robalong

I've bought several Sturmey Archer 3-speed hubs made in England back in the day with a view to refurbishing them. One had a couple of pawls that, though clean enough, didn't spring back up very well, so I ordered and bought the circular spring and the two pawls. I later browsed around for information on drive pawls, and didn't find anything that went into the topic in any real depth. What follows is my 'deep view', so far.

A driver pawl has several points of contact with other parts. A perfect pawl system would reveal no undue friction in the pawl's movement (no 'scrapiness' as it moves through its range), and no reluctance to return to the fully-expanded position when released after compression.

These points of contact are:

That where the rounded heel of the pawl sits in the rounded recess in the driver housing. This can be called the pawl 'seat'

Those where the spring sits between the split (the 'fork', if you like) in the pawl and on the pawl seat

The points of contact between the ends of the pawl fork and the hub's internal ratchet ring

The first two are dynamic, and the third (for practical discussion) is static. When the pawl is under load, it does not move.

I held the complete driver unit in my hands and pressed down on each pawl in turn. There was a noticeable 'scratchiness' when one of them was compressed. The other showed no signs of undue friction. Both sprang up nicely when released. But I am not satisfied. There is a detectable mismatch in their properties.

It's probably worth mentioning that the driver unit has functioned well for possibly thousands of cycling miles, and might go on functioning well for thousands more in its present state. However, I am trying to figure out each and every intricacy of these hubs, so I continue my investigation.

I have the initial issue to deal with. Why is one pawl kinda crunchy as it moves through its range? Perhaps the spring is dirty or corroded or both, and is rubbing against the internal faces of the pawl fork, which might also be dirty and corroded. If this were in fact the case, it is not bad enough to prevent the pawl in question springing back up when released. In this respect, the system works. But...for how long?

To cut to the chase, the problem seems to be the point at which the pawl seat rocks in the mating recess in the housing. How did I come to this point of view? Simple. I have a magnifier of the type used by those who repair watches. When viewed with this, the offending pawl seat and its mating recess are seen to be seriously scored. A feel with a fingertip or the scraping of a fingernail over the surfaces reveals nothing. An unaided visual inspection might fool one into believing that all is well.

The scoring, I conclude, has been caused by the massive pressures imposed on the parts over many years. Perhaps the system had been run when dry, or oiled but with bits of grit and/or metallic swarf between the pawl seat and its mating recess.

I have to decide whether I can trust the driver unit, in its present form when oiled, to last. To help me towards this goal, I will set this hub aside and begin inspection of the next hub. Hopefully, after having inspected the eight or nine hubs I have, I will be in a better position to reach a valid conclusion.

I'll post some pix soon, magnified to show the horrendous extent of the otherwise invisible scoring. It can be felt and heard, though, as my fingertip presses down on the pawl. The issue will not improve over time, obviously. The scrapiness would probably be reduced when oiled, but that's not the point. The sudden disintegration of a driver pawl could unbalance the rider and lead to extremely undesirable consequences. Replacing the pawl would solve nothing unless it sat on a new driver housing.

How much punishment can these parts take before scrapping becomes the only viable option? I'm starting to think that a new driver unit is the best way forward in all cases, even if the existing unit functions correctly.

Conclusion:

Magnification is essential in determining the condition of driver pawl seats and the mating surfaces of the driver housing. The hub's ratchet ring and other pawls in the hub will be examined later.

Andrew R Stewart 

I've only done a few dozen SA AW overhauls so perhaps not the expert but I have seen only a few pawls that were worn enough to warrant replacement. More spring failures but still not common. Never needed to take a magnifier to the parts to tell though lately I have started to use readers in general.

SA AW hubs are rather robust if not abused. At Geo Rennie's we would have a competition for the oldest AW we serviced. IIRC 1949 is my earliest hub shell date. Since these hubs are meant to run with a tad of bearing slop and a bath of oil most live for decades happily ticking away. The best way to abuse these hubs is to set the bearing adjustment too tight, never lube the hub, miss adjust the shift cable so the hub is never centered in a gear and then jump the bike a lot. Andy

dsbrantjr

I suspect that you are being overly pessimistic; "detectable mismatch in their properties" does not necessarily mean "imminent failure".

robalong

Here are the pix I mentioned, the best I can do at home. They show the mating surfaces of a pawl and its corresponding seating area. The first pic, of the driver housing, shows early signs of a crack, perhaps. Everything looks fine without magnification, but all that scoring is making the pawl a bit crunchy as it moves up and down. How much this matters is the issue.
Second pic is the pawl, the third the housing again.
Gotta dash out...back later.

base2 

If you are just working on the freehub mechanism:
A bit too much grease & or grease that is too thick can cause the pawls to get sticky. My suggestion is to thoroughly clean the pawl bed & spring ring groove. Like, 100% dry remove everything. Digging out old grease and any trapped grit with a toothpick & a cotton cloth works well enough absent a toothbrush & solvent soak that would be more appropriate for a complete overhaul job. Do the same for the pawls as well.

Check the mating surfaces. Then lightly grease the pawl bed with a touch of generic axle grease. When pressed firlmy they shouldn't stick down. Sticking down means too much grease. Wipe off the excess until the pawl returns smartly on it's own.

After that a small smear of grease with the mating saw teeth the pawls engage to for quietness & carry on.

Good luck.

