50th Anniversary Of Jet Fire Orange

1970 Harley-Davidson XR-750

I’m talking about the Harley-Davidson XR-750, which last month marked the 50th Anniversary since it’s debut.

From 1953 to 1969,  Harley-Davidson manufactured the KR750, the backbone of American dirt track racing.

The motorcycle engine was an air cooled, side valve 4-stroke 45° V-twin (flathead), 45.125 cu in (739.47 cc) displacement built for racing.  Unique for Harley’s at that time, the KR model shifted on the right, like a British bike, which worked great for dirt track.  It wasn’t until 1975, when DOT specified that all motorcycles sold in the U.S. had to have a standardized, left-side gear shift.

Harley-Davidson Flat Track Racing

Prior to 1969, the American Motorcyclist Association (AMA) rules for the Grand National Championship were structured to favor “sidevalvers” (side-valve engines) rather than overhead-valve (OHV) engines.  The intent was to deliberately favor American made bikes such as those from Harley-Davidson with their side-valve engines, and disadvantage the competition which was mainly from British manufactures i.e., Triumph, BSA, and Norton. The AMA rules allowed side-valve engines of up to 750cc capacity but OHV engines were limited to 500cc. The 50% engine size advantage stacked the odd in the favor of the side-valve bikes.

As you might imagine, the British manufactures complained…about everything—the rules, the manufactures, the officials, the drivers, the races, and the racing itself.

Harley-Davidson XR-750

As a result, in 1969, in prep for the 1970 race season, the AMA approved that all professional Amateur & Expert dirt track and speedway engines could be 750cc, regardless of configuration or valve style. This rule change eliminated the 250cc penalty for OHV engines that had existed since 1933.  Many British manufacturers begin designing and developing OHV 750cc engines for competition. To be approved by the AMA (for Class C competition), a motorcycle must be a standard catalogued production model and at least 200 units of the same model with identical engines and transmissions and must be available for inspection and/or purchase within the United States.

XR-750 Engine – Ported and Polished Heads

Unhappy with the decision, but with a desire to continue the racing legacy, Harley-Davidson set out to create a new overhead-valve racing motorcycle.  The Milwaukee motor company leveraged their OHV V-twin racing engine based on the Sportster XLR.  However, it’s engine had a displacement of 900cc (55 cu. in.) and would need to have its capacity reduced to 750cc. Harley-Davidson engineers accomplished this by decreasing the engine’s stroke from 3.81″ to 2.983″ and increased the bore from 3.0″ to 3.2″ bringing the engine in just under the 750cc maximum.

The AMA approved the Harley-Davidson “XR”, a 750cc V-twin overhead valve engine, for Class C competition on Feburary 27, 1970. It had been tentatively approved in late-1969 as the “750 Sportster”, but the motor company lacked having 200 units available for inspection at the time. The motorcycle is dubbed the “iron XR“, or “Iron Head,” due to its steel cylinders and heads.

Even Knievel

For the 1972 race season, there were a number of changes.  A vote was taken on November 18, 1971, and the AMA Competition Congress voted to allow qualified women to compete in all forms of AMA Racing.

The Water-Cooling was approved, as long as it is an integral part of a production motorcycle.  Titanium frames were outlawed from all AMA competition. The AMA approved the Harley-Davidson XR-750, an updated version of the XR, for Class C competition on April 12, 1972. The updated engine used aluminum cylinders and heads to address the overheating issues that plagued the XR model. However, due to delays in getting all 200 units completed, it wasn’t approved in time for the Daytona 200, but debuts at the Colorado Springs national on April 30, 1972.

Speaking of aluminum heads, they were made, then shipped to Jerry Branch of Branch Flowmetrics in Long Beach, California to be ported and assembled. The new cylinder head design included larger valves. The cylinder heads were then shipped back to Harley-Davidson’s factory in Milwaukee for fitting to the new engines. This V-twin engine was not quite of the same dimensions as the Iron Head. The bore was increased to 3.1” and the stroke reduced to 3”. Carburetors were 36mm Mikuni, one for each cylinder. The exhaust systems were mounted high on the left side of the motorcycle well away from the carburetors.  Power was 82hp at 7,700rpm giving the bike a top speed of around 115mph.

Harley-Davidson Flat Track Racing Team

Branch wrote engineering books on his engine air flow work and eventually sold Branch Flowmetrics to Mikuni in the late 1990s.  Branch was the only independent company to ever supply Harley-Davidson ported and polished heads!

In 1972, Harley-Davidson was the first-ever “Grand National Manufacturer’s Championship“, which compiles the highest finish of each brand at every Grand National Championship event.  Between 1972 and 2008, the XR-750 won 28 of 37 AMA Grand National Championships. The XR-750 racked up more wins than any other motorcycle in AMA racing history and earned the description of being the “most successful race bike of all time.”  In addition, the XR-750 became a cultural icon with legendary stuntman Evel Knievel at the handlebars. Evel Knievel began jumping an XR-750 at the height of his career from 1970 to 1976.

Harley-Davidson created one of the greatest bikes in the history of American motorcycling.

For 2020, the Harley-Davidson Factory Flat Track team will use the updated Harley-Davidson® XG750R flat tracker, powered by the liquid-cooled, fuel-injected and race-tuned 750cc Harley-Davidson® Revolution X™ V-Twin designed for the Street 750 motorcycle.

Full details on the Flat Track team can be found HERE.  Flat Track racing news is HERE.

Photos courtesy of Harley-Davidson

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Resolutions For 2012

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, 2017 — Added 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 Hotrods, American-V,  Wikipedia, MSL Magazine,  Jay Leno Garage, HOG Magazine (#011, 2011)

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