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How To Make a BSA Clutch Work #233704
01/20/09 9:21 pm
01/20/09 9:21 pm
Joined: Aug 2001
Posts: 125
United Kingdom
P
PaulM Offline OP
BritBike Forum member
PaulM  Offline OP
BritBike Forum member
P
Joined: Aug 2001
Posts: 125
United Kingdom
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.


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Re: How To Make a BSA Clutch Work [Re: PaulM] #233779
01/21/09 6:10 am
01/21/09 6:10 am
Joined: Oct 2008
Posts: 4,871
Gnashville
DavidP Offline

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DavidP  Offline

BritBike Forum member
Joined: Oct 2008
Posts: 4,871
Gnashville
Sounds like an awful lot of trouble.
Any chance of mounting a Rocket3 clutch?


Stepping on others doesn't make you stand tall.

71 A65L "Zelda"
92 BMW K100rs "Gustav"
Re: How To Make a BSA Clutch Work [Re: DavidP] #233794
01/21/09 10:43 am
01/21/09 10:43 am
Joined: Aug 2001
Posts: 888
Annapolis, MD
Dennis B Offline
BritBike Forum member
Dennis B  Offline
BritBike Forum member
Joined: Aug 2001
Posts: 888
Annapolis, MD

Paul,
While I do agree with some of your advise here, I would warn others NOT to take all you have said as gospel. I disagree with your statement on always replacing springs. Aftermarket springs aren't always better than originals.
And, "add the plates lightly oiling as you go along"
I never oil any of the plates, I always put them in clean and dry.
And as for the clutch hub nut,
"use loctite on the threads"
True, but use medium strength, not high strength.
"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."
This is terrible advice. Torque this nut to 40 ft lbs. That's plenty.
And I don't put car wheels on with an air rachet, I use an air GUN. Have been for 40 years now.
If I tightened this nut as tight as I can it would snap like a twig.
And your use of a piece of brazing wire is unnecessary. Just eyeballing with the inner case works fine.
I'm not trying to rustle any feathers here, I'm just sayin.
Cheers
Dennis B


Member # 182
'73 750 Commando
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Re: How To Make a BSA Clutch Work [Re: Dennis B] #233799
01/21/09 11:35 am
01/21/09 11:35 am
Joined: May 2004
Posts: 3,569
Sydney Australia
B
BSA_WM20 Online content
BritBike Forum member
BSA_WM20  Online Content
BritBike Forum member
B
Joined: May 2004
Posts: 3,569
Sydney Australia
Just to froth the oil a bit more.
I always use some sort of indicator if trying to true up a 6 spring clutch.
Some who are more anal than I go as far as to use a dial indicator, they never seem to have clutch problems on the road, then again they take a whole day just to adjust a clutch.
The 6 spring is fundamentially a bad , no, a very bad design from any engineering point of view and was a devious way of BSA getting around other companies patients not a better original design in the first place.

The idea of having the drum rely on a heavy pressed plate acting against a 1/8" lip on the end of the center to run true is an abombination , not engineering.
The contact points , both between the plates & the drum and the plates & center are way too small for the type of shock loading that they recieve.
The slots in both the drum & the center should have been hardened much more than they were so that any mushrooming occurred in the easily replaceable plates.
Next we come to the pressure plate itself.
Stamped out of a sheet of flat plate it relies on the stresses induced when it was cupped to overcome the bending moments which are highly sensative to the orientation of the grains and as such are stiffer in the rolling direction than across the rolling direction.
Add to that the plates were stamped out on one press then cupped on another then the holes were punched on yet another press with the parts being batched into bins between each press so the spring holes ended up with a random orientaion to the rolling direction of the plate which explains why some bent like a leaf from new while others were still rock solid 50 years latter.
So I would argue that the chances of having a good clutch relies more on the luck of the draw in getting good parts in the first place than any amount of carefull preperation, and I haven't even started on the idiot lifting mechanism .
Bike beesa
trevor


Bike Beesa
Trevor

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