I am restoring my first BSA, a 1956 A10, Road Rocket (not completely original). Gearbox is stamped with "STD". It has a six-spring clutch. The clutch centre (part no. 42.3107)needs to be replaced as it is damaged. I ordered from SRM a new part, but it does not fit, the conus inside is too small, the clutch assembly is therfore not in line with the primary sprocket. They refunded the money, so far no problem. But I still don't have a clutch centre. I thought to bring it to an specialist to adapt it. Before I do so, I wanted to find out, if maybe there is an explanation for the problem. Is it possible, that I have an earlier gearbox with other dimensions? Did the Golden Flash have the same gearbox (clutch) or the 4 spring type? All tips about this issue are most welcome, thanks a lot.
I am not familiar with the six spring clutch as I also have the triumph four spring, it, to me, is a very good clutch when set up properly, the biggest improvement I had found was the teflon - PTFE clutch cable.
I fail to understand though why a four spring is better than a Six. Sorry I also am unable to answer your questions Zambu.
LJ. ******* 1940 BSA M20 500cc Girder/Rigid- In Bits! 1947 BSA M21 600cc Girder/Rigid-Green 1949 BSA A7 500cc Girder/Plunger Star Twin-Black 1953 BSA B33 500cc Teles/Plunger-Maroon 1961 BSA A10 650cc Golden Flash-Blue 1961 BSA A10 650cc Golden Flash-Red
Re: A10 clutch centre problem#18518 12/06/068:20 pm12/06/068:20 pm
I would also suggest to use a 4 spring clutch. You would need the above along with a complete new clutch asm. I would think SRM would have everything. You may find the spockets do not line up, if so, shim the front spocket. I kept the front "cush" and used a "cush" clutch center with no issue. rick
"Back in the garage with my bullshit detector Carbon monoxide making sure it's effective... ----THE CLASH-----
Re: A10 clutch centre problem#18520 12/07/067:51 am12/07/067:51 am
At the moment I would like to keep the 6 spring clutch. Money is one reason. And it worked for the last 50 years...should do some more.
See also the pictures. The new clutch centre is quite far away from the "sliding plate". So I will have to grind it out to match. The damaged one seems to be in the correct place, but I will have to confirm this before I adapt the new one.
Re: A10 clutch centre problem#18521 12/07/062:44 pm12/07/062:44 pm
Rick, thank you for the idea. The difference is 5mm, isn't that too much to correct with shims or spacers? Also the nut to retain the clutch basket does not go completely with all threads. But I will defintely check it again, grinding is more complicated than shimming.
Re: A10 clutch centre problem#18524 12/07/068:17 pm12/07/068:17 pm
I have been down this path with new centre and first tried packing engine sprocket to align but then could not get nut onto crankshaft far enough to fit split pin. I was also concerned about clearance between nut and outer cover. I ended up getting the centre machined to fit main shaft. I found there should be about 3/4 inch thread clear of the centre when in correct position. Make sure you get a good machinist as there is not much to remove. Check your main shaft for bulging in the key area and stone off if any. The centre is hardened. The taper is 3 deg. 40 min. according to my machinist. Good luck.
Re: A10 clutch centre problem#18525 12/07/069:52 pm12/07/069:52 pm
As trev said, I have also seen this problem. I machined a bit off the face of item 85. This allowed the nut to go on futher but added to the cush pre-load. But since I was using a cush clutch center, I did not worry.
Also, you may/should use lapping compound on your new center/mainshaft taper, this will remove/reveil any high spots.
"Back in the garage with my bullshit detector Carbon monoxide making sure it's effective... ----THE CLASH-----
Re: A10 clutch centre problem#18526 12/07/0610:10 pm12/07/0610:10 pm
I like 'everyone' I know who actually rides their BSAs have ditched the POS 6 spring clutches and many/most are using the later 4 spring clutch with modern Barnett clutch plates. This is the clutch that was OEM in the later '61 -'63 A10s and Gold Stars.The parts are listed in the A10 parts catalog. All of the pieces are the same as Triumph parts except the splined adapter that fits the BSA mainshaft.
The olde 6 spring unit had a host of design problems and even when new would both slip and drag, especially if it wasn't adjusted near perfectly. I always used a dial indicator on the pressure plate in an attempt to adjust the springs evenly. Bear in mind it was yet another item carried on from an earlier era of low power 20-25 hp engines on the insistance of the 'bean counters' who were less interested in building a quality bike than in maximizing profits.
As has been mentioned, check and shim the engine cush/sprocket for proper chain alignment when a 4 spring unit is installled. This is fairly easy to do using a straight edge with the inner primary cover off and out of the way.
Strangely on some bikes much shimming isn't required other riders have told me. However I've found it necesary to shim the cush out ~ 100 thou. And as Trev in OZ has mentioned this makes it a bear getting the crank nut started.
