BMW Airhead rocker arms and posts

70-73 | 74-75 | 76-84 | 85-on | replacing bearings | shafts | upgrades

There were four rocker arm systems used on /5 and later Airheads. Each system includes the rocker arm itself, the rocker blocks, the rocker shaft and the mounting posts on the head.

Since valve adjustment is near and dear to the heart of every Airhead, and valve noise goes hand in hand with the adjustment and the rocker system, some might take the opportunity to upgrade their bikes to more robust and quieter rockers.

The aftermarket has also provided quieter rocker systems. One example is the one-piece rocker bracket from Motoren-Israel which is applicable from '76 onward. Also there were conversions available in the '70s which added thrust bearings to the rockers.

Whenever a cylinder head is disassembled, the rockers should be disassembled, cleaned, and inspected. The oil is fed to the rockers by the upper stud passages, which have very low flow rate and get very hot. It's not unusual to see solid oil deposits in the rocker bearings. This will also let you find cracked bearing cages, which aren't uncommon, and worn rocker shafts.

Controlling end play is important because the pushrods are angled. If a rocker has too much end play, some of the pushrod action is used up moving the rocker to the other end of the rocker shaft rather than lifting the valve. With good tight rocker action, all valves are lifted uniformly.

/5 type with bushings

The early rockers were solid metal riding on a shaft without bearings. Setting the rocker end play required pressing the two blocks together until the correct clearance exists (once you replace the original wave washer with flat washer 11 33 1 257 825). For all pre-85 rockers, the specified clearance is essentially zero; free movement without noticeable end play.

Rocker blocks were 14mm wide, with a pad for the bearing surface of the 14mm stud nut. With the sealing sleeve, the post is 20mm.

Early /6 type with needle bearings

These early needle bearing rockers were used on the '74 and '75 models. The change to the fully-enclosed stud supports probably didn't coincide exactly with the rocker change, but it was close. Rocker blocks were the similar to the /5, and the rockers are 57.5mm wide.

'76 to '84

Even with the indexing provided by the bottom of the rocker block, there's still enough movement to allow you to affect the end play when you tighten the cylinder studs.

These rocker blocks are 16mm wide, with larger pads on top for the 15mm nuts used from here onward. The rockers themselves are correspondingly narrower (56mm).

'85 and later

These rocker blocks have 14.5mm alignment dowels in the bottom, and the buttons are gone from the heads. Indexing is very accurate, and the rocker endplay is set with shims to .03~.07mm. Due to the tight indexing, end play is entirely unaffected by attempts to press the rocker blocks together when tightening the stud nuts. Don't even try; just measure the gap and change the shims accordingly. Shims are available in 0.20, 0.25, 0.30, 0.35, and 0.50mm thickness, typically two will be needed.

Rocker blocks remain 16mm wide, but with a much smoother surface and tapered shape on top. The rocker arm itself is just over 52mm, and the remaining distance is taken up with a 3mm plastic bushing and the shims.

Replacing bearings

Early needle bearings tended to break out of their cages. If you disassemble a rocker and find a cracked cage end, don't worry about trying to reassemble it. Just order two new bearings for each affected rocker arm and replace them.

Press both bearings out to one side, then press a new bearing in from each side until its cage is just below the end of the rocker. Photos to come.

Rocker shafts

/5 rocker shafts are 91mm long while later ones are 92mm long. All are 14.5mm in diameter. '74-'84 shafts are end-drilled and then cross drilled to provide oil from the stud passage to the upper bearing (it trickles down to the lower bearing) which is why the end with the plug in it has to face upward. Later shafts are drilled once diagonally to provide the same effect. That end is marked with a punch, and the dimple should face up and out. Both of these latter shafts are functionally identical and in fact the diagonally drilled shaft has replaced the T-drilled shaft within the BMW parts system.

Upgrading

Every style can be easily upgraded one level.

• /5 heads can be upgraded to '74-'75 rockers. The recess in the bottom of the '76-'84 rocker block is too small for the /5 post with sealing sleeve, so if you want to go to those rockers you'll need to seal the sleeves somehow.
• Early /6 heads can be upgraded to the '76-'84 rockers, because the post is small enough to fit into the recess. This will give the added durability that comes with the better heat treating and the 15mm stud nut (the narrower collar on the 14mm nut tended to distort).
• '76-'84 heads can be upgraded to the '85-on design, because by pulling the button out you are basically left with an '85-on rocker mount.