Ironhead Rocker Box Assembly
Text and Pictures by Mark Trotta
The rocker boxes on top of your old Sportster engine were well designed, but through age and wear they'll eventually need to be overhauled. This generally includes removal, parts inspection, checking clearances, and replacing worn rocker arms, shafts, and bushings.
Rocker Box Differences
Ironhead Sportsters have specific front and rear rocker boxes and they do not interchange. The best way to tell one from the other is to look at where the oil lines are - they're on opposite sides.
Early and Late Covers
From 1957 through 1970, front and rear rocker boxes carried part #'s 17514-57 and 17515-57.
From 1971 up, they are listed as # 17514-71 and 17515-71. The later 71-85 style have a thicker crossover piece but fit 57-70 as well.
All years will interchange, but early ones are harder to find.
**********
Rocker Box Removal
If your motor is still in the frame, the rear rocker box cannot be removed by itself. The rear head and rocker box need to be removed as one piece.
If you try to remove just the rear rocker box, you may damage the gasket surface. This design quirk was addressed and changed on the 1986-up Evo Sportsters.
The front rocker box can be removed by itself, as there is enough room between the rocker box and the frame.
Clearances
Before disassembling, check the play between the rocker arm to shaft. The easiest way to do this is with a feeler gauge.
The factory manual states rocker arm end play should be between .005" to .010".
**********
The shaft bushings are fairly easy to press in and out.
Note: 1986 and up Evo Sportsters have the same shaft bushings as Ironheads, but with the addition of a small oil hole. It is not recommended to use the later Evo-style bushings in Ironhead rocker boxes.
Tools Needed
To remove rocker arms, you'll need a 5/8" wrench or socket, flat-blade screwdriver and a 5/16" Allen key.
Rocker Arm Differences
Ironhead Sportsters have four different rocker arms.
To add to the confusion, the two intakes and the two exhausts look the same, but none are interchangeable.
If you mistakenly install a front exhaust for a rear intake or vice-versa, your bike will still run, but the push rod/rocker arm alignment will be out of whack. I'm sure there's more than a few old Ironheads out there with mismatched rockers, so be careful when assembling.
Part Number vs Casting Number
The numbers stamped on original H-D rocker arms are not actual part numbers. These are referred to as casting numbers, and will help you identify which rocker arm is which.
Note: Sometimes due to an upgrade or manufacturing change, Harley would change a casting number, but the part number would remain the same.
All year Ironhead Sportsters used the same rocker arms. If your rockers were replaced with aftermarket ones, they'll have different casting numbers/part numbers from the factory rockers.
The rocker arm part numbers listed below are from the Harley parts book:
Front Intake 17396-57A
Front Exhaust 17394-57A
Rear Intake 17397-57A
Rear Exhaust 17395-57A
Which Rocker Arms Have The Oil Hole?
Upon close examination, you will notice two of the four Ironhead rockers have a small oil hole. These are the exhaust rocker arms; the holes are there to help with the extra heat. The two intake rockers do not have oil holes.
If the rocker arm pads are slightly worn, they can often be renewed on a grinder, providing the original curve is followed. Best practice here is to compare wear on old worn rocker to a new, unused rocker.
**********
Rocker Arm Shafts
Ironheads have early and late style rocker shafts, and they are interchangeable. The early shafts (1957-1970) have a round slotted end plug.
A design change for 1971 saw a slightly wider O.D shaft, and the end plug was switched to the Shovelhead-style red plastic "button".
Colony offers complete sets of replacement rocker shaft end plugs, nuts and washers.
Rocker Shaft End Cap Kit For 1957-1970 Sportster work with the late style rocker shaft, and are available in chrome or cadmium-plated.
Rocker Shaft End Cap Kit For 1971-1984 Sportsters are available in chrome or cadmium-plated.
**********
If you need replacement rocker arm shafts you can buy them here.
Mounting Bolts
There are seven bolts that hold each cover onto each head, and there is an early style and late style:
For 1957 through 1976 rocker box bolts click here.
For 1977 through 1985 rocker box bolts click here.
**********
Rocker Box Gaskets
On 1957 through 1969 Sportster engines, there were no rocker box to cylinder head gaskets from the factory. Suggested practice was, after a good cleaning, apply a light coat of aluminum paint to the head surface before mounting the rocker box.
Starting in 1970, gaskets were installed from the factory.
Do I Need To Use Gasket Sealer With Gaskets?
Gasket sealer is really only needed to hold the gasket in place while it's being bolted down. So you don't need to apply any sealant.
As an alternative, you can spray them with copper gasket spray, because it leaves the thinnest coat. I've also heard of techs that spray them with high-heat engine paint.
After gaskets are installed, the middle part serves no purpose and can be cut off with a razor blade (although some people leave them on).
Here's a tip if you have a pre-1970 bike and want to keep it original but don't want it to leak. On a dead-flat surface, lap the bottom of the rocker box with fine sandpaper. This will help allow it to seal. This is also a good idea with chrome rocker boxes.
**********
Chrome vs Polishing
We all know the enemy of an internal combustion engine is heat. This is even more true with air-cooled motors. Chrome-plated engine parts hold in heat, and the part will pit and flake over time. Polishing aluminum is always the better choice for motorcycle engine parts.
After spending several hours filing and sanding each one, they polished up nice on the bench sander.
It's time consuming, but the results are worth it.
**********
Top End Gasket Kit
The best gaskets available for your Ironhead, James Gasket Top End Gasket Kit.
The gasket set replaces H-D # 17030-72 and includes everything you need to reseal your top end; copper head gaskets, oil seals, O-rings, and all other gaskets necessary to completely rebuild a 1973 through 1985 Ironhead top end. James Gaskets are made in USA.
NOTE: Original rocker O-ring seals (OEM #11101) were rubber. Most aftermarket seals are nylon.
**********
Notes and Misc
Ironhead rocker boxes are similar to those later seen on 1966-1983 Shovelheads, but share no common parts. Curiously, the Big-Twin versions have only two part numbers for their four rocker arms. The rear exhaust is also the front intake, and the rear intake is also the front exhaust.
**********
Related Ironhead Articles:
Cylinder Head Removal
Cylinder Head Cleaning and Inspection
How To Polish Aluminum Motorcycle Parts
Ironhead Engine Build
Ironhead Top End Rebuild
Install Sportster Cams
