1967 Merc 950 SS will crank but doent have spark

[JM4]

Ever since I had a Marine shop work on my vintage boat motor "changing the water pump impeller" I have not been able to get my trusty Merc to fire.
The shop had to beat and pry off a siezed lower unit to access the water pump which in turn broke off two pieces of the upper half of the motor. Therefore they welded the pieces back on.
This motor has the thunderbolt ignition system. Could the welding on the motor have damage one or some electrical parts?
The motor will crank and I have troubleshoot to the point where I put an inline spark test light on all sparkplugs and I have no fire on any. I have replaced the start solenoid and I have rewired the Mercontrol box completely, due to chaffed and correded wires. What should the next step be in troublehooting?

Thanks for your help

 

[BatDaddy1887]

Re: 1967 Merc 950 SS will crank but doent have spark

It would be better if you could change your own impeller as on most engines it is a relatively easy job. Here are some check points to follow:

 

[turtles11756]

Re: 1967 Merc 950 SS will crank but doent have spark

did you check all the wiring on the internal wire harness ?

 

[emckelvy]

Re: 1967 Merc 950 SS will crank but doent have spark

Most likely they "nuked" your sensitive ignition parts when they welded on the upper end of your motor.

Does your ignition system look like the one in this link?: http://www.maxrules.com/oldmercs/Wiring/0_1965a/10.pdf

If so, that ign box is expensive & difficult-to-find. If you do have 2 wires coming from the distributor, which connect to one terminal on the Port side of the switchbox, you have a points-fired dual distributor with capacitance-discharge ignition.

You can eliminate the points (and the mercury-filled tilt switch) as a problem, by disconnecting all wires at the single terminal.

Then, turning the ign swtich to "ON", momentarily ground the single terminal with a short length of wire. You should get a spark with every make-and-break connection.

If not, likely the switchbox is "fried". I seriously doubt they would have burnt up the coil.

There's a way to "haywire" a newer-style Mercury CDI switchbox so it'll work with your ignition system. If you have the dual-points/CDI-style ign, and find the switchbox to be bad, let us know and I'll post a solution for you.

If you have a later-style distributor with 3 wires coming out and connecting to (3) each respective terminals on the Port side of the switchbox, you have a different ignition system, and there's a test to eliminate the distributor as a problem. Which will most likely point to the switchbox as the bad part.

Anyway, hope that helps and let us know what you find.........ed

 

[JM4]

Re: 1967 Merc 950 SS will crank but doent have spark

Ed,
I have the later style distributor with 3 wires; all on the port side of the switchbox. This setup still has the mercury tilt switch.
Will the test you mentioned by disconnecting all wires for the 2 wire distributor still work for the 3 wire setup or will I need to perform a different test?
If the same test will work, which terminal post will be the "make and break" ground connection to test the switchbox for spark?

 

[emckelvy]

Re: 1967 Merc 950 SS will crank but doent have spark

Here's a test for the type of Merc C-D ignition with a 3-wire trigger:

MERCURY BATTERY-POWERED CDI TEST FOR DISTRIBUTOR MODELS

This test is for the 332-2986 switchbox used from 1967-1978 on all the inlines.

This test assumes your coil is good (problems with CDI coils are rare).

DISCONNECT BATTERY

1. Turn off ignition;

2. Disconnect all 3 distributor wires on the Port side of the switchbox (and the ?mercury switch? if present);

3. Remove the HV lead from the ign coil to the center of the dist. cap (remember it unplugs from the coil and unscrews from the cap);

4. Reconnect the HV lead to the COIL only;

5. Position the free end of the HV lead approx. 3/8" from ground (block, shrouds etc), and find a way to hold it there;

6. Jumper the brown and white terminals on the dist. side of the switchbox to each other.

RECONNECT BATTERY

7. Check that you have +12V at the red terminal (even with the ign off);

8. Turn on ignition and verify +12V at the white terminal (same side as the red terminal);

9. Ground the black terminal on the distributor side of the switchbox - this should cause a spark each time you touch ground.

If you get spark with the distributor bypassed, and it won't fire with the distributor connected, the trigger is bad and the entire distributor housing assy must be replaced.

If you get no spark using the test, the switchbox is probably bad. In that case, be sure to check for correct power on the switchbox, check all connections, and check the coil's resistance to make sure it's OK.


Since this was (presumably) a failure brought on by a high-current magnetic field, I'd suspect the switchbox. Normally the distributor is the most common cause of failure, but in this case I'd bet that the sensitive electrical components in the switchbox would be more prone to failure.

If you do this test and find out the switchbox is bad, that doesn't necessarily rule out a bad distributor. You'd have to get another switchbox and give it a try. At least the 3-wire switchbox isn't as expensive and can be found used on ebay.

You might even have luck finding a parts motor or ign parts in your local Craigslist "boats" category.

HTH & let us know what happens.........ed