Forum bmwbike.com

My R27 was reassembled without the rubber spacers 26 11 3 038 184 on each side of the Hardy disk in the drive coupling. There are a total of four spacers.

My restorer says these spacers are not very important and that the earlier singles did not have spacers. I think the spacers may keep the disk centered between the drive flanges and extend its life.

How important are these spacers, and what will happen without them?

Allan:

Not that I am an expert, but if you can get them, I would use them. They were there for a reason. The Germans are nothing if not precise. That is why you and I are riding around on 40 year-old bikes today!

-- Andrew

I do want to use them, and I am getting them. But the whole completed restoration has to be torn apart to install them. Either the motor and transmission must be moved forward, or the bench seat, fender and swingarm must be removed.

My restoration mechanic says the spacers are not a neccessity. I am wondering exactly what happens if they are omitted. My R27 has worked perfectly for 1300 miles without them.

Hello Allan

I think it very important that you pass on the following information to your restorer before he gives further incorrect information to other BMW owners regarding the Hardy disk. In addition, if your restorer assembled your R27, he should carry out the fitting of these 4 hard rubber spacer rings under guarantee...after all, he is a BMW expert, and he should know the following:
The hardy disk remained unchanged between 1936 (R5) and 1956 (R67/3) being made out of black natural rubber and a thickness of 25mm. The R24 to R25/3 had the same dimensions, but a slightly softer rubber. Today we don't differentiate and use the same hardy disk in all these models. (BMW technical letter)

With the introduction of the R26 in 1955 and the much longer rear end travel, the conventional hardy disk of 25mm thickness was unsuitable as it would have a very much reduced life through the excessive up and down suspension movement. BMW used a thinner black rubber hardy disk of 17mm thickness in conjunction with the 5mm hard rubber spacer rings on the coupling. This allowed greater freedom of movement at the coupling joint without excessive stress on the hardy disk. Later, this 17mm black rubber hardy disk was replaced by a light brown urethane disk which BMW referred to as "Vulkalan".

BMW even wrote in a factory technical letter to all dealers that the conventional 25mm thick hardy disk can be replaced on all models with the urethane disk in conjunction with the 4 hard rubber spacer rings.

If you do not use these 4 hard rubber spacer rings, then the following will happen:

The hardy disk has no axial resistance and is free to travel back and forth along the couplings. As the couplings are seldom parallel, the hardy disk tends to tilt, and without axial support and due to being out of "line", tends to be chewed up by the lugs of the coupling. As it is no longer centered between the couplungs by the spacer rings, it is free to move in a "figure 8" manner which will cause it to scuff and wear the aluminium cover that covers it (models R26 and R27 and late R51/3, R67/3 and R68) and also scuffs the axle lugs on the gearbox cover holding the clutch lever pivot.

Failure of the 17mm hardy disks is 99% due to failure to place the 4 hard rubber spacers.

Best regards,

Mark
Mark Huggett GmbH

Mark,

Thanks for the info on the spacers. What do you think is the easiest way to split the coupling and install a new disk and spacers?

One way is to remove the bench seat, remove the rear fender, then remove the rear swingarm. This is the method I plan to use.

The other way is to remove the remove the muffler, suppport the motor and tranny, undo the top and bottom rubber mounts, and shift the motor/tranny forward. There may be enough room under the tank to do this without removing the tank which also requires removal of the bench seat. There is only about 2,5 cm between the points cover and the downtube of the frame, which may not provide enough space especially if the frame is wrapped to protect it, and it will he hard to control the mass of the motor/tranny.

Hi Allan,

The first method is the correct one to use. I know that its a dog, but there are no shortcuts.

We were really impressed with your restoration home page...thats why I phoned.

Regards,

Mark
Mark Huggett GmbH