Hot and cold coils

[belfastguzzi]

Trying to start 850 LM, noticed that left header stayed cold while right side got hot straight away.

 

There is spark, though left side may be a weak spark or even intermittent (yes I know all sparks are intermittent, but you know what I mean?).

 

Both coils show about 3.3 ohms on primary circuits. I can't get any reading on secondary circuits for some reason (should be about 6 ohms?).

 

The left coil gets warm quickly. Right coil stays stone cold.

Is it normal that one coil might heat-up and the other stay cold (during start-up period anyway)?

 

If there's a fault I suppose that it's likely to be further back, maybe contact breaker? Due to various interruptions, I didn't get any further testing done and I couldn't start bike after swapping coils over, probably because battery was too weak by then.

[guzziownr]

One hot and one cold would indicate that one coil is not being triggered. For my bike (950 SP motor) it was a sign of immanent Dyna death. With points I would look for gapping and grounding issues. Charge up that battery and have at it. A dead coil would be a neat solution -- How often do we see it? Not very.

 

DW

[pete roper]

The coil that is getting warm is being energised because the points are closed and electrickery is running through it. The one that is remaining cold isn't being energised. This DOESN'T necessarily mean that it isn't connected right, when the engine is not running one or 'tother of the sets of points is most likely to be open so that coil won't be being energised.

 

The fact that the engine is running on one cylinder indicates that there is power getting to one coil at least. The way they are supplied is that there is a (?) white wire carrying current to one coil +ive and then a small loop of wire bridging that terminal to the +ive on the other coil. Check that hasn't fallen off.

 

Then chack to see that both coil -ives have their wires on them, one red, one green.

 

Next it's off with the tank and check the connections where the red and green wires connect onto the points wires from the distributor. There are two spade connectors up under the tank that do this. If they are connected then it' time to move on to the distributor.

 

Off with it's lid and out with the multimeter.Turn on the ignition and make sure that each live contact is getting voltage. Turn the ignition off and turn the multimeter onto 'Ohms'. Disconnect the red and green wires from the distributor and then using the ohm meter on the distributor wires and the timing marks on the flywheel set the timing by gapping the points so that they separate at exactly the right time. Unless it wasn't running before or the points have been replaced tehre should be no need to buggerise around with moving either the distributor or the *Floating* set of points on the backing plate, in fact if you do it will simply make your life about a zillion times harder!.

 

Once it's timed up correctly this way reconnect the red and green points wires to the distributor, smear a little bit of grease on the distributor cam in front of the heel of each set of points, slap the lid back on and the tank and see if the bugger runs.

 

Pete

[belfastguzzi]

Thanks. The coil wires are all in place. I didn't have time** to take the tank off and explore further. Hopefully do that tomorrow and try the various steps.

 

 

** I had to go in and watch Ireland THRASH the Englishers at the historic Croke Park match. Sorry about that, Guzzirider etc

 

"Rampant Irish Crush England"

 

[Guest Gary Cheek]

Hoping and assuming you still have points rather than the Die a matic Dyna. Another contributing factor to coil heating is the breaker point gap AKA dwell angle. Since this regulates the duty cycle or ratio of time on to time off for the coils it can cause a difference in coil temps.

The coil secondary or HT terminal is a couple thousand times higher in resistance typically around 7,000 Ohms or higher DC resistance.

 

Pete's guidelines should get you to zero in on the problem . I just wanted to mention another cause for different coil temps. A dead engine resting with key on and points closed is still the leading cause for overheated coils. In fact the main purpose of the "ballast resistor" is to limit the current that can flow into a saturated coil when the key is on and the points are closed.

[dlaing]

On my V65 (RIP) I would simply switch the coils to make sure they were not the culprit.

Both times the failure of spark at one plug was the Dyna S ignition.

Still I prefered the Dyna S to points, although I got pretty good results with some points for a volvo/bmw cross reference that required drilling the points plate to let them fit.

Maybe if I was better at diagnosing condensor problems I could have stayed with points.

With a score of 36-13, I think BFG has all the points he needs

[Guest Gary Cheek]

Looks like you have experienced at least two more Dyna Failures in (x) years than I have had points failures in 40+ years! Thats why I prefer points, on most bikes originally equipped with them anyhow.

 

Then again I have had the experience of fixing a few Dynas. Too often a riding buddies bike dead at the roadside

I have learned to dread Dynas .

