Rear shock mod tips

CBR 600 RR converted shock to fit an R arm in a Tillis.

This has been done for 10 years now. I've compiled everything I can find in those threads. Here it is:

Showa Rear Shock Mod
This procedure is about replacing the stock TL1000R rear shock with a better shock. The stock shock pictured uses a rotary damper for compression and rebound dampening. The assembly works poorly and weighs 14lbs with the spring assembly. A new Ohlins or Bitubo shock costs $1500. This substitute can be made for about $200. This modification only works for the TL1000R. Not the TL1000S.

Showa Shocks that work
MAL-601 - Most popular for this job. 11" long - 46mm pistonOD - 49mm BodyOD - 95-96 Honda CBR600 F3
MAL-621 - Similar to the 601 - 11" long - 46mm piston OD - 49mm BodyOD
MAL-G01 - 11.5" long - 43mm OD - 40mm BodyOD - less damping range adjustment

These are the only shocks readily available that were found to work because of their length. The click stop adjuster on the bottom of the Showa shock moves the spring .050" per step which is 50 lbs of spring preload. Therefore, 5 steps is 250 lbs at 1/4".

Remove the silliness they call a rotary damper and the spring. Next is the frame cutting and grinding. There are 2 tabs that need to be ground away to make the Showa shock fit. THIS WILL BE A PERMANENT MODIFICATION. IT WILL REQUIRE WELDING TO EVER GET THOSE 2 TABS BACK. See picture on what needs to be cut away. You will have to cut deeper than the original tab mounting surface to get enough clearance for the new HyperCoil spring.

THIS IS A PERMANENT STEP. NO TURNING BACK!

Next, drill out the lower shock mount bushing from 10mm to 12mm. The stock bushing is 10mm ID x 17mm OD x 39mm. It is hardened steel (Rockwell 40), so you will need to bore it out with a carbide bit. Drilling does not work. A bearing with a 12mm ID was sought at a bearing supply house, but was not found.

You'll need a HyperCoil rear spring ($80 on Ebay) that measures 6" tall and 2.25" ID with a weight rating of 1100 lbs for a 160-200lb rider. Use an 1150lb spring if you weigh over 200lbs. You could use the existing spring that comes on a Showa MAL-601 but it is too soft with an 800lb rating. You might think to ratched the pre-load adjuster all the way up and leave the stock upper spring perch in place to increase the rating of the 800lb spring, however, the spring rate is too hyperbolic and bottoms out too fast. This blue spring are also for sale at www.hrpworld.com with a brand name of HyperCoil.

You’ll need motorcycle spring compressors to remove and install coil-over springs. I paid $33 for one on Ebay. Spring compressors for a car have fingers that are too fat and won’t fit within the spring. Others have tried using ratcheting cycle-straps too, however, a short spring with a high weight-rating will not move enough using cycle-straps.

Next, the bottom spring seat of the shock can be used as is OR you may need to grind the top-half of the stopper blocks away to get the bottom seat to sit lower than it is originally. The 2 tabs are spot-welded on on both ends.

Again, the click-stop preload adjuster on the bottom of the Showa shock moves the spring .050" per step which is 50 lbs of spring preload.
The upper spring seat may not go high enough so you need a part machined to replace the original Showa seat with one that goes 1/4" higher. I've seen it made from steel, however, aluminum works too which would be less expensive and be lighter.

Others have used these shock settings
1/4 turn out from bottom for compression.
1/2 turn out from bottom for rebound.