Darmah Ignition Repair Adventure

[tim61]

I recently went through a trouble shooting process on the ignition of my 1978 900SD Darmah, and Steve thought it would be helpful for me to share my experience with other Bevel Heads. So, here it goes…

After finishing a long drawn out cosmetic restoration on my Darmah, I thought I was ready to fire her up and go for my first ride. The Darmah ran great when I took it apart, so I had no reason to think it would not still run great. So, I turn on the fuel, turn the key, and hit the button. Nothing. Not even a click. Great. It wasn’t supposed to be like this.

I back tracked through my resto in my head to see if I could come up with a likely culprit. I had cleaned the outside of the solenoid, and in retrospect I though I may have forced some solvent into the body of the solenoid. It didn’t occur to me that a suitable replacement for the Lucas solenoid would be available (I have since learned that many Japanese solenoids work, and even Ford solenoids are said to fit nicely!). Instead, I decided to take mine apart and find the problem. I drilled the 4 rivets out that hold the body halves together. Inside I found what looked like the wreck of the Titanic. There was so much corrosion it was hard to tell what was what. I cleaned and polished all the pieces, and reassembled the solenoid, sealing the body halves with Permatex and replacing the o-rings that seal the main terminals. I replaced the 4 rivets with 4 machine screws washers and nuts. After installing the solenoid on the bike, I poked the starter button. The engine immediately turned over. Problem solved.

I decided before I tired to actually fire the bike I would back up and check to see if I had spark. I removed the plugs, grounded them, and exercised my new solenoid. No spark. I thumbed the kill switch on the right handlebar, and I saw a spark!?! I checked the kill switch and it tested fine. I tried again. No spark. I thumbed the switch again, and got a spark. A quick question to the BevelHeads newsgroup confirmed that the kill switch grounds the coils when turned to off, causing the field in the coils to collapse, providing a spark. This is in essence exactly what the rotor passing by the ignition pick ups does. So, I know the coils/igniters are good, because I can produce a spark. But I also know I am not getting a signal from the ignition pick-ups to deliver that spark when the engine is turned over.

Backtracking again through the resto in my head, I remembered something. When I removed the clutch cover to polish it, I also replaced the bakelite gland nut on the ignition wires with a new metal one (they are still available directly from Ducati!). When I removed the old nut, I noticed that the wires from the Bosch ignition pickups were loosing their insulation. It appeared to be dried up, and cracking. Being that it ran fine, I made the mistake of assuming it was OK. I know, I am a little slow on the uptake!

So, I removed the cover again and took a closer look. Upon peeling back some of the outer loom containing the 2 pairs of pick-up wires, I could see large pieces of the insulation cracked and missing. A quick check with the ohm meter confirmed that both pick-ups had continuity to ground. Again assuming that the pick-ups would be made of the same material as the rest of the Darmah (Unobtanium), I decided to attempt a repair. I went to the electronics supply store and purchased several yards of 3M heat shrink with the adhesive inside. I did not want to have to re-time the engine, so I decided to try to re-insulate the wires while the pick-ups were still in the cover. Not impossible, but time consuming. I removed the gland nut and the female spade connectors on the ends of the pick-up wires where they plug into the igniters. I carefully stripped all the rotten insulation off the wires. Most of it was soft and gooey. The rest was brittle and cracked. I guess Italian wire does not like hot oil. After thoroughly cleaning the wires with alcohol, I slipped the heat shrink onto the wire. After heat shrinking all 4 wires, I slipped the 4 into a bigger piece of heat shrink to replicate the original harness. I soldered the spade connecters back on, and reinstalled the cover and wiring.

Back to step 1. Ground the plugs, thumb the starter button…SPARK!!!! Hooray! I installed the plugs, flipped the choke lever, and VAROOM, the Darmah came back to life. The Conti’s had never sounded so good!

Hope this story may help a few ‘Heads get their bikes rolling again. Now go out and ride…

Tim O’Mahony
1978 900SD Darmah

[enslinfallbrook]

Tim;

Wow! Your write up was unbelievably helpful to me. (Long story short); Witnessed the same mess you described where the pickup wires leave the clutch case. All four wires were stripped bare under the "corroding" rubber harness!

It's no wonder when trying to start the bike that it sounded as if it were timed completely wrong; as in cam timing, ignition timing, and every other type of timing that can go wrong! The spurious signals the pickups were transmitting
along this rats nest made spark timing an entirely random event!

Will get around to the repair this weekend. However, the wires seem to terminate at the pickups by disappearing directly into the pickups themselves. Nothing in the way of a connector. Did yours look the same?

I'm also wondering about your experience with the 3M stuff; is it holding up well inside the clutch case itself? I'll probably do the same thing, but am a little concerned about the "burn though rate" of the stuff inside the clutch cover.

Isn't this what forums are for-revealing how AR we are about this kind of stuff!

Bill

[BevHevSteve]

Yes the wire disappears into the pickups, no connectors. What i did was replace the wires themselves. To do this, I cut each wire about an inch from the pickup, after making a careful drawing of which wire goes where. I soldered on new wire that i was told couldhandle the oil bath and heat, then I used THREE BOND - also sold as YAMABOND at your local yamaha store to coat the exposed parts of the wire. I used the glue inside expensive 3M heat shrink stuff around the pairs of wires extending it out the gland 3 inches. I used vacuum hose [it resists heat great] to cover both pairs of wires, extending it inside the gland an inch and going all the way out to the 4 gang connector. Some of our bevels don;t have this connector which makes removing the cover a PITA with all the wires still connected. If your bike doesn;t have one, install one about 18" up from your cover [it will sit on the little cross frame piece under the fuses etc].

