Sturmey archer actuator plate HSA470

[Brucey]

All NIG (No Intermediate Gear) toggle chain SA hubs (with the exception of CS- models) have a thing inside called the actuator plate. It fits to the driver and helps to engage/disengage the driver pawls under certain conditions. Part number HSA470, retail cost about £1.50.



In standard (drum brake or rim brake) hubs the driver has two pawls which are potentially disconnected by the actuator plate when freewheeling or backpedalling. In coaster brake hubs there are four pawls fitted; the two forward driving pawls work as per the non-coaster hubs; the other two pawls face backwards and engage with the brake mechanism. In coaster brake hubs the actuator plate needs to be in good order if the brake is to work correctly.


actuator plate shown in red, in the position where the driving pawls are pushed inwards (freewheeling or back pedalling). The empty pockets would hold the (extended) second pair of pawls in a coaster brake hub


shows how the sliding clutch can turn the actuator plate thus pushing the driver pawls out of engagement


a four-pawl driver to fit a coaster-brake hub.

One of the things that sometimes fails inside the current 3s hub is the actuator plate. There appears to be two modes of failure

a) the plate comes separated from the driver and gets into the gap between the driver and the sliding clutch (eg in third gear) and then gets further broken up.

b) the 'ears' on the actuator plate break off and the shrapnel thus created further damages the hub.

I've seen both types of failure. At one time there were bikes being shipped with faulty actuator plates and bike shop owners were expected to change every single one they sold.

a) is still a problem; I suggest it is prudent every time you have a NIG hub apart to check the fit of the actuator plate. Usually it is pretty loose and because it is only retained by the 'D' shaped dimples in the side, it can faily easily slip off. This can happen when freewheeling or backpedalling in gear 1 or gear 2 and gear 3 is selected; the sliding clutch will tend to drag the actuator plate off the driver it it can. You can adjsut the fit of the actuator plate by bending it slightly. It shouldn't be a draggy fit on the driver, but it shouldn't be loose either.

b) is also a potential mode of failure. If you habitually backpedal or freewheel when shifting, the actuator plate has more work to do. I don't think it can last indefinitely in any case, but if it is in good condition when inspected, and the gears are usually shifted whilst pedalling forwards (without force until the gear is in) this will maximise the life of the actuator plate.

The highest forces on the actuator plate appear if you wheel the bike backwards in gear 3 whilst obstructing one pedal (e.g. with one foot on a pedal or with the kickstand extended). Some users report that their 3s hub works OK without an actuator plate fitted but if for some reason the sloping faces of the cutouts in the base of the sliding clutch don't work then the hub will be broken when wheeling the bike backwards in gear 3.

If you inspect the actuator plate and you find a crack in it, it must be replaced. I recently found this picture on the interweb which rather suggests that SA have at times been shipping parts which arrive with a crack in them; no wonder they sometimes break;


there seems to be a crack in the actuator plate on this new part.

You can remove the driver and change the actuator plate in about fifteen minutes; you don't have to remove the entire internal to do it, you just have to unscrew the RH cone to gain access. Whilst you are at it, it is an excellent idea to fit the correct lockwasher between the RH cone and locknut too.


part HMW147; deemed as essential in SA hubs for at least sixty years, now not fitted by SA presumably in the name of cost-saving

The manufacturing costs of a washer like that are fractions of a penny; without it the RH cone can precess into the hub workings and destroy the hub (and with it SA's reputation). Talk about false economy....

cheers

[Greystoke]

Remember Rover cars....k series engine cost savings? Accountants never learn.

So is it better to use a NIG or an older pre-NIG SA 3 speed if it's properly adjusted?
The old pre-NIG can fit extra sockets as it is.

[goatwarden]

Remember Rover cars....k series engine cost savings? Accountants never learn.

The full story is far worse; accountants rarely can be bothered to understand technical issues so can be easily fooled by vanity projects. K series worst problem from the start was head gasket failure due to small pores in the head face bridging the lip seals of the vanity project head gasket and causing water to oil leaks. Had we been able to overcome designer's vanity and gasket supplier's marketing, we could have used conventional head gaskets (like those employed very successfully by racers using K) and Rover might still be here. Had the finance and purchasing peplo been interested in questioning the need for the expensive new gasket, the world might have been different.

Right at the end "Project Drive" was all out stupidity of cost savings, but the harm had been done years before.

In truth a properly cost controlled project would not have resulted in K as we knew it; millions of pounds of government subsidy were spent pointlessly on various styles of new clothes for various minor emperors at Longbridge. Some good things came of it, but few that are still usefully exploited today.

[Tiberius]

I recently had my NIG hub apart to sort out this very failure…actuator plate failure. I have never had one of these hubs apart before but thanks to some excellent advice from Brucey (on another thread) I managed to get the whole thing rolling again. My hub was never quite right from day one, however I have changed gear whilst not peddling forwards so maybe I contributed to it’s failure. Who know?

