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1947 Airone Magneto ID

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Tim wrote: I have a Marelli magneto with the letters & number MCR4E stamped on it then there is a number 1590559 below that . Is this the correct mag for the airone ? And how do you tell if you have a mag for a twin or a single cylinder ?

The magneto on the bench is the MCR4E and the one on the bike is a different shape & size and I don't see any numbers on it being it's on the bike.

IMG 8004 IMG 8005
 
SED Sci replied with...
For 1947 you should have a BL cable advance mag. After '52 or so they switched to auto advance MCR mag. They are interchangeable (if correct rotation and timing). If you switch to the auto-advance MCR you loose the cable timing control and must set timing at full retard instead of full advance.

Both are single cylinder mags with only one spark plug wire. The attached file will help you decide if it is correct for the Guzzi - counterclockwise rotation and 15* static advance.
 
Tim replied... about 6 yrs. ago when I first owned this bike it had no cable for the this magneto on the bike so I assumed it was an auto advance and the bike started up for me. I never got a chance to test ride the bike ,,,, long story.

I now have checked the simple things and I have no spark at my spark plug. However, my spare MCR4E mag has spark as I did a bench test just by spinning the shaft by hand and a spark plug in the HT wire …. I also found a resistor spark plug in the bike ,,, and from what I have read that's not a good thing for a magneto.

What is the correct modern day spark plug used for this little guzzi ,, book says a CW175 ET which is probably a Marelli plug with a 1/2 inch reach
 
Kristian S replied, I found mine needed a 5/8 in plug which don’t exist anymore (cw225). I have used both a 1/2 in with a long nose and a 3/4 with two crush washers and both worked fine.
 
Tim wrote: I removed the Marelli BL mag from the bike for further inspection. I did a bench test by attaching my 2500 rpm drill to it and sure enough it sparks the plug with a full spark across the electrode . I varied the speed of the drill and it continued to spark.
Now it was mentioned here on the forum that the MCR4E mag should be set at 15 degrees full retard. But I see stamped on my BL mag is 11 degrees counter clockwise rotation . Which setting should I use ?? and at what advance setting full retard or full advance on my BL mag. The serial number I assume is also stamped on one side and I'm not sure if it's # 1331837 or # 133 1 B37 anyone else have a BL mag that can verify this? And I also discovered that the woodruff is bugger up on the shaft of the mag …. always something.

IMG 8012 IMG 8011 IMG 8008 IMG 8009 IMG 8010
 
Your mag should spark down to less than 200 rpm. Magneto rpm is 1/2 engine rpm so 200 rpm represents 400 rpm kick start speed - pretty fast. It should spark consistently at that rpm with a 5mm plug gap in air. At 2000 rpm it should spark across and 8mm gap consistently.

Follow the tests in the article to determine if there is a problem with the coils. You can also have corrosion or grease adding resistance at the slip ring or high tension pickup or even spark plug wire. A good ohm meter is a great help. My Friend's BL had good coils, but had corrosion between the secondary coil and the slip ring and needed a capacitor, then the engine would run. My similar LAN mag need the secondary coil rewound.

If it has been 10 years or more since the BL mag was re-magnetized it has likely lost some of it's magnetism. The AlNiCo magnet in the MCR will hold its magnetism better, but it is also harder to remagnetize.

If you install the BL mag, set the cable advance lever to full advance and use the timing spec from a 1950 or earlier Airone manual. It will tell you the distance in mm between the arrows on the flywheel and timing cover before the points open. With a bright light it is possible to see where the points open. Timing can be adjusted by adjusting the cable stops, adjusting the point gap, or moving a gear tooth. Timing doesn't have to be perfect to get the engine to run. You can fine tune it by road testing or with a timing light after it's running

If you use the MCR it will be held at full retard by the auto advance springs and you will time it at full retard - again mm between the arrows but maybe 40-50 mm less than the full advance number. This number should be in 1954 and later manuals. As far as I know the only way to adjust timing is by altering point gap or jumping a whole tooth on the timing gears.

