference in materials under temperature. I agree there is a lot of variables that come into play, various temperatures from cooler at the cylinder base to hotter as you go towards the head. As well the different materials, and their densities that effect expansion.

I have no way to even get to the root of how to calculate the various parts of the top end as to what they will expand, and how much or little the studs allow expansion, etc.

Don mentions that BH Ken once took some effort on a TC to see what expansion was. In my mind a value of 0.018" could be close to what possibly the combustion area may grow, or a little less. I need to dig more, see what I can find. 

The thing is that things grow at a different rate when using degrees F or C. If you are going the grind out the numbers, they might as well be right..  The growth will be time 5/9 for F.

I'll agree that the expansion rate will be different between top to bottom of the cylinder.  Maybe not that much tho. Cylinder head is what? Maybe 280 on the intake side?  330 on the exhaust? Engine oil temp is pribabably close to oil temp.. 220? I guess you could map it with a IR temp sensor.

I forget how Ken came up with the number but it seems reasonable.

What are you looking for?  Pushrod plunger change in the lifter?

Yeah, I looked back at it last night and see where I was wrong. I was surprised by my findings of 0.069" and 0.036", I should have questioned myself when I posted.

I made a new post from the lifter posting because I wasn't really looking for that. I adjust lifters about 0.120" down, and with limiters two flats from the bottom and call it good.

I'm just trying to gain a better understanding of what the upper end growth is as it concerns the combustion chamber. I realize there are complex variables with heat and where it is, and where it's different. The longer I think about this I don't know that anyone has more then some idea what happens in a given combustion chamber as far as volume changes, if there are any worth being concerned with.   

[Bikerscum]

Does compression play a role in this... 200+ PSI pushing up against the head? 

[actonern]

"...Back to cylinder studs. They are made of steel, which has a lower coefficient of expansion than aluminum. And thus why when the engine gets hot, the clamping force between the heads/cylinders/block increases. Yes, the studs will expand also when heated, but not nearly as much. They will indeed get longer, though, due to force on them from the expanding aluminum parts. This is by intended design, and why the (stock) studs neck down between the threaded ends. If the studs constrain the growth in length of the heads/cylinders, that then turns into distortion of the cylinder walls. That aluminum has to expand somewhere, right?..."

On the issue of why studs are necked down between threaded ends this is interesting...

https://www.cycleworld.com/how-does-stress-concentration-affect-motorcycle-engine/

[Don D]

In the chamber we have another set of expansion elements happening simultaneously but they are divorced from being constrained by studs. You have an aluminum piston, alloys vary, and a forged steel rod, plus the elements from the crankshaft. It is an interesting study because we do operate with some close squish on these engines and with a little carbon build I have seen the pistons hit the head.

Bruce also brings up some very interesting information about the cylinder ballooning. My goodness, we are trying to get these perfectly straight and true at the inception. We can compensate with torque plates to some extent. Even that is a bit of smoke and mirrors as S&S has proven with their case that has a large measurement hole and a head and cylinder can be bolted on for measurement. So after all of this is said and done we find some of the most detailed of builders are fine tuning some elements while the foundation is on tooth picks and sand. This is just my impression and opinion but we still manage to make some pretty fine results and we push components and strength of materials pretty hard.

I have always thought that the studs are purposely chosen for material, heat treat, and sizing in order to assure a constant preload on the head surface for constant gasket sealing under all conditions. When we change them to larger or different material or change the torque the original design goes out the door. There are some guys that found this out on the M8s loosing head gaskets using hardened studs, "special" bolts, and the "special" lubricant that goes with the system. The M8 designers chose another clamping method, torque to yield bolts which are stretched beyond elasticity. The twin cam uses the studs to accomplish the same task but neither the bolts or studs are stressed past their proof load.

[hrdtail78]

Does compression play a role in this... 200+ PSI pushing up against the head? 

Probably not, but add fuel, compression and spark and now the same pressure pushing down the piston will be pushing up on the head.  I am working on a way to read this pressure vs crank position.

[Ohio HD]

I am working on a way to read this pressure vs crank position.

Dynamic compression, that would be very interesting to see. I hope you can accomplish this.   

[chaos901]

Reading this, you can certainly tell it is winter now. 

[Admiral Akbar]

Does compression play a role in this... 200+ PSI pushing up against the head? 

  Under full throttle, it's more like 1200 to 1600 psi.  You can calculate the what's pulling on the studs. 

[Admiral Akbar]

"...Back to cylinder studs. They are made of steel, which has a lower coefficient of expansion than aluminum. And thus why when the engine gets hot, the clamping force between the heads/cylinders/block increases. Yes, the studs will expand also when heated, but not nearly as much. They will indeed get longer, though, due to force on them from the expanding aluminum parts. This is by intended design, and why the (stock) studs neck down between the threaded ends. If the studs constrain the growth in length of the heads/cylinders, that then turns into distortion of the cylinder walls. That aluminum has to expand somewhere, right?..."

On the issue of why studs are necked down between threaded ends this is interesting...

https://www.cycleworld.com/how-does-stress-concentration-affect-motorcycle-engine/

In this case the stud threads were cut not rolled.  HD TC studs are rolled.

[Admiral Akbar]

I am working on a way to read this pressure vs crank position.

Dynamic compression, that would be very interesting to see. I hope you can accomplish this.   

I am working on a way to read this pressure vs crank position.

Dynamic compression, that would be very interesting to see. I hope you can accomplish this.   

If it's cylinder pressure, I don't think it's dynamic compression tho I guess you could figure out what the pressure is at TDC. Would it be a good read? Spark lit the mixture some degrees before TDC.

If you want a dynamic compression ratio, can you calculate it from the VE tables in a Delphi EFI system? 

