Awesome Quality garlock oil seals
Exquisite Craftsmanship.I previously published an extensive article on
the EARLY AIRHEAD FORKS INTERNALS. That article, with photos and
sketches, described the /5 through /7 forks internals, including
modifications for sport-handling and race-handling. The article is no
longer in my files, and was published on the Airheads LIST before I
started this website. If you can find it in the archives, please refer
to that article for those early forks; and then PLEASE forward me the
information on where/how to copy the files, so I can edit and updated
them and re-publish on this website. Otherwise, the project will need
to be done all over again, & I still have many of the pencil note
references I used when I made the original. Now and then I may find
notes that led to those articles. I will put such in an ADDENDUM at the
end of this long forks article.
I never did the same thing for the 1981-1984 forks, or the even later forks, both series of which are different internally. In this FIRST section of the following relatively lengthy article, is of a sketch, and description, of how these 1981-1984 forks operate, some information about the modifications the FACTORY did during production to REDUCE NOISES and IMPROVE OPERATION, etc. There were THREE stages of these changes. While the factory never identified these as stages, I, as others have, identify them as Mk1, Mk2, and the final as Mk3. AFTER 1984, many of the forks used MUCH of the Mk3 design. The below photo of a sketch is of the 1981 fork, but with the last version of the factory modifications, which I call Mk3.Awesome Quality garlock oil seals Exquisite Craftsmanship.
The 1981 forks were of a very different design. They also made a lot of clicking and clunking noises. BMW’s first fix was to install SHIMS below the valve body, which did reduce noises. The rebound spring above the damper valve rattled, but relatively quietly. This change lasted into 1982. The new valve had a shortened length body and a special tabbed (on upper face) spring washer was used to push…well, force…the valve body against the top recess of the original orifice plate. This change was probably done primarily to eliminate hand-shimming in production. Another modification was to eliminate the original steel washer that controlled the oil flow. Instead a thick Teflon ring was used, which fit tighter and was quieter.Awesome Quality garlock oil seals Exquisite Craftsmanship. The upper face of the valve body was machined to fit the thicker ring, and movement was thereby restricted, between bump and rebound, giving MORE bump damping too.
The final change, shown in the sketch to the left, which I call the Mk.3, came in 1983. The valve mechanism was SHORTENED, and the bottom had a recess containing a spring, same as the rebound spring. This prevented any oscillation. It also improved the fork operation during AGGRESSIVE transitions between bump and rebound conditions. The springs also improve the operation of the hydraulic ‘stop’.
NOTE: Because of how these forks are designed, it is very important that the oil have a very good anti-foaming characteristic.
The over-all damping is dependent upon oil viscosity. Certain characteristics of fork operation are dependent on fork oil level (or, call that fork oil amount). BMW lowered fork oil levels, republishing the specifications. Those who modify the forks for one or another purpose know about these things, and more.Awesome Quality garlock oil seals Exquisite Craftsmanship.
I will BRIEFLY describe how these forks work:
When you hit a bump in the road, the ‘slider’ (fork lowers) go upwards, and oil moves from the lower area inside the fork, through the gap between the piston rod and the valve body. The valve ring pushes against the orifice plate, and oil moves to the upper chamber area by means of the gap under the ring. The gap itself IS THE RESTRICTION.
On REBOUND, the piston descends, and oil is forced against the ring, sealing it to the valve body. The oil path is the small orifice at the upper end of the piston rod, which passes oil MORE SLOWLY than the gap below the ring, thus providing stiffer rebound damping. As the slider descends, the lower chamber becomes larger in volume, and oil comes from inside the piston rod, via the orifice at the LOWER end of the rod.
The gap below the valve ring and the upper piston rod orifice determine the relationship of bump and rebound damping(s).
That article was done by Randy Glass. Lots of images. Highly recommended! This is the GOLD STANDARD for basic motorcycle fork alignment.Awesome Quality garlock oil seals Exquisite Craftsmanship.
Periodically I check this, but, STILL, as of September 26, 2014, the above link will NOT work properly in the various browsers I have checked it on. The problem is, I think, that the article was written using a very old version of Microsoft FrontPage and Arachnophobia. Duane was informed years ago about this. I suggest that you try the following link, which avoids you trying to play with code and settings to TRY to get it to work
You may be intimidated by that article. It IS comprehensive and detailed; but….it is not a difficult job. Randy’s article, which was written as he worked on his BMW Airhead quite some time ago is/was so good that I never wrote one like it myself, I just refer folks to it. I admit to minor contributions to that article. The photos really tell you what you need to know if you wanted to get into it in depth. But, whether you do a complete job like Randy spells out, or not… it is good to know what the proper and best procedures might be. Most will not have forks that are in dire need of the full alignment…but most would be improved considerably. Reading the article will let you know what CAN be done and HOW it is done. You will see as you read the article that some much simpler checks may well be all that you need.Awesome Quality garlock oil seals Exquisite Craftsmanship.
