AIr Cooled vs Liquid Cooled

The real difference is the size of the fins necessary to keep the heads from overheating. As displacement increases, the amount of heat that needs to be drawn off the heads also increases. Just as the V-twin made it possible to squeeze more displacement into a narrow design, going to water cooling for the heads reduces the fin requirements and allows even larger engines in the same narrow package.

When an air cooled head does overheat, the bike has trouble idling and won't restart if it stalls. If you have the time to let it set and cool, it's no big deal, although it is a good idea to change the oil afterwards. The only time I ever had it happen, was while going through the MSF instructor course in 1981. It took a long day on the range, using middle range rpms a lot, while going very slowly.

Sound isn't much affected, since the water jacket doesn't wrap around the casing, cylinders or valve train. It's only in the heads, on the V-twins I've owned. The factory exhausts on my air cooled Harleys were always louder than the firing of the cylinder, and those exhausts were every bit as quiet as my 84 GoldWing exhaust was.

With the old side valve engines, you had the entire top of the heads to put fins on. With the higher performance overhead valves, you lost some available fin area. With even higher performance overhead camshafts, you lose even more fin space on top of the heads. Large displacement cylinders with overhead camshafts would require much larger fins to do the same amount of cooling as pushrod engines. That's the bottom line, you can give up some performance and go with air cooled or you can give up some style points and go with water cooled.

What cruisers do best is go down a straight or mildly curving road at a steady 60 mph. That takes less than 15HP, so it really doesn't matter if you ride an air cooled 50HP bike or a water cooled 70HP bike. It only takes about 40HP to ride along at 110 mph.

regards,
Joe  

One of the things that shorten the life of any engine is  a wide range of operating temps. In order for an air cooled engine to last lots of slow cruising in hot weather, or getting stuck in slow traffic a lot, will shorten the life of an engine. Long distance riding with most of the miles on the open road with a GOOD steady airflow is important for an air cooled engine, more so for large displacements. and in an aircooled V-Twin, the rear cylender get even hotter in slow riding. A liquid cooled V-Twin like 75% of the metric V-Twin cruisers have very steady engine temps, which is why they last for 100,000 miles with proper maintenance. One thing that everyone who reads this thread should know is that with engine/transsmission units that use the same oil, it is very important to change the oil closer to every 2000 miles as the transmission will break down multiweight oils ability to maintain it's multiweight properties due to the shear action of the gears on the oil. If you were to take oil that has been in the engine/tranny for 3500 miles tested you would find that your 20w50 oil is now straight 20 weight by then. 10w40 is usually good for 1500 miles, and 20w50 for 2000-2250 miles. since most motorcycles use 3-3.5 quarts of oil, it still cheap insurance.  

Montanaghost, you should stop and think about some of the things you're saying.

With "proper maintenance" even the cheapest modern small displacement street bike should last 100,000 miles. Water cooling has nothing to do with it. I put 265,000 miles on a 70's era air cooled V-twin. That bike was used for everything from desert rides in summer, stop & go riding in city traffic and winter trips across the northern US.

Oil viscosity is mostly affected by contaminants (fuel & condensation). Most of this happens in the first 800 miles. There is very little change in viscosity after that. That's why commercial fleets can get away with filtering out the contaminants, while continuing to use the same oil for tens of thousands of miles.

Transmissions have very little shear action, unless they have a worm drive in them. Motorcycles do not use worm drive transmissions. You'll find your camshafts do far more shear damage to the oil molecules than the transmission does.

regards,
Joe  

Joe,

Montanaghost's post is still valid in regards to the variable temperature of the engine. While you have had incredible success with your 70's era air cooled engine, we cannot look to an engine's success to finds it's failing point, we need to look to a failed engine to find it's failing point and none of us can refute the core issue which is the fact that an air cooled engine likes to keep moving to stay cool and excessive heat is the enemy of any combustion engine.

