Race Tech Suspension Upgrade on a 1974 BMW R60 /6

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Race Tech shocks (left) and emulator valves (center left, with old damping piston) give a BMW R60/6 suspension new life.
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1. Here’s our project bike before we started. To make life a bit easier we used a motorcycle/ATV jack. The BMW’s engine sits low, so a broad board helps for lifting. It’s easy to balance and very stable on the lift.
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2. With the wheel off and the forks still together, remove the rubber caps at the bottom of the forks. With an oil pan to catch the fork oil, use a 13mm socket to remove the damping rod nuts under the cap.
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3. With the damping rod nuts off, slide the lower fork legs off the fork tubes, then remove the large 36mm nuts holding the forks to the top steering yoke and remove the fork tubes. Here are the fork tubes removed with damper rods attached.
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4. To remove the damping rods, you first have to remove the snap ring at the bottom of the fork leg. It comes out with standard snap ring pliers.
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5. Next, you have to remove two threaded collars and a bushing. Use your snap ring pliers with the bits inserted into the two slots on the threaded collar. Remove the outer collar, followed by the bushing, followed by the inner collar.
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6. Now you can gently pull the damping rod assembly from the bottom of the fork tube. Note the snap ring, collar, bushing and collar (left to right) on the work bench.
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7. Here are the damping rods removed from the fork tubes. Note the upper rod is missing a rubber bushing still in place on the lower unit. It had completely disintegrated with age. We replaced both rubber bushings.
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8. Remove the damping pistons and the check valves. The pistons were stubborn, so we shocked them off with an impact wrench. The check valves came out easily by inserting a small Phillips head screwdriver through an orifice hole to hold the rod while removing the check valves.
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9. Here are all the component parts removed from a damping rod, with the damping piston at left above the rod, followed by the damping piston bushing and spring, and at the other end (minus the rubber bushing) the disassembled check valve assembly. Clean thoroughly.
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10. The top of the damping piston must be removed, as the emulator will replace its orifices for fluid control. This photo shows the piston before cutting, with piston rings removed to avoid damage.
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11. Pat Slimmer at Slimmer’s Auto lent a hand here, using his lathe to cleanly cut the tops of the pistons off. A band saw would work equally well, as would a bit of patience and a hack saw. The metal is quite soft, so it’s a pretty easy cut to make. Here’s a piston with its top cut off.
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12. Race Tech said to enlarge the compression orifices at the bottom of the damping rod to 5/16-inch and to ensure there are four holes total, which the BMW had. Drill the holes, then remove any burrs and lightly chamfer the holes with a small round file. Race Tech now suggests a total of six holes, but at 6mm in size instead of the 5/16-inch (approx. 8mm) originally suggested.
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13. The emulator valve needs a minimum of 5mm clearance between the nut on the bottom of the valve and the hole at the top of the damping piston. A little more doesn’t hurt anything.
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14. Next, cut an adapter to fit between the emulator and piston out of 3/4-inch Schedule 40 PVC plastic pipe. We ended up with a piece just over 1-inch, which is what Race Tech suggests for the BMW conversion.
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15. Now it’s time to start putting it all together. Here’s a cleaned damping rod ready to go back together, but missing the rubber bushing we had to replace and only because we forgot to photograph it.
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16. Install the spring, bushing and damping piston on the top of the rod and the check valve at the bottom. Note the small piston rings have been installed on the piston. They slip on and off with very little effort. We used pliers to hold the piston tight while simultaneously tightening the check valve assembly.
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17. Next, install the damping rod into the fork tube. Our manual said to install from the top, but we found it easier working from the bottom of the fork tube. Line up the gaps in the piston rings first and position the rod for assembly.
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18. To protect the rings from the threads in the fork tube, place a 4mm feeler gauge blade so it covers the ring gaps and a 5mm blade across from it, then gently push the damping rod into the fork tube. It should slide easily. Remove the feeler blades.
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19. Next, slide the rubber bushing on the rod, followed by the threaded collars, bushing and snap ring; install the fork tube into the fork leg. This photo shows the damping rod protruding from the fork leg, and the lower fork leg cap and bumper, which we also removed and cleaned.
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20. Screw the fork leg cap into the bottom of the leg. Ensure the threaded extension of the check valve assembly is centered in the cap. Tighten the cap fully. Screw the nut onto the damping rod extension and tighten it using a 13mm socket and locking pliers, with an allen key holding the rod from spinning.
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21. Our installation required new fork springs (fine by us; we knew the originals were weak), as the stock springs are too long for the conversion. The Race Tech springs are almost six inches shorter, but this is made up for with the addition of the emulator/adapter assembly and a spacer made from 3/4-inch PVC placed on top of the spring.
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22. Race Tech suggests 5/8- to 1-inch of preload, meaning the amount the top nut will compress the spring. We measured the nut from its contact point with the spring to its sealing seat and got 0.825 inches (which was right in the ballpark for our desired preload), then measured from the top of the installed spring (fork fully extended) to the top of the yoke.
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23. Subtracting the first measurement from the second gave us a 3-inch spacer, shown above. Gently drop the emulator spacer/adapter from step 14 into the fork tube, followed by the emulator (coil spring facing up) and then the new spring, and check for any binding. The washer shown sits between the spring and the final PVC spacer.
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24. We then filled the forks with Race Tech’s US3 15wt synthetic fork oil. Race Tech suggests 130mm of vertical air space (forks fully compressed, emulator installed only); we opted for 160mm as we can easily add more oil if necessary. We then loosely installed the forks and dropped the springs back in place.
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25. With the forks fully extended we dropped the steel washers, followed by the 3-inch spacers, into place. Compress the fork slightly and gently push up and down on the spacer to make sure the emulator and adapter have seated properly. We found they dropped right in place. Reinstall the top nuts and washers and tighten securely.
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26. Replacing the rear shocks is a simple nut and bolt affair, but note the left upper bracket; we had to file off a small amount of metal to clear the top of the shock body. We also replaced the shock mounting bolts except for the right lower one, which is a stud in the final drive assembly.
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27. And that’s it! With everything reinstalled and after a final check over, our BMW suspension overhaul was done, leaving us with one of the nicest riding Beemers we’ve ever experienced.