When I got the hub apart and sussed out how it worked and what had failed etc, it seemed to me that the hub was essentially a clever/well designed/well made bit of kit with one really nasty flaw in it, namely the actuator plate. It is a rotten ‘Micky Mouse’ bit of pressed steel, when you have it in your hand you just KNOW that it is going to fail one day…I actually ordered two (cheers SJS) as I just KNOW it will fail again.


I’m glad this thread is now out there. When I was repairing mine I found that there was lots of info available on the early hubs but a lot less on the NIG version. Studying the diagram in this parts list helped a bit...

https://web.archive.org/web/20140807171 ... ed_Hub.pdf

[Brucey]

…..So is it better to use a NIG or an older pre-NIG SA 3 speed if it's properly adjusted?....

the only reason why the NIG three speed even exists is arguably because if you make a coaster brake based on that design, the brake doesn't work if the gears are not well adjusted. This means if you are daft enough to sell a bike with only one brake and it is that brake, you are going to be in trouble.


The current NIG AW has a few things going for it; you can buy shiny new ones, you can buy new spare parts, the axles ought to be stronger, there are more longer axle options, it will come with a warranty, you can convert it using a BWR driver to make it into a hybrid gear system. There is no 'neutral' regardless of how badly adjusted the gear cable is.


The old pre NIG AW has pluses too; it will accept two sprockets right away, if the gear cable gets slack the gear starts to slip in gear 2 and this (without damage to the hub) alerts you to the fact that some adjustment is due. Spare parts (where not the same as in current hubs) can be robbed from innumerable old AW hubs which can be had for peanuts.

So which is 'better?' I think the old AW is, in the hands of an average user, less likely to break. The slippage in gear 2 which occurs when the gear is badly adjusted is superficailly a problem, but is actually the gear's saving grace. It is obvious to even the most ignorant person that there is a problem and this ought to be the best persuasion to ensure that the gear gets some attention.

By contrast in an NIG gear if the cable goes slack (which BTW is made more likely because with most of the current shifters there is nothing to stop you from pulling hard on the cable when you are already in bottom gear....) you are quite likely to be running between first and second gear when first is selected. The same thing can happen if the shifter overshoots and sticks when shifting 3-2. In any event this breaks the hub; the tips of the high gear pawls get broken off, because they are trying to engage but cannot engage fully. I have seen very many NIG hubs (both 3s and 5s) which have gone bad this way. I have seen very much fewer non NIG hubs fail this way, even though it can happen just the same and there are millions more of them about, and I think the main reason is that it is simply more obvious that attention is required.

in both 3s and 5s hubs the shiny thumbshifters are often responsible for the death of the gear; these have backlash from the start and develop much more through wear. They also stick between gears. You can just about use a new shifter with a new hub but once there is wear or even the slightest misadjustment you are soon in a position where the hub is going to be broken unless you remember to pull the shifter back to the detent after every downshift. Even then because you can pull hard on the cable when shifting into first gear, the adjustment may not stay set for very long. One of the adaptations I am toying with is to fit a preloaded spring into the mechanism so that the peak tension in the gear cable is limited, and the adjustment is less likely to change by itself.

BTW I forgot to mention; there is an additional parasitic loss in an NIG gear because the clutch spring pressure is always brought to bear against the toggle key. Also the planet gear bushings in the current NIG AW are incredibly slack from new (think 6.0mm planet pins, 1/4" holes in the planet gears); I can't think that this will improve efficiency.

cheers

[Greystoke]

Interesting reading.
Can you 'feel' for the gears using a friction shifter?

[Brucey]

really you are asking if you can feel for second gear (i.e. in a 1-2 or 3-2 shift), since the others (in a 3s) are full slack or full tight. I think the answer is a conditional 'yes' with a non-NIG hub and another (differently conditional) 'yes' with a NIG hub. I wouldn't advise it with a single-toggle 5s hub.


With both types of 3s hub you can feel in a 1-2 shift when 2nd starts to pick up and just add another mm or two of cable slack to ensure that the high gear pawls are fully extended.

Shifting 3-2 with a non-NIG hub you have to pass through a neutral and add another ~3mm of cable pull. Arguably with a NIG hub as soon as you are out of 3rd gear you are good.


I ran a SA IGH on friction shifters for years and I found it most convenient to have a mark on the shifter that corresponded with 2nd gear, or to have the DT lever pointed straight back at me in second gear. The only time this gave me any trouble was when the friction shifters started to misbehave; either excessive friction or slippage (which of course happens when you are giving it some uphill, usually because the cable is being pulled by frame flex) are possible.

cheers

[Brucey]

this is the neutral position between 2 and 3 in an old AW, which requires at least 3mm cable pull from full engagement in gear 3



from https://hadland.wordpress.com/page/5/

You can see that in order for the clutch cruciform to be full engaged with the ring gear (for gear 2) then it has to be pulled 3mm from the position shown; much less than that risks slippage. In practice the correct shifter pulls more than the amount of cable required; enough to allow for slack to be taken up and for some bad adjustment too.

cheers