Pistons in BSA Engines, by Mike Scott-Coomber
When the time comes for a re-bore, and new pistons are required, your localengine rebuild or machine shop, if you are lucky enough to have one, can runinto difficulties in locating suitable pistons and may not be aware of all theBSA requirements. Steve Mansfield, as always, can often help from his stockbut even that is not infallible.
One might think that armed with the key dimensions of desired oversize bore and gudgeon pin diameter it would be a simple matter to find an alternativepiston from something else that would do the job.
The photo shows a number of different pistons from my stock, all of which are nominally suitable for the BSA 1OHP engines. However, all need some modifications and some are better than others. The recent article on lubrication oils highlighted the importance of piston clearances and ring specification, so choosing a piston is not as simple as it may seem, especially when the choicemay be restricted to old stock.A new section has been added to the Issue 2 Trike Manual, which also covers the Scout and T9 engines, giving much more details on these matters. This is available from the usual regalia address. For those who have already bought the manual, send me an S.A.E A5 size and I will update you.
One might think that armed with the key dimensions of desired oversize bore and gudgeon pin diameter it would be a simple matter to find an alternativepiston from something else that would do the job.
The photo shows a number of different pistons from my stock, all of which are nominally suitable for the BSA 1OHP engines. However, all need some modifications and some are better than others. The recent article on lubrication oils highlighted the importance of piston clearances and ring specification, so choosing a piston is not as simple as it may seem, especially when the choicemay be restricted to old stock.A new section has been added to the Issue 2 Trike Manual, which also covers the Scout and T9 engines, giving much more details on these matters. This is available from the usual regalia address. For those who have already bought the manual, send me an S.A.E A5 size and I will update you.
Mike Scott-Coomber
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