Moto-Witt DMC on '74 3C question about the toothed ignition rotor position

G

gpzkat

Full member
Location
Mission Viejo, California
My bike is #2054 and was built in July 74, titled as a '75. I have installed the Moto-Witt DMC/32 with the charge coil, and it runs and charges, but I haven't been able to get the timing exactly right. It's close, but I have run out of adjustment on the assembly plate. It's retarded too much. Like me, I suppose. Right up to the end of advance adjustment, it's still about 7 degrees retarded.

The stator has a dotted line for TDC peened into it, and three faint rectangular glyphs about where the advance should be. Be that as it may, I've verified the advance with a strobe and a degree wheel, and it's advancing correctly.

The Woodruff key on the crankshaft end ensures the stator rotor's positioning. Carefully checked TDC on 1&3 lines up the small slot on the engine cover to the dotted line on the rotor.

Here's my issue/question: My stator rotor has an inner metal U-shaped protrusion (U groove). It's for aligning the original single-tooth ignition rotor, which has no set screw.

The DMC's instructions say that the "pickup position should be close to the 4th tooth on the trigger wheel." I did that, as best I could, but given the stator's U-groove, it is tricky to set it so the stator rotor fits onto a tooth correctly and with the 4th tooth position right. I've done some measuring and have the stator on a tooth 'correctly'. It's in the only position it can be, and I think it's incorrect for the timing.

I suspect that this U-groove in the stator rotor isn't quite in the right position vs. the toothed ignition rotor. Since the new toothed rotor has a set-screw, the U-groove isn't needed for positioning, and I'm inclined to do away with it by some means (remove the two 'ears'). That would allow the adjustment I need. There'd be no going back to the HKZ! I'm a little hesitant to do surgery and wonder if anyone has advice on the matter?
 
Last edited:
Dellortoman said:
?? How can a stator be keyed to the crankshaft? That would make it a rotor.


OK, now I'm really confused. What is a stator rotor?

Maybe some pictures would help.
Click to expand...
Sorry, long day. Yes, the rotor. I see Laverda calls it the flywheel magneto. I'm used to the flywheel being a different thing entirely, on cars anyway. #14 and its support #7 on this picture, i.e. the rotor. In my head I call it the stator rotor, but left off the rotor part. Obviously, I'm not an electrician!

Laverda.jpg
 
Last edited:
As your bike does not have the indent on the crank journal for the rotor set screw, adjustment can be a bit tricky. Your diagram shows the later HKZ alternator/flywheel assembly, your bike would have had the ignition rotor located by the ears at the inside of the flywheel with the rotor floating on the crank and pushed into the slot by a large spring, different set up all together.

What is unclear is which DMC version you have. You state "toothed rotor"... how many teeth? Have you retained the original pick-up/alternator base plate or replaced it with the single pick-up version? The OE pick-ups work with 2 teeth on the rotor, the single pick-up uses a 12-tooth rotor.

In either case, the "ears" inside the flywheel can be done away with to ease adjustment.

Stock spec 1000 triples are set to 32° BTDC full advance. DMC idle advance usually ends up at around 3-5° BTDC, which isn't nearly enough for a steady idle. I work around this by using one of the 30 or 27° curves and setting this to 32° when strobing. The newer DMC32 units with the single pick-up have been improved in this regard, idle ends up around 5-8°BTDC.

The late idle timing is a precaution against damaging the starter freewheel through kick back from too much ignition advance. It all works fine as long as the battery is nicely charged. Wonky batteries can cause erratic timing during starting causing severe kick back, quickly damaging the starter freewheel. Questionable starter motors can cause 200A or more to flow to the starter, leaving insufficient current for the DMC unit. Current can drop to under 8V during starting, leaving the DMC "wondering" what it's expected to do... current should not drop beneath 10V at the battery during starting to keep the DMC reliably within its' working window of 6-18V. Old wiring can further reduce a drop in current, even though 10V might still be available at the battery when checking.

Who supplied your DMC? Why did you not recieve the original manual with it? I have manuals for the earlier DMC I, DMC II and DMC32 versions, would need to check if I have one for the DMC 32 12 - 2 version.

piet
 
Thanks, very helpful. It's a single pickup, 12-tooth rotor. DAMclassicracing supplied it with paper instructions, which mention only what I quoted above on the 4th tooth position vs the pickup, and centering the plate for adjustability. I've got copies of other instructions, can't spot anything more detailed about this one issue, or the trigger orientation that Shuggie mentions. I can see by his picture of the 2-tooth that it would be critical on a later model with a set screw indent on the crank journal, but when fitted correctly, it would be correct vs. positioning, and simpler to figure out. Anyway, I'll remove the ears and time it per your method.

The pic of the diagram above was to clarify what I meant by 'stator' to Dellortoman. I had called it the 'stator rotor' to distinguish it from the ignition rotor, but later on I left off the word rotor, now corrected. I didn't notice the set screw in that pic until just now. I use a '75 Parts list PDF for reference, but realize it's a bit later, with some differences - for instance, no spring due to the use of a set screw. This issue overall really gave me a workout mentally and physically.

The big Suzuki GS fours are known for the same kickback issue. I got a GS1100E given to me that occasionally had a nasty clank, and supposedly needed surgery. It was a weak battery.

DMCignition.jpg
 
Last edited:
How are you going to secure that rotor to the crank? I hard the forked set up years ago on my 74 3C but after an accident it was damaged and I could only get the later rotor with the grub screw. It worked well for a while but eventually it came out and ripped the pick ups apart.
 
pf1 said:
How are you going to secure that rotor to the crank? I hard the forked set up years ago on my 74 3C but after an accident it was damaged and I could only get the later rotor with the grub screw. It worked well for a while but eventually it came out and ripped the pick ups apart.
Click to expand...
It has a set screw, just no indent, which would simplify things, location-wise.
 
You must log in or register to reply here.
Back
Top