After Same revs, less noise, now it's time for same revs, more speed, and so today's interesting task is swapping out the gearbox sprocket. I encountered a proliferation of moderate annoyances that amounted to a considerable pain in the ass at absolutely every single step of the process, for something that should have been simple and straightforward. Good grief.
This is something I would have liked to get done well before the Old Irons rally last year, but as usual there just wasn't time and/or something else always got in the way. The gearbox has an 18 tooth item at the moment, we're moving up to 19 to reach what should be (on paper at least) the optimal ratio for all around use. A stock A50 Royal Star uses an 18 tooth at the gearbox and a 47 tooth sprocket at the rear wheel. As far as I know, the twin-carb "Wasp/Cyclone" that was sold on the US West Coast had a 17 tooth gearbox sprocket, which must have made that thing wheelie and shoot up hills like a modern-day 2 stroke. But back to the Rising Star: when this bike was first built I had initially fitted a 50 tooth sprocket and later switched to a standard 47, which made a noticeable difference. Reaching the ideal ratio is something I've had in my mind as one of the few essential tasks to get done in order to get more out of this bike. Not just more speed, you have to understand this is about expanding the range where this machine can be both useful and enjoyable. My only concern going into this is about whether or not the bike will be able to "pull" the larger sprocket when tackling the climbs we often face when touring in the mountains. I can live with downshifting, going slower and even taking a break if needed; I feel it would be worth it to gain a more usable cruising speed in fourth gear.
Replacing the sprocket requires removing the primary cover first of all. It is secured with 12 Phillips-head screws (but before I get to those I also have to remove the footrest and drop the rear brake pedal out of the way).
I noticed the heads were all pretty badly chewed up, which surprised me. Then I remembered that years ago we had meant to replace them but none were available in time for the riding season and so we just put them back thinking "at some point we'll have to take care of that"; well, those chickens definitely came home to roost as two screws in particular (obviously the hardest ones to get at) were so stripped out I couldn't get the screwdriver to engage. I was eventually able to free one by using some duct tape over the impact driver bit and it gave it just enough purchase to crack it loose. No such luck for the other one, so I had to resort to a damaged screw remover, courtesy of Andrea (whom I met through Lele at the Old Irons rally last year).
This thing takes some finessing and some careful hands but it works a treat. I was very relieved when I felt it bite and begin to turn the screw out.
I could have used the drain screw to let most of the oil out, but decided not to disturb this and just catch any oil that might still have been in there when I removed the cover. Under no circumstances should you pry it apart with a screwdriver or anything like that.
Surprisingly, there was oil in the primary, and it was in good condition as well as the correct quantity, more or less.
I made a cardboard holder for the screws as there are different lengths, which I can use as a reference for the new set of replacement screws that I got in the meantime.
The new screws have an Allen head, not original spec but very nice.
One thing I did was to clean out each corresponding hole in the crankcase to make sure there was no Loctite or sealant residue in there. For those who don't think this is needed, take a look at the next photo to see just how much gunk I got out of there:
This all gets packed into the blind holes in the crankcase and if there is enough of it, when you tighten the primary cover screws it can compress to the point where it will crack the crankcase. You have been warned...
The primary cover itself came off easily enough after a few gentle taps with a nylon mallet to break the seal, and I can now get at the alternator, clutch and primary drive.
Wonderfully compact, the BSA unit motor had plenty going for itself; too bad it didn't last into the 80s or early 90s, it could have evolved into something very special.
Before touching anything else, I checked the triplex chain for tension and found it in perfect condition; this thing is very strong indeed and definitely overengineered for the sort of horsepower and torque it has to handle here. At this point I can slacken the primary chain tensioner all the way. The threaded bolt that protrudes underneath the primary cover is protected by a sleeve nut, which you will rarely find on a BSA A50/A65 these days. Replacements are available but a lot of people seem to be unaware that this part even exists.
We're now looking at the clutch, which is the next component that has to be disassembled. The three spring nuts come off and you can then pull out the springs and their cups, then lift the pressure plate off. I'm not disturbing the clutch pushrod adjuster at this stage, we'll get to that later.
Now it's time to remove all the clutch plates, and once we have emptied the basket we can install a clutch locking tool:
If you have some discarded clutch plates lying around you could also very easily make your version of this tool by drilling through a couple of plates (steel and friction) and bolting them together:
For the love of God do not forget this inside your clutch when you put it all back together or you will have a bad surprise when you start the engine and your day/garage is going to be ruined. To help avoid that costly fuck-up, it might be a good idea to paint this red so it's easier to see.
