XS650 Clutch cable experiments and tidbits

[TwoManyXS1Bs]

Grading/Scoring

To help make sense out of the raw data, we'll use a scoring scheme, same as what was used on the clutch worm experiments. The score is mills-per-pound (shown as 'Sc' in the below reports). A higher number is better, it reflects a more efficient transfer of energy.

1 - 650Central EZ-Pull cable, 2.5mm (0.100") core diameter, no elbow.
2 - Motion Pro 05-0013, 2.5mm (0.100") core diameter , 12° elbow
3 - My old cable (16 yrs old, from Yamaha, similar to Motion Pro), 2.5mm (0.100") core diameter , 18° elbow
4 - MikesXS 51-6502 (KSI 3L1-26335-00), acquired several years ago, 2mm (0.080") core diameter , 20° elbow
5 - Yamaha 447-26335-00, 2mm (0.080") core diameter , 30° elbow

Straight/unrouted cables:
-- <30 lbs spring preload> | <40 lbs spring preload> | <60 lbs spring preload>
# - <Pull> - <Force> - <Sc> | <Pull> - <Force> - <Sc> | <Pull> - <Force> - <Sc>
1 - 0.405" - 10.5 lbs - 38.6 | 0.375" - 12.5 lbs - 30.0 | 0.355" - 16.5 lbs - 21.5
2 - 0.475" - 12.5 lbs - 38.0 | 0.455" - 15.5 lbs - 29.4 | 0.435" - 19.0 lbs - 22.9
3 - 0.485" - 13.0 lbs - 37.3 | 0.465" - 15.5 lbs - 30.0 | 0.435" - 20.0 lbs - 21.8
4 - 0.425" - 12.0 lbs - 35.4 | 0.420" - 15.0 lbs - 28.0 | 0.405" - 20.0 lbs - 20.3
5 - 0.445" - 12.5 lbs - 35.6 | 0.425" - 16.5 lbs - 25.8 | 0.415" - 19.5 lbs - 21.3

Cables routed on the bike:
-- <30 lbs spring preload> | <40 lbs spring preload>
# - <Pull> - <Force> - <Sc> | <Pull> - <Force> - <Sc>
1 - 0.355" - 13.0 lbs - 27.3 | 0.330" - 16.0 lbs - 20.6
2 - 0.450" - 15.5 lbs - 29.0 | 0.415" - 18.0 lbs - 23.0
3 - 0.425" - 14.0 lbs - 30.4 | 0.405" - 17.0 lbs - 23.8
4 - 0.415" - 14.0 lbs - 29.6 | 0.375" - 16.0 lbs - 23.4
5 - 0.420" - 14.0 lbs - 30.0 | 0.385" - 15.0 lbs - 25.7

For the straight/unrouted cables, you can see a pattern where the 0.100" cables score slightly higher than the 0.080" cables. They also have less bend in the elbow, which probably contributes to this.

For the routed cables (more realistic), the pattern changes. The 0.080" cables score similar to the 0.100" cables. Cable #1's score is strangely lower.

However, what I believe is the most important cable ranking measurement is the overall 'pull travel' in the routed (realistic) configuration. In this ranking, cable #2 is the leader, and will be used as my replacement cable.

The actual travel of the cable barrel fitting in the clutch lever is 0.600". The most that could be expected from cable #2 will be less than 0.500". With this in mind, the comments on the ideal worm arm clevis hole position (expecting 0.600" travel, as noted in the worm actuator experiment thread) can be ignored since the worm arm will not experience any significant overtravel with stock cable free length.

 

[TwoManyXS1Bs]

Shortening and modifying a Motion Pro clutch cable for a 1971 XS1B

As a result of the cable testing, selected the Motion Pro 05-0013, 2.5mm (0.100") core diameter , 12° elbow, clutch cable.

This cable is about 2" too long for a comfortable fit on this early XS. Plus, I needed an excuse to replace the potmetal cable barrel (the part that fits into the clutch lever) with a polished stainless barrel that is better fitted to the opening in the clutch lever. Was considering doing the split nylon bushing barrel style, as on the other cables, but lazyness prevailed.

This cable shortening process is old news for the experienced hats here. Just thought that a detailed procedure may be helpful for those who have never done this.

Pic #1 - Wrap some tape around the cable core to prevent unstranding. Mark the cutoff spot. Carefully cut with a Dremel cutoff wheel.

Pic #2 - Dress the end, remove sharp corners. Withdraw from cable sheath (outer housing).

Pic #3 - Measure and mark the sheath cutoff point. Dremel cut the sheath only a little at a time, giving it time to cool between cuts. If the sheath gets too hot, it will melt/burn the nylon inner sheath, and possibly ruin the project.

Pic #4 - Save the cutoff part, you'll need the trim endpiece.

