Useful Upgrade: Lucas 6CA Points Assembly
If your like me, you might find yourself spending a lot of time on eBay searching for parts
In fact, I’m sure you might have run into a scenario similar to the one below..
Once the search results are loaded and displayed you might see various auctions and lots throughout the pages
Popular lots you might come across may include Lucas contact breaker assembly's that are sold next to nothing
Since most folks upgrade to EI (electronic ignition) the cost of points, plates and advance-units is pretty cheap these days
So is there anything in those parts lots worth purchasing or bidding on?
The answer is YES
For those who have the early 4CA points plate and set-up, the later 6CA points plate is what you should be keeping an eye out for
I'll tell you why below
Today we are going to talk about a useful upgrade on most vintage Triumph and BSA twins prior to 1968
This "upgrade" will offer you better reliability, accurate timing, better performance and economy
So what's the upgrade you might ask?
The upgrade consists of removing your old 4CA points plate assembly and upgrading to the later 1968-1972 6CA plate and assembly (should you still be running points)
Before we cover this post I want to make somethings clear
I do NOT recommend yanking your points out of your bike and begin replacing your entire set-up
If you're building or re-building your old Triumph or BSA and you want something "better", by all means give it a shot..
Now that we got that out of the way, let’s dive in..
Lucas 6ca history and development
In 1968 Lucas developed a new contact breaker points assembly called the 6CA
The 6CA points plate assembly was designed to replace the older outdated 4CA units as used up to 1967
Now I haven’t read this, but I assume Lucas developed this new contact breaker plate due to the development of the Triumph and BSA triples that where introduced in 1968
Triples require each cylinder to fire independently and accurately
Unlike the early 4CA plates, the 6CA points plate assembly’s will also allow you to adjust each contact breaker independently on your Triumph and BSA twin, just the like the triples
Does making each contact breaker "independent" and "fully adjustable" on the 6CA plate better than the 4CA plates?
Short answer: yes
Know the difference
4CA points plate
In order to explain why the 6CA plate is a better plate and design, I must cover the early 4CA plate and its flaws
Lets cover some of the details below that the 4CA plate has to offer (or lacks)
- The 4CA points plate is NOT fully adjustable
- Features 2 (sometimes) hard to mount condensers
- 4CA points plate is not as accurate as it could be / should be when compared to the 6CA units
6CA points plate
Now that you know what the 4CA plate offers (or lacks), lets go over some details on what the 6CA plate has to offer and why I find it to be an "upgrade"
- 6CA points plate is fully adjustable - that includes points gap, timing and an adjustable secondary plate. Each contact breaker is 100% adjustable to time cylinder #1 and #2 with precise timing
- 6CA points plate does not feature condensers. This gives you more room to work with and also keeps your condensers out of the hot timing chest
- 6CA points plate feature felt "wicks" to keep the advance-unit lobe lubed
- Easier to find parts both new and used
The key advantage to the 6CA plate assembly is the fact that you can now adjust each cylinder independently
Those that have the 4CA plates may understand that cylinder #1 might be "spot on", however, cylinder #2 might be off a few degrees
What do you do in a case like that?
Split the difference, or use a 6CA points plate..
Useful part numbers
There are a few useful part numbers you should know for the Lucas 6CA points plate assembly
Below are both Triumph and BSA factory part numbers which happen to all be interchangeable (not all superseded numbers may be listed below)
*click on the blue hyperlinks within the chart to be taken to the replacement part
|Part type||Part number|
|Condensers||54420128 & 19-1847|
|Eccentric screws||54419220 & 99-0769|
|Contact breakers (twins)||54419827, 99-0772 & 19-1849|
|Points plate (complete)||54419097, 99-0768 & 19-1841|
All Lucas contact breaker plates will have a 2 digit stamping on the back signifying the month and date of manufacture
The one as shown in the photo is rather blurry but reads "9-70" which would be September, 1970
Checking the date is important as plates from 1973-1978 would be the 10CA points plate, which is similar to the 6CA
All 6CA points plate both Triumph and BSA are interchangeable
Applications & Retro-fitting
The Lucas 6CA points plate assembly was used on the following models as OEM from the factory
|Triumph||(all) 650 unit twins||1968-1972|
|Triumph||(all) 350 & 500 unit twins||1968-1974|
|BSA||(all) A50 & A65 unit twins||1968-1972|
Retro fitting the later Lucas 6CA points plate assembly's on early models can be done on a budget
You can re-use your original advance unit, however you will have to use the later condensers and mount them externally on your machine
The Lucas 6CA points plate assembly can be used on some of the following models to replace the early 4CA assembly (non-distributor or magneto models)
|Triumph||(all) 650 unit twins||1963-1967|
|Triumph||(all) 350 & 500 unit twins||1963-1967|
|BSA||(all) A50 & A65 unit twins||1962-1967|
It is optimal to make sure that your vintage Triumph or BSA twin is running in top shape
Sometimes small "upgrades" can be proven to have the greatest impact
The 4CA points assembly works and will continue to work, however, if you happen to have an extra 6CA points plate assembly laying around your shop, or you plan on building another project, I highly recommend the conversion
Timing accuracy is something that shouldn't be overlooked, after all, your engine depends on it
I was reading my book by Stan Shelton called "Triumph Tuning" and I happened to stumble across a chapter in regards to this very own topic
Within the book the chapter briefly covers 4CA and 6CA points plate while listing the advantages and disadvantages between the two
I found this article to be excellent and well worth the read especially for racing purposes
This book has other great details and can be found on eBay by clicking here (I have no affiliation to the seller)
Thanks for reading
Thank you for reading today's blog post
I hope that you have found this article to be helpful and informative
Feel free to drop us a comment in the section below
Thanks and ride safe!