For sure... But guys did it later on flatheads for a variety of reasons. Most commonly, a full race motor that needs lots of timing at higher RPMs is super hard to start when using a dizzy or magneto with static timing. If it's adjustable, you can retard the timing for the start procedure and then advance it once you are ready to rock.
All of the Roto faze distributors have that feature. I would imagine that’s where the Roto in the name came from. The adjustment cable I posted above has an indexing feature so you can count the clicks and get back to where you were…
Man I just saw someone make a base plate like this for a flathead maybe it was @JR-69 roadster? I can see it plane as day in my head. If not maybe @jordabennett did it?
Pricey and too new, but it offers 15° with good control . https://www.summitracing.com/parts/msd-8680 https://www.msdignition.com/products/2-step_and_rpm_control/timing_controls/parts/8680
If you study or take a distributor apart all these parts in the way their machine and aligned affect correct true timing not including time and chain Cam & gears , there even adjustable rotor ****ons this just a generic parts breakdown
In the photo you can see the outer ring holding the actuating cam for the points that is moved be the cable. An external spring biases retarded & the tension on the lever holds it in place
Kind of intrigued by all this as I had never heard of this before. Trying to understand how it would work. In this pic, I circled in purple what looks like the cable, in red the twin coils mounted to the firewall, and in yellow a return spring?
In this pic, I circled in purple where I’m guessing the cable would attach, and the blue line represents the parting line between the fixed section of the housing above the blue line, and the movable (rotating) section below the blue line. Is this correct?
It wasnt me, but I don’t see why you couldn’t modify a front cover to have a slip plate to allow it to rotate by lever. Wouldn’t need to modify the dizzy do the modifications in the engine plate itself. would be similar to how early HD timers worked with and advance lever as mentioned above. Aftermarket Magnetos for HDs are a fixed base and have a slip plate for advancing.
Thinking about this. The trick would be to have it stay put after the cable or lever is pulled. I wonder if you make it with a series of detents and small spring loaded balls between the two plates so it has a positive stop. With some geometry, you could figure out various degrees advanced or retarded for each detent stop.
Just watching this cool vid, and at the 20 min mark, the owner/builder shows how the manual spark advance works with a cable. pretty nifty stuff.
Let me just put this on the record. I got one of these from @KiWinUS and if you are in the market for an indexing plate, stop looking. This is the best one I have ever seen. Period. It is not just a part. It is jewelry pretending to be hardware. The kind of thing you hold in your hand longer than necessary, turning it in the light, wondering how something this clean and this precise ended up bolted to a hot rod instead of locked in a gl*** case somewhere. It is overkill in exactly the right way, which is the only way overkill should ever exist.
This relates to a few thoughts I've had — not Flathead-related: sorry — about rigging manual timing control to distributors not so equipped. The obvious way would be to modify a vacuum advance mechanism, so any distributor that has provision for vacuum advance potentially has provision for manual control and, importantly, possibly vice versa. What I'd really like is both vacuum advance and manual control on the same distributor. My question is this: would these be better in series or parallel? Do we need OR logic or AND logic? Is there any situation where we'd want the full range of vacuum advance plus the full range of manual advance on top of that? Or is it a case of being able to use either way within what would ordinarily be the vacuum advance range? I'm thinking a nominally series linkage which pulls the vacuum canister away from the distributor base by means of a cable etc. That would use up part of the range available for vacuum advance, so that a vacuum signal would still result in advance through the remainder of the range. That would obviate the need to modify the base to enable a larger advance angle: hence my question. Perhaps this needs its own thread, though the thought isn't yet fully formed even if it has already taken in the idea of a distributor-magneto hybrid. Apologies for the tangent.
On a Triumph, you just reach down and give the distributor a twist. At speed. At Bonneville….. Chuck Zeglin owner/builder/rider
The Jalopy Journal
