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Cut-Away of 103 cu in “Twin-Cooled" Engine

Cut-Away of 103 cu in “Twin-Cooled” Engine

The ideal heat exchanger design and cooling calculations have been a major topic in the Harley-Davidson motorcycle community for some time.

The rumors that Harley-Davidson was eyeing a liquid-cooled motor design have been circling for years and now with the introduction of the 2014 models, it’s the first time (sans V-Rod), that the company jumped into the “water” with their touring models.

There were a number of changes which came out of the RUSHMORE project, but on the new touring models, the core ethos of change seems to start at the motor itself, where Harley-Davidson calls it “Twin-Cooled” cooling.  BMW calls their new partially water-cooled boxer engine setup “Precision Cooling.”

Backside Cut-Away of 103 cu in “Twin-Cooled” Engine

Backside Cut-Away of 103 cu in “Twin-Cooled” Engine

This is a little like the rabbit calling the donkey “Big Ears”… what’s in a name?!

Well everything if you’re a marketing jock.

You have to admit that “Precision” cooling implies something better and has a certain performance connotation attached to the name vs. “Twin-Cooled or the alternative “Partial” liquid-cooling.

The fact of the matter is that Harley-Davidson patented the clever way of adding liquid-cooling to its iconic V-twin motor design back in 2009.  Some elements of the design date back to 2007 when Erik Buell had a hand in the process.

Some of the patent specifics can be reviewed at:

  • US 2011/0114044 A1 – Nov 18, 2009 (File Date) May 19, 2011 (Publish Date) – CYLINDER HEAD COOLING SYSTEM
  • US 7654357 —  Jul 2, 2007 (File Date) Feb 2, 2010 (Publish Date) – Buell Motorcycle Company Radiator coil mounted on a motorcycle
  • US 20090008180 —  Jul 2, 2007 (File Date) Jan 8, 2009 (Publish Date) – Erik Buell Resilient mounting arrangement for a motorcycle radiator
Lower fairing coolant piping diagram

Early patent filing of lower fairing coolant diagram

At any rate, the “Twin-Cooled” system is thermostatically controlled, and uses an electric pump to circulate coolant.  The liquid coolant, is based on glycolethylene, the same coolant blend as in the V-Rod – a 50/50 premix that uses long life coolant.  It is routed through the cylinder heads, which is the most thermally stressed parts of the engine and in the area around the exhaust valves.  It’s then ducted to heat exchangers located in the left and right fairing lowers.  The new dual radiators are compact and the V-twin iconic barrel cooling fins remain.

Liquid-cooled Heads

Early patent filing of Liquid-cooled Heads

The expectation of this new setup is that riders won’t feel the crotch-melting temperatures in slow traffic because cylinder head temperatures are lower and the reshaped fairing lowers improve venting of cooler air to the rider and passenger.

Important to note is that the V-twin engines still use air/oil cooling for the barrel assemblies which to a certain “degree” retain that heritage of Harley’s air-cooled technology.  And the air cooling still does the heavy lifting.  Meaning it remains as a high percentage of the total cooling formula of the system.

Production Version of the Twin-Cooled Engine

Production version of the 2014 “Twin-Cooled” Engine

Harley-Davidson has yet to provide specs on the increased weight of the new cooling system vs. the previous air/oil cooling system.  But, it’s projected to be in the 10+ pound range, however, when has H-D been concerned with weight on the touring bikes given all the chrome dripping off those models.

There are a couple of oddities with the new liquid cooled change.  The first being that liquid cooling has no effect on service intervals.  Harleys with Twin-Cooled or standard air/oil cooled engines require service after the first 1,000 miles, and 5,000 miles thereafter.  And unlike oil and air-cooled engines which adjust timing to avoid spark knock as temperatures increase, Twin-Cooled engines retain the same timing.  I’m not sure what’s behind the thinking on this.

In addition, you might think that Harley boosted engine output.  They did, between 5 and 7%, but it wasn’t all due to liquid-cooled heads.  They also applied new cam profiles with higher lift and duration, which aids overall performance on both the standard and Twin-Cooled engines.

I’ve heard some rumblings from a riding buddy with contacts at the Arizona Test Track, that Harley-Davidson is having some issues with the 110 cu. in. Twin-Cooled ability to truly keep the heads cool(er).  This might be a first year implementation issue, but I believe Harley’s Twin-Cooling system is here to stay, and will likely expand throughout their lineup of motorcycles.

Photo of cut-away engine taken by author at 110th Anniversary factory tours, all others courtesy of H-D.

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Happy New Years!

Now that the champagne toasts are made and the ball dropped, it’s time to start thinking ahead:  What’s your riding resolution for this year?  Will you ride your motorcycle more often to work?  Take that epic journey or stay close to home?  Will you buy a new ride or enhance the existing one?

Before going forward let’s take a quick look back.