As for the issue of oil and maintenance schedules, I'll leave that issue for the 10 billion "experts" out there on that subject.

FYI.....This isn't a bias towards water-cooled as my current bike is a 113 CI air cooled Star Roadliner, and in my humble opinion it is the absolute best cruiser on the market today and one of it's GREATEST attributes is its air cooled monster engine which is a work of art.  

I have a 2004 Yamamha Road Star Silverado, air cooled.  My experience has been while riding I have no problems, even in 100 degree weather and sunny.  But if you are in a parade or group ride and there is lots of starting and stopping, parade ride, etc.  it will usually stall out.  I tend to turn it off in those situations and just crawl with it, otherwise it will overheat and you have to wait for it to cool down.  If I ever get another bike I will weigh this experience on a new bike, it may not make up my mind but I will consider it.  

mjolnier, bikes that are asked to spend a lot of time idling, require very careful adjustment of the idling fuel mixture and rpm. Carbon buildup and fouling occurs mostly when the engine is idling.

Most bikes idle rich, for easy starting. Some people adjust the idle even richer to avoid exhaust popping during deceleration. A rich mixture during idle will result in the engine rpm slowing down, eventually stalling if it's let idle too long.

Increasing the idling rpm slightly will usually lean out the mixture slightly, but will also result in more heat production. It's a delicate balancing act, getting the idle mixture and rpm just rght for parade use.

regards,
Joe  

I have heard a few bikers say that their air cooled bikes would overheat in very slow stop and go traffic. These bikes were all big inchers. I have a '97 Sportster 883 with a 9:1 compression ratio. I have added an oil dip stick / Temp. gauge and low restriction mufflers. After riding the bike a couple of hours I parked it on my asphalt driveway in the sun. Ambient temperature was 105 degrees F.and the air was still. The bike idled for one hour and 20 minutes. The oil temp reached almost 200 degrees in the first 40 minutes but never got any higher. I use Mobil 1 V-Twin 20/50 oil. It is my opinion that if my bike was a 1200 Sporty it would have probably overheated since both bikes have exactly the same fin area.  

Old School older dude here.  Give me air cooled anytime.  They are noisier, hotter, and alot cleaner(looking) than most any pumper out there.  I refuse to add anti-freeze to a motorcycle.  I wish they still made air cooled VW beatles, I owned a '72 Super.  Have you ever seen a water tanked "Bobber"?  It just isn't right........  Water cooled bike are ok but I haven't any use for one.  The choice is yours.  I've ridden air cooled Triumphs, BSA, Norton, Honda, Yamaha, HD, Hodaka, and others.  Only failure was a clutch on a 350 Honda in the little San Bernadino mountains with too much weight on the bike.  That's hundreds of thousands of miles without any motor problems from Death Valley in the summer to Argentia Newfoundland Canada in the winter.  Yep, give me air cooled...........Mike  

It does come down to a matter of choice.
As stated by people in this thread who mostly all have more experience than I on the matter...reliability really isn't an issue.
Things that I have noticed with the bikes that I've owned (air and water cooled)
Air:
Less comfy in slow (parade slow) traffic or if you're stopping often due to the roasted inner thighs that occur.
MUCH cleaner looking...
less weight due to no coolant for the same displacement, but more weight due to larger fins for cooling (it pretty much evens out in the long run)

Water:
Not so clean looking, but more comfy in traffic.

Both:
You can do pretty much anything you want with the exhaust note these days.

I'm not sure if the water cooling affects it or the fact that my current bike is an 1800cc V-Twin, but it seems to have quite a bit more power than other bikes that I've ridden in the past.  

a friend punched his 83 HD shovel out after 300K miles a couple years ago.he loves that bike. the honda 1500cc six cylinders will go 300K and still have afew more miles left on them without needing to be bored out.Personally ive gone from a 1967 250cc 2 cycle kick start to a 2000 1200cc fuel injected,ABS motorcycle.its all relative in how you want to go from point A to point B for me.