AnkleWork

There's the clue. Going forward, just change the oil frequently enough to soothe your fears.

robalong

Indeed. I think I'll take a stone to smooth the seat of the pawl and a thin, round file to smooth down the ridges on the housing. I doubt very much whether all that will affect the operation of the pawls. I can take the risk in pursuit of knowledge, as I have about four hubs more than I expect to use.

Thanks to others who took time to comment.

I do think it's worth having a magnification system that includes a holding stand for the parts and a lamp. I used one of the eyepieces (with attached light with a switch) from a cheapo Chinese binocular thingy that was useless as intended because the two eyepieces couldn't be lined up to show a single image. The magnification is really impressive. I paid the equivalent of about US5$. They are on Ebay at half that price, with free shipping. Below is a pic of them, the same as mine. Well worth the money if you really want to know the true condition of parts.


PS: My pix of the parts earlier were taken freehand with me holding the eyepiece onto the lens of a now-antique silver digital camera. The driver housing sat on the bench, and the pawl held in a clip on a stand. Camera flash was off, the eyepiece light on. Not a bad result for the money .

robalong

I am neither physicist, mathematician nor metallurgist, but I have an inkling of how amazing it is that these pawls can bear such enormous pressure, per square-almost-nothing . So small, but can drive a bike, rider and luggage for years and years and years, even when not regularly serviced, it seems.

The sun gear and the planetary gears of the hub under observation show no real signs of wear. When mounted dry in place with the pins, the planet gears have barely-detectable free play. Quite astonishing. When oiled, there will be no discernible play! How's that for top-notch engineering? Maybe forty years on, and fighting for the next forty!

robalong

I appreciate that the topic of Sturmey Archer 3-speed hubs really ain't that sexy these days . But if any of you come across one, with or without the wheel, say, at a yard sale, do buy it and get it to someone who knows about these things. Posterity, recycling, and all that. Shame to see even one melted down. These hubs represent the very best of those that took the time to actually care, back in the day.

I reckon it's well worth googling 'sturmey archer heritage' and 'sturmey archer wiki'. Geared bicycles didn't drop from the sky ready to go. Mr Sturmey and Mr Archer were real people. It's not just a brand name.

Merry Christmas!

Kovkov

Your pictures are showing the new style of low gear pawls that use the new style circular spring. Those were introduced pretty late. The classic robust aw uses rhomboid shaped low gear pawls that look similar like the high gear pawls and they use the same „r“ shaped spring.

robalong

Thanks for your input, adding to my pool of knowledge.

I took a stone to the pawl seats, and scratched around the housing seats with a hard pointy file. Reassembled...about the same degree of scrapiness from one pawl in the driver housing. I swapped the pawls around...no change...scraping from the same seat in the housing. Then came the lightbulb moment as I pressed down on the pawls while looking at the driver unit.

The circular spring sits in a channel, each end of the spring loosely aside a pin set in the channel. One pawl is much nearer to this pin than the other. When I press down this pawl (the non-scrapy one), the spring lifts up away from contact with the bottom of the channel and does not move in relation to the channel. However, when I press down the scrapy pawl further away from the pin, the spring does NOT lift. In fact, the end of the spring moves almost a couple of millimetres towards the pawl as the pawl goes down. The bottom of the spring is scraping along the bottom of the channel! I proved this to be the source of the scrapiness by lifting the end of the spring up with a needle, and moving the needle back and forth with the spring as the pawl was pressed down so there was no friction between the spring and the needle. No scrapiness! The scrapiness I detected is built in. It's the way it is.

Fascinating stuff, huh?

What have I achieved? Satisfaction with a successful result to the investigation, and a degree of knowledge. The knowledge will be consolidated if this scrapiness issue is repeated on the other driver units I will be inspecting over the coming days and weeks.

Cheers!

AnkleWork

Yet again first-hand experience and direct confrontation triumph over fear.

robalong

Worth the time, as is any challenge. Not quite Everest this time . I should have noticed earlier how the spring reacted to pawl pressure...hindsight blah blah. But I noticed, and that's the main thing. It doesn't excuse my poor thought trains, so I will stay behind after class and write a hundred times...
Obviously when everything was new, what I now call the spring's 'long action' slid smoothly in the channel. I've managed to reduced the scraping ('spring drag' is perhaps a better term) by seriously attacking the spring with yellow sandpaper (we have that in Europe, about five inches wide and sold by the metre...seriously good stuff on grime, but won't affect metal). Quite a lot more grime came off, and I've now noticed the inner face of the spring is somewhat pitted due to age. I believe these springs are no longer available separately. It would probably be worth shaving a couple of thou from the inside of the spring with a cylindrical stone held in a hand drill, but what the heck. I let my granddaughter test the smoothness of the pawls before the serious cleaning. She noticed the scrapiness of one pawl. I handed the reassembled unit back to her after the cleaning, and she judged it to be better. Good enough for me!

My conclusion:

The inner of the spring should have been machined just slightly flat, to match the flatness of its channel. Or the channel rounded, to match the roundness of the spring. A slight curving up of the spring end on the long-action side would have been advantageous.

I know. I WILL get out more, promise !

Cheers!

robalong

I'm checking out the assembly before going to bed. The feel of the two pawls in action are now matched.

It's funny, really, because this assembly would probably have been fine in operation if I'd just degreased it with a quick wash and done nothing more. But I have gained something.

What exactly that gain is...it's a pleasant feeling, in the end. Perhaps little more than that. I now trust the assembly to function well, as intended. There's a part of me in it now. There's something of it in me.

I cared. We should all care, always, about everything and everyone.

I will sleep well.

Merry Christmas!