The BSA A7-A10 Forum

Technical => Lucas, Electrical, Ignition => Topic started by: roadrocket on 23.06. 2019 14:29

Title: Best cam ring, where?
Post by: roadrocket on 23.06. 2019 14:29
Hello

I have realised that my inability to time the bike stems from a worn cam ring. On cylinder fires way before the other. Who sells the best cam ring? Also, is there a way to ensure that the plastic shoe on the moving point is true? Is someone selling a better product that the black plastic stuff?

Otto in DK
Title: Re: Best cam ring, where?
Post by: RDfella on 23.06. 2019 20:16
Are you sure it's a worn cam ring? Just had a real hassle with what I thought was a worn or inaccurate cam ring, only to find when I clocked it that it was perfect. It was the bore in the cam ring housing out of concentricity with the armature bearing.
Title: Re: Best cam ring, where?
Post by: roadrocket on 23.06. 2019 20:26
Hmm, it is new, but from a very reputable expert. Has not run well with either of the two cam rings I have. Maybe time to go electronic?
Title: Re: Best cam ring, where?
Post by: RDfella on 23.06. 2019 20:42
Are the points gap different? That would be a likely indicator that the problem is the housing, not the ring. It's easy enough to take the ring out, put it in a lathe and run a dial gauge on the cam surface. To check the housing, you'll need to take it off, mount it by putting the cam ring recess in a lathe and put a dial gauge on the armature bearing.
Title: Re: Best cam ring, where?
Post by: JulianS on 23.06. 2019 21:02
Worth checking that the bearings are sitting square in their housings and are properly shimmed, if the insulator gets damaged when bearing being fitted it can cause bearing to be off centre and points assembly to run out of true.

It is not just the points gap but also the firing point which is important.
Title: Re: Best cam ring, where?
Post by: Swarfcut on 23.06. 2019 21:09
Rocket & RD... The more you consider the design of the K2F the more amazing it is that it actually provides the sparks in more or less the right place, bearing in mind that any inaccuracy in the cam ring and housing is magnified by the pivoted points arrangement.  All working way beyond their original design life.
  The idea of a steel cam ring moving in an alloy housing on a manual maggy is a recipe for short term accuracy, not something to be relied upon 50 years later. So if the cam ring proves to be fine, an expensive modern CNC end housing could be the answer, providing the basic assembly as outlined by JulianS is OK.

  As regards sourcing a new ring, my usual go to's Priory and Brightspark no longer list them, so it will be a bit of a gamble from any supplier you choose.


 Swarfy.
Title: Re: Best cam ring, where?
Post by: Triton Thrasher on 23.06. 2019 22:04
As Swarfy says or implies, you can stone the the ramps or shim the corners of the housing or jam shims around the cam ring and get pretty accurate and equal timing, but not for all that long.
Title: Re: Best cam ring, where?
Post by: beezermacc on 23.06. 2019 23:31
Don't worry too much about the points gap provided the discrepancy isn't ridiculous. Check the opening points are 180 degrees apart. If not, get the Dremel out and, carefully (?!) keeping grinding a small amount off the lifting ramp which is firing soonest.