Ignition coil diodes for Lucas Rita
Ignition coil diodes for Lucas Rita
I'm installing Dyna 12V coils on my 77 900SS that is currently running a Lucas Rita ignition. The standard wiring for this system is two 6V coils wired in series. You can run two 12V coils wired in parallel, however the wiring diagram states you must have diodes from the negative trigger lead from the ignition box, which attaches to the two negative terminals on the coils. There is no value given for this diode, and it identifies it only as a "Marconi PM6A6" diode. Anyone know the value for this diode, or know a source fo this diode, or an acceptable substitute? Thanks.
1982 Laverda 180 JOTA, 1975 Moto Morini 3 1/2 Sport, 1993 Moto Guzzi Daytona, 2010 KTM Adventure 990, 1974 Laverda SFC #17188
Spub,You can get around all of that by using a single dual output ign. coil.
The Rita setup fires both plugs at the same time anyway. I've used an Accel coil for a Harley on my 77 SS race bike for about 20yrs. If I remember correctly the coil primary resistance is 3.0 ohms. The only trouble I've ever had is the ign. pickup falling apart. And that was fixed with big blobs of JB weld and some stainless bolts.
The Rita setup fires both plugs at the same time anyway. I've used an Accel coil for a Harley on my 77 SS race bike for about 20yrs. If I remember correctly the coil primary resistance is 3.0 ohms. The only trouble I've ever had is the ign. pickup falling apart. And that was fixed with big blobs of JB weld and some stainless bolts.
I've got a Lucas Rita on my 76 900SS, originally with the 6V PVL coils but I converted to a dual output Dyna green (3 ohm) coil a couple of years ago. No diodes :-)
I had the coil go on me after about 2 years and the consensus (on the bevel list, talking with Dyna, and also with Mistral Engineering in the UK - they sold the Rita until recently and can check it or put you in touch with someone who can; they checked out my complete system and the coil for me after the failure) was that - perhaps - the system would benefit from either the 5 ohm (black) Dyna dual output coil or the 3 ohm plus a 1.5 ohm ballast resistor in series. I had a spare 3 ohm green so I've added the 1.5 ohm ballast as a precautionary measure. I came across at least one other who had the same problem with the Dyna 3 ohm green failing, even though both Dyna and Mistral originally felt the 3 ohm would be ok. The additional resistance limits the current in the coil, less potnetial for overheating, apparently.
The PVLs (or Lucas), even though they're 3 ohm, being the 'wet' oil-filled type of coil are less prone to overheating and are able to disperse the heat better, allegedly.
But no diodes... It's a very simple fit of a dual output Dyna.
Cheers
Geoff
I had the coil go on me after about 2 years and the consensus (on the bevel list, talking with Dyna, and also with Mistral Engineering in the UK - they sold the Rita until recently and can check it or put you in touch with someone who can; they checked out my complete system and the coil for me after the failure) was that - perhaps - the system would benefit from either the 5 ohm (black) Dyna dual output coil or the 3 ohm plus a 1.5 ohm ballast resistor in series. I had a spare 3 ohm green so I've added the 1.5 ohm ballast as a precautionary measure. I came across at least one other who had the same problem with the Dyna 3 ohm green failing, even though both Dyna and Mistral originally felt the 3 ohm would be ok. The additional resistance limits the current in the coil, less potnetial for overheating, apparently.
The PVLs (or Lucas), even though they're 3 ohm, being the 'wet' oil-filled type of coil are less prone to overheating and are able to disperse the heat better, allegedly.
But no diodes... It's a very simple fit of a dual output Dyna.
Cheers
Geoff
Wdietz and Geoff:
Thanks for your replies. After giving this more thought, I've decided against 2 12V coils a this would require too much of a current draw. I actually had lying around (for another application) 2 6V Dyna coils which are rated at 1.5 ohm each and wired them up in series, to try. Bike starts first kick and runs, no problem. These coils are dual output, so I had to ground the rear outputs (as suggested by dyna), and this works. Too bad they do not make 6V single output coils.
I formerly had 2 6V PVL coils, but one went bad, and this was what caused my tinkering to begin with.
Agreed, one dual output 3ohm or 5ohm coil would likely be a better solution, but I'll see what happens with these two 6V Dynas.
Thanks for your replies. After giving this more thought, I've decided against 2 12V coils a this would require too much of a current draw. I actually had lying around (for another application) 2 6V Dyna coils which are rated at 1.5 ohm each and wired them up in series, to try. Bike starts first kick and runs, no problem. These coils are dual output, so I had to ground the rear outputs (as suggested by dyna), and this works. Too bad they do not make 6V single output coils.
I formerly had 2 6V PVL coils, but one went bad, and this was what caused my tinkering to begin with.
Agreed, one dual output 3ohm or 5ohm coil would likely be a better solution, but I'll see what happens with these two 6V Dynas.
1982 Laverda 180 JOTA, 1975 Moto Morini 3 1/2 Sport, 1993 Moto Guzzi Daytona, 2010 KTM Adventure 990, 1974 Laverda SFC #17188
In response to an inquiry I sent to Mistal Engineering, the company who produced the RITA units, they state two 12V coils in Parallel are not recommended, even though this is an option formerly given by them in Trimuph applications. They feel current draw would be too much, and suggest two 6V wired in series. Just in case anyone out there with a RITA ignition gets any ideas like I had....Also, the 2 6V Dyna coils (1.5 ohm each) have really done the trick for starting, bike now starts first kick, and I mean before that kick even reaches the bottom of the stroke....I attributed the hard starting in the past to carburation, but it appears igntion issues have a lot more to do with it.
1982 Laverda 180 JOTA, 1975 Moto Morini 3 1/2 Sport, 1993 Moto Guzzi Daytona, 2010 KTM Adventure 990, 1974 Laverda SFC #17188