Oil question

[T. Cotten]

Unfortunately, Freeman,...

We have no base data to compare. Pyrometer readings are difficult on a cruising machine (without a sidehack), and static readings seem to change as you watch them.

Observing the surface temperatures involves many variables beyond time and ambient air. Since heat flows to where it is not, the higher front readings may only mean that is where the most heat is leaving the motor at that time.

I have come to believe the front cylinder of a v-twin always "appears" warmer, although a 50°F difference is curious.

.....Cotten

[Freeman]

Well, that's a loaded question when answering if that's "normal" . Yes and no. I'd like to ask first where on the engine cylinder areas are you "exactly" measuring these temperatures. Me knowing that is important in my answer.
Merry Christmas as well!

Exhaust position

[Freeman]

Unfortunately, Freeman,...

We have no base data to compare. Pyrometer readings are difficult on a cruising machine (without a sidehack), and static readings seem to change as you watch them.

Observing the surface temperatures involves many variables beyond time and ambient air. Since heat flows to where it is not, the higher front readings may only mean that is where the most heat is leaving the motor at that time.

I have come to believe the front cylinder of a v-twin always "appears" warmer, although a 50°F difference is curious.

.....Cotten

Yes, the front cylinder should theoretically be lower than the rear cylinder, which is strange. Can we speculate that the lubrication inside the front cylinder is reduced?

[T. Cotten]

I am not schooled in thermodynamics and such, Freeman...

So my understanding is primitive, and my explanations are conjured!

My suspicion is that both cylinders are nearly the same, but heat is drawn most to the surfaces where it radiates most quickly, and that is all that our pyrometers can detect.

Many improvements to the distribution of oil in the cases were made over the years, such as reversing the rods and such, yet the front cylinder still shows more heat even upon modern OHVs with their internal oiling.

....Cotten

[dukekleman]

I've used/use Thermo imaging equipment on VTwin American design engines for development testing and calibration tuning. In conjunction with Thermocouples placed in various locations. One common area, amongst others, on the Vtwin I'd place them for temperature monitoring was at the base of the spark plugs. One of the simple targets was to achieve 300 F at both cylinders while at low load cruising speed and around stoichiometric. I've seen many people try to measure for this target number with an infra red gun and get kinda of close but as Cotton mentioned above this can be tricky or even deceiving. For standard Road testing when I'm not in the test cell room, I'll use a digital meter that resembles a fluke DVOM meter. It has two channels so both cylinders can be monitored at once with individual Thermo couple input. Now I'm not going to expect most to go out and do this procedure and)or purchase the equipment. I just wanted to let you know how it's accomplished. What you do is then adjust the AFR for each cylinder and the ignition timing for each cylinder to achieve equal temperatures. When doing so and operating the machine, you'll feel it smoothen out dramatically in the floor boards if things were off much.
This is pretty easy to do (I may be opinionated) on modern motorcycles with individual coils, fuel injectors and ECM's. However it's more challenging in the sense of your hands being tied on carbureted models and you have to be more creative.

[T. Cotten]

Valuable insights, Duke!

So you are able to adjust each cylinder individually to its optimum, so I really must ask:

Was there a pattern that distinguished the two?

Like usually advancing one more than the other, or usually enrichening one more than the other? Thanks!

....Cotten

[dukekleman]

With the commonized intake manifold design and fuel delivery via a single carburetor, challenges present themselves.
Dual pattern, asymmetrical camshaft design helps tremendously in cylinder fill and end combustion efficiency balance.
Another avenue was to change the lobes for the front cylinder verse the rear cylinder when using a single point ignition. This was an economical option in manufacturing to try to achieve cylinder balance and harmony when dealing with dual fire ignition systems.
As we know HD designed Panheads in the early 60's with dual points and dual coil single fire ignitions for these reasons. We also know that camshafts were designed with different intake events from front cylinder to rear cylinder ( just as an example) for this very reason. These designs hold true on all current production Milwaukee 8 ignitions and camshaft production today in 2023.
So when dealing with the challenges of cylinder balance and efficiency on vintage HD's I like to use a replica H grind camshaft reproduced by S&S cycle nowadays. They are made as I mentioned above. I'm very particular on my valve stem heights when I replace valve seats on the Serdi. The goal is to obtain equal port volume and wet/dry flow dynamics.
Next is to make sure the intake manifold is sealed properly for the front and rear cylinder head. This is talked about a lot on the forum I've noticed. This is Very critical otherwise the AFR from one cylinder to the other will vary more than normal.
On symmetrical camshafts designs especially, it's normal to see a richer AFR on the rear cylinder verse the front. This causes a cooler rear temperature and a hotter front temperature. Ways to deal with this situation is to run a camshaft as I mentioned and/or angle the manifold approximately 3 degrees and /or notch the main nozzle biased towards the one cylinder.
Lastly if we can advance or retard the cylinders independently of one another, we can change our AFR measured in the exhaust which changes our temperature measured at our spark plugs. Of course heat range on our porcelain can change these temperatures as well. All this truly aids in a smoother drivetrain, smoother push on a common crankpin for our connecting rods and equal piston thrust wear. I hope my explanation was Ok, sometimes I don't do a good job of explaining.