This must be done on ALL Bosch ign bevel drives. You are fixing 2 problems. Bosch was never told by Ducati that their pickup wires were going to be in a hot oil bath or running right along side a header pipe. BAD ducati.

[Mad Max]

Why did I not check the forum before I got the tools out?

I to recently gave my '82 SS a tidy up which involved pulling the frame from the engine to get access to the rear head. When I did this the ignition pickup wires snagged on the frame, and I damaged them. (Does the clutch cover need to come off before removing the frame from the engine?) When I reassembled the bike and tried to start it I found I had spark on one cylinder only. I knew I may have damaged the pickup wires so I removed the clutch cover and found the same thing you guys are talking about inside the clutch cover, and also that the insulation was very brittle outside of the cover. I removed the pickup assembly without realising it was a timing adjustment and replaced the wiring. When I replaced the wiring I did not take into account the polarity of the pickups! Now the bike runs OK, but I have lost some power and revs. Have I got a sensor wired backwards? (Does it matter?) How can I re time the engine?

Thanks

[Craig in France]

Hi Steve

FWIW ..

A small point, but I don't think it's the oil that causes the insulation to fail. The same pick-ups and wiring were used on Laverda triples, safely installed in an oil-free environment - and the insulation comes off the wiring just the same ...

So, for this at least, we can't say it was Ducati's fault. Rather lay the blame (such as it is, after 30 years!) at Bosch's door!

Ciao

Craig in UK

[Mad Max]

To answer my own question, it does matter if the pickups polarity is reversed, the auto advance does not work. After making a timing wheel to screw into the end of the crank behind the brass plug I discovered that this area is the oil feed for the crank and big ends, I ran the engine briefly with the timing wheel attached but was losing to much oil so abandoned that plan. (The timng wheel may come in handy for valve timing experiments in the future anyway so nothing lost). I then made a rough perspex "gear gazer" for the rear triange bevel cover so I could point a timing light at the bevel gears. This froze the gears as you would expect but I did not see any advance. I reversed the pickups and found that the advance worked correctly on the front cylinder but not the rear. I then reversed the rear cylinder pickup again but still no advance. I then connected an analouge multimeter on 0.3V scale to the front pickup and found the meter flicks postive with the (+) lead in the LHS of the plug when the engine is slowly turned over wth the kicker. The rear cylnder pickup flicked the same way but at much lwer voltage. I loosened the external screw that holds the pickup plate and moved it closer to the rotor until the voltage looked the same as the front one and ran the engine again with the timing light on the bevels. I now had correct advance on both cylinders. I cannot say I have the timing exactly right but I do know that the bike seems to run normally and I can see the advance working now. Next time I will mark the bloody wires!

[pilotg]

Greetings from NZ,

After a long, (and somewhat more expensive than I first imagined) rebuild of my 1981 SD900, I today turned the key and hit the switch for the first time. Turns over fine, good spark, and lots of loud bangs (my ears were ringing after 2 minutes trying). I've got a brand new, fully charged battery.

In renewing the sprag I took a good look at the pick ups. They were rewired by the previous owner. The soldering looks ok but the two wires from one pick up look terribly close and one has a breakdown of the 'goo' that the soldering is coated with.

Two things: firstly I may have inadvertently knocked the pick up during the replacement of the side cover on the rotor. That might have disturbed the setting. I'd given the cover a tap with a rubber mallet in frustration before I realized what was preventing it mating with the casing.

Secondly can someone tell me the correct name of the 3M product mentioned above with the adhesive inside? I'd like to re do the soldering.

The Threebond might be difficult to source down here so will any oil resistant gasket goo work?

After checking the pick up setting (I have a setting tool) I'll try cleaning out the 38mm PHMs. I have a pair of PHF 32s I'm refurbing as well. In the meantime I want to get riding this machine. It looks fantastic, but stationary!

On a different track, I checked the compression with an el cheapo guage. This was with a cold engine that has no recent (last ten years, top end rebuild prior to that) use at all. The pressures were a bit low at 120 ish. Should I be worried at this stage? I figure there might be some build up on the valves after all this time. I'm hoping a good run with some fresh oil might sort that out. Am I right?

Many thanks

George

[pilotg]

It's ALIVE!!!!!!!

It appears even professional auto electricians can make mistakes....

After a restless night I once again drained the oil from the sump, removed the clutch cover and starter motor and headed off to the sparky's place. He was confident the pick ups were sound and that the soldered joints weren't the problem. He tested the pick ups and they both showed just over the 220 ohms mark. He was also very confident that he had wired the pick ups to the connector block (as per Steve's post above). However, he wasn't so sure that he had done the same with the coils.

Back in the shed I re checked the pick up settings and they were both within the tolerance set out in the official Ducati workshop manual. I refitted everything and then swapped over the coil wires. Tank on, fuel connected..

With not a little apprehension I twisted the throttle twice and with one light press on the starter the beast roared into life. It couldn't have started easier. I'm not ashamed to say that I was grinning from ear to ear.

It still needs tuning and the idle resetting but it starts and sounds like a big bevel twin.

Tomorrow it's off for the warrant (govt inspection), registration and then for the first time in 15 years it will be road legal. I can't wait.... photos soon...