Pic #5 - Square-up and chamfer/bevel the sheath end. Again, go slowly, a little at a time, to avoid overheating.

Pic #6 - Clear the nylon inner sheath. For a 0.100" cable, start with a sharp/new 0.100" drillbit, slowly cutting using only your fingers. Could also use an X-acto knife to clear and chamfer the hole. Work your way up to about a 0.110" drillbit. Test for smooth clearance by using the 0.100" drillbit or the remnant stub of the cutoff cable core.

 

[TwoManyXS1Bs]

Removing and reinstalling the trim end.

Pic #1 - The trim end is factory crimped. To loosen, lay it on a solid flat surface and gently tap on it with a small hammer while slowly rotating it. You're trying to make it rounder, by flattening the crimps. Doesn't have to be perfect, just enough to release its tight grip. Then clamp it in a vise with the end just above the vice jaws.

Pic #2 - Using two screwdrivers, carefully work it up and off the sheath.

Pic #3 - Trim endpiece removed.

Pic #4 - Select a drillbit that just snugly fits the endpiece, and clamp it tightly in a vise. This particular endpiece was dimpled as well as crimped. Gently tap the sides flatter with a small hammer. As it opens up, use a larger drillbit.

Pic #5 - Test fit the endpiece. Doesn't have to be perfect, but you want a press fit.

Pic #6 - Endpiece press-fitted to the cable sheath

 

[TwoManyXS1Bs]

Fitting the barrel end.

Pic #1 - The stock barrel end is a cylindrical solder/potmetal blob that is 8mm diameter, 10mm long. Barrel ends made from brass are commercially available, and easily accept soldering. For this cable project, I wanted a round, closer fitted and polished stainless steel barrel that will be mig welded to the cable. This new barrel is 8.1mm diameter, 11mm long, a much better fit to the clutch lever cable pocket. The cable hole is 0.099" for a snug fit, and the weld pocket was drilled 0.190" about halfway through.

Pic #2 - The cable is reassembled and the barrel is fitted. I wanted a slightly longer freelength, about 5.40" versus the stock 5.25"-5.35". So, the freelength is measured, and cable fine-trimmed until this freelength and appropriate recess into the weld pocket are achieved.

Pic #3 & #4 - Finished barrel end after mig welding, grinding and polishing.

 

[TwoManyXS1Bs]

The new, modified clutch cable.

Pic #1 - The cable freelength is now 5.40", slightly longer than the stock 5.25"-5.35".

Pic #2 - As fitted and routed on the bike, and into the sidecover, with clutch lever adjuster screwed fully in, the worm arm clevis hole is at the 4.15" position.

The clevis hole will be perpendicular to the worm center at the 3.7" position, the max leverage position. Expecting about 0.45" of cable travel, the clevis hole should sweep in the 3.70" to 4.15" region. We'll find out...

 

[TwoManyXS1Bs]

Tested this new cable on configuration #9.

Wow, the pull force really dropped! Only 10.5 pounds, really feeling light.
But, the worm actuator travel dropped quite a bit. Only 0.050" of travel.
Wasn't expecting that. Something's wrong here. There's not enough load here to cause that amount of excessive cable stretch.

Clutch lever pull and actuator plunge distances of the 'ultimate' clutch worm, old versus new cable:
(from the clutch worm actuator experiments)

Configuration #9 - Ultimate worm, 1.65" clevis hole distance, modified cable/elbow entry angle, original/old cable
Configuration #A - Configuration #9, New/modified Motion Pro cable

#9: Pull-test = 14.0 lbs, Actuator travel = 0.058", Cable tension = 84 lbs
#A: Pull-test = 10.5 lbs, Actuator travel = 0.050", Cable tension = 63 lbs

Score value is mills per pound:

# Score Travel Pull - Description
#9: 4.1 0.058" 14.0 - Ultimate XS worm, 1.65" clevis hole distance, mod cable entry angle
#A: 4.8 0.050" 10.5 - Configuration #9, New/modified Motion Pro cable

The score value jumped up, that's great, but would prefer to not use any configuration that didn't produce at least 0.050" of travel.

In the pull tests, the new cable demonstrated equal if not better pull distances compared to the old cable. But, as installed, about 0.060" of cable motion is getting lost somewhere. Nothing else has changed except for the new cable. This is a bit of a mystery. Was considering welding/moving the worm clevis hole in to 1.5" to get more travel, a viable solution, but it doesn't reveal this mysterious loss of travel. By all rights, as expected from the pull tests, the worm actuator travel should have increased just a little.

Continuing the experiments...

 

[TwoManyXS1Bs]

Well, this little experiment/project has grown by leaps and bounds. I have 5 cables, 2 worm bodies, 3 worm actuators, a MikesXS worm unit, and 4 different types of pushrods. Been working and recording measurements on numerous, various combinations of these (*gasp*), simply trying to isolate the mysterious loss-of-cable travel, doing the normal mechanic's method of swap-out, and try and try again.

