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merc 40 no spark

guido2

guido2

Regular Contributor
serial # 2779...with thunderbolt/points ign. on the single cyl. 4hp. Does anyone have the stator specs on this one? Or can I exchange the entire ign. system off a parts motor I have serial # 3937... A new stator is out of reach for this guy @ $360. Maybe someone can help me with the specs. There is a vintage Mercury site on the internet but they want $20 for their info. Might be worth it but maybe you folks know another source for specs. Thanks, Guido
 
guido2 said:
Or can I exchange the entire ign. system off a parts motor I have serial # 3937... Thanks, Guido
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Hi Guido....that's a question I've been looking for an answer as well. I have the same engine here and would like to either up-grade to breakerless or down-grade to magneto. It all hinges on the block; were there differences in the block over the years that would prevent complete swap over of the different systems.

It's a tough question....not many people would know without having both versions of the engines torn down for analysis.

The ignition system you and I have was used on a lot of engines from 3.9 HP up to 20. There are tons of them in salvage yards because of the rust-prone carbon steel driveshafts. My plan would be to pick up a powerhead with a working ignition system and swap the parts over to my pristine one. But; is it possible?

CDI makes a stator for our models....but it sells for over $200....better than OEM but still a lot to invest in system that doesn't get the best acclaim. CDI #174-3996

Chuck
 
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I do have both versions in front of me and looking at the top of the block, crank, etc...Customer just left and is unsure to fix or just put it back together and hang on the wall. I did the stator test and the polarity is reverse with about 120,000 ohms resistance instead of the 20 to 30 K. When I configure the pos to the green stator wire and neg to ground, I get 60K......instead of open. Wondering too, I checked coil.....its ok and close to the listed parameters. Ground wire ok too, although it was missing one of the three mounting screws. Another strange thing is that when the points are open, I get about 100k ohms conduction to ground through the white coil wire at a point very close to the plastic block at the points attachment strap. Is this enough continuity to inhibit proper operation of the breaker points? The insulation on this points wire seems to be breaking down......but maybe 100k is not enough to worry about?????
 
I'm no authority but from what I read...these systems generate very high voltage which has great tendency to short to ground anywhere it can. I've heard that in the dark they can put on quite a light show from under the flywheel....

So; as far as you can tell.....are your two systems swappable? From your Serial # of the donor engine...it has the stator with the replaceable coils; like this?

Chuck

6.jpg
 
kimcrwbr1 said:
To crank the engine over get a flat piece of steel that fits between the pull start tongs on the flywheel drill a hole in the center of it and put a bolt in it so you can use a drill to spin the engine over without putting the cover on. It should jump at least 1/4 inch spark gap the more the better with a crisp blue snap.
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I just use various combinations of socket adapters that allow the use of 3/8 or 1/2" sockets on a drill. It's easy to piece together something that works. Makes it real easy to check spark or compression on most any small engine with an accessible flywheel bolt.

Chuck
 
Just got back from the car show and happy to discover all this info. Thanks everyone. I will get back to the motor tomorrow. My guess is the stator bad as it has a crack in the epoxy coating over the main body. Yes.....Mercs are really kinda "over-engineered", old OMC's are brutal/primitive/durable and very interchangeable. I enjoy the Mercs for the challenge.....and they run so nice when their right. They are good looking motors too.
 
On the bigger Mercs I have drilled and tapped three 1/4" holes in the hub/webbs and pulled the prop with a steering wheel or flywheel puller.......after soaking things down. Here in Minnesota, you don't run into a problem as often. Anti sieze is a must.......even here, I use it on everything religiously........but yeah.........My old 90 Power Tower is awesome.......what an animal! Hell..... how 'bout those "dock busters" Mercs are pretty cool........no one else would consider such a thing.......lets go skiing, bro.
 
I have both motors opened up to the crankcase. The crankshafts are the same, differences in the crankcase but not in the upper bearing retainer area. I'm pretty sure the top end will transplant to the 1974 parts. Both cranks use the same roller main bearings and upper needle bearings, keyways and taper for flywheel. Stator with removable coils tests perfectly. I'm going ahead now to attempt transplant/retrofit. If it doesn't work I'll be devastated.
 
Yeah, right.....still uses breaker points. Will set timing/carb opening to your specs. I was also looking at an early serial # 2017... with conventional ignition. This maybe would work too (Merc 39). I recovered one of these submerged for 1 year in a local lake. It still turned over and had nice crisp spark. The old conventional ignition was really quite reliable. The cowling is badly corroded so I never put it up for sale. I just pressure washed off all the debris, then dried it in the sun, spraying with compressed air, then lubed it up through the carb and in the cyl. Never even looked under the flywheel. I turned it over by hand on the flywheel and the spark was there........unbelievable! The diver who found it was totally amazed. The motor is really ugly now.....but it runs great! I have 3 other 39's too. They are the best little motor on the planet......and I am an OMC guy! They are built like a high quality chain saw engine......only water cooled with transmission........through prop exhaust......not bad for a 4hp motor.
 
Guido....that's really what I want to know.....will the magneto system work.

What's the point of using a $300 stator on an engine that would barely be worth that on the resale market. I'm looking forward to you telling me that they systems completely interchange; then I can resurrect this pristine 4 HP that I have sitting here.

Chuck
 
Oh; all the 3.9's used a stator? From what the OP was saying I thought his 3.9 had just a coil, points and condensor; similar to OMC's system.

Chuck
 
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