Replacing BMW Airhead Push Rod Tubes and Seals


 
This pages show how to access the push rod seals for replacement and if necessary how to replace the tubes themselves.

In this example the tubes were replaced with after market stainless steel versions.

New stainless tubes and seals
    
The replacement parts needed are shown on the right.

As well as the seals and tubes, a new head gasket was needed and it was also planned to install a cylinder base gasket on this R60/6 to reduce the compression and the risk of pinking.

Other non-reusable parts included the gudgeon pin circlips and some O-rings for the cylinder studs.

New parts. (Click to view).
  
A drift tool was made up to the dimensions shown for the removal of the old push rod tubes.

Also prior to the work commencing; the exhaust nuts were soaked in penetrating oil for a few days as they were known to be difficult to remove.

Drift drawing (click for printable PDF)
  
The exhaust system was removed from the bike; the silencers were removed first, leaving the downpipes and balance pipes on the engine.

A finned nut spanner was used to unscrew the nuts. On this bike after an initial tap with a rubber mallet the nuts unscrewed easily by hand.

If the nuts begin to tighten whilst unscrewing, it is advised to cut them off and replace them, as the cylinder head threads are easily damaged. Some sensitivity is needed here to make the right judgment on what is happening whilst the screws are being undone.

Undoing an Exhaust Nut
    
With the exhaust nuts removed some hits with a rubber mallet were needed to release the exhaust from the headers.

The photo on the right shows the orientation and order of the two sealing rings that sit inside the nut.

The split ring sat nearest the cylinder with the chamfered face towards the nut. The second ring was orientated to match the split ring with the square shoulder facing the nut.


Exhaust Sealing Rings

   
Both spark plugs were removed and both carburetors with their air box pipes.
Removing a Carb.
 
The rocker covers were removed by first undoing the hidden 10mm nuts in the cylinder fins. [Two nuts each side at the 10 o'clock and 4 o'clock positions].

Then the central nut was undone to remove the cover.

A drip tray was used to catch oil remnants in the head.

One of the hidden rocker cover screws.
(2 each side)
 
The 4 rocker nuts were removed and the rocker assemblies and push rods were extracted and layed out in sets so that they would go back in the same place.

Then the two cylinder head nuts we undone.


Rockers and Push Rods.
 
The head was removed with a wriggle and a few taps from a rubber mallet.
Removing a Cylinder Head
 
The head gasket was discarded and the cylinder pulled out slightly to lift the push rod tube seals clear of the crank case.
Removing Head Gasket

Push Rod Seals Pulled Clear
 
If just seals are to be replaced then they can be removed at this point most easily done by rotating them with some pliers about the tubes.
New seals should be installed in the same orientation and lubricated with some engine oil from the rocker covers before fitting.
 
To replace the tube themselves the cylinder barrel was removed from the bike keeping the piston in the cylinder, to avoid the need to re-compress the piston rings.

The piston was removed from the connecting rod by pulling the barrel outwards to expose the gudgeon pin.

Then both circlips were unclipped and the pin was removed by tapping from front to back with a wooden drift.

Warning. Stuff a rag into the crankcase hole to avoid loosing the circlip in the engine. Also wear eye protection for this step.

One circlip Removed
   
With the pins removed, the cylinder barrel was slid free from the cylinder studs.
Another warning : Don't let the connecting rod drop down and "chink" the crank case as this can promote an oil leak at the cylinder base. To avoid this stuff a rag in the crank case under the connecting rod and support it using a screwdriver across the cylinder studs.

Removing Barrel and Supporting Con Rod
 

The engine Dismantled
 
Before removing the old tubes some measurements were taken of the position of the sealing ring. This was important because the seals would have to be compressed enough to stop oil leaking but not so much that they split.

The distance to the underside of the support ring was the important dimension.

Measuring the tube length
 
The angle of the tube was also measured so that an angled block of hardwood could be machined up.
Measuring Tube Angle

Drilling the Wooden Block.
The hardwood block was drilled to take an M12 bolt.
 
The old push rod tubes were tapped out using the drift tool and a mallet.
Drifting Old Tubes Out
 
A piece of 12mm threaded bar was used to pull the new tubes into place.
Oil on the nut helped the tool provide the compression needed to slide the tube into place. The depth was checked frequently to get the correct distance plus 0.5mm to allow for the new cylinder base gasket.

Pulling First Tube into Place
 

Checking Tube Position

Pulling Second Tube into Place

 
Re-assembly

The new push rod seals were pushed on to the tubes and orientated to match the originals.

Two new o-rings were placed in the top two cylinder stud holes.**

** not all models have these.

Locating the O-rings
 
If required the O-rings can be held in place with a dab of grease. However in this case the new cylinder base gasket would capture the O-rings during re-assembly.

The cylinder base gasket was smeared with a thin layer of gasket sealant on both sides.
This is optional and originally there would have been no sealant used.

Fitting New Cylinder Base Gasket
 
Before attaching the connecting rod, the piston was checked for correct orientation.

The arrow on the crown should point to the front of the bike.
Likewise the smaller of the valve clearance depressions should be at the front.
Click the image on the right for a close up view.

Piston Orientation (click to View).
 
The cylinder and piston assembly were slid into place along the cylinder studs.
At the same time the connecting rod was held to slide into the piston and the gudgeon pin tapped into place (rear to front).
New Circlips were fitted both sides.

Note: some Circlips have a sharp edge and rounded edge; the sharp edge faces inward, toward the piston.

Again a rag in the crank case and eye protection is recommended as the clips frequently escape.

Aligning the Piston and Con Rod.
 
The new push rod seals were smeared with engine oil before the whole assembly was pushed into place.
Sliding the Cylinder Barrel into Place
 
A new head gasket was installed.

Note only one orientation aligned with the push rod holes correctly.

Head Gasket Incorrect

Head Gasket Correct
 
The cylinder head was then replaced along with the push rods and rocker assemblies in their original place.

All cylinder head bolts were progressively tightened in sequence using a criss-cross pattern :10 o'clock, 4 o'clock, 8 o'clock, 2 o’clock. Then 6 o'clock and 12 o'clock.

Three stage torques were used of 11, 18 and 26 ft-lbs.

Cylinder Head Torquing Sequence
 
Before fitting the rocker cover, the valve clearances and rocker end float was checked in accordance with the procedures detailed here. Clearances were expected to be quite different with the new cylinder base gasket installed.
 
The exhaust and carburetors were replaced. A rubber mallet was needed to get the down pipes to fully seat in the cylinder heads.

A Nickel based Anti-seize was used liberally on the exhaust nuts and clamp parts. Nickel anti-seize is well suited to higher temperatures.
The finned exhaust nuts were just tightened using a gloved hand rather than with a spanner or to a specific torque.

Anti-Seize for Exhaust Nuts.
 
Images showing the improved look of the stainless tubes and the absence of leaks.

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