Race Tech Suspension Upgrade on a 1974 BMW R60 /6

Modern performance with Race Tech cartridge emulators and shocks

| May/June 2010

  • Race Tech shocks (left) and emulator valves (center left, with old damping piston) give a BMW R60/6 suspension new life.
    Photo courtesy Race Tech
  • 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.
    Photo by Landon Hall
  • 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.
    Photo by Landon Hall
  • 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.
    Photo by Landon Hall
  • 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.
    Photo by Landon Hall
  • 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.
    Photo by Landon Hall
  • 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.
    Photo by Landon Hall
  • 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.
    Photo by Landon Hall
  • 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.
    Photo by Landon Hall
  • 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.
    Photo by Landon Hall
  • 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.
    Photo by Landon Hall
  • 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.
    Photo by Landon Hall
  • 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.
    Photo by Landon Hall
  • 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.
    Photo by Landon Hall
  • 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.
    Photo by Landon Hall
  • 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.
    Photo by Landon Hall
  • 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.
    Photo by Landon Hall
  • 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.
    Photo by Landon Hall
  • 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.
    Photo by Landon Hall
  • 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.
    Photo by Landon Hall
  • 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.
    Photo by Landon Hall
  • 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.
    Photo by Landon Hall
  • 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.
    Photo by Landon Hall
  • 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.
    Photo by Landon Hall
  • 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.
    Photo by Landon Hall
  • 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.
    Photo by Landon Hall
  • 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.
    Photo by Landon Hall
  • 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.
    Photo by Landon Hall

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.

Richard Backus
5/7/2010 8:41:05 AM

Larry, apologies for the no-show on the update, we've found ourselves in the obnoxious position of not having the opportunity to get in some good road time. Our overall impressions from about 100 miles of riding are of a totally transformed machine. We're thinking about reducing the preload on the front forks just a tad to make it a bit more compliant for city riding, and we need to play with the rear shock rebound adjustment to soften it up just a bit. If we were really pounding the pavement it’d be about right as it is. But this bike's not a racer, so we want to tune the suspension to be just a tad more comfortable. That said, the improvement in suspension control is fabulous. No more mushy front end on stopping, no pogo-ing running over irregular road surfaces. The result is greatly improved control, which means a safer, more predictable ride. It's lovely. Richard/Motorcycle Classics


Larry Lahickey_1
4/28/2010 11:58:33 AM

I've checked several times and I don't find an update to the BMW Suspension upgrade article concerning riding impression etc as the article states. Your article was timely since I had just purchased the same fork kit for my R100/7 and have just begun installation. Also, in response to the comments above concerning the rear shocks interfering with saddlebags on the '70's BMW's, I've checked the relationship of the saddlebag mounts to the rear of the stock shock and it appears a shock with a piggy back reservoir will not fit. The reservoir needs more space than the approx 2.5" (from memory) that is separating the shock and the saddlebag mount. Otherwise, the Race Tech shock would fit ok with saddlebags. I haven't checked but maybe they make the same shock without a reservoir. I'm looking forward to your riding impressions and any other comments concerning the project.


Richard Backus
4/20/2010 9:04:30 AM

I can't see how it would create any problems. The Race Tech shocks shouldn't stick out to the side any more than the stock units. I'd think that'd be the only concern, but I don't know if the reservoir sticking off the back of the shock would interere with your bags? Richard/Motorcycle Classics




The sound and the fury: celebrate the machines that changed the world!

Motorcycle Classics JulAug 16Motorcycle Classics is America's premier magazine for collectors and enthusiasts, dreamers and restorers, newcomers and life long motorheads who love the sound and the beauty of classic bikes. Every issue  delivers exciting and evocative articles and photographs of the most brilliant, unusual and popular motorcycles ever made!

Save Even More Money with our RALLY-RATE plan!

Pay now with a credit card and take advantage of our RALLY-RATE automatic renewal savings plan. You save an additional $4.95 and get 6 issues of Motorcycle Classics for only $24.95 (USA only).

Or, Bill Me Later and I'll pay just $29.95 for a one year subscription!




Facebook Pinterest Instagram YouTube Twitter

Free Product Information Classifieds