I never did the same thing for the 1981-1984 forks, or the even later forks, both series of which are different internally. In this FIRST section of the following relatively lengthy article, is of a sketch, and description, of how these 1981-1984 forks operate, some information about the modifications the FACTORY did during production to REDUCE NOISES and IMPROVE OPERATION, etc. There were THREE stages of these changes. While the factory never identified these as stages, I, as others have, identify them as Mk1, Mk2, and the final as Mk3. AFTER 1984, many of the forks used MUCH of the Mk3 design. The below photo of a sketch is of the 1981 fork, but with the last version of the factory modifications, which I call Mk3.Awesome Quality garlock oil seals Exquisite Craftsmanship.
The 1981 forks were of a very different design. They also made a lot of clicking and clunking noises. BMW’s first fix was to install SHIMS below the valve body, which did reduce noises. The rebound spring above the damper valve rattled, but relatively quietly. This change lasted into 1982. The new valve had a shortened length body and a special tabbed (on upper face) spring washer was used to push…well, force…the valve body against the top recess of the original orifice plate. This change was probably done primarily to eliminate hand-shimming in production. Another modification was to eliminate the original steel washer that controlled the oil flow. Instead a thick Teflon ring was used, which fit tighter and was quieter.Awesome Quality garlock oil seals Exquisite Craftsmanship. The upper face of the valve body was machined to fit the thicker ring, and movement was thereby restricted, between bump and rebound, giving MORE bump damping too.
The final change, shown in the sketch to the left, which I call the Mk.3, came in 1983. The valve mechanism was SHORTENED, and the bottom had a recess containing a spring, same as the rebound spring. This prevented any oscillation. It also improved the fork operation during AGGRESSIVE transitions between bump and rebound conditions. The springs also improve the operation of the hydraulic ‘stop’.
NOTE: Because of how these forks are designed, it is very important that the oil have a very good anti-foaming characteristic.
The over-all damping is dependent upon oil viscosity. Certain characteristics of fork operation are dependent on fork oil level (or, call that fork oil amount). BMW lowered fork oil levels, republishing the specifications. Those who modify the forks for one or another purpose know about these things, and more.Awesome Quality garlock oil seals Exquisite Craftsmanship.
I will BRIEFLY describe how these forks work:
When you hit a bump in the road, the ‘slider’ (fork lowers) go upwards, and oil moves from the lower area inside the fork, through the gap between the piston rod and the valve body. The valve ring pushes against the orifice plate, and oil moves to the upper chamber area by means of the gap under the ring. The gap itself IS THE RESTRICTION.
On REBOUND, the piston descends, and oil is forced against the ring, sealing it to the valve body. The oil path is the small orifice at the upper end of the piston rod, which passes oil MORE SLOWLY than the gap below the ring, thus providing stiffer rebound damping. As the slider descends, the lower chamber becomes larger in volume, and oil comes from inside the piston rod, via the orifice at the LOWER end of the rod.
The gap below the valve ring and the upper piston rod orifice determine the relationship of bump and rebound damping(s).
That article was done by Randy Glass. Lots of images. Highly recommended! This is the GOLD STANDARD for basic motorcycle fork alignment.Awesome Quality garlock oil seals Exquisite Craftsmanship.
Periodically I check this, but, STILL, as of September 26, 2014, the above link will NOT work properly in the various browsers I have checked it on. The problem is, I think, that the article was written using a very old version of Microsoft FrontPage and Arachnophobia. Duane was informed years ago about this. I suggest that you try the following link, which avoids you trying to play with code and settings to TRY to get it to work
You may be intimidated by that article. It IS comprehensive and detailed; but….it is not a difficult job. Randy’s article, which was written as he worked on his BMW Airhead quite some time ago is/was so good that I never wrote one like it myself, I just refer folks to it. I admit to minor contributions to that article. The photos really tell you what you need to know if you wanted to get into it in depth. But, whether you do a complete job like Randy spells out, or not… it is good to know what the proper and best procedures might be. Most will not have forks that are in dire need of the full alignment…but most would be improved considerably. Reading the article will let you know what CAN be done and HOW it is done. You will see as you read the article that some much simpler checks may well be all that you need.Awesome Quality garlock oil seals Exquisite Craftsmanship.
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