After removing the heads, I found loose needle bearings from one of the rocker arm assemblies. This is not uncommon. The needle bearing cage has a lip that folds over the top and bottom of the cage to contain the needle bearings in the cage. According to Bob Fleischer in an Email to me:
“The cage is a metal sleeve that is rolled-over and inwards at the ends, forming a captive area for the needles [BROOK: What I call the “lip”]. The rolling wasn’t enough, and the cage was riding on the shaft, breaking at the rolled end.”
The lip has broken off on the left exhaust rocker arm and I find needle bearings inside the valve cover as I remove the pillow block on the rocker shaft that attaches the rocker assembly to the head. But, not all the needles can be accounted for. I presume someone did what I just did, lost some needles down the push rod tubes, and just put what needles they had in the damaged cage and put it all back together again.
I wasn’t able to find all the needle bearings inside the valve cover. There should be 31 needles in the bearing cage. It’s not uncommon for them to fall down into the oil pan through the push rod tubes. They don’t cause any problems as they just sit in the pan. When I removed the oil pan, I found the missing bearings.
After I remove the heads, I remove the valves, clean the heads and inspect the valves, valve seats and springs. I don’t know if the original valve seats are still in the head. The original ones can wear faster than expected due to the removal of Tetra-Ethyl Lead (TEL) from gasoline in the late 1970’s. The heads were bored for dual plugs at some point and it is possible the seats and valves were replaced at that time.
Based on my inspection, I plan to have the heads rebuilt with new seats, valves and valve springs as the valve faces are worn and the springs have sacked. I suspect the seats are original.
I use a valve spring compressor to remove the valves from the heads. There are a number of different styles of this tool.
Here is information about the valves and heads.
- Bob Fleischer: All About Valves
- Bob Fleischer: All About Rocker Arm Assemblies
- Bob Fleischer: Setting Valves
- Duane Auscherman: Setting and Adjusting Valves
- Duane Auscherman: Specifications for BMW motorcycle engines
The rocker arm bearings are available at any BMW dealer: (Part#: 11 33 1 261 712). There are two needle bearing cages per rocker so I need eight needle bearings.
This is straight forward. The heads are secured with six nuts, four on each of the four cylinder studs and two at 12:00 and 6:00 that fit on the two studs in the top of the cylinder. If all you need to do is replace the needle bearings in one or more rocker arm assemblies, you can remove the two nuts holding one rocker assembly leaving the other four nuts holding the head attached, remove the rocker assembly, remove the two old needle bearing cages, install the new ones and then install the rocker arm assembly and torque the two nuts. I’d check the torque on all six of the nuts while I was at it.
Since I am removing the cylinders, pistons and connecting rods and dissembling the valves, I remove the heads completely.
The procedure to remove the heads on the R100RS is the same as for the R75/6. You can read about how to do this here.
- 1975 R75/6 Rebuild: Project Index
There are spots of rust on the right side valve springs, keepers and rocker arm. This fits with the rusty areas I’ve found elsewhere. The bike got parked for sometime and water condensed.
When I remove the rocker arm assemblies, I put each into a separate zip lock bag and label it so I can put the rocker assemblies back where they came from when I reassemble the heads.
Replace Rocker Arm Needle Bearing Cage
Since there are two bearing cages in the rocker arm, one at the top and one at the bottom, I drive both of them out at the same time. I decide to replace all the rocker arm needle bearings as earlier cages had too small a lip and are prone to this problem.
Here is what the needle bearing cage looks like when all the bearings are inside the cage. There are 31 needles in my needle cage and there is a gap between the bearings that is little less than the diameter of a needle. According to Bob Fleischer in an Email to me:
“They’ve been made with 30 (early) and 31 (now) needle rollers, both are fine….the 31 needles version has very slightly smaller diameter rollers.“
The cage is recessed about 1 mm from the edge of the rocker arm.
When I install the new bearing cages, I’ll recess them the same amount.
I found a socket that was just a bit smaller in diameter than the bearing cage.
I use a socket extension and mount it backwards into the socket. That way the solid face of the socket is against the bearing limiting the ability to have the socket get cocked and damage the bearing cage.
I use a 2 Lb mallet to drive the two old bearings out of each rocker arm.I mount the rocker arm in my vise with the rubber jaws. I am careful to keep the arm with the tappet from contacting the vice jaws so I don’t put any force on them when I drive out the bearings. Then I use the socket with an extension and a 2 Lb maul to driver both bearings out of the rocker.
I don’t want the new cage to deform nor have the needle bearings fall out while I drive the bearing cage out of the rocker arm. I insert the rocker arm so it’s part way inside the bearing cage.
I drive one cage from the top of the rocker. When the cage is flush with the rocker arm I recess the cage 1 mm by tapping the socket a bit, measuring how far it has moved and repeat until it’s recessed 1 mm. Then I drive the second bearing cage in from the bottom of the rocker and again recess the cage 1 mm.
When both bearings are seated in the rocker arm, I use some engine assembly lube to lubricate the needles and then slide the rocker arm inside the bearing cage to keep the needles in place and put the assembly in it’s labeled bag.
I use the valve spring compressor to remove each valve from the head. I label four zip lock bags for each valve assembly.
I adjust the spring compressor so the arm is centered on the face of the valve and the spring collar and then tighten the screw until the spring compresses enough to pop free from the spring collar.
Here is a complete valve assembly with the bottom and top spring collars, the valve spring, the valve and the two collets that fit into the grooves in the top of the valve stem.
Inspect Valves and Springs
I measure the spring height of the uncompressed spring. According to Duane Auscherman’s engine specifications, there are different color springs with different uncompressed spring heights. These springs are “brown” as they have a dab of brown paint on the top of the spring coils.
They are all 45 mm or less. The specification is 45 mm so all of them are ready to replace.
The valve face lip can wear. I measure them and find several of the valves have lip thickness as small as 0.5 mm. The valve lips are unevenly worn with part of the lip at 1 mm and part at 0.5 mm. So, new valves are in order.
At this point, I plan to have the heads rebuilt with new seats, valves, springs and collets.
What brand is your spring compression tool?
No Clue. I borrowed it from a vintage British bike shop I was working in a couple days a week.
A Google search shows what I think is the same tool available from multiple outlets:
I hope that helps.
THanks for all this info I am about to replace the needle bearings for my R90/6 from 1974 and they are in the freezer, and I intent to heat up the rocket and insert the cold bearing with the axisi inside. I am concerned about pounding too much on the bearing cage. When you state above “I drive one cage from the top of the rocker.” how do you do this specifically? Thanks!
If I recall, I believe I used a suitable socket as the drift to drive the bearing onto the shaft. I show all the details of this in several pictures in the write-up.
I hope this helps.