MAGNETO INSTALATION- SQ4- 1939

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Henning G
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MAGNETO INSTALATION- SQ4- 1939

Post by Henning G »

Hello and Mary Christmas. I have a question regarding magneto installation on my sq4, 1939. There are 2 holes in the engine block where the magneto is installed, but should there be a screw and a guide, or maybe two guides. Recall to have seen guides underneath a Lucas magneto, but I can’t remember how much they were sticking out of the magneto. Maybe there shul only be guides, because there is a mounting strap as well. Hope someone can help with info. Regards Henning
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paul.jameson
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Re: MAGNETO INSTALATION- SQ4- 1939

Post by paul.jameson »

According to the 1937-38 parts book, there are two dowels and and bolt in the base of the magneto. The dowels are simply a 3/8" rod, threaded whitworth one end and with a screwdriver slot across the other end. the bolt is a 3/8 whitworth one. You should be able to work out the lengths easily enough. Looking under my Square Four (1937) this appears to be what is fitted but obviously I can't be certain how many dowels there are without removing the magneto.
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Pete.Silson
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Re: MAGNETO INSTALATION- SQ4- 1939

Post by Pete.Silson »

There is one dowel and one bolt.
MN1E base 1.JPG
MN1E base 2.JPG
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Re: MAGNETO INSTALATION- SQ4- 1939

Post by nevhunter »

ONE bolt on a corner surely cannot be enough? Nev
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Re: MAGNETO INSTALATION- SQ4- 1939

Post by Henning G »

Hi Paul, Thanks for your reply. Therefore, there should be one dowel, one bolt and the strap to secure the magneto. Believe the dowel should just be flush with the underside of the casting, when installed. Must be a nightmare to removes the bolt when the engine is installed..
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paul.jameson
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Re: MAGNETO INSTALATION- SQ4- 1939

Post by paul.jameson »

Note the chamfer around the top of the dowel in Pete's excellent photo. You need this in order to get the magneto in place. Fitting and removing the bolt with the engine in place is probably easier than fitting and removing the three similar bolts on a swinging arm single. You need a socket and suitable extension. The clamp over the top of the magneto and dynamo is the reason why you only need the one bolt in one corner. The clamping mechanism did change after the first few bikes though.
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Former Machine Registrar & Archivist, General Secretary and Single Spares Organiser (over a 25 year period).
Now Archivist (but not Machine Registrar), Gauges and Clocks Spares Organiser.
Henning G
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Re: MAGNETO INSTALATION- SQ4- 1939

Post by Henning G »

Thank you for your always fast and very professional answers. Because the privies owner has alter the crankcase where the magneto axel comes through, I’m forced to install an oil seal , and I will go with the VITON, 20x26x4mm. So nice to only have one dowel instead of two, makes it a bit easier to slide the magneto in place. Thanks a lot Paul.
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Re: MAGNETO INSTALATION- SQ4- 1939

Post by nevhunter »

The strap changes the picture entirely. BSA's singles mostly only have a strap and dowels and they are gear driven which must be more accurately placed that a chain requires. Nev
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Re: MAGNETO INSTALATION- SQ4- 1939

Post by Henning G »

God point, and I believe that some attention is required to align ad maybe adjust the magneto installation, to run perfect on the chain.
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