Some (all?) of the OEM 4 spring chain wheels had a 'dished' back face which positioned the sprocket inboard relative to the bearing face. This would sure help with the chain alignment. All of the repop chain wheels I've seen in recent years have a flat inner face. Does anyone have more info on this issue? Pre unit Triumph guys? John Healy?
The thrust face on the BSA clutch adaptor p/n 42-3170 used with the 4 spring unit, will wear it's way into the back face of the chain wheel, pushing the bearing race out of place. This will cause the chain wheel to wobble even more than customary, causing more chain and sprocket wear. aarrgh. A great fix for this design problem is to use a Tony Hayward clutch adaptor he sells for his belt drives for preunit BSAs. It has a much larger diameter thrust face plus it uses a bronze thrust washer as the later OEM 3 spring clutches. It's also made from a much harder/tougher steel and the splines won't be wearing out so soon.
dave - NV
Re: A10 clutch centre problem#18527 12/08/069:23 am12/08/069:23 am
I have a six spring clutch on my '55 Flash which I spent a fair amount of time setting up. First I set up the centre with the inner plate secured by the bearing race onto a spare mainshaft and machined the plate true. I made a radial/mushroom type lifter and modified pressure plate. Set up with a pointer for square lift. In practice it still dragged until I fitted a clutch lever with 1 1/16" fulcrum. This clutch is now as good as any with no problem selecting gear or neutral while stationary. The Flash is to R.R. specs and the clutch is handling the load well.
Re: A10 clutch centre problem#18529 12/09/0610:37 am12/09/0610:37 am
to add further to this debate below is a article I wrote several years ago for the star Magazine
4 or 6 Spring Clutch
There are Many arguments as to whether a 4 or 6 spring clutch is best, most people will argue that 4 is best however the truth is that the six is just as good but harder to set up. The following procedure should be used for both clutches to get that smooth as silk gear change. The main reason for clutch problems can usually be traced to a badly set up clutch or even overlooking the simplest things. To set up properly we must go back to basics and think like an engineer which means check every component thoroughly to ensure they are not defective. First although this may seem strange check that the woodruff key is a snug fit in the mainshaft if loose replace it, next job is to check the taper on the main shaft for any signs of burrs or scouring. If there is a problem here take some fine valve grinding paste and lightly lap the centre onto the mainshaft ensure that all paste is removed prior to assembly. Next job is the Basket; these are different from 4 to 6 spring, so I will start with the four. Visually inspect for obvious signs of wear paying particular attention to the bottom lip of the flange where the plate sits. If this lip is unevenly worn, the clutch can not sit square, so if the bottom lip is uneven replace it. The basket can be split inside you will find eight rubbers they are only cheap so replace them. The six spring basket is much simpler, basically check the wear it fits on the centre and file any burrs also check the studs that the springs fit over if they are loose they can be peened over from the reverse. The chainwheels all though having different centres need to be treated exactly the same, check the sprocket area again if it is worn replace! Secondly were the slots are that the plate slides into file any burrs off. We will now look at the part or partís that causes most trouble THE PLATES, again file any rough edges and make sure they are clean lightly sand the steel plate. Now get a straight edge and a feeler gauge and check for flatness if they are warped replace also check the thickness of both pressure and steel plates against the dimensions in the workshop manual again if they are worn replace do not forget the pressure plate at this stage. Springs the manual gives the free length to check these, personally I can not be bothered and replace them as a serviceable item once more they are cheap. If all the above has been done and all partís are in good condition then assembly is the easiest part. On six spring clutches place the centre on the mainshaft not forgetting the woodruff key or the plate that goís on first, on four place the centre on the bench and fit the chainwheel over it now place in the rollers and carefully fit the centre onto the mainshaft. Now on both models fit the basket ensuring that the tab washer is not forgotten also use loctite on the threads and tighten, how tight? BSA never released torque settings so the one I use is AS TIGHT AS YOU CAN. If you have an air ratchet for putting car wheels on use that, I DO. Next, add the plates lightly oiling as you go along and finally fit the pressure plate. Now place the springs on and tighten the nuts equally until the heads are level with the threads on four or there is room for a locknut on six, now kick the bike hard with the HT Leads off if the clutch doeís not slip we can true it up if it does tighten equally until you can kick it hard. Now get a piece of brazing wire and securely attach it to the inner primary case then bend it until it just touches the plates. Remove the plugs to make kicking over easy and kick the bike with the clutch lever pulled in. Now as you kick the bike use the wire to check if the pressure plate is spinning true if not adjust the springs until the pressure plate spins true. Now fit the primary case and go for a spin if everything is okay fine if it slips tighten the springs and retrue once your happy with it reseal and fill with oil if your gear change is lumpy unscrew the large nut under the box a quarter of a turn. Well you should have a good clutch now if not you skipped one of the above BSA Clutches are easy.