Britbike forum Forums British Motorcycle specific Brands Bsa bulletin board Front drive Sprocket

Hi,

I'm pretty new to doing my own maintenance on my families 68 BSA A65L so was hoping to be able to get some advice on the below topics.

1. I wanted to change front and rear sprockets as well as the chain due to wear. after starting this project I see that you have to remove the clutch etc in order to get to the front sprocket but my concern is that this will mess up the timing. Can anyone provide some guidance on how this is to be done so that I can get it back together in one piece?


2. In my haze to get the primary case cover removed, I missed the marking on the left foot rest warning of the Left hand thread and thus stripped the bolt. I see I can purchase a replacement online but so I don't do any more damage, does anyone know how to remove the old one?

Thanks everyone!

Hi,

1. Removing the primary drive will not disturb your ignition timing. Timing is set by adjusting the auto advance unit and breaker point plate(s) on the other side of the engine.

2. Assuming you have a dry-frame (pre-1971) BSA: You can grab the old footrest stud with (whatever, e.g., vise grip) and unscrew it from the frame. It is also left-hand thread.

You must have cranked pretty hard on that footrest nut the wrong way to strip it. Word of advice: If you have to apply an inordinate amount of force, something is wrong. Back off and study the situation before resuming.

Thanks Mark,

You are quite right, it did take a good bit of force which I put down to not being removed for some time. Don’t worry, I learned my lesson on this one.

What is the best strategy for removing these parts. Is there a way to remove the clutch assembly as one by slackening the chain and removing the center nut, or do I need to mess with the spring screws?

Thanks again

The entire clutch had to come apart to get it of the shaft. Then, the entire alternator hear to be removed to get the front socket loose, as you can't get the clutch basket off on its own.

Considering your experience with the foot peg, I would recommend you partner up with someone who's familiar with this process, or leave the sprocket in place.

You'll have to remove the spring screws and pressure plate to get to the center nut of the clutch hub (different from the center nut/screw that adjusts clutch throw that is set in the pressure plate). The clutch plate basket will have to be removed to get to the access plate behind it to get the front sprocket. That also means you'll have to slack off the primary chain, but I've found there isn't enough play to remove it without removing the stator, rotor, and front primary sprocket as well.

If you remove the clutch centre from the hub (the part mounted on the mainshaft) and take out all the rollers the chain can be worked off one tooth row at a time from the engine and chainwheel sprockets. Still need to remove the generator stator.
However, the centre splines on the hub are generally tight enough that trying to remove it that way will be frustrating and taking off both sprockets will be faster. The whole chainwheel, centre and hub can come off in one unit.

I believe your manual and/or the parts book mention that left hand thread. They'll also show you all about your primary drive.

I don't know about that particular nut, but every left-handed nut I've encountered on these old bikes has an L stamped on it.

Also, get the clutch hub removal tool! And, maybe a socket that will fit the countershaft nut.
PS what sprocket are you going for?

Spares you will need, Gearbox main bearing oil seal, clutch back door oil seal, might as well change them while you are in there.
Clutch thrust washer, the old one is probably worn.
Tab washers for rotor and sprocket nuts.
Gaskets for primary and clutch back door.
Stator leads grommet.
Cush drive rubbers, or new complete centre hub unit ( recommended), these are often well worn.
The clutch will have some wobble on its bearing, you might assume they are goosed, unless obviously worn/ pitted dont bother replacing, the new ones will wobble as well.

Tools you will need,
a big screwdriver with a slot ground in the centre for the clutch springs.
Clutch centre puller/ pusher.
1 and a 1/2 " AF deep socket for the sprocket nut, a british leyland Mini Ball joint socket works for me. Or saw the square drive off a short one and weld it to a tube .
A couple of 1/4 BSF screws and a strong back or two legged puller to get the motor sprocket off.
A 2 foot batten for the rear brake pedal
Two magnets
Marking fluid.

Some means of warming the Stator leads ( hot air gun?) , these get brittle , before removing the stator warm them up so you can move it out of the way without cracking any brittle insulation.
A proper Work Shop manual.
Fix the footrest first it will be handy.
My method.

Slacken foot rest, leave dangling down, drain case, remove screws and inspection caps, knock around joint, pull case with fingers in cap holes.
Note long screws to front, short to rear.
Refit brake pedal and footrest temporarily, use the 2 foot batten pivotted off the footrest to apply the rear brake when undoing rotor nut..If you have an impact gun , the brake may not be needed.

Warm the stator leads and remove the stator, there are small cut outs in the casing to allow small wedges , it should be tight on the studs, the wedges help unseat it from the housing, , ideally remove it completely, I sometimes leave it connected and park it on the top of the cases, but it needs to be threaded through the chain if still connected. If you remove the tails , fit a new grommet on rebuild

, knock back rotor nut tab, bike in gear , apply back brake to undo nut.
Back off and remove chain tensioner, watch for spacers, one on the spindle and the red buffer at the top of the adjuster ( this is often missing)

Slacken clutch springs a turn at a time, if you fully slacken one the others will be more difficult to get off, slacken evenly,keep a blunt knife handy to ease the locking pip on the screw past the spring end.
Before removing pressure plate and springs / cups, mark them so the same bits go back in the same holes.

