Electrical issues

[bone9999]

I have a 82 merc 40 hp that i need some help with. The description is a bit long so bear with me.

Heres the deal, i was having an issue with a weak spark. Stator tested good for resistance and DVA voltage when disconnected from switchbox however when connected it was only putting off <10v on the black/yellow at the pack. Determined this to be a bad switch box so replaced with a new cdi but still the same issue persisted. Called CDI and they wanted to test out the box to be sure it was not faulty from the factory. Box tested good, so the next possible culprit is the stator even though initial testing shows that its good.

Replaced the stator with a new one along with the new switchbox and bang it is fixed - at least for about the first 20 min. of testing. Voltages are all within range >180v on the black/yellow while running and the pack is putting out a solid 150v to the coils. After making some adjustments to the timing figured i would go back and recheck voltages.

That is when the black/yellow at the box began showing ~90v and the pack to the coils is now back down to ~2v just like with the old stator.

I need to understand how this could happen. Both coils, the stator, switchbox are new. Trigger tests out good. The majority of the wiring from the harness up has just been replaced. Everything is testing good on its own and for that matter everything was working properly for a short amount of time after replacing the stator.

Seems to me the stator has just fried again somehow, but rechecked the resistance and it is still good.

PLEASE HELP IM READY TO USE THIS MOTOR FOR AN ANCHOR!

 

[Faztbullet]

Re: Electrical issues

Make sure there is no voltage on blk/yell kill wire with key on or off(not running) and your using a DVA adapter on your meter. Also a bad rectifier can short and damage stator...

 

[bone9999]

Re: Electrical issues

The kill wire has been checked and i do get ~0.15 v on it when the key is switched on. From what i understand this isnt enough to cause an issue, correct me if im wrong. I am using a DVA adapter for the testing on stator and such.

I have also checked the rectifier and it also tests good.

Not to question your expertise but I am a little confused as to how the rectifier can damage the ignition stator. Since this model has a seperate charging stator which is the one connected to the rectifier.

 

[CharlieB]

Re: Electrical issues

ANY voltage fed into the switchbox from the ignition switch can damages the switchbox.

Replace your ignition switch.

Un-plug the black/yellow switchbox wire and retest for spark, if still weak, you've already damaged the box.

 

[bone9999]

Re: Electrical issues

Thanks for the reply charlie, but i would put money on the box still being good. By testing each piece of the ignition system everything points to the box being bad. However, this is the same box that i have already sent back to CDI for testing because all tests point to it and they say there is nothing wrong. CDI hasnt done me wrong yet. The voltage on the kill wire was also there before sending the box back.

Something is killing the stator. I know it still tests good disconnected, however i gaurantee something has shorted in it as it did with the original stator. Now could that small amount of voltage be the issue with the stator?

Ive always heard you dont want any volts but <2 is Ok on the kill wire and even then its usually the switchbox that this causes issues with.

Thanks for the help Charlie and fast

 

[CharlieB]

Re: Electrical issues

DVA test the stator with the switchbox connected, then DVA test again dis-connected.

Wrote down all your results.

Be sure to leave the black/yellow switchbox dis-connected for all tests AND for your spark test.

Added: Be SURE to ground ALL spark plug wires during any spark testing as any dis-connected plug wire will not allow the switchbox to un-load/discharge the stored current/voltage, and can damage the switchbox.

Carefully inspect your old stator for ANY contact or rub marks from the flywheel as a worn top bearing can allow the crank to move just enough for the flywheel to rub, which doesn't always damage the stator but it definitely lowers output as during the moment of contact the magnet and stator become one, and no electricity is generated.

 

[bone9999]

Re: Electrical issues

Heres the results:
with the stator connected to the box ~60v which is actually a drop from yesterday, it was ~90v.
with the stator disconnected from the box i get >180v
both tests done while cranking and the plugs are grounded.

I know these results point to the switchbox but like i said before cdi has already restested it and it shows good. The only thing that has fixed the issue has been to replace the stator, but that only lasted for a few minutes. Now the stator is surely shorted or at least weak under load.

Good idea on the flywheel but no dice. Magnets still have paint on them and the stator looks good.

I am really leaning toward the rectifier possibly shorting when it has a load and maybe backfeeding through the ground to the stator? I know this is a stretch based on assumptions but that is the only piece of the electrical that hasnt been changed.

Unfortunately i am at my wits end with this and really dont want to spend the money on a new rectifier and another stator just to find out i was wrong.

 

[Maxz695]

Re: Electrical issues

Check the wires where they come out of the stator very closely. 40 HP engines are notoriuos for the wires wearing out and grounding to the block or trigger cover can,t remeber which.

 

[CharlieB]

Re: Electrical issues

Third test, dis-connect both yellow wires to the rectifier then repeat DVA and spark tests.

A bad rectifier CAN cause interference within the fields in the stator and lower voltages. This test can confirm or disprove a rectifier.

 

[Faztbullet]

Re: Electrical issues

A defective rectifier can cause the battery charge windings on stator to over heat basically turning it into a heating element, which in turn damages the low and high speed windings of stator.

 

[CharlieB]

Re: Electrical issues

Cranking speed must be a minimum of 300 RPM.

If you can tell much difference in cranking plugs out vs spark plugs in, then it is time to check/clean all battery cable connections, bright and tight, including the starter cable. If that doesn't make a difference, clean the starter commutator and lube the bushings lightly.

Now retest DVA.

I'm assuming that you have already checked out your battery and are recharging it to keep it up.

 

[bone9999]

Re: Electrical issues

Sorry for the delay.

Disconnected the charging stator from the rectifier and still had the same low voltage issue and weak spark. The way it looks the new stator is shot.

Cranking speed is up to par, the battery has a full charge and the motor actually starts easy considering how low the voltage going to the plugs is.

After speaking with an electrician friend who said rectifiers can and do fail ocassionally only under load , i think i may check with the local battery shop to see if they can load test the rectifier.

I have also rechecked all the wiring from the harness and stator for shorts, everything checks out good.

Also, could the charging stator itself be the issue? I would think that a bad charging stator would cause the rectifier to fail. I have not come across any testing method for it.