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Rebuilt my Mark V headstock but still had speed control problems - idler sheaves were jamming open at speeds above "P".

See attached PDF. Pulled the headstock apart again and had a closer look at the idler sheaves. Measured 6-8 thousandths diametral slop between bore and shaft which I thought was excessive (?). I think that slop was allowing the sheaves to cock-lock at high speed even when well oiled. Worn out?

Not wanting to buy a new idler sheave assembly, I inserted a piece of .002" stainless shimstock in the sheave bore to take up most of the slop. Has anyone tried this fix?

Also looked closely at the porkchop sector gear teeth and hinge. Teeth were deformed, filed them until they ran smooth enough. (aluminum gear in this application is really a bad idea). Also saw a lot of hinge axial slop. Decided to do the Bill Mayo hinge upgrade using a long #10 screw. The #10 screw took out most of the radial slop, and the shim washers took out the axial slop so now the gears mesh nice and the porkchop has no slop. Thanks Bill.

So with these two fixes, headstock runs fine and speed changes are smooth, but I have not put headstock back in service. I am worried that the shim I stuck in the sheave bore will start shifting around. If anything can go wrong...

Also just noticed - part of the speed control dial is "blocked" so cannot access the higher speeds. See attached PDF. I remember Jacob Anderson warning against going way up in speed (and I never have) but I did not realize there is a physical block on that dial. When was that introduced?

I have a spare (not new) Idler, the Control Sheave measured 0.626" bore with calipers. The shaft actually measure the same with the same calipers. Subjectively, I don't feel any slop. So I agree 6 - 8 thousandths seems excessive. I have not heard of using shim stock for this. I'm also not completely envisioning how this wear (assuming wear?) would occur. The bore on mine is steel, and the only relative movement is sliding on the shaft. I'd share your concern about the shim stock staying put.

Good job on the Bill Mayo upgrade. Your pic answered a question I had about standardization of the unthreaded portion of the screw. Evidently not standardized.

I don't think those are stops on the back of the speed dial. It's more of a detent feel when the speed control goes past those points. I think they've been there a long time, maybe since the "B" headstock was introduced.(?) I don't want to take apart my Greenie to prove it to myself though. The high speed stop is that long setscrew in the speed control. Low speed stop is not adjustable, I think it is just the travel limit of the control sheave.

- David

I'd be concerned about that piece of shim stock working it's way out off the shaft. I don't recall any slop on idler sheaves. I guess 6-8 thousandths is a lot but assuming it is well lubricated I think other problems are more likely to cause a lockup. Poor positioning or movement of the quadrant would put radial pressure on the sheave, or a bent or off-round part like the shaft or the key could also do it.

DLB wrote: ↑Mon Nov 22, 2021 11:02 am I have a spare (not new) Idler, the Control Sheave measured 0.626" bore with calipers. The shaft actually measure the same with the same calipers. Subjectively, I don't feel any slop. So I agree 6 - 8 thousandths seems excessive. I have not heard of using shim stock for this.

- David

Thank you for responding.

The idler shaft/bore is a nominal 5/8" diameter, but of course it needs to be a close clearance fit, certainly no more than .002 diametral (.001 radial clearance all around). It is at high speed when the shaft/bore are at their minimum engagement length where we would see "cock lock" if it is going to happen. Vibration + high speed might cause such wear over time. I have never pushed the speed but after 30+ years of use...

The shim wraps around the whole shaft/bore (but clears the keyway) and being SST it wants to flatten out, causing a spring tension in the bore which resists the shim from being pulled out. A good thing.

Lube won't fix this problem. I did measure more wear on the end of the shaft than further up, which is consistent with the problem. No bore egging was measured. I was surprised when the .002" shim fit in there with room to spare. Just enough to soak up the slop and leave enough clearance.

I'm reading of others who are having speed shift problems, maybe this is the cause and cure.

I am re-installing the headstock later today and will post if the fix fails.