Over the years I’ve posted the occasional summary of the more popular and least liked stories from the past 12 months.  It’s not my “helper-monkey”, but the good folks at WordPress.com state their rankings algorithm is based on how many people read a particular article.  The average is the sum of views divided by the number of days and its gets even more complex if you are the sort of person who likes to verify computations.  I don’t.

The final tallies can be a little mystifying, to be honest.

Are readers giving a “thumbs-up” because they liked the content of the article or just the topic itself?  I don’t find these summaries a really useful exercise because some of the better written articles (IMHO) will sometimes have the fewest views.  It’s the old adage that writing about or reposting the nip slips, exposed undies and ever-presence dysfunction from the celebrity train wrecks for the whole world to see will bring a whole lot more views if that’s your goal.  But, if nothing else, the summary does provide a snapshot of what struck in my readers’ collective fancy during the past year.

In 2011, I posted 88 new articles (about 7 per month).  That brought the total archive on this blog up to just over 800 posts.  I uploaded 165 pictures (or about 3 per week).  The busiest day was September 25th (during the Vagos and HAMC shooting in Reno) with 1,120 views on an article I posted in 2008 (HERE).  Clearly the social behavior and the attraction of the events in Reno was a big draw, but I’m mystified why the more current article (HERE) had fewer views?  Maybe it’s a SEO thing.  I also want to provide a shout-out to the large number of UK viewers who consistently visit the blog.

Here are the 2011 most viewed highlights:

Outlaw Motorcycle Gangs Flying Colors in Oregon
OCC Family Feud Ends
Outlaw Motorcycle Gangs Are New Media Darlings
Vagos MC Meeting In Grants Pass
Harley SAMCRO Limited Edition Motorcycle
Harley-Davidson’s SwitchBack
Vintage Motorcycles – Honda CB750
Harley Engine History
“Green Nation” Busts On Saint Patrick’s Day
No Angel
The Day Laughlin River Run Changed
Men Of Mayhem
A “Legend Bell” Full of Mystery
Harley Snubbed In Benjamin Button Movie
Operation Black Rain Nets Oregon Mongols

I enjoyed this past year—and I hope you have, too.  If I’ve done my “job” right as editor of this blog, then your visits will have helped make your motorcycle hobby a bit more meaningful.  Hopefully you’ve become closer to your motorcycle and grown your relationship with friends that you’ve met on the road.

Happy 2012!

Photo’s courtesy of WordPress.com and Northwest Harley Blog.

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UPDATED: April 24, 2017Added a tab “Engine History” on the blog home page with updated V-Twin engine history including the Milwaukee Eight.

Have you ever wondered about the history of Harley-Davidson engines?

Compared to other motorcycle manufactures or custom shops, Harley works on a complete different time clock with new engine designs.

They seem to launch every 15 years or so. Between 1936 and 2003, engine designs released by Harley represented a constant tweaking of the same V-twin, 45-degree, air-cooled engine design. In 2001, Harley released its first new design in a commercial motorcycle, but it was still based on a V-twin. There have been only seven major engine revisions during the company’s 105 year existence:

Revolution engines – Manufactured starting in 2001. The Revolution engine is currently used on only one Harley model — the “V-Rod” or VSRC. While all of the engines mentioned are largely the same and represent incremental improvements, the Revolution engine is different. This engine is water-cooled rather than air-cooled and its V angle is 60 degrees rather than 45. It has four overhead cams rather than two cams in the crankcase and is fuel injected. This engine is smaller — only 69 cubic inches (1,130 cc). It has a much shorter stroke, allowing it to rev to 9,000 RPM and it produces 115 horsepower.

UPDATED: August 11, 2011 – With the 10th anniversary of the V-Rod (2012 Model’s) the motorcycles receive an engine upgrade to 1,250 cc.  H-D reports it at 125 horsepower at 8,250 RPM and 85 ft.-lbs. of torque at 7,000 RPM.

Twin Cam 96 engines – The Twin Cam 96 launched in August 2006 and was manufactured from 2007 through the current model year.  At 96 cubic inches (1584 cc) it claims an 8% increase in torque from the TC88 now at 93 ft.lbs.  All Twin Cam 96 engines are fuel injected. The bore is 3.75in (95.25mm) x storke is 4.38in (111.25mm).  Harley left the bore the same, but lengthened the stroke from 101.6 mm on the TC 88.  The TC 96/96B motor also adopted a pair of computer-controlled valves, one each in the exhaust and intake systems to help meet the EU noise and emission standards.  The TC 96/96B crankcases have a new crankshaft assembly versus the TC 88, with lighter, shorter connecting rods and redesigned, less heavy pistons delivering a raised 9.2:1 compression. New camshafts deliver revised valve timing in the re-ported cylinder heads, with an up-rated oil pump to enhance lubrication by 8% for the dry-sump motor. Harley also completely remapped the Delphi ECU controlling the sequential port fuel-injection (ESPFI).  The TC has cam chain tensioners with nylon composite shoes.  Harley changed from spring loaded to hydraulically loaded tension on the shoes in the Dyna line for the 2006 model year and for all Twin Cams with the introduction of the TC 96. The variability of cam timing introduced by inconsistent tension on the cam chain continue to be an issue best resolved by after market gear drive cam sets (S&S and others).  The 96B version contains gear-driven counterbalancer to reduce engine vibration.

