Dyna S ignition problem

I took my bike out for a ride today and decided to check the timing when I got back. I installed a Dyna S ignition about 15 years ago and havent checked in about 10 years. I took apart the mechanical advance, cleaned and lubed it. I put it all back together and it ran great. I went for another ride and decided when I got back to check the compression. After the compression check I put the plugs back and and fired it up. It was only running on number 1 and 4. I checked the connections all was fine. After some trouble shooting it turned out to be the # 2 and 3 cylinder power module on the Dyna S was bad.
I know the Dyna S is old but what would make the module die?

Are you sure you have 12 volts to the other side of the coil.
Are they stock coils?

One weak area on the Dyna "S" is where the power wire is spliced into the bike's wiring.

This type of connection is a real pain to troubleshoot due to moisture getting into the joint and corroding. Even though the connection may look good, it may not be electrically connected.

For a much better connection, I recommend soldering the connection and then covering it with heat shrink tubing.

When you do the compression test, you know to short out the plug wires to the head, correct? If you don't, all that spark energy can't go anywhere and it usually causes a coil to go bad or the electronic ignition to go bad. This is because if there is no way for the spark to discharge, a huge voltage is forced on the primary. Coil insulation breaks down or the ignition transistor pops (or the clamp zeners pop) or all of the above.

You can also just disconnect the coil primary wires when doing the compression test.

Yeah I think what I did was burn out the 2&3 module. I did not ground the leads. When I switched the module wires I got spark at the 2&3 coil so I know the coil is not bad.
I have been checking the compression for years without grounding the leads and have gotten away with it. I know better than that. I ordered a new Dyna S ignition. Thanks

Bummer Paul, I think I have a Dyna with one good pick-up. It's yours if you want it.

Mark

Loud....

Interesting, didn't think of this.....

Here's my question though... If he was compression testing cylinder 1 for say, since 1 & 4 use the same coil, should be ok then regarding the sparkie grounding?

Or is it still a possible coil/Dyna damage concern due to #1 plug not being grounded...

Me likey this subject....

OMR

If one end of the coil is disconnected, the damage can happen. The safest is to remove the power from the coil.

In most transformer/coil/alternator type devices it's safer to short them than to have them open. It's because induced voltage can get very high and cause insulation breakdown.

Same thing happens on tube-type guitar amps. If you use it without a speaker, and leave the output transformer open, it'll blow the transformer in no time. To safeguard against this, they put a shorting jack where the speaker plugs in. It shorts out when you unplug the speaker.

"If one end of the coil is disconnected, the damage can happen. The safest is to remove the power from the coil."

I get the concept of neither spark plug of a given coil pair not being grounded.... I was speaking in the regards if he had at least one plug #4 as in example still grounded then damage to this coil should have been minimized or elliminated due to the current path trhough the coil was still occuring...

Trying to ease his mind a little...

And yes, totally removing power would be the safest route no doubt... Thanks for the thoughts on this...

OMR

can't you just turn the handlebar switch to "off"?

Old Man Rock wrote:

"If one end of the coil is disconnected, the damage can happen. The safest is to remove the power from the coil."

I get the concept of neither spark plug of a given coil pair not being grounded.... I was speaking in the regards if he had at least one plug #4 as in example still grounded then damage to this coil should have been minimized or elliminated due to the current path trhough the coil was still occuring...
OMR

Both plugs in the pair must have a path to each other. Normally this path is incidently going to ground, but it's not necessary. What really needs to happen is the current muct go from one plug wire to the other plug wire on the same coil.

The engine is used to complete this path, and yes the engine is grounded. It would work the same even if engine was not grounded. (Unlike in a classic car where the engine is part of the ground path to the coil.)

The sprk plugs for one coil are in series, not parallel, so both plugs are needed to complete the path.

Kidkawie wrote:

can't you just turn the handlebar switch to "off"?

Only if this allows the starter circuit to still function.

Normally, no, but it is very easy to swap two wires in the handle bar switch so you can crank the motor with the kill switch off. I've come across a few bikes that were miswired this way. No harm in it, as long as you remember to turn the switch on while cranking when you are trying to start the bike.