Moving on to the front of the engine, the stator is held on with three self-locking nuts; once undone, the stator can be pulled off and gently rested hanging from its wiring. Then, once the tensioning slipper is backed all the way off and removed, we can proceed with undoing the retaining nuts at the end of the crankshaft (a 9/16 goddamn Withworth)
and gearbox mainshaft (a 1/2 goddamn Withworth) (the latter holds the clutch center or hub in place on the mainshaft spline). Both have a normal right-hand thread. I'm using the same nylon block that I used on the Sportster to lock the primary as I then use a long cheater bar for the clutch center nut, and a regular well-fitting wrench to break the rotor nut free; no need for the impact wrench here. Have an extravaganza of pullers at the ready, if you're lucky you won't need them all, but luck favors the prepared...
You'll need one to remove the rotor from the crankshaft, one to remove the clutch hub from the mainshaft and finally one to remove the sprocket from the crankshaft. As there isn't a specified service tool for the crankshaft sprocket, it is up to you to find a couple of very long bolts with the right thread and make your own puller: good luck out there.
This is a beefy, sturdy tool, you shouldn't skimp on this type of thing: just because you can find a €5 piece of chinese crap online, doesn't mean you should get it.
I found this amusing bit of advice that came with the hub puller: "when using this tool, please have some mechanical sympathy, and take up the load on the puller, then give the hub a sharp whack to release it from the shaft. Simply winding up the tool and hoping for the best will likely strip the threads on some that have been fitted for years. Apply common sense liberally..." Alright fella, don't fret.
The clutch hub is held to the clutch chainwheel by means of a "clutch sleeve" which is really just a dummy spline that presses into the spider of the clutch hub's shock absorber. See 34 & 37:
In my case, seeing as I only needed to get at the sprocket, it can be removed as an assembly and set aside. The only thing I'll do later on will be to give the inside of the basket a good clean. Taking all of this apart would have been hazardous without a press, and time-consuming to put back together: there are 20 rollers that the clutch basket rides on (which you can see in the tiny drawing below around the aforementioned clutch sleeve), these are just loose rollers and can be a bit fiddly to replace; you can use a little bit of grease to help keep them in place but don't overdo it (the last thing you want is grease fouling up your clutch).
As I mentioned before, I had to MacGyver a puller for the crankshaft sprocket but luckily I was able to free it with relative ease. I am not going to disturb the Woodruff keys at this time, but it's always something to pay attention to.
It should go without saying that you're removing the crankshaft sprocket, the clutch basket and the triplex chain together. As you do this, be mindful of those rollers I mentioned earlier, as there is a remote possibility they could fall off.
With the entire primary drive removed I can now take off the backplate, which gives access to the gearbox sprocket. Six screws with the shallowest slot took a real effort in care and concentration to remove without damaging them.
The backplate itself will typically be rather stuck on, and you must resist temptation to pry against it to get it to budge. Once again, a few gentle taps with a plastic hammer are usually all it takes to break the seal. Speaking of seals, check the oil seal at the center of the backplate as this is a crucial item that should be replaced if perished. In my case it still looks in perfect shape and there are no leaks at the back, so I'm leaving it well-enough alone.
We now have access to the sprocket itself. I left the final drive chain on in order to undo the nut, which has a normal right-hand thread, using what I can only describe as chopper acrobatics: the front wheel locked in the lift vice and with a chock, my left foot bearing down hard on the brake pedal, my right hand pressing firmly on the huge box wrench and my left hand heaving down on a long tommy bar to get that sucker to budge.
I then removed the chain just before lifting the sprocket out (guess what, this is also a good opportunity to clean and re-lube your chain, do it!).
A quick visual inspection of the gearbox outer case and the mainshaft oil seal reveals that all is in good order and nothing needs replacing. The new sprocket went on easily. There is a safety tab washer for the retaining nut that really ought to be replaced anytime you're in here (same goes for the retaining tab on the crankshaft nut as we'll see later on), you can surely see why:
Here's the new sprocket and new safety washer installed:
As soon as the sprocket is on, the final drive chain goes back on as well, I was just able to reuse the one I had by moving the wheel axle all the way forward in the hardtail's adjusting slots; then the new safety washer and the nut. There is no torque setting specified in the original workshop manual for this particular nut, and because of the protruding mainshaft as well as the size of the nut and location, it is really difficult to use a torque wrench here (you'd have to weld an adapter to a long pipe wrench, etc.). I estimate a reasonable torque setting could be around 60lbs/ft. In my case, I used a properly fitting box wrench to undo and re-tighten.
I also spent a little extra time making sure the chain and sprockets all line up properly, and it all looks true and straight. I'll keep an eye on the chain but hopefully it won't give any trouble at all.
