Home › Forum › Ask A Member › 1916 Evinrude 4 cycle Twin model AA
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The Boat House.
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April 11, 2024 at 9:19 am #286658April 11, 2024 at 10:27 am #286661April 11, 2024 at 6:25 pm #286668
I’ve seen lots of pics and it looks like one wire comes out of the bottom of the mag and goes into the ‘distributor’ and then 2 spark plug wires come out of the ‘distributor’ and they go to the spark plugs. We’re missing the distributor. Pictures seem to show a normal Evinrude RBM magneto plate assy. It can’t be just 2 plug wires tied to one coming out of the mag or only one plug would spark.
In the 1919 Evinrude parts book, the only ignition difference between the AA 4-cycle twin and the common 2HP single is the flywheel $18, empty mag plate $1.70, and distributor with wires $2.50.
April 12, 2024 at 6:38 am #286672The flywheel may be a different part number than the common RBM because it may be rope start, only on an AA.
Found pics of the ‘distributor’ on F by Mr Scratch. It is geared to provide spark to one plug at a time, alternating as it rotates on the end of the camshaft. These show one design of the distributor.
April 12, 2024 at 7:32 am #286675Interesting motor for sure.
I found Bob Grubbs on YouTube, and
it runs incredibly smooth.https://youtu.be/acC8-Iz6qwI?si=iVd3_w6_w9u-uwGq
Prepare to be boarded!
April 12, 2024 at 9:32 am #286678
Smoother than I thought it would be
or is it just too heavy to vibrate?
TubsApril 14, 2024 at 11:06 pm #286740The distributor is driven off the cam shaft, so the rotor spins at one-half crankshaft speed. Thus the flywheel magneto supplies spark every revolution as per usual, and the half-speed rotor sends it to alternating sides of the engine. When it works, its OK. When it doesn’t, it can drive you around the bend figuring out what to repair.
As acquired, my magneto was stone cold dead, so I hooked up my buzz-box and was getting spark delivered to each plug as designed, but it wasn’t as consistent as I liked, so I did some rehab work to tighten things up in the distributor and eliminate what I considered to be excessive slop in the assembly. The housing is Bakelite and you have to be careful about applying pressure on it anywhere, so this is not a simple job, but it got completed and the rotor fit in the housing as well as the housing fit in the crankcase cover is much more stable than it was, so the rotor wobble is pretty much eliminated.
I can’t get my motor to run quite properly yet, but I think its a valve problem and not so much the ignition. I know that compression can be an issue in these motors, but I’m generating 55 lbs per cylinder so I don’t think lack of compression is a contributing factor. but I digress….
I haven’t figured out how the motor Harry is working on managed to be built and sold without the distributor assembly being on it, but that appears to be what has happened. Very odd. Would be interested to know what Brook Newcomb can tell you about it.
if worse comes to worse, you could hook up an Elto coil and try and run it like that. You’d be firing both plugs every revolution, but my Detroiters and Cross Seagulls run that was as well and since they are true four-stroke engines, it has no effect on how they run, as for every other revolution the plug merely fires at the end of the exhaust stroke and accomplishes nothing.
Hope this helps.
Best,
PM T2April 15, 2024 at 10:10 am #286746
It is isn’t a issue to have a spark plug fire on
the exhaust stroke as long as it fires on the
compression stroke. A failing plug that doesn’t
fire on the compression stroke but will in free
air, ignites the fuel on the exhaust stroke as
there is no pressure, because the exhaust valve
is open. This will result in a backfire through
the exhaust. The result can just be a loud bang
up to damaging parts of the exhaust including
blowing it off the motor. Not a common
occurrence but something I have experienced,
more than once, with this type of ignition.
Tubs
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