The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: 7iain7 on 10.02. 2024 12:57
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hi all, Did the pre 1954 A10 engine not use a crankshaft seal?
many thanks, Iain
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Do you mean 67-0674? Its a long time since I stripped a bolt up A10 bottom end so I can/t remember. Is there space for it?
Interestingly the Draganfly website uses the bolt engine parts diagram and it doesn't show a seal but does list one (perhaps for later engines):
https://draganfly.co.uk/product-category/bsa/sparesparts-for-bsa-a710-b3133-c101112-m202133/engine-gaskets-gearbox/crankcase-abcm/pre-unit-a-group-crankcase/
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Seal fitted from 1953 season models - BA engine number prefix.
Seal first mention in parts bulletin 4B from October 1952 which listed "New components for 1953 models"
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Do you mean 67-0674? Its a long time since I stripped a bolt up A10 bottom end so I can/t remember. Is there space for it?
Interestingly the Draganfly website uses the bolt engine parts diagram and it doesn't show a seal but does list one (perhaps for later engines):
https://draganfly.co.uk/product-category/bsa/sparesparts-for-bsa-a710-b3133-c101112-m202133/engine-gaskets-gearbox/crankcase-abcm/pre-unit-a-group-crankcase/
No space for a the seal, I ordered a gasket set for pre-unit A10 and was surprised to see a crankshaft seal. The Bike was first registred April 1952. Makes sense now if the seal wasn't added until 1953. Cheers all.
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Along with the seal goes the different crankshaft drive sleeve 67 2071, listed above. This has a smaller periphery to fit the seal lips. Earlier type has a larger periphery to be simply a close fit in the crankcase. Forum posts about this part abound, some are plain, with a smooth edge, some have a scroll. Fitting a later smaller sleeve to an earlier none seal engine is a simple mistake, it all fits fine, but primary case will fill with oil. If you have a plunger bike with this syndrome, there's a possible answer.
Early non seal crankcases can be machined to take the seal, and assembled with the later drive sleeve.
Later S/A engines use a different sleeve, which changes over the model years. Early ones run on the seal, later type has a spacer. Seal itself is the same part for all models/years since its introduction.
Swarfy.
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Interesting second page of a letter dated February 1953 from Hap Alzina, the US West Coast importer to a Colorado dealer concerning some A10 chaincases being "sucked dry" by crankcase vacuum.
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That is extremely interesting, so which way round does the oil seal fit? I'll be building the bottom end in a week or two and was going to fit the seal to prevent oil from the case migrating to the chain-case, but this suggests it may be better the other way round.
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Fit the seal spring to crankcase.
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Thanks, yes that was my plan.