Boring and stroking a 1000cc Ironhead
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From: OH
Back in the day we called them "parts eaters"
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From: CA
There's really not enough meat in the cylinder walls to achieve any practical increase by boring. You can stroke the engine and take it up in size. My '72 CH was stroked to 77 inches, and with the hot cams, head work, and bigger carb, ran like a scalded dog. I also spent all my spare time working on it.
There are big bore /stroker kits available, too. I've seen a 118 inch Sporty, but it wasn't something that I'd call streetable. Biggest street Ironhead I remember was an 89 incher. He worked on it more than he rode it. Everything was stressed way past design and things had a habit of breaking.
When you put a big bore kit on an Ironhead, you usually have to fly-cut the spigot holes in the cases to allow the cylinders to fit. Too big and the cases are weakened too much. Next step is to build up around the spigots and then redeck them for some added strength. Stroking can get crazy, too. To get the big inches the stroke has to get pretty long. That increases piston speed and that means more wear on cylinder walls and pistons. Plus stroker pistons often have to have shorter skirts in order to clear the flywheels and so they tend to rock in the cylinders meaning more wear, again.
You can also get into all the extras - stroker plates under the cylinders to allow for increased piston travel, new top motor mounts because the engine is taller, new intake manifold because the cylinders are further apart at the top, longer pushrods, ...
If you are seriously interested in a big inch Ironhead there are a few excellent sources. It's best to get a complete kit from one source, and also have them do any machine work needed. I'll see if I can scrounge up a couple addresses and get back to post them.
There are big bore /stroker kits available, too. I've seen a 118 inch Sporty, but it wasn't something that I'd call streetable. Biggest street Ironhead I remember was an 89 incher. He worked on it more than he rode it. Everything was stressed way past design and things had a habit of breaking.
When you put a big bore kit on an Ironhead, you usually have to fly-cut the spigot holes in the cases to allow the cylinders to fit. Too big and the cases are weakened too much. Next step is to build up around the spigots and then redeck them for some added strength. Stroking can get crazy, too. To get the big inches the stroke has to get pretty long. That increases piston speed and that means more wear on cylinder walls and pistons. Plus stroker pistons often have to have shorter skirts in order to clear the flywheels and so they tend to rock in the cylinders meaning more wear, again.
You can also get into all the extras - stroker plates under the cylinders to allow for increased piston travel, new top motor mounts because the engine is taller, new intake manifold because the cylinders are further apart at the top, longer pushrods, ...
If you are seriously interested in a big inch Ironhead there are a few excellent sources. It's best to get a complete kit from one source, and also have them do any machine work needed. I'll see if I can scrounge up a couple addresses and get back to post them.
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jmb79
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Dec 8, 2014 12:09 PM