After that, it's a reverse of what we dismantled (paying particular attention to the hammerhead bolts and the clutch rollers if you do take them apart) until the primary cover is ready to go back on. One thing that you cannot skip at this stage is inspecting and cleaning the clutch basket, the clutch center and each plate individually. Each slot is checked for burrs, and cleaned. Each steel plate is checked for warp (thankfully all of mine were fine) and any signs of unusual wear. Each friction plate is cleaned and checked for nicks or breaks in the friction material itself. The workshop manual doesn't specify that they should be soaked in oil before assembly, but this has never been a noisy clutch, so I'm leaving it well-enough alone.
Incidentally, I found that we had previously adjusted the spring nuts to where the ends of the bolts were well below the nut opening, which I found strange; the clutch does have a rather heavy feel at the lever though (even the new, improved item) so this could be at least part of the reason for that. I'm going to try a more standard setting as per the workshop manual and then take it from there. That means adjusting the nuts so that the end of the bolt comes flush with the nut opening. Of course you still then need to adjust each one individually to make sure the domed pressure plate lifts off square from the clutch stack, but that should be a good starting point, and I can replace the springs if needed.
I had grand plans to splash out on a big upgrade for the clutch by fitting some special parts that SRM make, but figured this really wasn't needed and would have been an unwise expenditure on a bike I use so seldom (not to mention I already spent plenty on all the other spares and jobs). That said, I do have a simpler upgrade that I bought over a decade ago, when I gathered all the parts needed to build the Rising Star, but never fitted. At the time, the guy who rebuilt my engine thought, as did I to be fair, that it was better to rebuild everything to stock specification, "see how it runs" and think about messing around if needed, also depending on actual use.
Specifically, this is a modified pushrod, supposedly made of harder steel than the standard item, and segmented to include a ball bearing:
The idea behind this is that the ball bearing allows the clutch adjuster at the center of the pressure plate to rotate independently of the pushrod, which should eliminate mushrooming of the pushrod, drag, flexing, sticking and all manner of undesirable symptoms. Because it uses a special adjuster bolt that goes into the mainshaft (as opposed to the standard item, which meets the pushrod outside of the mainshaft), this modification should provide for a more "square" lift of the pressure plate. Please hold your skepticism until I've actually tried it.
The "Performance clutch rod!"... Ah, I'm not taking this too seriously to be honest, but it does tickle me so.
These seem to have disappeared from the market, it was one guy making these in his garage and it looks like that's no longer the case, meaning this is now an ultra-rare, new old stock custom item to make certain friends lose their minds. Also in terms of upgrade this is more in line with the Rising Star: yes it's an upgrade but it's not high-tech, it's a custom-made, simple but (hopefully) effective detail that will make the bike better to ride.
It makes sense to do it now that the primary cover is off: I can be as precise as possible with regard to the adjustment, and lock it in place with ease. You could install this through the small inspection hole in the primary cover as well, but room is far more limited in that case. There is also another small but important detail to consider: the clutch rod rides inside the gearbox mainshaft (much as it does on the Norton) but whereas on the Norton the mainshaft is just a hollow shaft, on the BSA there is a bush that's pressed into the starboard end of the mainshaft to support and guide the clutch rod:
This bush is not visible or accessible without dismantling the entire timing side of the engine, so if it becomes dislodged or damaged you are in trouble.
All it took was a bit of "fiddling around" to get it to fit and work properly; and maddening as it is, "fiddling around" is what it takes to work on British machines.
All it took was a bit of "fiddling around" to get it to fit and work properly; and maddening as it is, "fiddling around" is what it takes to work on British machines.
One quick shot of the rotor retaining nut at the end of the crankshaft, and the safety tab washer:
That notch in the tab washer is supposed to locate in the Woodruff keyway in the rotor (below) but it comes nowhere near it and is more of a suggestion.
I have to say there appears to be no quality control whatsoever in these parts, the new one was even worse than the one I found. I punched it out a little more but it's be no means ideal.
It also makes sense to check the triplex primary chain tension while the cover is off. As for the Sportster, best to check tension in a few spots. Just like the Sportster, this BSA has an endless chain but you may find that earlier models were fitted with a regular chain with a master link, in which case pay attention to the direction of the retaining clip when refitting this to the bike.
Rather than using the typical silicone sealant I normally go for, I've started using this gasket cement called Ermetico Vittoria. It takes itself so very seriously that it proclaims to be "a triumphant affirmation of Italian industry". Jeez...
Everything else that needed to go back on the bike found its way back and there were no bits left over, which is ever so reassuring.
Now, please remain on the edge of your seat until I can test ride this new ratio and see if it's an improvement over the 18-tooth sprocket. In practical terms that will happen if and when I can go ride to the mountains, either to the Old Irons rally or some other destination, but basically it's only then that I'll know how this really affects the bike.
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