Round or Square head design

Brains

New Member
Jul 21, 2008
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Adelaide Australia
Just trying to get clarification on what is the diffrence in square or round head design, is one better than the other, internals of the engines are they all the same,
 

VaporKing

New Member
May 15, 2008
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Hi.

Being that there are no responses, I thought that I would contribute my some of my priceless knowledge.

The square head design has the advantage over the round for being able to accomodate more cooling fins, which means that there is more surace area dedicated to cooling the engine.

However, the additional weight imposed by the square head design is an efficiency drawback. Round heads are lighter and more efficient, but require more air circulation to cool the engine, than a square headed engine would.

A good illudstration of this form/function relationship would be the design of air-cooled 2-cycle aviation engines. Their heads are almost always round, because they need to be lightweight, and air is always circulating around them. This would be in contrast to a motorcycle engine, which does not always neecesarily have air cooling the head (like when the cycle is stopped at a 5 minute stop light, where many 2-cycle engines get "baked" into the junk-yard).

Hope this helps.

VaporKing
150 Miles/Gallon
 

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
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up north now
What is the physical difference and how can you tell them apart at a glance?

I have had six engines and they are all different, but I can't say they are round or square heads, they are kind square with rounded corners.
 

misteright1_99

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Mar 21, 2008
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Treasure Coast, Florida
What is the physical difference and how can you tell them apart at a glance?

I have had six engines and they are all different, but I can't say they are round or square heads, they are kind square with rounded corners.
I have a Grubee 48cc Spitfire Roundhead. I believe there are differences in the port design that make them different from the square headed engines, but this is just what I have been told.... Not a very good picture but it shows the head and cylinder is round. I love the engine very smooth, quick revving, but I this is mu first engine so I have nothing to compare it to....
 

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lennyharp

New Member
Jul 19, 2008
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Mesa Arizona
Sounds to me like the square ones are desireable for bicycle use as bikes are slow and in my experience, stop at all stop lights. Cooling advantage over cooleness advantage of the round as in Misteright1's photo.
 
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shiloh0

New Member
Jun 28, 2008
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i have one of each and can't tell much difference. at first i thought the squarehead had more power, but now i think there's very little difference. the square one looks more beefy and it's the one i have a 27T sprocket on.
 

Xcel

New Member
Jul 20, 2008
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The only real round heads i have seen are Grubee 50's (or accurately 48's) when you see one youll know.

I have one and it is an excellent lower powered engine.
 

eDJ

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Jul 8, 2008
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Wayne National Forest
I've been to alot of bike shows over the years and looked at many of the sixties Japanese motorcycles. Styling was something they brought to America with their early 50cc bikes. In later models the square heads began to show up by mid sixties. I think the first I saw to use it was a Yahaha twin jet 100. (but there may have been others)

I think that since there is the option of round or square heads, the use of the round ones on a bike that you want to look retro would benefit by using the round early cylinder head design. Like earlier bikes used.

From an efficiency view the larger head with more metal used to cast it and more fin area should cool better. But.....ya gotta watch the big fins as vibration leads to stress cracks where fins break off. The Japanese bikes used to wedge small hard rubber disc between the fins to dampen the vibration and prevent that problem. I had a 500 cc single that had dozens of those little "hockey puck's" wedged in the head and larger cylinder fins.