The mysterious loss of travel remains. The data collected is too enormous to post here, but analysis has revealed some insight that I think can be shared here, in a somewhat rambling format.

Initially, cable stretch was assumed to be a combination of core stretch, sheath compression, and liner crushing. Turns out, there's a fourth factor, core cable stiffness, and its reluctance to contour with the sheath. Eventually, the cable will take a 'set', and the core will develop bends that better follow the sheath contours. But this bending stiffness remains, even more so with the thicker 0.100" cables, and it takes a considerable force to get the core to straighten after a turn.

To confirm this, did a simple experiment to remove some unwanted curvature and eliminate the potential slack take-up there.

Pic #1 - Notice how the cable exits the elbow at a lesser angle than the elbow. This part of the cable will span across about 4" to the clutch worm arm clevis hole, arcing across the entire distance.

As an example, if this arc deviates 0.3" from the straight-line path, then by comparing an arc segment to its chord, it will take about 0.060" of cable travel just to straighten it out. And the amount of cable tension required to do this straightening will be quite significant.

 

[TwoManyXS1Bs]

Pics #1 & #2 - So, I made and attached a plastic cable guide that forces the cable to 'straight-shoot' to the clevis pin, eliminating much of the curving arc.

(Don't recommend ya'll do this, it's just part of the experiments.)

Sure enough, slack take-up reduced a little, pull force remained the same, and the worm travel went up about 0.003". Not as much as I hoped, but it confirmed this phenomenom.

 

[TwoManyXS1Bs]

The routing of Dogbunny's clutch cable was very revealing. His cable has basically only 2 large swooping curves, first exiting the pullback handlebar lever perch, swooping forward and down, then at the rear, gently swooping down to the sidecover. Basically a large S-curve. This setup gives excellent cable and worm travel, and low pull forces.

With only 2 large curves, a stiff core doesn't fight the routing, easily follows the sheath curvature.

Routing on my stock XS1B involves more and tighter curves (about 5). For every curve entry and exit, the cable naturally exits at a deviating arc, and each of these must straighten before true cable travel occurs.

In some of the tests, the smaller 0.080" cables demonstrated equal if not better travel values, demonstrating their ability to tolerate many tighter curves better than the larger/stiffer cables.

I just don't remember dealing with this much excess slack with the cables of 40 years ago. However, I did read of the new low-friction cable designs, using more cable/sheath clearance, and possibly a differerent liner material. The liner on my new cable DID feel softer (as I was trimming it) than I remember. Interestingly, there's banter on other web forums of similar clutch cable problems.

And, larger clearances mean more room for the core to arc away from true straight. Imagine if the sheath was a piece of 1/2" tubing. It would take a lot of cable pull travel to tightly follow the contours and get rid of this slack.

The amount of cable tension to remove this type of slack is substantial, and the efforts to improve the worm mechanical efficiency are causing this 'slack' phenomenom to rise to the top and become a significant player. As the worm force demands drop, the cable 'slack' become more like a spring, taking up precious cable travel.

Since the clutch worm is simply a screw with no real stop positions, not like the 3-ball actuators on other bikes, adjusting-out this slack simply puts the load on the worm, and onto the pushrod. My clutch setup currently has a 50:1 mechanical advantage ratio (6:1 at the lever, 8.3:1 at the worm). A 1" movement at the lever should yield 0.020" travel of the pushrod. A 1 pound force at the lever, ideally yields 50 pounds force on the pushrod.

When I have the clutch setup properly, any worm/pushrod adjuster clearance that may have initially been there is completely gone. I read about 2-3 pounds of lever force just to get through the inital slack zone. Simply subtracting 1 pound for the worm arm return spring, still leaves 1-2 pounds, which translates to 50-100 reactive pounds being applied to the pushrod. It's like 'riding the clutch'.

Thinking about that, maybe that's why there's been far too many reports of clutch slipping than we had long ago.

Rambling mode off.

Experiments continuing...

 

[TwoManyXS1Bs]

Status update.

Riding around during our temporary reprieve of winter weather, hoping to break-in this new cable.

Pull force still at 10.5 pounds, but clutch worm travel has risen to 0.054".

Updated Score values, mills per pound:

# Score Travel Pull - Description
#9: 4.1 0.058" 14.0 - Ultimate XS worm, 1.65" clevis hole distance, mod cable entry angle.
#A: 5.1 0.054" 10.5 - Configuration #9, New/modified Motion Pro cable, settling-in.

The score value nudged up a little to 5.1.

I was hoping for this, expecting that the cable would settle-in and start conforming to its routing curves.

Video of clutch lever action:

Also, running the new pushrod made from 304 stainless. The heat-up expansion is less now, requires 1 turn of the handlebar adjuster to return to original clutch action.

