I remove the top end (valve covers, rocker arms, push rods, head, head gasket, cylinder and piston) before I take the engine out of the frame so it’s easier to remove it. The design of the airhead engine makes removing the top end a simple job that can be done with the tools in the on-board tool kit. For the 1983 engine, I also need a set of snap ring pliers to remove the wrist pin snap ring, but on earlier models that used the wire clip to retain the wrist pin, you could remove that with the flat blade screw driver. 🙂

Here is a short video showing all the steps. In all honesty, it takes just about as long to take one side of the top end off as it takes to watch the video.

VIDEO: 1983 BMW R100RS How To Remove the Top End

Remove Valve Covers

First I remove the spark plug.

The insulator on the plug looks okay, perhaps just a bit rich.

The valve covers are secured by three nuts with washers; the center chromed nut and two 6 mm nuts at the upper left and lower right corners of the valve cover. I remove these and pull the valve cover off.

This version of the of the valve cover has “R” or “L” stamped in the middle to indicate which side the cover goes on. The letter should be on the bottom when the cover is mounted correctly so the horizontal strips are level.

This one has silicone gaskets. I don’t like them, so I put them in the appropriate storage bin. I will replace them with solid gaskets.

NOTE:
When I had the heads rebuilt, the head valve cover mating surface was not flat and I had it machined flat. This is why someone used the silicone gaskets as they can seal a leaking valve cover caused by the head mating surface not being flat.

Someone repainted the covers and the paint inside the cover is flaking off. That’s not helpful as it can fall into the oil pan and potentially get circulated through the oil pump before it reaches the oil filter. I’ll clean this up when I repaint the valve covers, but of course I won’t get any paint on the inside of the covers.

Remove Cylinder Heads

With the valve cover off, I can see the exhaust (left) and intake (right) rocker arm assemblies.

Each rocker arm assembly slides over two of the cylinder studs that are screwed into the engine block and the rocker assembly is secured with the two cylinder stud nuts. There are also two other nuts at the 12:00 and 6:00 positions of the head that secure it to the cylinders. Once these six nuts are removed, the head comes off.

Check For Damaged Cylinder Stud Threads

Before I remove the rocker assemblies, I use a torque wrench to test the cylinder stud threads in the engine block. These threads can pull out if someone has over torqued them and now is the time to find out if any of them are damaged. I set the torque wrench to 25 FT-Lbs and tighten each nut. The wrench should click indicating the cylinder stud can hold that much torque. If it won’t click and the nut keeps turning, then the threads in the engine block are damaged and you have to repair them.  You can see how to do that here:

• 11 BMW R75/5 Repair Stripped Cylinder Stud Threads

These cylinder studs were tight so no need to repair the threads in the engine block.

Loosen Tappet Adjusters & Remove Head Nuts

I loosen the lock nut on the tappet adjusters and then back the adjusters all the way out until I can spin the push rods and the rocker is loose.

Then, in a cross-wise pattern, I loosen each of the six nuts holding the head on a small amount, maybe an eighth of turn. I continue loosening in the cross-wise pattern a bit more until the nuts are easy to remove with my fingers. The 12:00 and 6:00 nuts will loosen almost immediately, but the four on the cylinder studs will take several rounds if loosening until the nuts are free. Since the heads are aluminum, an ounce of caution is worth it to avoid the possibility of warping the heads.

The four nuts on the cylinder studs have a round boss on one end that fits against the face of the pillow block.

Remove Rocker Arms

Once the six nuts are removed from the head, I grasp a rocker assembly by the upper and lower pillow blocks and pull it off the cylinder studs. Some rocker assemblies have needle bearings inside, so pinching the assembly by the pillow blocks keeps them in place. And these rockers have a machined hole that aligns them on the bushing at the top of the cylinder studs to center the assembly automatically. Earlier designs did not have this feature.

If you inspect the finger of the rocker arm, you may see discoloration. This is not abnormal but is caused by the heat treating that hardens the steel in the tappet of the rocker arm.

I put each rocker assembly along with the two nuts in a labeled bag, e.g., LEFT IN-take. I don’t want to mix these up when I put the heads back on.

Remove Push Rods

Once the rocker assembly is removed, I pull each push rod out.

If you do it slowly, you will feel resistance and then rod will pop free. Push it back in and do this again. This slight popping of the rod indicates the ball on the lower end is seated in the cup of the cam follower. This is what you want to feel when you put the push rods back in to ensure the bottom ball on the rod is seated in the cam follower cup.

DANGER:
It is possible to put the push rod in the push rod tube and have it rest on the edge of the cam follower. If you assemble the head this way the push rod and cam follower will be damaged.

I put a label on each push rod to indicate where it goes, and which end is at the top, e.g, “L-EX-TOP”. Although the balls on either end of the rod are the same, each ball has mated to it’s corresponding part and it’s nicer to keep the rod orientation the same.

Pull Head & Head Gasket Off the Cylinder

I often use a rubber mallet to tap the fins around the bottom of the head to break it free from the head gasket. Gentle taps toward you around the perimeter while you pull the head toward you are enough. It will slide out on the cylinder studs. Then I remove the head gasket from the top of the cylinder.

