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Author Topic: BSA 1937 HN21 single  (Read 897 times)

Online orabanda

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BSA 1937 HN21 single
« on: 23.03. 2012 03:26 »
Hi all,
A friend needs to know how to time one of these.

It is a sidevalve single.

Can anyone direct me to a website, or manual, or article?

Thanks,
Richard
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Offline Brian

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Re: BSA 1937 HN21 single
« Reply #1 on: 23.03. 2012 03:54 »
G'day Richard,

H defines it as 1937 but a B21 is a OHV. A B20 is SV.

Ive attatched a scan of the valve timing for the 1937 B models, if its a SV then the ignition timing is 5/16" BTDC but if its a OHV its 7/16".

Tappets for a SV are inlet .004" and exhaust .006"
Tappets for OHV are just free.

Drop me a line if I can help.
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Offline BVSR

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Re: BSA 1937 HN21 single
« Reply #2 on: 25.03. 2012 20:52 »
Hi Richard,

I am quite sure that Your friend has M21 600 cc sidevalve single. I have only engine, not more. Timing is as Brian wrote.

Markku
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Markku
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