[dlaing]

Looks like you have experienced at least two more Dyna Failures in (x) years than I have had points failures in 40+ years! Thats why I prefer points, on most bikes originally equipped with them anyhow.

 

Then again I have had the experience of fixing a few Dynas. Too often a riding buddies bike dead at the roadside

I have learned to dread Dynas .

The problem I had with the Dyna S was that the only way I knew how to fix it was to replace it, and carrying a spare is expensive.

The OEM points seemed prone to pitting, and would not hold the timing for long at all.

Maybe other small block owners had better luck

Big block Guzzi owners seem less happy with Dyna

The Volvo points seemed to hold the timing, pitted less, and were a lot cheaper.

I considered going back to the Volvo points but after the second Dyna replacement the Dyna then provided years of fine service until I gave up on the bike

I am sure the umpteen point failures and 2 Dyna failures had something to do with my maintainance ability and possibly a voltage regulator problem.

The Points on the Honda 500F were not too bad, but required somewhat frequent maintainance...again, probably a result of my lack of skill.

The Dyna on my Honda 500F was flawless and required no skill from me.

[Guest Gary Cheek]

Nope, the small block Guzzi seemed to have exceptioanally piss-poor contact systems and I doubt you were doing anything wrong. Sorry to say Guzzi dropped the ball big time on those buggers.

The sma;; block Guzzi is the reason I said on "most" bikes.

 

In the case of the Honda I would gladly perform a little maintenance at home rather than risk a roadside melt down. Not that all Dynas fail , just too many of them. When they take a crap, you walk. Most point failures are presictable, preventable and /or repairable. Dynas are like Russian Roulette. Not every player drops the hammer on a live round.

[belfastguzzi]

Hoping and assuming you still have points rather than the Die a matic Dyna. Another contributing factor to coil heating is the breaker point gap AKA dwell angle. Since this regulates the duty cycle or ratio of time on to time off for the coils it can cause a difference in coil temps.

The coil secondary or HT terminal is a couple thousand times higher in resistance typically around 7,000 Ohms or higher DC resistance.

 

Pete's guidelines should get you to zero in on the problem . I just wanted to mention another cause for different coil temps. A dead engine resting with key on and points closed is still the leading cause for overheated coils. In fact the main purpose of the "ballast resistor" is to limit the current that can flow into a saturated coil when the key is on and the points are closed.

Thanks Gary. You recommend staying with points then?

Edit: oh, yes, I see your other posts

 

With a score of 36-13, I think BFG has all the points he needs

It was 43 :!:

[Paul Minnaert]

when I read the post, the left cylinder header stayed cold, and the left coil was hot. When connected to 12v dc the whole time, that's when the points don't open, the coil will get hot, and die in the end. When connected to 12v, with 3.3 ohmns resistance gives 12/3.3 = 3.6 amps. That will generate heat.

So points aren't opening. Or the capacitor is faulty.

 

The schematics are very simple: one side of the coil is connected to the +12v of the battery. The other side of the coil is contacted to one side of the points, when point is closed, it is connected to ground( = -12v).

When point closed, there flows a current through the coil ( 3.6 amps), at the moment the point opens, there isn't current flow, but the capacitator that is connected over the point contacts, togehter with the coil inductance generate the spark.

[belfastguzzi]

when I read the post, the left cylinder header stayed cold, and the left coil was hot.

That's correct

...So points aren't opening. Or the capacitor is faulty.

OK, good. I suppose it's a good idea to replace the capacitor(s) anyway.

[pete roper]

 

OK, good. I suppose it's a good idea to replace the capacitor(s) anyway.

 

The condensors are a PITA to get at because Guzzi bought the entire distributor assembley as a lump from Magnetti Marelli. Any old .2-.22 microfarad condensor will do but simply disconnect the ones screwed to the distributor and connect the new ones to the coils where they are easy to get at.

 

Pete

[belfastguzzi]

The condensors are a PITA to get at because Guzzi bought the entire distributor assembley as a lump from Magnetti Marelli. Any old .2-.22 microfarad condensor will do but simply disconnect the ones screwed to the distributor and connect the new ones to the coils where they are easy to get at.

 

Pete

where from? a car / motor factor?

[Paul Minnaert]

other way to check: take a 12v bulb, connect between ground somewhere and the wire from the point to the coil, now if the key is on, turn the engine on the crank, the light should be on when points are open, and off point closed. try both points, should give same results.