Quote:
Originally Posted by Jeff Higgins
(Post 8269717)
Uh, no...
Both the heads and cylinders are cast iron on an Ironhead Sporty. On a Shovelhead, the cylinders are cast iron and the heads are aluminum. Additionally, the Sportster has always been a unit construction design with the motor/primary drive/transmission all sharing a common case (actually one of the first), whereas the "Big Twin" (early sidevalves, Knuckles, Pans, Shovels, Evos, and now Twin Cams) have always had three separate cases - engine, primary drive, and tranny all run in their own individual cases. Two entirely different machines. So, no, an Ironhead Sportster is not a Shovelhead.
As an aside, Trock Cycle did, however, make what they called a "Shovester" kit to put Shovelhead heads on Ironhead Sportsters. They allowed for bigger valves and ports, which we all discovered was a step in the wrong direction on these motors. The real "trick" heads were the old Robeson Industries "Thunderheads", which were aluminum and more or less mimicked XR750 heads, but fit the cast iron cylinders of the 900 and 1000cc Ironhead Sportsters.
So, um, yeah - let's get these designations straight. It's pretty clear you really aren't "an old Harley guy" after all...
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^^^^^^^^^^^^^^^^^^^^^ This is completely correct^^^^^^^^^^^^^^^^^
Although I would add that there is more cast steel - than iron in those castings - Harley wanted cheap but also weight was an issue so there is more cast steel - than iron. Pretty good design / castings really considering the R&D and prototyping occurred late 1940's and production early-mid 1950's with the "K" model.
The issues with the "Shovester" conversions were 3 problem areas: 1) The stock head intake ports were already a little too large on the Sportster. So unless you were stroking it substantially the performance below 4500rpm's was
worse. 2) The intake / exhaust ports on the Shovel head engines were too big as well so putting these on a stock displacement sporty
killed the low-mid range. 3) The valve / rocker arm angles are way different between the two because the Sporty has
4 cams and the push rod angle is perfectly straight to the rocker. Shovels have
1 cam push rod angles are just that.........
angled to the rocker arm. The most severe being the front exhaust push rod.
Then came "Thunder heads" because everyone realized that the Shovester conversions really don't work under any circumstances. The Thunderheads were aluminum, had way better (modern) combustion chamber and valve angles and the port volume was actually
smaller. Big gains could be had but there were limitations. If you stroked it or put big cam / carb on it the heads would not support the airflow. Also using 1 carb with "Y" intake hurt potential performance compared to the XR heads at that time ( 2 carbs - cross flow ports intake / exhaust)
To summarize the Thunder heads were
really good for stock displacement Sporty that was not too highly modified - which was the broadest market intended. BUT they were very expensive, relatively speaking, at the time and sales were not what the company had hoped and ultimately went bankrupt.
Note - I cannot help myself here W/O posting a picture of my "Iron Sportster" :D
http://forums.pelicanparts.com/uploa...1411220289.jpg