Hope this helps!
 
Thanks for the info ,,, I don't have a cable that operates the advance. There wasn't one when I first bought the bike so I assumed it was auto advance. I going to try the air gap test again and see what I get for a spark at slow speed.

I also noticed that the gear for the BL doesn't fit the shaft of the MCR. Can anyone tell me if the BL mag uses a pin to hold the gear ? The gear presently on the BL has a keyway slot but as you could see in the picture I posted before there doesn't look like there was a slot but maybe a pin ?? And my parts book doesn't show or list a BL mag.

Should I switch to the MCR mag or keep what I have ?? These and other questions as time goes on …...

Tim

IMG 8009
 
Here is a Airone parts book with the BL mag:
https://www.rpw.it/Files/Guzzi_Airone 1949 - (Sport 1s) Catalogo ricambi.pdf

The 1951 Airone I've worked on has a key slot with a 1/2 moon key. The keyway is cut into a brass shaft that is an extension of the armature's brass end cap as in the fist picture. The second picture shows an LAN shaft that looks the same (keyway backside of shaft):

IMG 6661crop

IMG 4712sm

Is your shaft steel with no taper? Does the gear have a taper? I wonder if the brass shaft was stripped and repaired?



As for using BL or MCR - my impression is that the MCR is easier to rebuild because the armature does not need to be disassembled to replace the capacitor and the coil is a replacement part not a bobbin to be rewound but I've not worked on an MCR.



BL parts image:

BLmag
 
Antonio replied: the shaft of the mag ends with a taper before the threads; it looks like your taper has been removed.. Zipolo
 
It is a bit difficult to see what is going on in the photos, but there appears to be some definite issues with the keyway. If it was my bike, I would carefully file the bodged pin flush with the taper then gently lap the tapered bore in the gear to the tapered shaft with some fine valve grinding compound. The function of the woodruff key is primarily to index the points in the magneto to the timing gear and that function can be done by careful fitting and a bit of trial and error. The woodruff key offers very little in maintaining the position of the gear on the shaft; the taper does that. If the taper on the gear maes full contact with taper on the shaft and the nut holding the gear on the shaft is properly tightened, the gear will not slip. As long as the points open at the appropriate time as indicated by the marks on the flywheel (or better yet with a degree wheel), the ignition timing will be good. It might take a few tries to get it spot on, but it will be a lot easier than refurbishing the magneto shaft. The BTH magneto on my Velocette has no keyway for the timing gear, and it is relatively easy to time the ignition. Admittedly, the keyway ln the Marelli magneto makes the Guzzi somewhat easier to time, but the lack of a key way allows the tuner to get the ignition timing spot on.
There is a good explanation of how to set the Falcone timing here:
thisoldtractor.com/mg_manuals/falcone_ignition_timing.pdf
I expect that the timing on the Falcone is pretty much the same as the Airone.
Alan in Roberts Creek
 
The mag gear needs to have the same number of teeth as the cam gear or it will go out of time. The fiber gear looks like a dynamo drive gear. I think all the mag gears are steel with straight cut teeth.

Guzzis didn't get the auto-advance MCR mag did until 1952 or later so if your Airone is really 1947, BL is the original style mag.
 
Thanks Alan for the insight on the repair of the taper on the shaft ,,, your the second person to mention that method and that way seems to be the best way to go.

As I've mentioned a couple times here there is no advance cable used here on either of the two magneto's I have... and what little I have read for both the falcone & airone timing instructions they both mention the moving of a cable.

The parts book doesn't say which mag gear should be used and with the number of teeth. But for now I do know I can only use a gear with straight cut teeth with the cam I have. More still to learn. Tim
 
The mag gear and the cam gear have to have twice as many teeth as the pinion gear on the end of the crank. This is for any 4 cycle engine. That phenolic gear is for the generator drive.

JerryK
 
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