Can switch box fail if hot?

[taob]

Have 1984 60 hp 3 cyl Mercury. It started fine, but would stall & quit as if turned off when accelerated past 1500 rpm. Bought manual & set timing and other adjustments. Removed carbs and blew them out. Put in water, had same results. Reset all adjustments again and backed into water. Outside temp was 95 deg. So engine parts were some warm. It started right up. Ran about 5-10 seconds and quit. It would not fire again. Connected timing light, NOTHING.
Pulled home and rechecked with timing light. No flash or spark. Tried this couple times. It did flash eractically couple times. After outside temp cooled down it started, but only ran a few seconds.
Just for fun I strapped an ice pack on the switch box & laid one on top of fly wheel. Waited about 10-15 minutes. Motor fired right up and kept running.
Does anyone have a suggestion?

 

[j_martin]

Re: Can switch box fail if hot?

Have 1984 60 hp 3 cyl Mercury. It started fine, but would stall & quit as if turned off when accelerated past 1500 rpm. Bought manual & set timing and other adjustments. Removed carbs and blew them out. Put in water, had same results. Reset all adjustments again and backed into water. Outside temp was 95 deg. So engine parts were some warm. It started right up. Ran about 5-10 seconds and quit. It would not fire again. Connected timing light, NOTHING.
Pulled home and rechecked with timing light. No flash or spark. Tried this couple times. It did flash eractically couple times. After outside temp cooled down it started, but only ran a few seconds.
Just for fun I strapped an ice pack on the switch box & laid one on top of fly wheel. Waited about 10-15 minutes. Motor fired right up and kept running.
Does anyone have a suggestion?

On a hot day, run it till it quits, (apparently seconds) then follow the ignition troubleshooting guide in the manufacturer's manual with your DVA in hand and find out which part to replace, switchbox or stator.

Yes, electronics and also electromechanical (stator) parts are often temperature sensitive when they fail.

hope it helps
John

 

[taob]

Re: Can switch box fail if hot?

I have only a multimeter to test with. Following the manual I have tested the leads coming from the stator. The one that causes me concern is the Red. Specifications say set to r x1000 & there should be not continuity when grounded to power head. My meter is does not have 1000, but 2K
The Red reads 151 at 200 ohms & .151 at the 2K setting.
The Blue shows not reading at all.
It started this afternoon for about 2 seconds then quit. No fire at any cylinders. Let sit for about 10 minutes it, started and ran for several minutes then stopped. Again no fire on cylinders.
Checked reading on the Red wire from stator and it had increased to 160 at 200 ohms & .160 at 2k.
I have checked the other leads from stator and they seem, fine reading almost identical.
Do not think it is coils as that should only effect one cylinder. Right?
Hate to put much money into the motor it is an "84". Stator are running $180 or more and not even sure that is the problem.

 

[Barnacle_Bill]

Re: Can switch box fail if hot?

Go to an electronics store and buy a can of freeze or whatever its called these days if its still available. Get the motor to where it no longer sparks then spray the switchbox with the freeze, then check again. This stuff used to be part of our kit back in my TV repair days and used to isolate parts that were breaking down after getting heated up. No guarantee this will work as the part may be too deeply imbeded in the switchbox. But its worth a try,

 

[j_martin]

Re: Can switch box fail if hot?

No continuity means infinite resistance.

I don't have the book or diagrams for your engine, so I don't know how it's wired exactly, but 151 to 160 ohms is "much" continuity.

That said, what you're saying here doesn't make much sense to me at all.

Most stators have at least 2 windings. The battery charger windings feed a bridge rectifier, and so neither lead from that winding (usually yellow) should have any continuity to ground. Usually there's a very low resistance between them.

Usually, one end of the charge coil winding is grounded, either internally or through a ground wire from the stator. The red and blue wires connect to taps on that coil, so they should have some resistance between them, and to ground. The "open" blue lead sounds like the troublesome reading to me. If you're using a 5 dollar digital meter and the 2k range, the blue wire probably would not register. I would expect it to be 5k ohms or better.

In any case, this might be a single turn shorting in the stator, in which case ohmmeter readings would likely be normal. That fault can only be properly diagnosed with a DVA.

When I fix 25 year old motors, I usually put used parts on them if I can get them.

hope it helps
john

 

[taob]

Re: Can switch box fail if hot?

Thanks J. Martin & bhile for input. Freezing product sounds interesting.
I will recheck my readings using higher scale.
However I did test the rectifer and it appears to not have the readings in manual. It also seems to have the dull finish in about 2/3 of it, plus it is raised up some. Would a bad or failing rectifier cause the problems I described?