75 860GT ignition question

If you need technical information or help with your early crossover gearchange squarecase Ducati 860/900 engine - post your FAQs, comments & questions here.
blaine.hale
Mariana
Posts: 48
Joined: Thu Jun 26, 2014 10:05 am

75 860GT ignition question

Post by blaine.hale » Mon May 30, 2016 2:06 pm

I have a 75 860GT with the stock ignition unit, stock stator, stock transducers and stock volt reg (the old aluminum box type.) However, I'm doing a custom wiring job with a Motogadget m-unit. With the given components, do I just need to run 12v from the stock volt reg to the stock transducers to get spark or is there another component needed in there?

ducadini
750 Sport [BEVEL]
Posts: 211
Joined: Sat Jul 31, 2004 8:54 am
Location: Antwerpen

Re: 75 860GT ignition question

Post by ducadini » Tue May 31, 2016 11:59 pm

No.
The ignition works independent from the 12V.
So there are just the wires going form the stator to the two transducers to run the bike.
HOWEVER : to stop the engine from running there's a wire running from each transducer to a relais inside the headlight. This is actuated by the contact and DISCONNECTS the transducers from the earth when the contact is in ON position. Thus enabling to produce a spark.
A simple version of this setup is on Bevelheaven manuals 860 page 151

Timing of the ignition is fixed in the stator and it happens (now those things are getting OLD) that one of the stationary windings break, so no spark on that pot untill approx 2000 rpm then the high rev kicks in.(No easy but still usable for racing :-)

Alternatives (WITH use of 12V) are available

caio
ducadini
Nego i ricordi peggiori
Richiamo i migliori pensieri

blaine.hale
Mariana
Posts: 48
Joined: Thu Jun 26, 2014 10:05 am

Re: 75 860GT ignition question

Post by blaine.hale » Wed Jun 01, 2016 5:21 am

Thank you so much. That helps out a ton!

blaine.hale
Mariana
Posts: 48
Joined: Thu Jun 26, 2014 10:05 am

Re: 75 860GT ignition question

Post by blaine.hale » Mon Jun 06, 2016 7:42 am

Just a follow up. Pretty cool system, actually. It's almost like they were meant to race with that independent, self powered ignition system.
Hooked the transducers up, grounded them on the frame, left the ignition kill unit off, hooked up the spark plugs and got spark! Very, very weak spark, though. Checked voltage on the cables coming from the ignition/stator unit and I'm getting about 1v on a heavy kick through.
I'm going to go through and clean connections, but what voltage should I expect at those wires when kicking the motor over?

ducadini
750 Sport [BEVEL]
Posts: 211
Joined: Sat Jul 31, 2004 8:54 am
Location: Antwerpen

Re: 75 860GT ignition question

Post by ducadini » Tue Jun 14, 2016 5:45 am

Sorry, no info on that and the engine I have here WAS used for racing : NO kick.
I suggest You compare the two wires.
I suspect the voltage is dependent of the speed of rotation so measuring that will be a challenge.
Some Digital meters can be set on a peak value, try that.

ciao
ducadini
Nego i ricordi peggiori
Richiamo i migliori pensieri

blaine.hale
Mariana
Posts: 48
Joined: Thu Jun 26, 2014 10:05 am

Re: 75 860GT ignition question

Post by blaine.hale » Fri Jul 22, 2016 5:28 am

Searched around a bit but can't seem to find the knowledge:

What kind of compression are you guys getting on the cylinders? Still haven't gotten my bike to crank so I did a quick compression check with the carbs off. I got about 128 on both cylinders. That seems way low. Could be the reason for not cranking. Valves are definitely fully closing too.
Apparently the previous owner of this bike changed the pistons and rings but the bike only had 13k miles on it. Luckily I still have the originals in a box.

ducadini
750 Sport [BEVEL]
Posts: 211
Joined: Sat Jul 31, 2004 8:54 am
Location: Antwerpen

Re: 75 860GT ignition question

Post by ducadini » Fri Jul 22, 2016 11:23 pm

There have been a few different pistons available for the 864 twins, but 128 is indeed a bit low.
Put a drip of oil in the cilinder and then get another compression check.
The oil wil seal the valves and rings so you should get a better reading.
Be sure that cam timing is correct, with some of those overlaps that give a difference.

ciao
ducadini
Nego i ricordi peggiori
Richiamo i migliori pensieri

blaine.hale
Mariana
Posts: 48
Joined: Thu Jun 26, 2014 10:05 am

Re: 75 860GT ignition question

Post by blaine.hale » Sat Jul 23, 2016 12:14 pm

ducadini wrote:There have been a few different pistons available for the 864 twins, but 128 is indeed a bit low.
Put a drip of oil in the cilinder and then get another compression check.
The oil wil seal the valves and rings so you should get a better reading.
Be sure that cam timing is correct, with some of those overlaps that give a difference.

ciao
ducadini
Well you were right about the oil trick. Put a little too much in the vertical cylinder and got over 160 on the compression gauge. Now I can stand on the kicker and it not move with how much compression I'm getting.
Keep in mind, these are new pistons and rings. I'm going to try to clear out that oil and get some in the horizontal cylinder and see if I can finally get combustion.

ducadini
750 Sport [BEVEL]
Posts: 211
Joined: Sat Jul 31, 2004 8:54 am
Location: Antwerpen

