XS650 Clutch Worm Actuator experiment & tidbits

[TwoManyXS1Bs]

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.

 

[TwoManyXS1Bs]

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).

 

[TwoManyXS1Bs]

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

 

[TwoManyXS1Bs]

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?

 

[TwoManyXS1Bs]

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.

 

[TwoManyXS1Bs]

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.

 

[TwoManyXS1Bs]

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?

 

[I am Carbon]

That's very cool.
quite a good read.

 

[jd750ace]

Reversing the arm on the shaft should reduce travel losses from negative torsional twist loss. With the arm hanging off the end, it tends to try to bend the unit away from the mounting face. If the center of pressure is off the end of the part, it wants to bend it sideways as it loads. If that pressure is moved inboard, you have effectively reduced the amount of leverage it has to bend things sideways.
It's a lot like flipping a 15 degree offset boxed end over against the "knuckle clearance" when you can, if you are having difficulty staying on the fastener. It places the plane of leverage down to the shank of the fastener instead of off the top of it. Helps a lot when breaking torque in a tight area, in my experience.
Good write up.

 

[peanut]

blimey strewth twomany I thought I was anal lol

thats fantastic bit of work well done. its exactly the sort of thing I get up to every day with the toaster vacuum cleaner sink faucet or whatever . Drives her indoors up the wall.

Can't leave anything alone .

Can I just throw an extra variable into the equation if I may.

I refurbed my worm mech recently and found that whilst it worked perfectly loose or fixed finger tight . As soon as I fully tightened both the screw fixing into the cover , the worm started to sieze up badly . Something is pulling the worm out of alignment and I haven't had time to check what yet.

I thought it might be a useful additional factor to take into consideration as other worm mechanisms are clearly not all created equal lol

Some stiff /poorly operating clutches could be due to the worms being distorted under full fixing torque which might not get noticed if you didn't check before closing the cover

 

[peanut]

That's very cool.
quite a good read.

not a sexy as Minton Mods though eh !

 

[TwoManyXS1Bs]

blimey strewth twomany I thought I was anal lol

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...

 

[TwoManyXS1Bs]

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...

 

[gggGary]

 

[5twins]

I've acquired several of these in my parts scrounging over the last few years. I'm going to have to try some of this on one. I have an early one and I tried it but being so short, it was a very hard lever pull. I didn't run it long at all. I may have at that one as I'll never use it as it is.

Yes, the plastic female part of the worm assembly distorts and binds very easily if you make the two mounting screws too tight. They can't be much past snug really.

 

[TwoManyXS1Bs]

I've acquired several of these in my parts scrounging over the last few years. I'm going to have to try some of this on one. I have an early one and I tried it but being so short, it was a very hard lever pull. I didn't run it long at all. I may have at that one as I'll never use it as it is.

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

 

[5twins]

I never did have that exact one, it's just a pic I pulled off eBay. The short one I do have actually came out of my dealer's boneyard and I'm pretty sure I pulled it from a 500 or 400, maybe even a 360. He has no 650 stuff to speak of back there.

 

[TwoManyXS1Bs]

I never did have that exact one, it's just a pic I pulled off eBay...

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...

 

[peanut]

the basic design isn't necessarily bad as a clutch operating mechanism . its just clear that it is one of the parts that the Yamaha 'bean counters' got to to save a few yen.

It might be interesting to look to see how other bike manufactures have solved this problem of mechanically operating the clutch.

Its a pity but this is would be a difficult part to re-manufacture on a DIY basis in the shed other than small numbers for own use I should have thought.

I threw up a youtube video of my clutch worm mechanism installation back in September . I found that I couldn't even tighten my worm gear fixing screws at all without the arm becoming too stiff to operate. I thought at first it was a hydraulic effect of too much grease but from what 5twins has said it looks like the fixings are distorting the body somehow.

I'll need to find a cure pdq as the bike is nearly ready to use and the worm drive is still only finger tight.
Excuse the hyjack twomany but I thought this problem was sort of relevant and could effect other owners

 

[gggGary]

+1 on this being a poor design all around. I THOUGHT there was an early 3 ramp but have not been able to find one now don't know where that idea came from....

Honda CB350 used two plates with ball bearings and ramps Seems like a more robust, lower friction design. But the Honda twins forums have guys pulling their hair out getting the CB clutches adjusted right also. One downside is if the cable is too tight it pulls the balls beyond the ramps, and there you sit with no clutch!





Maybe I'm extra lucky, but really I have not had a "bad" XS clutch yet???? The problems I have found have resolved by cleaning and replacing defective parts, cables seem to be the sneakiest with rusted and or broken strands inside the cable and "funny" routing they seem OK until there is real pull on them then they bind up and cause heavy clutch pull effort..... Motion Pro cable, correct routing, problem solved.