[hrdtail78]

I am working on a way to read this pressure vs crank position.

Dynamic compression, that would be very interesting to see. I hope you can accomplish this.   

I am working on a way to read this pressure vs crank position.

Dynamic compression, that would be very interesting to see. I hope you can accomplish this.   

If it's cylinder pressure, I don't think it's dynamic compression tho I guess you could figure out what the pressure is at TDC. Would it be a good read? Spark lit the mixture some degrees before TDC.

If you want a dynamic compression ratio, can you calculate it from the VE tables in a Delphi EFI system? 

No, I am trying to measure pressure in a cylinder of a running engine. Looking for peak pressure compared to crank position.  This way peak can be changed by spark tuning to get peak pressure at optimum crank position. 

[SP33DY]

For equipment to measure cylinder pressure and temperature in a running engine see TFX.

TFX

[kd]

Thanks for posting that.  Lots of interesting information to drag me down the rabbit hole.

[hrdtail78]

For equipment to measure cylinder pressure and temperature in a running engine see TFX.

TFX

.
Absolutely, as of right now they have nothing for our bikes that can get the resolution needed from our flywheels.  But the do have a lot of it figured out.  Why I am going a different route over the HDdelphi system.

[Don D]

So what you are attempting is to optimize the ignition timing everywhere. Setting for MBT to occur about 10° to 15° ATDC with a variable spark lead according to the findings. Today at best there is a lot of guessing plus trial and error with the only data feedback being ion sense data or the new system on M8. I have always told my customers tuners that avoid the timing if the bike does not ping are leaving a lot on the table. Many tuners don't touch timing. Not just power but economy and midrange drivability are sacrificed. We all know how bad these performance Vtwins have reversion in certain areas. Timing requirements there I suspect are very different. This is a very cool pursuit, I like it.

[hrdtail78]

So what you are attempting is to optimize the ignition timing everywhere. Setting for MBT to occur about 10° to 15° ATDC with a variable spark lead according to the findings. Today at best there is a lot of guessing plus trial and error with the only data feedback being ion sense data or the new system on M8. I have always told my customers tuners that avoid the timing if the bike does not ping are leaving a lot on the table. Many tuners don't touch timing. Not just power but economy and midrange drivability are sacrificed. We all know how bad these performance Vtwins have reversion in certain areas. Timing requirements there I suspect are very different. This is a very cool pursuit, I like it.

Exactly what I am trying to do.  The dyno has a couple of useful features for feedback with timing as well. Straightening out fuel and hitting a target is simple these days.  I find more power and benefits to the tune with ignition changes than I do with fuel target changes.  (after VE's are mapped of course.)

If you are willing to read crank case pressure.  You can detect knock on any Vtwin.  Look at my crank case pressure thread.  I ask what would disturb ring seal.  Knock will.

Sorry for hijacking your thread Ohio.  All for nothing if I am not smart enough to get it to work or run out resources.

[Ohio HD]

Sorry for hijacking your thread Ohio.  All for nothing if I am not smart enough to get it to work or run out resources.

No problem at all. This is of great interest to me, and I'm sure others.

[Hossamania]

I'm lost on much of it, but it is intriguing reading.

[cheech]

This is an excellent site. Very informative.
Article 17 goes into cylinder pressure analysis.
http://www.epi-eng.com/

Seen a Gale Banks video a while ago also where he mentions and shows the system he's using to record combustion pressures.
Searched for it.
Its right at beginning of video.

[turboprop]

Does compression play a role in this... 200+ PSI pushing up against the head? 

Probably not, but add fuel, compression and spark and now the same pressure pushing down the piston will be pushing up on the head.  I am working on a way to read this pressure vs crank position.

This technology (sort of) has been around for at least twenty years in the bicycle racing community. Has been awhile since I was into triathlon, but back in the day, there were rear wheels that had a 'dyno' integrated into the wheel. Coaches and bike fitters would use the various data points to for different purposes. I was on one a couple of times and was amazed to see how much the torque on the crank would change with the height of the seat and its for/aft position. Back then we could see torque at the crank as measured every couple of degrees. The major engine labs have to already have this technology. If you and your buddy Cole (Poke <smile>) figured out a way to do this that could be used en masse, well, that would be something really good.

[hrdtail78]

If you and your buddy Cole (Poke <smile>) figured out a way to do this that could be used en masse, well, that would be something really good.

Steve isn't apart of this project.  He has his own tuner and company to run.  BUT I do consider Steve to be a friend.  He has helped me out tremendously over the years.  Just like others have.  I have been blessed enough to surround myself in the industry that are in the know.  From people that have actually written in the code of our ECM's to some great engine builders, to people that really know the in's and out's of stand alone tuners.  I continue to learn and continue to get better at my craft.

[turboprop]

If you and your buddy Cole (Poke <smile>) figured out a way to do this that could be used en masse, well, that would be something really good.

Steve isn't apart of this project.  He has his own tuner and company to run.  BUT I do consider Steve to be a friend.  He has helped me out tremendously over the years.  Just like others have.  I have been blessed enough to surround myself in the industry that are in the know.  From people that have actually written in the code of our ECM's to some great engine builders, to people that really know the in's and out's of stand alone tuners.  I continue to learn and continue to get better at my craft.

Very happy for you. Still, if you or anyone pulls this off for the masses, it would be significant. I would not be surprised if the dyno manufacturers were not already looking at this. Now that I think of it, Axtell has a stand alone engine dyno that is tooled up for a bunch of different sensors. I bet there is software that could be leveraged against his dyno to collect this type of data. Too bad Hilferty passed away. No doubt he could mak it work. Best of luck with this. Following.