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4CA to 6CA Conversion
#9371 03/23/06 11:08 pm
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I want to replace my 4CA points plate on my 1964 A65R to the 6CA plate for easier setting of teh pionts. I don't want to go to an electronic ignition because my bike is 6V + earth and I don't want to convert to 12V. Even so, I think I want to stick with points.

Will my 4CA advance unit work with a 6CA ignition? The workshop manual says the ignition advance for this engine is 37°. Did Lucas make a 37° advance unit for the 6CA plate? if not what advance unit should I use?

TIA,

Bob Elliott

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Re: 4CA to 6CA Conversion
#9372 03/23/06 11:57 pm
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In Remembrance
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Bob , from what I have been led to believe , the early advance unit is a big art of the trouble withthe early points setup on a BSA , and should probably be replaced . The later advance,if I am not mistaken is usually a 12degree unit with slightly different cam profile , ad if you find one at a swapmeet ,make sure it rotates CCW as it looks very similar tothe Triumph unit that spins CW.

Re: 4CA to 6CA Conversion
#9373 03/24/06 2:57 am
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Ah, interesting. How do you tell a CW unit from a CCW unit?

Norm

Re: 4CA to 6CA Conversion
#9374 03/24/06 4:01 am
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The difference is in the direction off the ratation as the flyweights open .

Re: 4CA to 6CA Conversion
#9375 03/24/06 11:37 am
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Bob

Advanatages of a 4CA - the points open and close

Disadvantages of a 4CA - cam profile causes point bounce, you can't set timing individually, condensors fail easily due to heat, etc.

Advantages of 6CA - you can set timing individually, has a good profile to the cam, condensors are away from the heat

Disadvantages - good ones are getting hard to find and pricy. Springs are no doubt shot and need replaced.

6CA advance unit is longer to allow for the extra height on the points. You really need to change as a set. Watch the CW vs CCW thing. It does bite the unwary.

For the cost of a good 6CA unit, you can go EI. You have the 6V coils. Convert the bike, unless this is a mostly non rider to 12V. With the 3 wire alternator, it is easy to do. Just need one of the modern charge control units (I prefer Podtronics). Hide the charge control unit, use a 4A AGM battery (it fits the early battery tray), add EI and some 12V bulbs (which are much easier to find than 6V). No one will know the difference, you will have a better electrical system.


Never underestimate the human ability to elevate stupid to a whole new level!.
Re: 4CA to 6CA Conversion
#9376 03/24/06 11:59 am
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CW and CCW advancers can be differentiated by watching the cam position shift as the bobweights are moved, by hand, out against the springs.
Advance is opposite to the designed direction of rotation, ie: a CW advancer will move the cam CCW as the bobweights are moved apart.
I resisted fitting a Boyer for a long time but after spending significant money building a new engine I decided that the very smooth advance curve of the Boyer would have to give it an easier time than very choppy advance of the std advancer.
Not sure if BSA used ET ignition at any stage but be aware that if they did the advancers for that system had an advance span of only 8 deg, generally 8 or 12 deg is marked on the back of the advancer plate.
As indicated by others the conversion to 12V is pretty easy and your existing 6V coils should be good with the Boyer.
Gratuitous advice from an ex ignition Luddite ? smile Fit a Boyer.


1969 TR6R
7.62 x 51 is not a maths puzzle.
Re: 4CA to 6CA Conversion
#9377 03/24/06 12:19 pm
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Quote
Originally posted by Bob95065:

Will my 4CA advance unit work with a 6CA ignition? The workshop manual says the ignition advance for this engine is 37°. Did Lucas make a 37° advance unit for the 6CA plate? if not what advance unit should I use?
Bob Elliott
The manual means set ignition timing to 37 degrees before top dead centre, with the auto-advance fully advanced.