[T. Cotten]

Please let me ask more directly, Duke...

From your experience, before tuning to correct it, might one cylinder be typically hotter than the other?

If so, which one?

(Assuming everything else is in order, of course!) Thanks again,

....Cotten

[dukekleman]

Yes, I'll see the front cylinder hotter. I see this all the time and to me is the norm. I use Thermo image camera equipment that shows different areas of heat and thermocouple probes that give me a digital temperature number.
I'm guessing what I just said in regards to which cylinder is always hotter is a controversial statement. Many assume it's always the rear as I've heard from many people over the years. I'm the person that typically won't say anything to correct them...

[T. Cotten]

A couple of decades or more of motor autopsies, Duke,...

Made me a believer that the front suffered the most heat, as you cannot argue with burnt hardware.

It is counter-intuitive, of course, but true.

So we must ask: why?

.....Cotten

[dukekleman]

Well, yes indeed it's true...the front cylinder inherently runs hotter. Most technicians go on the basis of the rear cylinder running hotter because of it's location. Seems like a logical analogy with some common sense. However, when research into the fact that the front cylinder is actually prone to temperature increases when compared to the rear, it becomes more apparent as to why...while it is a little complicated, it's really not. I was always the little kid growing up asking and wondering "Why" . The urge to know and understand, propels me every day in this industry and never gets old. I could continue on this conversation path but in short, it's what made me become a member of the AMCA to begin with. I'm glad I did.
When we analyze the firing order of the 45 degree V Twin, along with it's shared induction pulse signals in a commonized intake manifold that carburetion relies on, things become a little more clear as to why the front cylinder runs hotter upon it's load demand. The question through years of engine development was, how do we keep things equal and working in a harmony of partnership over miles, verses just getting by and wearing out sooner than expected if you will.
We are fortunate to have seen various attempts of this by the motor factory over the years. In my opinion, it started with the intake manifold designs you see on early knuckleheads. It has changed back and fourth over decades of development as we can now analyze because it's history. This post all began as an enthusiast asking about engine oil and temperatures. It's something my family , which are engineers , have contracted with the motor company on. The subject is a little more complicated than most people give it credit for. Wether we are talking EPA compliance verse engine requirements, cost analysis, etc... something/someone has to give and bend if you will. In the end, I truly believe and teach that "everything connects to everything" so there is seldom one common failure, it's a link of multiple things creating the issue. All things must be checked, verified and properly repaired if need be. This is the only way to resolve customer complaints. Problem with our society is most people want an easy button . Just being honest

[T. Cotten]

We agree, Duke,...

It can't be put it into words easily, or grasped without all of it.

But us common folks still want to know why the hottest parts are those that get cooled the most.

Its almost like reverse refrigeration.

.....Cotten

[chuckthebeatertruck]

[QUOTE=T. Cotten;n306221]

But us common folks still want to know why the hottest parts are those that get cooled the most.

Its almost like reverse refrigeration.

.....Cotten
[/]

here’s my understanding. The first law of thermodynamics is heat always flows towards cool. Other bits of physics cover how an item/ material moves heat via radiation, convection and conduction.

The end result is that a cylinder with good finning (aka conduction) is able to achieve much greater convection (aka as heat shedding) with a proportional increase of air flow. This means the cylinder being cooled more by air flow can also absorb more heat from combustion because it is more easily shedding heat.

That additional heat absorption shows up as a hotter cylinder compared to the rear which gets a lot more oiling from flywheel fling, but less from the air. Basically the cylinders both reach thermal equilibrium but the front can get rid of that much more heat, so it runs hotter.

interesting to me is that better oiling 80 years ago increased top end life, specifically bore wear and ring wear, but did not reduce running temperatures or the differential between cylinders, Flatheads and ohv still ran similar cylinder and head temperatures to when oiling was more poor. Even better oiling 50 years ago resulted in longer top end life and hotter oil tanks, but still the same running temps and still the difference in cylinder temperatures. Advances twenty years ago allowed even hotter oil tanks and all sorts of coolers came into vogue but still the same overall temperatures.

We got better at controlling heat flow over the ensuing decades but to this day thermodynamics still beats conventional wisdom in this case of which cylinder is hotter. Our motorcycle forefathers were much more clever than we oft give them credit. We are still talking about stuff they intuitively knew.

[T. Cotten]

The easy answer as to why motor temperatures were not reduced, Chuck,...

Is that flattys, and then OHVs, were designed to get up to their peak efficiency. Flattys need to be a hundred degrees hotter; Innovations were for longevity.

The enigma is: Why do parts of the motor most cooled show the most heat 'signatures'; It is almost as if the parts that had the most heat conducted through them suffered more, without actually getting that hot.

I am not schooled enough to understand what I read on-line, but I think this is called "flux"?

....Cotten

[tomfiii]

What is temperature on the day it was checked?