Suspension technology has come a long way since many of our favorite bikes first rolled off the assembly line. And while the basics haven’t really changed — hydraulic front forks and rear shocks — the way those components function has progressed radically.

Beyond adjustable preload on the rear shocks, the bikes of 40 years ago didn’t give you much to work with. Front fork valving was almost universally the tried and true damping rod and piston, which while certainly functional left — and still leaves — much to be desired.

The main limitation is the system’s fixed compression orifices, which control the flow of damping oil under compression. Most are calibrated to give smooth damping under light shock loads, but this usually results in a harsh suspension when larger, more abrupt bumps, which make the fork move faster, are encountered. Any modifications on damping and load control are limited to changing springs, oil viscosity and orifice size, and while a seasoned veteran can affect some good compromises, they end up being just that, compromises, because there’s no way to fully control the flow of oil through the orifices.

Race Tech’s Gold Valve Cartridge Emulator converts a damping rod fork into a cartridge/damping rod hybrid, with compression fluid forced through the emulator, giving controlled flow thanks to the emulator’s load-sensitive, variable flow rate abilities. In a nutshell, the emulator valve responds to the speed of the fork allowing oil to flow as needed to relieve compression, smoothing out the ride. That’s what modern cartridge forks do, most using thin, bendable washers that “give” to the rushing fork oil when the forks hit a bump. Cartridge forks are stiffer when responding to small movements and softer when responding to large, more abrupt movements, the reverse of a damping rod fork.

For this project we enlisted ad man Rod Peterson’s 1974 BMW R60/6. While never considered poor handlers exactly, there’s no denying 1970s BMWs could use a little help in the suspension department, equipped as they are with fairly soft front forks that transition rapidly to stiff action on big bumps and rear shocks that perform only adequately when pressed hard.
In addition to the emulator valves and a pair of Race Tech HP fork springs, we also installed a pair of Race Tech’s excellent G3-S piggyback reservoir shocks. Installing the shocks is easy; remove three bolts and the nut on one stud and swap — other than dialing in final preload and rebound preferences, you’re done. One note of caution: On our bike we had to file the bottom of the left upper shock bracket for clearance.

Installing the emulator valves and new springs takes a bit more time and patience, but it’s easily within the range of most weekend warriors. Take your time, have a good service manual to help you understand how your suspension goes together and, most importantly, read all the literature that comes with the emulator valves, because the questions you’ll have will almost certainly be answered in the supplied paperwork.

It’s definately time well spent, as the change to our BMW’s ride and handling is nothing short of amazing. It’s smoother and more predictable, with better ride control in every way. The front end is firm, with excellent rebound control and minimal dive, while the rear feels planted in a way it never did with its old (and admittedly worn out) shocks.

We’re still dialing in our suspension, but if you log on to MotorcycleClassics.com and search “BMW Suspension” you’ll be able to find updates on our project and riding impressions on the improvements we’ve seen with our Race Tech upgrade. MC

Published on Mar 31, 2010

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