Here is what the head looks like after it is removed.

The inside shows the valve faces. There is carbon build up, but it is not oily indicating the valve guides are not leaking oil.

Remove Cylinders

Before I remove the cylinders, I take the head gasket off. It should come off easily, but if it’s stuck, use a small screw driver blade to gently free it from the cylinder face. Don’t gouge mounting surface on the top of the cylinder with the screw driver.

The cylinders have a sleeve that fits into the bore of the engine block. Usually I can wiggle the cylinder while pulling it out and get it come out of the block. It it’s stuck, use a rubber mallet, as I described for removing the head earlier, and gently tap around the cylinder to get it loose.

As you pull it toward you, it will become harder to move. The push rod tube rubber seals interfere with the bottom frame tube. If you can, rotate the seals 90-degrees and they will slide by the frame easier. If they won’t rotate, just pull harder while rocking the cylinder back and forth to wiggle the seals past the frame. BUT, don’t get too aggressive as once the push rod tube seal clears the frame, the cylinder will slide very easily on the cylinder studs.

As soon as the cylinder slides freely again on the cylinder studs, I pull it out until the connecting rod is exposed and the piston is partially out of the cylinder. Then I take a piece of garden wire and run it under the connecting rod and over the top cylinder studs to suspend it. That way, when the piston comes free from the cylinder, there is no chance the rod will drop and nick the sealing surface of the engine block.

Remove Pistons

I pull the cylinder out farther until the wrist pin and snap ring are exposed but the piston is still in the cylinder. Then I use snap ring pliers to remove one snap ring. I like to remove the one on the intake side of the piston. It is a “use once” item, so I will replace them. I don’t remove the other one as it becomes a “handle” to help remove the pin from the other side.

The wrist pin often is loose enough that it can be pushed out to one side with my finger. This one is easy to slide.

But, if it isn’t sliding out under finger pressure, I use two 3/8 inch socket extensions, a short one and a longer one, and insert the square end of short one into the hole in the wrist pin. It will go in until the shoulder abuts the wrist pin. Then I gently tap on the end of the second extension to slide the wrist pin out. This is why I leave the piston in the cylinder so as I tap on the socket extension, It isn’t putting any sideways force on the connecting rod.

When the pin if far enough out the other side, I grab it and twist it while pulling it out to get it far enough out that the piston is free of the connecting rod. I hang on to the piston while doing this so I can feel when it is free. When the piston is free from the wrist pin, I can slide the cylinder with the piston still inside off the cylinder studs. But before I slide the cylinder any further off the cylinder studs, I use some green garden wire and wrap it around the connecting rod and tie the wire over the top two cylinder studs to suspend the connecting rod.

This suspends the connecting rod as I remove the cylinder and piston so the connecting rod does not fall and strike the machined surface of the engine block. Even with the wire there, I put my hand on the rod as I remove the cylinder just to be sure it’s suspended.

DANGER:
If you failed to secure the connecting rod from falling at this point, it can fall and nick the machined surface of the engine block. That will cause an oil leak. You do not want that to happen.

NOTE:
If you wish, you can keep the piston in the cylinder and if you are careful, you can pull the cylinder off the piston just far enough to expose the wrist pin and snap ring but not far enough to allow the piston rings to exit the cylinder. After you push the wrist pin far enough out to slide the piston off the connecting rod, you can remove the cylinder with the piston and rings captive inside it. This is a good way to remove the cylinder and piston when all you need to do is install new push rod tube seals. That way you don’t disturb the rings nor risk breaking them when you insert the piston back into the cylinder.

But in my case, since I am going to remove the piston and replace it, I just pull the cylinder off the piston after it’s free of the wrist pin. It will rest on the bottom two cylinder studs so it won’t drop onto the floor.

On the bottom of the cylinder is the push rod tubes with the rubber seals. These are hard as a rock which is why they are leaking.

On the 1983 engines, the top cylinder studs have a small o-ring that creates an oil seal.

Oil to the rocker assemblies flows out of the engine block along the cylinder stud hole in the cylinder. If these are missing when you assemble the top end, you will know it pretty quick as oil with be coming out around the top of the cylinders.

On the bottom of the cylinder where the sleeve goes into the engine block is a large o-ring. I will replace it when I put the top end back together.

Finishing Up

I pack the engine case with two shop rags, one on the bottom of the connecting rod and one on top. The bottom rag is additional insurance to keep the rod from dropping and nicking the engine case. Then I move the garden wire and put it through the rod bushing so the rod is doubly protected from falling.

Here is a view of the cam followers that the bottom ball of the push rods fits into. In the center is the cup the ball fits into.

DANGER:
When assembling the top end, if you don’t get the push rod into the cup of the cam follower, and instead, it sits on the edge, you will damage the follower and the push rod. That’s why testing by pulling gently on the rod to feel it “pop” out of the cup is important as that ensures the ball is seated properly in the cup.

The machined surface of the engine block the cylinder sleeve fits into has hardened sealant caked on to it. I will have to carefully clean this off before putting the top end back together.

Here is what the bikes looks like now. It’s almost ready to separate the engine from the frame.

Revisions

2019-11-21  Edits and typos.