Re: 75 860GT ignition question

Post by ducadini » Sat Jul 23, 2016 12:33 pm

Didn't know about the new rings : they need some running in and they probably weren't sealing very well.
Did I mention "a drip of oil" ? Too much and You would've gotten a hydrolock, damaging rods and/or pistons.
Just kick the bike without plugs and most excess oil will be dispensed in your garage :-)

ciao
ducadini
Nego i ricordi peggiori
Richiamo i migliori pensieri

blaine.hale
Mariana
Posts: 48
Joined: Thu Jun 26, 2014 10:05 am

Re: 75 860GT ignition question

Post by blaine.hale » Sat Jul 23, 2016 4:13 pm

ducadini wrote:Didn't know about the new rings : they need some running in and they probably weren't sealing very well.
Did I mention "a drip of oil" ? Too much and You would've gotten a hydrolock, damaging rods and/or pistons.
Just kick the bike without plugs and most excess oil will be dispensed in your garage :-)

ciao
ducadini
Haha, yeah. The second I got too much compression, I started ejecting the oil.
No dice on starting still. Pretty perplexed.

Getting great spark and I timed it to 35 degrees BTDC. Fuel is getting in too. To eliminate fuel as an issue, I tried starter fluid...for the first time in my life.

wdietz186
888
Posts: 663
Joined: Sun Sep 10, 2006 4:40 pm

Re: 75 860GT ignition question

Post by wdietz186 » Sun Jul 24, 2016 7:18 am

You may be getting great spark but i'll wager it isn't at the right time or it is getting blown out when compression is present. The stock ignition was extremely unreliable 40 years ago and unlike wine age doesn't improve it. You might try closing down the plug gap to about .020" and see if it shows any signs of life. And for your personal protection wear boots or hard sole shoes and use the ball of your foot on the kickstarter so when it kicks back it doesn't bruise your instep or make you bark your shin on the foot peg. Many new and blasphemous words have been uttered [screamed!!!] when it bites back. The solution is an aftermarket ignition.

blaine.hale
Mariana
Posts: 48
Joined: Thu Jun 26, 2014 10:05 am

Re: 75 860GT ignition question

Post by blaine.hale » Sun Jul 24, 2016 8:38 am

wdietz186 wrote:You may be getting great spark but i'll wager it isn't at the right time or it is getting blown out when compression is present. The stock ignition was extremely unreliable 40 years ago and unlike wine age doesn't improve it. You might try closing down the plug gap to about .020" and see if it shows any signs of life. And for your personal protection wear boots or hard sole shoes and use the ball of your foot on the kickstarter so when it kicks back it doesn't bruise your instep or make you bark your shin on the foot peg. Many new and blasphemous words have been uttered [screamed!!!] when it bites back. The solution is an aftermarket ignition.
I'll try out the spark gap here in a minute. I managed to get a couple chugs out of it while bump starting yesterday but that's about it.
Disappointing about the ignition system going bad on these. I was just praising how easy it was to set and how simple it was. Guess I'll be reading the aftermarket ignition system thread now.

For my own reference:

viewtopic.php?f=5&t=4036

blaine.hale
Mariana
Posts: 48
Joined: Thu Jun 26, 2014 10:05 am

Re: 75 860GT ignition question

Post by blaine.hale » Sun Jul 24, 2016 1:05 pm

Spark gap adjust and still no gurgle. Here's what I've done thus far.

-Set the ignition timing dead on, with a degree wheel, to 35 degrees BTDC. Spark looked good (white and blue)
-Carbs are rebuilt, with stock jetting, and I can confirm I'm getting fuel in them and into the cylinder. Pumpers are working as well.
-Set the valve lash and cam timing to close, if not dead on. The vert cylinder's index marks line up when they should and the valve lash is set at TDC on a compression stroke. The horizontal cylinder was a little weird. The index marks never lined up on TDC and the valves didn't close when they should, so I put that cylinder at TDC on a compression stroke (is that supposed to be 90 degrees from the other cylinders TDC?) then I pulled the cam out and rotated it so the cam lobes were the 90 degree version of the vertical cylinder (it's 4 and 8 o'clock on the vert cylinder) so the valves were fully closed and I adjusted lash from there.

I'm thinking I maybe could have gotten something wrong on the cam timing and valves perhaps?

Lumpy
SD900 Darmah
Posts: 307
Joined: Sun Mar 25, 2007 4:49 am

Re: 75 860GT ignition question

Post by Lumpy » Sun Jul 24, 2016 4:30 pm

The cam timing marks are hunting teeth. That is once they are lined up they won`t realign until the engine has been rotated X amount of revolutions. They won`t realign with each cycle of the engine. If you have messed with cam timing marks it might be worth your while to consult the manual and go back to the start and set it as per the book. Not sure if Duc`s are free running engines but be aware that if the timing is radically out valves can strike pistons with disasterous results.

wdietz186
888
Posts: 663
Joined: Sun Sep 10, 2006 4:40 pm

Re: 75 860GT ignition question

Post by wdietz186 » Sun Jul 24, 2016 4:38 pm

Blaine, The dots on the horiz. cyl. should be lined up when the vert. cyl. is at TDC. The intake valve will be open on the horiz. cyl. with the dots lined up on that cyl. There is a service manual on this site that will explain it all. When you adjust the valves on the horiz. cyl. you need to watch the intake close and then bring the piston up to TDC. Set the valves to .004" in and .005" ex. One thing that confuses everybody is that on the bevel drives the crankshaft turns clockwise, [backwards as you view it from the left side] unlike most every other bike [even the belt drives] which turn counterclockwise.

Post Reply

Return to “Squarecase Early 860/900 Crossover Gearchange Engines > 860/900 GT”