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Flathead Bobbers

Before Choppers, there was Bobbers...

The Flathead Bobbers website is dedicated to all Bobbers, Choppers, Oldschool motorcycles and Custom bikes powered by one of the many versions of the classic Harley Flathead Engine.

Check out this 1946 Harley UL Flathead Period Modified Bobber by Steve Barber of the 74 Shop While technically speaking a Bobber is a stock motorcycle with all parts removed that do not contribute to speed, you will note that most of those Flathead powered Harley Davidson D, V, W, U and K models are already very Spartan looking as they come.

So these Harley Flatheads don't really need a lot of work to turn them into a true Bobber. And with production years between 1929 and 1957 there is no need to query the use of a term like "Old School" either...

So for the puritans among us: please don't be disturbed or alarmed if you see a bike with front fenders on this Harley Flathead Bobber site.


HARLEY Flathead Bobbers

Harley "Flathead" Engine?

Click this photo to go to this 1942 Harley Flathead Bobber In 1928, Harley Davidson introduced the D models with a 45 cubic inch (750cc) V-twin side valve engine which later came to be known as the "Flathead" or "Flatty". A year later, the Harley D was joined by the V models which sported a 74 ci version of the Flatty. Six years later, in 1936, an 80 cubic inch Flathead became available with the introduction of the Harley model UH and ULH motorcycles.

In 1937 the Flatheads got the same recirculating oiling system that had been introduced on the Knuckleheads in 1936. Before that year, Flatheads had a rather crude gravity feed one-way total loss lubrication system whereby any oil that was not burnt in the cylinders eventually ended up on the pavement...

While neither sophisticated nor efficient, the Flathead engine design proved to be so reliable that the Motor Company was able to sell it for forty five years, from 1928 until 1973!

On top of that, certain design features of the 1929 Flathead engine survive even today.

Quad Cam Side Valve Engine Design

Click this photo to go to Mike's 1938 Harley VL Flathead Bobber project Due to the side valve design, the cylinder heads are pretty wide and flat, while the valve push rods are relatively short.

To mitigate the inefficiency of the gas flow in and out of the cylinder, the intake and exhaust valves have to sit side by side in a horizontal plane right next to the top of the cylinder.

As a result, on each cylinder the valve stems and push rods run parallel to each other, and the bottoms of the push rods end up about two inches apart. For this reason all four cams are on their own individual camshafts which are connected to the main shaft through a series of gears.

Harley Model K "Sports" Flathead

Click this photo to go to Joe's 1956 Harley Davidson Model KHK Sport Solo One noteable variation of the Flathead engine design was introduced on the Harley model K "Sports" motorcycle of 1952 which was introduced by the Harley Davidson Motor Company in response to the invasion of the American motorcycle market by lighter and faster import bikes, in particular the British BSA's, Triumphs and Nortons.

The 1952 K model had a compact integrated engine and transmission design, with the good old 45 cubic inch displacement and aluminium cylinder heads for improved cooling.

In 1954 the model K's engine was beefed up to 54 cubic inches (883cc) and the bike was named the model KH. The following year, Harley introduced the high performance model KHK which featured a speed kit: roller-bearing bottom end, hot cams and polished ports.

Roots of Today's "Sportster" Engine Design

Click this photo to go to this beautiful 1966 Ironhead XLCH Sportster In 1957, the model KHK "Sports" motorcycle with its 54 cubic inches side-valve Flathead engine was replaced by the model XL "Sportster" which boasted the more powerful over head valve Ironhead engine with the same 54 cubic inch displacement.

Except for the engine top end design, the XL "Sportster" model and the KHK "Sports" model otherwise looked virtually the same.

What should be noted is that the Sportster's "Ironhead" engine had the OHV technology of the 1950's Panhead engine, but retained the lower end design concept of the Flathead model KHK, including the position of the generator and the four cams on their own individual shafts.

A design going all the way back to 1929 - and surviving even today in the Evolution Sportster engine!


HD Flathead Oldschool Bobber and Chopper Gallery

 


Harley Davidson Flathead Custom Bikes

Some Harley Flathead bikes are neither a Bobber or Chopper, nor are they the original stock motorcycle.

These Custom Motorcycles are bikes with a character:

 


Harley Davidson Flathead Trikes

Although we often see similarities, we are not sure whether a Trike can ever be a Bobber. (Did people ever race Trikes?)

However, what we are absolutely sure about is that we do love Trikes and that we respect the love and care that their owners put into them! They are truly a class of their own.

 


HD Flathead - Original Stock Motorcycles

While our prime interest is Flathead Bobbers and Choppers, we regularly come across beautiful Flatheads that are fully dressed like when they were new. These bikes were made between 1929 and 1957, and at the time these motorcycles were the starting point of the original Bobber. What we mean to say: true Oldschool stuff.

Click this photo to check out this 1946 Flathead HD WL oldschool motorbike! We have decided to pay respect to these magnificent machines, and we therefore make space on this Bobber website to also show you the stock Harley Davidson Flathead Motorcycles in their original form or restored close to their original form.

Some Bobber puritans and nitpickers may not approve, well, to hell with them.

So, if you should ever wish to design a true Oldschool Bobber, please don't forget to have a look at these original bikes. For inspiration. Or just for your own enjoyment!

 


Click this photo to check out this classic 1927 Indian Chief vintage motorcycle!

INDIAN Flathead Bobbers



The Indian Motorcycle Company built flathead engines as well. Here's a selection of flatheads from our Indian Bobbers website:


INDIAN Oldschool / Chopper / Bobber Gallery

 

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AMT - Flathead Repair and Maintenance Specialists - Gulfport, MS, USA