How Does This Air Cooled Cylinder Stay Cool?

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nicholastanguma
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How Does This Air Cooled Cylinder Stay Cool?

Post by nicholastanguma »

Nevermind comments about needlessly excessive displacement, H-D pushrod hate, excessive engine weight, poor handling, etc etc, please just focus on the question at hand.

Over the decades a few enterprising individuals have made 3 cylinder H-D engines just for fun, from Shovelheads to Evolutions. My question is: how well does that front horizontal cylinder get cooled, considering its cooling fins are still configured for an upright cylinder, meaning not parallel to the ground?

As far as I know, all horizontal singles from Aermacchi, Honda, Moto-Guzzi, etc, have always used cooling fins that run parallel to the ground.

Does a cylinder's fin configuration not really matter as much as I think it does, perhaps?


Aermacchi horizontal single with fins configured parallel to the ground

Image


Shovelhead and Evolution triples with a front cylinder that's laid horizontal but still using fins configured for an upright cylinder

Image

Image
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Re: How Does This Air Cooled Cylinder Stay Cool?

Post by HeinzE »

Nicholas,
Your post really caught my eye since I have been campaigning two Aermacchi 350 vintage racer in AHRMA for over a decade (as builder tuner not rider).
I also have a lot of Harley Davidson experience going back to the Shovel heads and up to the new M8. Here's my 2 cents worth... First off, yes the
cylinders on the triple, if left to cool only by air, will absolutely not run at the same temperatures. Also, the horizontal fins on the Aermacchi
do quite a good job of giving the air flow a "better" chance of flowing over the finned area as opposed to having the fins vertical. But, all that
having been said, there are other factors at work in any air cooled engine beyond the air flow over the fins. The first and most critical is the
oil, or more specifically the amount of oil being circulated through the engine, where it is circulating, and how it's temperature is controlled.
I've read that a full third of the cooling in an air cooled engine is done by the oil, and I see no reason to doubt it, in fact if designed carefully
It will likely be even more. Look at the now very common oil jets added to quite a lot of motorcycle engines, including the Harley Twin Cam engines,
which direct a spray of oil to the underside of the piston to help keep piston temp under control. Notice also the almost ubiquitous oil coolers found
on most every high performance air cooled engine. Those things are there for a reason, and give the air cooled engine a much better lease on life.
In my own Aermacchi's I found reworking the oiling system flow and adding a cooler worked wonders for reliability.
Too, at least as it pertains to motorcycle engines that operate in an air flow being split and churned up by the front tire and forks, the air flow
is not really "over" the engine as much as it is "buffeting around" the engine. The only way to get the air to actually flow precisely over the engine is to incorporate some sort of ducting or vanes and try to guide it to the finned areas, which many motorcycle race teams did.
So, yes the three cylinder engine shown in your post will most definitely not get eaqual amount of air flow over the cylinder/head units. And
if that is the only form of cooling this engine had available, I think it would be in trouble. But a lot could be done internally via the oiling system
and oil cooling, which we don't know much about by just looking at the photo. And it could by that whoever built this engine was just looking
to do something wild and flashy and didn't really plan to ride it much, other than at a show or a short ride just for the heck of it. I sure hope
so. Because if this was built to go from LA to Bangor Main with passanger and baggage, unless a really top flight oiling system and maybe some air
flow direction vanes installed, I think this engine,as I said earlier, is in trouble.
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Re: How Does This Air Cooled Cylinder Stay Cool?

Post by nicholastanguma »

HeinzE wrote: Sun May 16, 2021 12:19 pm Nicholas,
Your post really caught my eye since I have been campaigning two Aermacchi 350 vintage racer in AHRMA for over a decade (as builder tuner not rider).
I also have a lot of Harley Davidson experience going back to the Shovel heads and up to the new M8. Here's my 2 cents worth... First off, yes the
cylinders on the triple, if left to cool only by air, will absolutely not run at the same temperatures. Also, the horizontal fins on the Aermacchi
do quite a good job of giving the air flow a "better" chance of flowing over the finned area as opposed to having the fins vertical. But, all that
having been said, there are other factors at work in any air cooled engine beyond the air flow over the fins. The first and most critical is the
oil, or more specifically the amount of oil being circulated through the engine, where it is circulating, and how it's temperature is controlled.
I've read that a full third of the cooling in an air cooled engine is done by the oil, and I see no reason to doubt it, in fact if designed carefully
It will likely be even more. Look at the now very common oil jets added to quite a lot of motorcycle engines, including the Harley Twin Cam engines,
which direct a spray of oil to the underside of the piston to help keep piston temp under control. Notice also the almost ubiquitous oil coolers found
on most every high performance air cooled engine. Those things are there for a reason, and give the air cooled engine a much better lease on life.
In my own Aermacchi's I found reworking the oiling system flow and adding a cooler worked wonders for reliability.
Too, at least as it pertains to motorcycle engines that operate in an air flow being split and churned up by the front tire and forks, the air flow
is not really "over" the engine as much as it is "buffeting around" the engine. The only way to get the air to actually flow precisely over the engine is to incorporate some sort of ducting or vanes and try to guide it to the finned areas, which many motorcycle race teams did.
So, yes the three cylinder engine shown in your post will most definitely not get eaqual amount of air flow over the cylinder/head units. And
if that is the only form of cooling this engine had available, I think it would be in trouble. But a lot could be done internally via the oiling system
and oil cooling, which we don't know much about by just looking at the photo. And it could by that whoever built this engine was just looking
to do something wild and flashy and didn't really plan to ride it much, other than at a show or a short ride just for the heck of it. I sure hope
so. Because if this was built to go from LA to Bangor Main with passanger and baggage, unless a really top flight oiling system and maybe some air
flow direction vanes installed, I think this engine,as I said earlier, is in trouble.