Amateur Loctite enthusiast.
Re: 4CA to 6CA Conversion
#9378 03/25/06 2:01 am
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Yep ! Suffering from flopped logic there. laugh
The first ever picture of a LH gearchange Britbike I ever saw was the result of a "flopped" [reversed] negative when the photograph was printed, similar cerebral principle. :rolleyes:
Well caught.


1969 TR6R
7.62 x 51 is not a maths puzzle.
Re: 4CA to 6CA Conversion
#9379 03/26/06 12:04 am
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Bob -
My information from my boss who was there selling and working on BSAs all through the 60's is this...

Only the early 4CA auto advance units (AAU) had the bad cam profile and these are (for the most part) spotted by their 10 or 11 deg advance, as marked on their backside.

You also must NOT use an ET ignition AAU which is marked 5 degrees.

If you have a 4CA AAU marked 12 deg, then by all means try it. Simply listen for pinging and watch for very hot running. If it seems OK, then while you ride you can be looking for a good 6CA AAU. You can use one from either a BSA or Norton, but NOT a Triumph. That seems like a fairly prudent course.

The 4CA AAU when used with the vastly superior 6CA points plate will just barely be long enough. But it will work.

Most all AAUs need at a minimum new springs and a good lube job. Lube ALL moving surfaces with high temp grease at least once a year. That means complete disassembly. A 5 minute job.

Then you have to set the timing again. That's not such a fast job.

BTW... If you'll buy one of these degree wheels you can strobe time the engine at full advance (2500 RPM) and really do a jam-up job. See eBay auction # 4623924999. These will work on ANY Brit bike with an AAU.

Hope this helps! :bigt:


Don't hide 'em, Ride 'em !!

RF Whatley
Cornelia, GA
Re: 4CA to 6CA Conversion
#9380 03/26/06 11:21 am
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You mean that it's possible for example to use the 4CA points plate together with the 6CA AAU?
BR

Re: 4CA to 6CA Conversion
#9381 03/26/06 11:40 am
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>>Only the early 4CA auto advance units (AAU) had the bad cam profile and these are (for the most part) spotted by their 10 or 11 deg advance, as marked on their backside.<<

As late as 1966 BSA was struggling with points bounce. So it is not just the early 4CA A unit. The problem was fixed with the 6CA. As BSA's are seemingly more prone to the points bounce problem, why would you risk it?

>>Most all AAUs need at a minimum new springs<< - use the Lucas replacement springs with "HD" at the end of the P/N. That is "HD" for heavy duty, not that quait little American motorcycle manufacturer laugh

These springs replace the worn out originals and give a slowed advance curve that reached full advance later. Much better set up.

>>You mean that it's possible for example to use the 4CA points plate together with the 6CA AAU?<<

Why would you? that is a retrograde step, IMO. You lose the advantages of the 6CA points plate and retain condensors on teh points plate and non independant timing adjustment. IMO, anythinr related to the 4CA is just a bad deal. They need to be off of a bike if it is a ride. But that is just me.


Never underestimate the human ability to elevate stupid to a whole new level!.
Re: 4CA to 6CA Conversion
#9382 03/27/06 1:17 pm
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Quote
Originally posted by Rich B:
You mean that it's possible for example to use the 4CA points plate together with the 6CA AAU?
No one ever said that. If you didn't have such a hair trigger maybe you'd stop and read these posts.

:bigt:


Don't hide 'em, Ride 'em !!

RF Whatley
Cornelia, GA
Re: 4CA to 6CA Conversion
#9383 03/27/06 1:30 pm
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Whatley

If you would READ ALL THE POSTS, you would see it is a quote from a prior post. I merely quoted a prior post and answered it with my opinion.

I FIRMLY believe anything related to 4CA ignition is better left as a shelf decoration than used on a daily (or even weekend ride A series BSA). Even mixing and matching is, IMO, a bad deal on a BSA. Those motors and that specific ignition didn't play well together. 2c


Never underestimate the human ability to elevate stupid to a whole new level!.

Moderated by  Allan G, Jon W. Whitley 

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