Cylinder firing order in a square four

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Akumar
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Cylinder firing order in a square four

Postby Akumar » Sat Oct 17, 2020 6:48 am

Dear fellow enthusiasts,

Couple of basic questions about square four cylinder firing order:

1. If I am looking at the cylinder block from above, which cylinder is considered the first, second, third, and fourth. Does the first image show it correctly?

2. What is the correct order to connect spark plugs to the magneto distributor? Should the order be same as the cylinder pattern shown in first image?

Square four block.JPG
Square four block.JPG (43.75 KiB) Viewed 237 times


Square four distributor.JPG

I appreciate your help.

Kumar
48 SQ4 (with 1937 engine), 43 NG, 51 NH, 53 VB, 58 Colt

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simon.holyfield
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Re: Cylinder firing order in a square four

Postby simon.holyfield » Sat Oct 17, 2020 7:40 am

Firing order is correct in both pictures, but that rotor arm looks like it's for the wrong rotation direction.
cheers

Simes

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john.bebb
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Re: Cylinder firing order in a square four

Postby john.bebb » Mon Oct 19, 2020 10:24 am

Hey - the pic of the distributor looks suspiciously mislabeled!
Sit on the bike - twistgrip hand is front pot #1 - number clockwise from there - thus clutch hand is front pot #4.
Pic #1 of the block is correct - Pic #2 is WRONG
The rotor duplicates the pot layout - the contact arm points to the respective pot which is firing.
The flat sector of the distributor body should be across rear of the motorcycle & (approximately) orthogonal to the direction in which the bike is driven.
Cheers, John

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Paul_Linden
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Re: Cylinder firing order in a square four

Postby Paul_Linden » Mon Oct 19, 2020 3:45 pm

I think it is just a convention that the flat side of the distributor faces the back. The firing order in the distributor is correctly shown in the photo; so as long as the points are just opening for pot 1 which should be at the right spot on its firing stroke, and the rotor arm points to the HT lead that goes to pot 1, then Robert is your mother’s brother.

As Simon correctly pointed out, it is the wrong rotor arm, the brass bit should extend the other way.
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chris.shearwood
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Re: Cylinder firing order in a square four

Postby chris.shearwood » Mon Oct 19, 2020 5:31 pm

Paul_Linden wrote:I think it is just a convention that the flat side of the distributor faces the back.


On the Sq4 magdyno the flat side of the distributor must face to the left of the machine, n'est-ce pas?
1946 4G, 1950 NG and 1951 VH

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Paul_Linden
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Re: Cylinder firing order in a square four

Postby Paul_Linden » Mon Oct 19, 2020 5:47 pm

I was talking about the coil ignition distributor - I don’t know what happens on a mag-dyno.
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Re: Cylinder firing order in a square four

Postby Gui.dorey » Mon Oct 19, 2020 7:28 pm

chris.shearwood wrote:
Paul_Linden wrote:I think it is just a convention that the flat side of the distributor faces the back.


On the Sq4 magdyno the flat side of the distributor must face to the left of the machine, n'est-ce pas?


Actually it doesn’t have to. On mine for some reason, if I do it that way I wasn’t able to get enough movement to set the ignition. In the end I have the flat pointing to 2 O’clock. One can also play with the tooth engagement to have no 1 firing on any of the HT pick ups. Important is that the order 1-4 clockwise is kept. Naturally it makes more sense to have the set to replicate the order of the cylinder barrel, and conventionally the flat should point to the oil tank.

Can’t say why mine didn’t work that way. I just din’t have enough space between oil tank and the Solex bowl to set it that way.

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Re: Cylinder firing order in a square four

Postby paul.jameson » Mon Oct 19, 2020 8:15 pm

Chris is absolutely correct. On the magdyno Square Fours 1936-48 the distributor base is cast as part of the magdyno end plate and so is completely unable to rotate. The position of the rotor arm can be adjusted instead.
On the Mk I and Mk II models 1949-59 you can rotate the distributor base to almost any angle if you try hard enough.
Paul Jameson
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Re: Cylinder firing order in a square four

Postby john.bebb » Tue Oct 20, 2020 6:28 am

Sure - maybes you can orientate the distibutor body wherever tickles your fancy...
Such does not alter the fact that when viewed from above; -
the "buisness end" of the rotor arm points to the cylinder which would be sparked.
I believe this to be true for both Mk1 & Mk11 coil ign machines.

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Re: Cylinder firing order in a square four

Postby Paul_Linden » Tue Oct 20, 2020 8:43 am

I’ve just seen in the picture that this is a mag-dyno square four - so my comment on coil ignition is not really relevant. :-(
Ariel Square 4 mk2, Ariel Square 4 mk3 (yes, really), Ariel Colt, Matchless G12, BSA C12. Room for one more......


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