Useful, thanks for taking the time to post! :hello2:
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Re: How Does This Air Cooled Cylinder Stay Cool?

Post by hoodeng »

As Heinz pointed out the three cylinder engines were an exercise in what someone could do, not a practical solution to a problem.

Cooling fins are roughly parallel to the path of the air. Not regarding oil cooling and its contribution here,heat paths are always hot to cold, heat generated in a piston is conducted into the rings and from the rings into the cylinder wall, the heat now builds up in the cylinder and fins until it is hotter than ambient, this is also conductance, that heat is now radiated to the atmosphere from its outer extremities, it is the path of air over the fins that heat is transmitted to the atmosphere via convection and drawn away from it. In an air cooled engine all surfaces are cooling surfaces, heads and cylinders obviously, crankcases, rocker boxes, gear case covers also contribute to the engines cooling.

There was a paper done on the effectiveness of air cooled cylinders in radial aero engines, the conclusion was roughly that fin spacing under .060" or so was not of any benefit... As cylinders could not be cast with the accuracy required to give this pitch the fins were now pressed and brazed onto the muff in instances.

Cheers.
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Re: How Does This Air Cooled Cylinder Stay Cool?

Post by Truckedup »

and on some the fins were cut with gang saws and by hand in very detailed areas..Mass production of the WW2 air cooled 2500 plus cubic inch radials with every internal part shot peened, nitrided and polished is almost on a scale of impossibility today....

Check the finning on this double row P&W R2800
https://www.si.edu/object/pratt-whitney ... 9580058000#
Motorcycle land speed racing... wearing animal hides and clinging to vibrating oily machines propelled by fire
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Re: How Does This Air Cooled Cylinder Stay Cool?

Post by emsvitil »

So how are the rods done on a 3 cylinder Harley?

A stock Harley uses knife and fork rods with roller bearings.

How do you do an additional rod?
Ed
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Re: How Does This Air Cooled Cylinder Stay Cool?

Post by nicholastanguma »

emsvitil wrote: Mon May 17, 2021 7:06 am So how are the rods done on a 3 cylinder Harley?

A stock Harley uses knife and fork rods with roller bearings.

How do you do an additional rod?

Firing order is 1 - 3 - 2, using rear cylinder as #1.

Firing impulses are 90 degrees, 315 degrees, 315 degrees.

https://www.youtube.com/watch?v=pUkOJ4jOrF4

https://www.youtube.com/watch?v=SQxZ9vpKpLo


Image

Image
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Re: How Does This Air Cooled Cylinder Stay Cool?

Post by englertracing »

I have some hate you didn't specify to exclude.
Horrible ports and over camming resulting in a power/liter close to that of a completely stock vw engine. Plap Plap idle and like 50hp.... a ducati 1299 lays down over 205 hp and idles smoothly.... that's how a v twin is done.
Oh and the riders they think they are bad asses but they are riding dump trucks that don't reward or encourage rider skill. Really for bottom of the barrel riders, no necessity to develop skills like a road racer, trials, mx, or sm rider.
Perhaps they stay cool by maintaining <.75hp/in
:lol:


Now that that's out of the way....

An answer to your question
Cylinder cooling just isn't as critical as head cooling.
fullloclspeedway.jpg
These kept their original Fins when they got laid horizontal and these make about as much power as a harley but at only 500cc

Perhaps the methanol has something to do with that though.
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hoodeng
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Re: How Does This Air Cooled Cylinder Stay Cool?

Post by hoodeng »

Gee Engler, you really have bottled up some hate there!!!

Cheers mate, and happy motoring no matter what you own!
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Re: How Does This Air Cooled Cylinder Stay Cool?

Post by Geoff2 »

Engler,

Are you aware that a 883 Harley Sportster ran over 170 mph.................And it did that was 56 years ago............. It did it with one carb & 4 gears, not multiple carbs & 5/6 gears.
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Re: How Does This Air Cooled Cylinder Stay Cool?

Post by englertracing »

Geoff2 wrote: Sat May 29, 2021 7:08 am Engler,

Are you aware that a 883 Harley Sportster ran over 170 mph.................And it did that was 56 years ago............. It did it with one carb & 4 gears, not multiple carbs & 5/6 gears.
The only HD hate exception I'll make is an xr750.
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Re: How Does This Air Cooled Cylinder Stay Cool?

Post by miniv8 »

Cooling fins are just heat sinks. Like all heat sinks or heat exchangers they love their turbulent coolant medium.
Linear airflow most likely cools less than turbulent, given the same air volume with the same fins.

Across, sideways, whatever, Just replace the air, don't let it go stale.

I just so happen to have a Harley now, it happened sooner than I thought. I had promised myself I'd get one when I'd stop riding. I found one with water cooling and dual over head cams. On my first weekend riding it I was blown away by the low end torque, and the second weekend riding it I was blown away by the top end charge. I keep getting blown away by it everytime I ride it.
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Re: How Does This Air Cooled Cylinder Stay Cool?

Post by nicholastanguma »

miniv8 wrote: Sat May 29, 2021 6:24 pm Cooling fins are just heat sinks. Like all heat sinks or heat exchangers they love their turbulent coolant medium.
Linear airflow most likely cools less than turbulent, given the same air volume with the same fins.

Across, sideways, whatever, Just replace the air, don't let it go stale.

Helpful, thank you.
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Re: How Does This Air Cooled Cylinder Stay Cool?

Post by Momus »

Well posted Engler.
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