UPDATED: May 8, 2009 – The motor company released Screamin’ Eagle models named TC103, a 103-cubic-inch (1,690cc) which is used in the 2009 Tri-Glide Ultra Classic (Trike) and the TC110, a 110-cubic-inch (1,803cc) in the 2009 CVO models (Fat Bob; Softail Springer; Road Glide; Ultra Classic Electra Glide).  The TC110 comes in an upgrade kit for the TC96.

Speculation is the Motor Co. moved to the Twin Cam not because the Evo had reached its power limits as a design, but because HD could not prevent other manufacturers from making clones of the design. With the Twin Cam, HD was able to preempt cloning via the U.S. Patent Office, thereby making it a lot more difficult and expensive for the aftermarket vendors to compete with the Motor Co. in the development and sale of upgrades or complete motors.

In order to comply with the increasingly-stricter EPA standards, all TC96 equipped Harleys come from the factory tuned very lean, which in turn creates a great deal of heat.  All ‘07 and later Big Twins are equipped with Electronic Fuel Injection (EFI) and 02 sensors for closed-loop operation, allowing an extremely lean tune to be safely, and consistently achieved. This has been a topic of much discussion in the Harley world, as many have commented that the excessive heat makes the TC96 too uncomfortable to ride in stop and go traffic, or in the heat of the summer. There are also concerns about heat’s impact on the longevity of the engine. To help combat this many owners re-tune their engines, run synthetic oil or add an oil cooler; and HD developed a “Parade” mode in which one cylinder shuts down on the Twin Cam to prevent damage to the engine.

UPDATE: August 11, 2011 – Bigger is better.  On all 2012 H-D motorcycle models with the exception of the V-Rod, CVO and Sportster models they now come with a Twin Cam 103.  H-D reports it’s about a 6% increase in torque.  Previously the 2011 line up of touring models had the TC103 available as part of a ‘Power Pak’ option.  The increased displacement from the standard TC96’s (1584 cc) to the TC103 (1690 cc) is the result of an increase in cylinder bore from 3.750-inches to 3.875 inches.  The stroke is unchanged at 4.375 inches.  In addition, the 2012 models with the TC103 receive an automatic compression release for improved engine starting.  Depending on 2012 model the increase in peak torque ranges from 92 to 94 ft.-lbs. at 3000 to 3500 RPM on the TC96 to a 97 to 100 ft.-lbs. at the same RPM on the TC103.

Twin Cam 88 engines – (aka “Fathead) was manufactured from 1999 – 2006. The Twin Cam gets its name from the fact that it has two cams in the crankcase to activate the valves. At 88 cubic inches (1,450 cc) of displacement, it was the largest Harley motorcycle engine at the time, and it produced 80 horsepower. The engine was air-cooled, and used overhead valves activated by pushrods. The 88B version (2000-2006) of the engine, which came out in 2000, contains counterbalancing shafts to reduce engine vibration.

Evolution engines – Manufactured between 1984 and 1999. Displacement is 81.8 cubic inches (1,340 cc), and the engine produces 70 horsepower. Although the Evolution 1340cc is no longer in production, the Sportster model line of motorcycles receives Evolution engines with 883 cc and 1200 cc displacements (manufactured 1986 to present).

Shovelhead engines – Manufactured between 1966 and 1985. Shovelheads displaced 74 cubic inches (1,200 cc) and produced 60 horsepower from years 1966 to 1977.  From 1978 to 1985 they were 80 cubic inches.

Panhead engines – Manufactured between 1948 and 1965. The panhead also came in 60 cubic inch (990 cc) and 74 cubic inch (1,200 cc) variations and produced 50 and 55 horsepower respectively. Big differences between the knucklehead and the panhead included aluminum heads on the panhead and internal oil lines, as opposed to external lines on the knucklehead.

Knucklehead engines – Manufactured between 1936 and 1947. The knucklehead came in 60 cubic inch (990 cc) and 74 cubic inch (1,200 cc) variations able to produce 40 and 45 horsepower respectively.

Flathead engines – Manufactured between 1929 and 1974. Flatheads did not have overhead valves. Instead, the valves ran alongside the engine and opened upwards into a chamber beside the combustion chamber. The advantage of a flathead was simplicity — no pushrods or rocker arms, and the head was a simple casting with a hole in it for the sparkplug. A typical Flathead engine had a displacement of 45 cubic inches (742 cc) and produced about 22 horsepower.

Sources: Various shop manuals, Chopper and HotrodsAmerican-VWikipedia, MSL MagazineJay Leno Garage, HOG Magazine (#011, 2011)

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