Continuing the experiment.

 

[yamimoto]

Status update.

Riding around during our temporary reprieve of winter weather, hoping to break-in this new cable.

Pull force still at 10.5 pounds, but clutch worm travel has risen to 0.054".

Updated Score values, mills per pound:

# Score Travel Pull - Description
#9: 4.1 0.058" 14.0 - Ultimate XS worm, 1.65" clevis hole distance, mod cable entry angle.
#A: 5.1 0.054" 10.5 - Configuration #9, New/modified Motion Pro cable, settling-in.

The score value nudged up a little to 5.1.

I was hoping for this, expecting that the cable would settle-in and start conforming to its routing curves.

Video of clutch lever action:

Also, running the new pushrod made from 304 stainless. The heat-up expansion is less now, requires 1 turn of the handlebar adjuster to return to original clutch action.

Continuing the experiment.

Very informative, helpful and interesting review. Thank you for all your work and posting it.
Yamimoto

 

[yamahammer]

You sir, are a fanatic. Great write-up.

 

[TwoManyXS1Bs]

Thanx, yamimoto and yamahammer! Yep, fanatic, OCD, and a touch of cabin fever.
This clutch thing has been buggin' me for 40 years...

 

[yamimoto]

Thanx, yamimoto and yamahammer! Yep, fanatic, OCD, and a touch of cabin fever.
This clutch thing has been buggin' me for 40 years...

If there's a test on this topic anytime soon I'm going to need more time to study the results.
Yamimoto

 

[TwoManyXS1Bs]

After fixing the front brake cable dust cover, (rubber bellows, pic #1), it dawned on me that a similar protective cover needs to be used on the clutch cable. The area around the sprocket is quite grimy, and that filth will work itself up the exposed cable, get into the cable elbow, and lead to severe cable drag. While I had the cover off, checked the cable in this elbow area, and dark grime is already appearing in there, after only 200 miles on the new/clean cable.

Pic #2 - An ideal cable cover would be about 3.5" long, hold pressure to the cable entry hole (to keep it sealed), and compress enough to allow the cable to be attached to the worm arm. Rubber bellows type dust covers are near impossible to find, unless you want to pay $20 for some BMW or such NOS item, and modify/lengthen it. A potential candidate is available at a UK custom car parts website for $2. Maybe our UK members would like to look into this.

http://www.carbuildersolutions.com/uk/rubber-cable-cover-bellow

Pic #3 - So, here's an alternate/experimental solution. Found a drinking straw of an appropriate diameter and glued it into the cable entry/exit hole. Cleaned and lubed the cable in the elbow area. We'll see how this gismo works...

 

[AtoXS]

I'm going to save this for reference later.

 

[vsop-dk]

Impressive, ill second the R&D Department statement TwoManyXS1Bs thats really impressive reading.

What lever is that in the youtube video, would like one of those.?

Status update.

Riding around during our temporary reprieve of winter weather, hoping to break-in this new cable.

Pull force still at 10.5 pounds, but clutch worm travel has risen to 0.054".

Updated Score values, mills per pound:

# Score Travel Pull - Description
#9: 4.1 0.058" 14.0 - Ultimate XS worm, 1.65" clevis hole distance, mod cable entry angle.
#A: 5.1 0.054" 10.5 - Configuration #9, New/modified Motion Pro cable, settling-in.

The score value nudged up a little to 5.1.

I was hoping for this, expecting that the cable would settle-in and start conforming to its routing curves.

Video of clutch lever action:

Also, running the new pushrod made from 304 stainless. The heat-up expansion is less now, requires 1 turn of the handlebar adjuster to return to original clutch action.

Continuing the experiment.

 

[TwoManyXS1Bs]

...What lever is that in the youtube video, would like one of those.?

Hey, vsop-dk. This thread has a little more on that lever:

http://www.xs650.com/forum/showthread.php?t=27152

And, amazingly, the lever set is still available on eBay. Note that this is for the hard-to-find 70-71 levers, but the vendor may have other sets. The clutch lever, however, should fit most of the later models.

Item: 650 Yamaha 70 71 1970 1971 XS1 XS1B Coated Lever Set NEW Clutch & Brake Levers

URL: http://pages.ebay.com/motors/link/?nav=item.view&id=300879166388&alt=web

Alt URL: http://www.ebay.com/itm/650-Yamaha-...ver-Set-NEW-Clutch-Brake-Levers-/300879166388

 

[vsop-dk]

Sweet, thanks for the links.. ill have a look at it.. allso where is that adjuster screw for the cable? im allso looking at this.. thats NOS and full lever incl Mount etc.

NOS Parts

 

[TwoManyXS1Bs]

.. allso where is that adjuster screw for the cable?

Is the adjuster you're looking for like the one in post #31 in this fun thread?

http://www.xs650.com/forum/showthread.php?t=26406