How To: Splitting Ironhead Sportster Rockers

Splitting Ironhead Sportster Rockers

Here is the second “How To” provided by Joe over at CrimeScene - this one is all about splitting the rockers on your Ironhead Sportster. I absolutely LOVE this look - really makes the Ironhead engine a looker. If I had one of these Sportsters, it would be at the top of my lists of things to do. Dig into it!

Splitting the Rockers on an Ironhead Sportster
By Joe CrimeScene

Here is the step-by-step sequence I did on splitting the rockers on my ironhead. Weyland was the inspiration for this method of cutting them, and in my opinion it is the best looking result. Just splitting them will leave you with mis-matched rockers (one square and one rounded) on the Ironhead.

Here is where I started. I sketched out some shapes first, until I liked the basic look.

See how they are square on one side and rounded on the other? That is the key thing to deal with. The brass nut is from Weyland, it screws into the end of the rocker shaft.

Splitting Rocker Boxes
I used a little pattern tool to pick up the shape on the curved side and transfer it over to the square side

Harley Davidson Rocker Box Splitting Sportster
OK, time to get serious. Fire up the mighty Do-All and whack off the corners.

Note that I made the cut short of the hole where the rocker shaft come out. I wanted to make sure I had enough room to weld and grind without getting into the holes. When I’m done I want this side to taper down _almost_ to the shaft hole to match the other side.

Rocker Box Splitting
We’ll need to do something about that hole or there will be a big puddle on the floor…

Rocker Box Splitting Ironhead Sportster
I cut out the “bridge” between the two sides. There is an oil port on the square side that feeds both shafts (through this bridge part). We’ll need to plumb both rockers later.

I attached the middle area with a no-load grinding disc (specifically for aluminum). I wanted to round it over and get a nice flow going.

Use the flat of the disc, not the edge, and it is really controllable.

Splitting Rockers
If you compare this with the shot of the rockers boxes just after they were cut apart you can see how much material I hogged off. It goes quickly enough.

I wanted to rough these in because I have to weld up the oil galley that runs all the way through the covers.

Once I hogged the buld of the material off I used a counter sink to bevel the hole and welded it up. Then I dressed it down a bit further with the belt sander.

The belt sander is one of my favorite tools. It can hog off metal, or do a really fine fine finish.

Split Rockers
Here is the middle section roughed in. Now we need to close up that ugly hole.

Split Rockers
And we need to weld up the oil passage too.

I did the “dirty finger” template thing, and started making a little plug to fill the hole.

Rocker Splitting Harley Ironhead Sportster
Here is the part fit into place.

Welding the rockerbox filler plug
I used a junk rocker shaft to try to control distortion, we will be making this really, really hot for a while. I welded around the seam, then build up the surface with several passes so that I had some material to shape.

Rocker Boxes welded up
Pretty much done, I checked the rockers side-to-side with a template to make sure they matched. I took them up to 320 on a D/A sander to get everything nice and smooth.

Rockers with brass nuts
With the brass nutz from Weyland mocked up (no shafts)

Finished Rockers, after chrome
Add chrome, polishing the nutz, Weyland’s hex covers on the pushrod tubes and some assembly and you get…


Thanks again to Joe at CrimeScene

6 Responses to “How To: Splitting Ironhead Sportster Rockers”

  1. Rowdy says:

    Very cool. I’m the owner of the motor he originally did that too.
    My rockers are polished not plated tho.
    The brass nutz look much better than I imagined. (mine are chrome)
    heres a shot (link)

  2. grail21 says:

    Awesome man. Looks killer, thanks for sharing the pic.

  3. Knucklebuster » Blog Archive » 2007 Year In Review: January says:

    […] Check out the best of January 2007: How To: Shaving Fork Legs How To: Splitting Ironhead Rockers How To: DIY Air Seat How To: Make a hand tooled leather seat Video: Johnny Chop Photos: Vintage Motorcycle Racing […]

  4. Blacksmithbilly says:

    Thanks for showing how its done!

  5. Angel_LosAngelesCA says:

    Where did you find those brass rocker arm plugs? I haven’t been able to find any. Do you got a web link for those to buy them?

  6. jason c. says:

    how do you get oil to the back rocker? i have a set of slpit rocker on my 74 iron head and tey put pressure fittings between the insides of the boxes and they leak. how could i fix it..

Leave a Reply