1977 Merc 50 HP Thunderbolt Ign

[Papaw Mike]

I have been troubleshooting for a no start. My serial # 4708498. I have no spark on all 4. My starter spins, I have fuel, (also tried starting fluid, no start). Checked rectifier with dvm. Showed multiple diodes bad. Have ordered new rectifier. I have question with stator. The magnets on the flywheel have good magnetism, checked on stator and none (Metal screw will not hold). Does the flywheel and stator have magnets, or just the flywheel. My reading on the stator are, low side is 9.74 k ohms, high side 65.2 ohms. Neither blue and ground or red and ground have cont. Thanks

 

[Chris1956]

Re: 1977 Merc 50 HP Thunderbolt Ign

The stator is a coil of wire, on an iron core. No magnetism in the stator. Did you run the trouble shooting test for your ignition? Did you disconnect the killer wire from the switchbox? I assume you have distributorless igniton with 4 coils?

 

[Papaw Mike]

Re: 1977 Merc 50 HP Thunderbolt Ign

I do not have an ignition analyzer. The pic are of my Type 5 ign system, thunderbolt flywheel Capacitor Discharge, pointless, coil per cylinder, 4 cyl, electric start. I have Seloc book on Mercury Outboards 1965-1989 repair manual. I have been following it to the best of my knowledge.
If the kill switch is the orange wire that runs from terminal E in the key switch, to the engine harness terminal 6, to terminal C on the right side of the switchbox, and the mercury switch, yes. (I don't believe I have a mercury switch, the drawings shows it is connected to a terminal block. I have the terminal block, but nothing connected.
I tested the stator, and trigger, both ohmed out within range. The rectifier is an open circuit on every diode. I have ordered a rectifier and should get it today. I answered my own guestion after reading Theory of Operation multiple times. My magnets are in the flywheel and the coils in the stator. I am not sure how the rectifier works on the AC voltage coming from the stator. If the AC voltage is sent to the switchbox where it is stored in a capacitor, the rectifier is on the two yellow/red wires outside of the switchbox. I guess the AC voltage is sent to the rectifier before it is sent through the high and low speed wires to the switchbox. Once I replace the rectifier I will post again. Thanks for any direction change needed on my part.

 

[Faztbullet]

Re: 1977 Merc 50 HP Thunderbolt Ign

Disconect the orange wire from the blk/yellow terminal connection on switchbox and retest, make sure plug wire are disconnected in case it starts..

 

[Papaw Mike]

Re: 1977 Merc 50 HP Thunderbolt Ign

I received my new rectifier, installed it, put everything back together. Removed the orange wire and no crank. Replaced the orange wire turned the key, the starter turned, the fly wheel turned, I noticed a small puff of white smoke coming from the area of my brand new rectifier. In a matter of seconds, my 30 years of fixing things brought back that sinking feeling in my gut that comes from pride and arrogance. I thought I did my homework, I checked each component. I can only suppose if I had the analyzer I would have seen a problem with the ignition system. Since the rectifier is connected to the positive lead of the battery,(through the key), and the stator, my stator is bad. That at best is a guess. Any help please.

 

[Chris1956]

Re: 1977 Merc 50 HP Thunderbolt Ign

Let's not overreact. First of all the Orange wire is the killer wire on multi-coil ignitions, of that year Merc. It is likely your rectifier is toast, however, you can get a replacement from Radio Shack for less than $5. Stators are real tough to burn out. You can test the charging coils with an ohmmeter. See if they have a short.

I would get a wiring diaghram for your motor from maxrules.com and trace out your connections. It sounds like at least one wire is incorrectly connected.

From the MerControl, Starter solenoid wire is yellow. Acc power wire is white. Ground wire is black. unfused power is red. Choke wire is grey. ign killer wire is orange.

 

[Papaw Mike]

Re: 1977 Merc 50 HP Thunderbolt Ign

I received the rectifier. Tested diode with dvm, just to ensure the old one was really bad. it was. I installed the rectifier, and all other parts I had removed. Took off the orange wire from the switchbox and tried to start. No start, no nothing. Reconnected orange wire and turned the key. Well my friends, this motor continues to humble me. I have always believed once you know the theory of operation repairing something is just a matter of time and you hope the least amount of money. Once I started the motor I watched the starter turn the flywheel and a small puff of white smoke came from the rectifier. Yep I just fried my new rectifier. At this point I only have guesses. I am sure I have missed a problem in the readings or I haven't tested something right. Now that I have been humbled by my own pride and arrogance, help.

 

[SeaKaye12]

Re: 1977 Merc 50 HP Thunderbolt Ign

You remove the orange wire from the switchbox and it will not crank?

I don't understand that. Removing the orange wire would dis-able the kill circuit; the key switch, mercury switch etc. It should not keep the engine from cranking.

Like Chris1956 says...you need to pour over a wiring diagram and check and double check all the connections.

What is the history here? Have you replaced other items besides the rectifier?

Chuck

 

[Papaw Mike]

Re: 1977 Merc 50 HP Thunderbolt Ign

At the beginning of the year I replaced the lower end. The trigger had to be replaced due to corroded wires. The stators wires were the same way, I was able to splice new wiring onto the old wires. My resistance checks are good. I had two problems that were minor, I thought. I had a hard start. Had to use ether to start engine. I wasn't able to obtain speeds over 20 mph. The day before the engine stopped starting I had a backfire when using starting fluid. After the flames subsided, I checked the wiring and nothing was burnt. Put the covers back on shot a little ether in and the engine starter fine and ran all day. Traveled around 40 miles that day, up and down the Green River. The next day I went back out and had crank but no start. Made sure fuel was traveling to carbs. Since I had a backfire I was concerned with junk in the carbs. I removed both carbs, inspected, found nothing out of order. Replaced gaskets in fuel pump area and reinstalled. Checked compression on all 4 cylinders. All where between 90 to 100 psi. Inspected spark plugs looked good. Checked for spark, no spark. All 4 plugs, no spark. Checked ignitiion coils, even though I didn't believe all of them would be bad. Used DVM and resistance check. Between + and - .02-.04 on R1 scale and ground to pigtail,(on and off powerhead), 9-12 R100 scale. Stator and trigger chacked good. Rectifier showed bad. Ordered rectifier. That brings us to date. I agree, it doesn't make since why removing the orange wire from the switchbox would prevent it from turning over. The powerhead has the terminal for the mercury switch, but the mercury switch is missing, was never there. I am going to ohm out every wire, from remote and battery to powerhead. This time I am using maxrule. I will post when done. Folks thanks for your support and help.

 

[SeaKaye12]

Re: 1977 Merc 50 HP Thunderbolt Ign

Don't use starting fluid. Especially not ether.

If you have to prime the engine to get it to start, use a spray bottle with the 50:1 mix in it.

Do not use starting fluid without a lubricant in it. Don't do it.

Also; lets get terminology straight. When you say that the engine won't "CRANK"...do you mean that the starter motor won't turn and spin the engine over? Sometimes when people use the word crank they actually mean "START".

Cranking means having the electric motor spin the engine over. Starting means "running"....

Just want to be sure I am understanding what you are saying.

Chuck