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Posts Tagged ‘Twin-Cooled’

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

"M-8" top view showing tubular rockers

“M-8” top view showing tubular rockers

It happens every year and often it’s big news.

This year the launch of the Harley-Davidson 2017 motorcycle line-up is anchored by the new Milwaukee-Eight™107 and Milwaukee-Eight™114 power plants.

A couple weeks ago I posted about a new eight-valve Big Twin and now we know the rumors are true.  The displacement of the standard version is 107ci (1,750cc) or in the CVO version it’s 114ci (1,870cc). The 2017 touring models get these engines first and may waterfall down to other models later in the year.  The 107 uses precision oil-cooled cylinder heads and will be in the Street Glides, Road Glides, the Electra Glide Ultra Classic, and Freewheeler trikes.  A Twin-Cooled version with liquid-cooled cylinder heads and radiators will be in the Ultra Limited models, the Road Glide Ultra, and Tri Glide models.  The CVO Limited and CVO Street Glide models will have the Twin-Cooled Milwaukee-Eight 114.

M-8: Four-valve combustion chamber and the dual spark plugs

M-8: Four-valve combustion chamber and the dual spark plugs

You might recall that the last major design evolution of the Twin Cam — and a significant part of the Project RUSHMORE and marketing campaign — was anchored on improving power plant cooling.  This took the form of circulating liquid coolant in tubes around each cylinder head’s hot exhaust valve seat and then to external radiators.  Many riders neglected to notice much in the way of decreased heat from this method of trying to get more power out of the 103.

So let’s talk details of the new eight-valve “M-8”.
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M-8:  Cutaway shows cooling areas of circulating liquid (Blue)

The 107 (3.937 x 4.375-inch bore and stroke) is cooled by pumping oil through it and then through a “chin radiator” ahead of the crankcase. In the 107 and 114 Twin-Cooled models (the 114 has 4.016 x 4.500-inch cylinder dimen­sions), water/antifreeze coolant is circulated through a cored heart-shaped passage that encircles the exhaust valves and then through radiators mounted forward to either side of the engine, as we’ve seen.  The new engine uses a nearly flat chamber of minimum surface area with four valves and abandons the large surface area of the traditional deep, modified hemi two-valve combustion chamber found in the old design.  The new engine operates at high compression ratios (as high as 10.5:1).  As a result, the 2017 Touring motorcycles will provide 10 percent more torque.  Harley states that will translate into two to three bike lengths faster from 0–60 mph, and one to two lengths quicker in top-gear 60–80-mph roll-ons along with improved fuel economy.

Overall airflow capacity of the “M-8” is 50 percent greater versus previous Big Twin engines, and the throttle body now has a 55mm bore.  Each cylinder has an acceleration-type knock sensor along with ECM control which protects the engine from detonation.  The new system is an improvement over the previous ion-sensing knock detection.  The exhaust components, including the catalyst, have been relocated to help move engine heat away from rider and the new engines have a single four-lobe camshaft with automatic hydraulic tensioner in place of the Twin Cam’s pair which will help reduced mechanical noise.

And in a first for the rubber-mounted Big Twin is a single counter-rotating internal balancer.  It’s meant to eliminate 75 percent of the engine’s primary shaking force.  In addition, idle rpm has been cut from 1,000 to 850 rpm all in a effort to give riders improved engine smoothness.  Other engine items of note is a new higher capacity alternator along with a new 1.6 kW (2.14 hp) starter that replaces the previous 1.2 kW (1.6 hp) units.  There is a self-torque-boosting clutch with Brembo hydraulic actuation for a lighter lever pull and the engine ECM has been changed from a mapped system to torque-based which will be interpreted as a call for a specific torque level, not a specific throttle angle.

On the motorcycle side, the front and rear suspension is new.  The new 49mm fork contains “dual bending valve fork technology” and uses cartridge-style variable-orifice damping valves, which Harley claims will deliver improved control at low speed without harshness over sharper bumps.  This wasn’t achievable with the old system of fixed damping.  Touring fork travel is 4.6 inches on standard models and 3.9 inches on low models.

After doing a quick H-D web site scan on the CVO Street Glide and CVO Limited models — it looks like the MSRP price went up $1K from 2016 ($36,799) to 2017 ($37,799).  The same $1K increase is also shown for the CVO Limited ($39,999 to $40,999).

Only you can decide if the new 117 engine, the new suspension along with the radio power adjustment warrants the price increase.

Photos courtesy of H-D.  Engine detail/stats courtesy of Cycle World.

All Rights Reserved (C) Northwest Harley Blog
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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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