Topic: '65 BigTwin 40hp 1/2 spark – Page 3 – Antique Outboard Motor Club,Inc

This topic has 37 replies, 12 voices, and was last updated 4 years, 11 months ago by fleetwin.

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May 21, 2019 at 9:52 pm #175724
labrador-guy
Participant
US Member - 2 Years
Sounds like you have done everything right. You have installed new points. Sometimes new points have a coating on the contacts that keep them from making a good connection. Try cleaning those new points! I have had this problem many times and it might solve your problem.

dale
May 22, 2019 at 3:09 am #175728
rapier
Participant
Cleaned the points with a card, brake cleaner and air dried; normally if they’re dirty the meter will show more than 0.1 Ohm higher than a reference reading with the multimeter tips held together. HIgher than that would indicate contamination on the contact surfaces (which they had before I started).
May 22, 2019 at 8:05 am #175738
fleetwin
Participant
US Member - 2 Years
Again, I love the nice neat and clean job you have done on that mag plate…. OK, so the borrowed mag plate assembly sparked on both cylinders…But, yours, even with all new OEM pieces refuses to spark on one cylinder….I am assuming it is always the same cylinder that refuses to spark, correct? I’m not that familiar with what the underside of an RD mag plate should look like, in terms of wire routing and clamping. I’m hoping someone will examine your nice pictures closely and see something….
Let’s back up a bit and review for me….Did this thing spark on both cylinders before you set out on this frustrating ignition project? Or, is this an engine that you just acquired, and you decided to service the ignition system….
You have replaced both plug wires with no change, correct? I find it hard to believe that the same possible bad connection has repeated itself every time creating the same issue. The only other thing I can think of at this time has to be some issue that has a way of repeating itself no matter how many times you pull this thing apart….
Perhaps, there is some sort of issue with the routing/clamping of the plug wires under the mag plate which is grounding that plug wire to the mag plate every time you reassemble this thing. Try holding the mag plates side by side so you can compare wire routing/clamping between the two mag plates. I would then remove the problem plug lead one more time (sorry) and have a real close look for pin holes in the lead or damage from clamping that might be grounding it….
If all this reveals nothing, then I would simply route a plug lead directly out of the coil and out from under the mag plate (no clamping or routing under the various pieces), then recheck for spark on that cylinder…..
May 22, 2019 at 8:15 am #175739
fleetwin
Participant
US Member - 2 Years
Just remind me again, which cylinder is not sparking….#1 (coil facing forward/over throttle cam), or is it #2 (coil facing toward the propeller)??
May 22, 2019 at 8:52 am #175740
rapier
Participant
Thanks, the mag plates can get pretty grubby and ‘damp’ if used in salt water. I wanted to ensure there was nothing left that could contaminate the points.

The motor came to me with the usual cracked insulation on the coils. It hadn’t been used for many years, but didn’t show the usual signs of having been ‘molested’, so I thought it’d make a good project motor.

The plug wires are brand new, or at least the cable is (copper core, 7mm diameter). I made them up yesterday, using the original boots and ‘springs’ and made sure that the wires were pushed well home into the coil. #1 is coil facing forward/over throttle cam.

The RD mag plate is exactly the same part number and is indistinguishable except for a slightly different profile on the cam and the kill circuit has a push fit connector that connects to the ignition loom (not the wire connectors that you splits with fingernails..).

The only procedure I haven’t done again is to isolate the kill circuit, perhaps there’s been a breakdown in the insulation of the wire UNDER the plastic sleeve on #1 kill wire..That’s the one that connects to the ignition circuit. It looks in fine condition, but it does move around under there, so will check again.
- This reply was modified 4 years, 11 months ago by Mumbles.
May 22, 2019 at 9:11 am #175743
lindy46
Participant
US Member
DId you check the vacuum cut-out switch?
May 22, 2019 at 9:22 am #175745
rapier
Participant
The vacuum cutout is completely isolated.
May 22, 2019 at 12:35 pm #175759
fleetwin
Participant
US Member - 2 Years
OK, want to make sure I got this right….I thought you had already tested with the stop wires removed from both sets of points, and still had the problem…Perhaps you just meant that you have not removed the stop leads during your latest test…Go ahead and try removing the leads one more time, just for the heck of it…
May 22, 2019 at 12:50 pm #175760
rapier
Participant
Just removed them from the points and taped the ends, still dead on #1 – they were undone from the anti-pop and the loom anyway, but as I’d starded from scratch and they weren’t an issue before…How do I create a spark at the points with a D cell?
May 22, 2019 at 1:34 pm #175764
rapier
Participant
In my desperation I started looking at the points again, sprayed with brake cleaner, blew them through with the airline and dragged a card through, when closed. As a result, I now have a spark.

Can only think that with the constant swapping over and checks that I contaminated them with greasy fingers, or the feeler guage, more likely the former, when I pulled them off the original (floppy) mag plate and re-installed them on the spare yesterday.

Am feeling relieved, but very apologetic at my insistance that they were ‘clean’. Am also very thankful to all the Gentlemen who replied and helped work it through, esp. fleetwin!

The original root cause was probably the mag plate with it’s extended lateral movement, but was not a solution I’d thought of.

Thanks again..
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