The speed indicator ring was changed from a step stop to a ramp when the A casting was replaced by the B casting. The A casting had an open top above the ring and had a movable pin that could be pressed to allow speed increasing above the stop. The B casting has the 'anti-rattle spring' that provides drag at the stop ramp(not very obvious, but tis there). The control sheave is where wear causes problems. I am surprised that an idler sheave could be so 'sloppy'. I have had very severe wear on the control sheave including keyway and key wear causing vane interference. But then it had almost a half century wear when it was replaced.

I do not think a slipped out of position .002 shim would cause any significant damage to other parts.

JPG wrote: ↑Tue Nov 23, 2021 2:39 am The speed indicator ring was changed from a step stop to a ramp when the A casting was replaced by the B casting. The A casting had an open top above the ring and had a movable pin that could be pressed to allow speed increasing above the stop. The B casting has the 'anti-rattle spring' that provides drag at the stop ramp(not very obvious, but tis there). The control sheave is where wear causes problems. I am surprised that an idler sheave could be so 'sloppy'. I have had very severe wear on the control sheave including keyway and key wear causing vane interference. But then it had almost a half century wear when it was replaced.

I do not think a slipped out of position .002 shim would cause any significant damage to other parts.

I 'interpreted' that the OP was referring to the Control Sheave. Something to watch for, this wear was surprising to me. But once it starts I suppose it gets worse relatively quickly. Same thing for the Floating Sheave, perhaps? I do have one of those with severe wear on the bore, but has not caused any operational issues.

- David

As for the Speed Indicator Ring.

The spring is pushed back as the Speed Indicator Ring goes up into the higher speeds. That action adds a bit more friction as the spring leaves the groove and onto the high range. I would suspect the spring being the problem if it won't go past the high-speed point. The spring seems to be acting as a stop instead of allowing the Speed Indicator Ring to continue past that point.

The "A" Headstock had a lock that required pushing the tab under the power switch to release the lock to go into the higher speeds. The "B" Headstock changed to having the spring to add extra friction going into the higher speeds and continued with the "C" Headstock.

Just now looked at the upgrade pdf. The sheave(not sure if idler or control) has excessive wear of the keyway. That allows misalignment of the sheave vanes which could cause the original jamming problem.

The ring pix appears to be the newer "ramped" version. Anti rattle spring ?????

Yesterday the control sheave fix (I previously called it an "idler" sheave) that I had put in, finally crapped out. The 0.002"stainless shim (that I put into the bore to soak up the excess slop) came out shredded. Couldn't believe how shredded up it was. I had expected the shim to stay put.

How did it fail? I did use some moly grease, and that grease had turned really adhesive and gummy. Maybe that caused the shim to dislodge when the speed control was cycled. Oh well, got about 20 additional hours from it.

Off to Shopsmith to buy a new control sheave assembly. Item 110 on the diagram. I note that they want to sell me a 515556 rather than a 504181. Anyone know what may be the difference?

Another problem. My "spindle assembly" item 62 is made up of a male spline pinned to a shaft (on which the 2x quill bearings are mounted). The spline shows a runout (wobble) when rotated. I have had this (spline and shaft) apart before and cannot find any defects in either spline or shaft - but when pinned together, the wobble shows up. Nothing bent. Pin is tight when installed. I get vibration in the quill and I think it is coming from this. Anyone here encounter this and have a fix? Shopsmith does not want to sell me just the 514066, now it is a 555088 which looks like the whole quill -for an ouchie price.

Control Sheave Assembly, 515556, says it includes the retaining loop and roll pin while 504181 does not, per my book. (504181 is part of 515556.)

I had a problem with a two-piece two-bearing spindle where the hole in the spline part was out of round for the pin. (Worn that way, I presume, though I don't know why there'd be wear.) In that situation the pin was still tight, but only to the other end of the spindle. I drilled both pieces slightly oversize to get round holes of the same diameter: viewtopic.php?p=275945&hilit=two+piece+spindle#p275945 Doesn't sound exactly like your problem but thought I'd mention it. Mine exhibited some radial free-play between the two ends of the spindle, noticeable that the splined end would rotate relative to the bearing end. IIRC my cheapo HF set of numbered drill bits gave me two oversize options before exceeding the hole size for a standard 3/16" roll pin.

- David