XS650 Clutch Worm Actuator experiment & tidbits

I've always had a love/hate thing for the XS clutch worm. My stock XS1B has a factory clutch worm in excellent shape, replaced 16 years ago, kept clean, lubed and adjusted. The clutch cable is also factory, in excellent shape, cleaned and lubed. Clutch action is fine (2-finger for me), but could be better. For a long time I suspected a possible engineering flaw, and after reading about all the clutch problems and improved performance gained by switching over to hydraulic, decided to experiment to prove a theory.

Took a junk clutch worm (pic #1), disassembled (pic #2), cleaned and inspected. There was a small crack starting on one side, but was still functional. Forgot to take a pic, but ended up looking like pic #3.

 

Then took the clutch worm and clamped it in the vise (pic #1). Notice how the actuator arm is offset to the left (pic #2).

 

A little heat from a torch plus 'percussive persuasion' moves the actuator arm to the right about 0.4"-.05"

 

Please ignore the bent grease shield housing, that was straightened later.

The idea was to offset the actuator arm so that it would end up 0.4" above the base mount surface level. Still plenty of clearance to the case cover webbing, could actually go lower, but this will work.

Notice how this puts the torque force more in-line with the nylon worm housing, and reduces the 'tip-over' effect of having the cable tension above the worm housing. Think about using a ratchet wrench, with a too-long extension and no upper support. Anybody crack a sparkplug using a too-long ratchet extension, and no room to hold the ratchet wrench steady?

 

To keep the experiment on apples-to-apples comparison, a second hole was drilled 1.3" from the rotational centerline, same as the original XS1B worm.
Forgot to take a pic, but looks like retiredgentleman's mod here.

 

This pic provided by gggGary, shows what my original XS1B cover/worm setup looks like. The important part was to ensure that the cable-attach pivot pin is at a specific full-forward-stop location, both to guarantee equality in the two configurations, and to achieve the best leverage in operation.

Measuring from the cable hole edge in the cover, to the center of the cable attach pivot, in full forward/relaxed position, both clutch worm arms were set at 4.3". At this position, as the clutch cable is pulled, when 1/2" is traveled, to the 3.8" distance, the worm lever arm is perpendicular to the cable, the highest leverage advantage point. Total cable travel is 0.65", on this stock setup.

 

The clutch cable is stock, with the normal bent entryway tube (pic #1).

Tests were done on both configurations. To recap, both configurations are identical with the exception of the modified lever arm, working in a worn/cracked worm housing. Lever pull tests were done at the lever end, 6" from the lever pivot. Actuator plunge measurements were taken with a depth guage on the side cover housing and worm outer edge.

Stock: Pull-test = 26 lbs, Actuator travel = 0.065"
Modd: Pull-test = 18 lbs, Actuator travel = 0.070"

The clutch lever pivot to cable end distance is 1", giving a 6:1 leverage to the cable (at this measurement point), which gives cable tensions of:

Stock = 156 lbs
Modd = 108 lbs

I measured the torque required to rotate the clutch worm, without clutch lever input, by measuring torque at the (tightened) adjuster nut. Both setups required 7 ft-lbs (old/weak clutch springs, but still apples-to-apples). To get this 7 ft-lbs torque, on a 1.3" lever arm, would require (in a frictionless environment) a cable tension of 65 lbs. We'll just call the excessive tension: The 'heavily-taxed overhead' of the contraption, and is:

Stock: 156 lbs - 65 lbs = 91 lbs overhead, 150% of needed force
Modd: 108 lbs - 65 lbs = 43 lbs overhead, 66% of needed force

If this were a frictionless environment, the clutch lever force (at 6") would be about 10.5 lbs.

Other fun facts:
- The clutch worm is a 4-start thread of 8mm pitch, giving total pitch of 32mm (1.26") per turn.
- This works out to .09mm (.0035") of worm travel per degree of rotation
- At 0.65" of cable travel, the early short-arm worm should produce 3mm travel, later long-arm version (1.8" to cable attach pivot) should get 2mm
- Actual worm travel achieved here was about 1.7mm, enuff to work, but very short of expected
- To install the worm, place the lever arm at the 3 o'clock position, then CCW to 7 o'clock position.

Some members have reported excellent clutch action using the new, black, harder composition worm bodies available from MikesXS. I wonder if this experiment would show any improvement on these?

 

Hahaha, yeah, it's nice to know the disease isn't rare!

JD750 - Yes, the flip-over of the angled box-end wrench is an excellent example!

This has been bugging me for over 35 years. Everytime I see a pic of a clutch worm, with that offset lever, the hackles on the back of my neck stand up. Willing to bet that this was the result of some early engineering-manufacturing miscommunication, and it's propagated to this day. Amazing...

 

When new, the early clutch worm looks like pic #1 (thanx, 5Twins). The only difference I've seen, so far, between different types is the lever arm.

Just for fun, took another junk clutch worm, and dremel-ground off the 3 tack welds on the lever arm (pic #2).

Then pressed-out the worm from the lever/cover (pic #3), ended up with pic #4.

You can see that the seal/cover is just thin metal, somewhat delicate...

 

Hey, 5Twins! Do you still have this one? (One of my favorite pics) Could be a VERY hard pull...

 

Interesting! Look at the thread angle, and the arm & springhole orientation. Works backwards, wondered if it's a photoshop joke, with a 447 number and 3-start thread...

gggGary commented on 3-thread worms 2-4 years ago, but never seen this on early XS's. Wonder if it's real, but mismarked for a different bike...