Remove the plate stack, use the two magnets to draw out the plates, if you are reusing it, mark one row of tabs and the drum slots so they go back in the same place. Bag this as one lump for the time being.

Undo the clutch centre nut, this will be tight, again , impact gun or back brake to lock shafts. there should be a thick spacer washer under the nut remove it.

In theory this is when you use the puller / pusher tool, screw it into the female hub threads, clean these first. Buy this tool from a reputable supplier , and make sure it is for your model year, threads changed over time and Makes, . To use it , screw in the body to the centre, turn the jacking screw to touch the shaft then tighten as much as you dare, bang the jacking screw with a 4 lb hammer, dont go mental or you will knock the bearing housings to bits.
Good luck , be very cautious of this tool, they never work for me, some shafts have very minimal threading to allow it to engage , if you get lucky the clutch comes off completely with a bang.
If you get unlucky and the puller threads strip you can pull the clutch cush drive drum off its spline, allowing the chain wheel to fall off the bearings, plan for this with a magnet under the drum to catch the 20 loose rollers, you are now left with the chain in the way, pull the motor sprocket and chain.
if the centre is well stuck on there be prepared to sacrifice it , split with cutting disc and chisel, or try a 3 legged puller, either means buying a replacement.

Once the clutch is off the rest is easy, remove back door, gearbox sprocket tab/ nut, sprocket , oil seal, fit new bits, clean all joint faces, rebuild.

I agree with all that's written above and I would add that it's worth leaning the bike over on to its right side whilst working on this area. This should give you better visibility and help catch the rollers when the clutch is disassembled.

If all goes well and the clutch hub comes off its taper without too much effort, if you're very careful the complete clutch hub, chain drum, primary chain and sprocket can be removed in one piece without the rollers falling out everywhere, the trick is to keep the chain drum pressed against the hub so the rolllers cant escape. This method can be used when assembling and grease helps keeps the rollers in place. It takes time and patience to get this right, dont be too worried if you end up with rollers scattered over the floor, persistence pays.

And, don't spend all day crawling around the floor searching for the 20th roller. Chances are the previous owner only put 19 in there when he put it back together.
Just be certain that you put 20 rollers in there when you put it back together.

Excellent Gavin, just one minor detail. The -68 has the 3-spring clutch, and they have no tab washer for the clutch centre nut.

Regards

Thanks for the correction Ola, I have ammended the splurge.

Some more thoughts on this job.
After buying the spares but before starting the strip down its a good idea to clean the gearbox sprocket black hole gunge pit.This is a filthy area
Do this before opening the primary case,Caution ! plug the engine breather port before using pressure type washers or you will blast dirt into the DS cam bush, otherwise this is one occasion where a steam jennie or pressure washer carefully wafted will safe a bit of griminess later.
To plug the breather port a 3/8th dowell will fit, you will need a good light and long nosed pliers to find/ reach it.

I have never got the clutch off in one lump, my mainshaft has / had minimal threads and whatever tool I offered stripped. I hope you get lucky, it makes life a bit easier if it works.

One last thing, put keepers on the rotor magnet faces while its off, and stick the woodruff keys to it so they dont go missing.
I didnt know that before about the keepers, I eventually had to replace my rotor because it had lost a lot of magnetism, never having fitted keepers while it was off, the replacement came with keepers attached , they now live in the tools drawer, two simple arcs of steel to cover the poles.
It was only after reading one of Magneto mans posts about how much magnetism is lost when mags are stripped that it dawned on me the Alternator probably needs the same pampering.

Good point Gavin, and I would also add that its worth placing the rotor in a plastic bag immediately after removal, otherwise every conceivable piece of swarf/metallic debris will find its way onto the rotor and is really hard to remove.

51north: I hate to spoil your fun but are you sure the front sprocket needs to be replaced? I would take the chain off and have a good look at the level of wear before starting to take it apart. As well are you sure the sprocket you have will fit through the opening?

Gordo

Well, this all turned out to be a much bigger job than anticipated but I appreciate the support.

So far, I have removed the primary drive assembly etc with no issues. I am left with the clutch center that sits on the taper but cannot seem to get this off. I purchased the tool for it but I’m scared to apply too much force to this.

Any additional tips for this before I have to either abandon the project or cut it off?

I would try using the screw in extractor tool you already have together with plenty of heat from mapp gas torch. Make sure the extractor is fully screwed in and try not to over tighten the central bolt. If it doesn't budge leave the extractor tightened on and keep applying heat every hour or so, eventually something should give.

If you manage to strip the threads on the extractor, you could just buy another and try again and it might also be possible to use a 3 legged puller engaged in the groove behind the splines. Ideally you would want one which keeps the legs pulled together to prevent them slipping off, maybe something similar to the one used on Triumph and Norton timing pinions like This one

I'm sure you will get the hub off eventually without destroying it, its just a matter of keeping at it.

Thanks gunner I got it off!

Now to change out the sprocket, chain and get it back together again.