The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: 63a10r on 26.10. 2006 01:37
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will pistons made for a 58 a10 road rocket work in a 62 da10r superrocket? there is a cherry pair of +.060 piston/ ring set on ebay, and the price is right , so far. need answer soon. also, is +.060 stretchin it a bit far? this will be basically a commuter bike (40 miles a day, plus some weekend runs. not plannin to hot rod it)
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Yes they will work but I would not bore your cylinders to + 60 unless they need it. If I recall correctly, +60 was regarded as the biggest rebore you could risk without weakening the barrels too much. The Road Rocket used 8.0 : 1 pistons as opposed to 8.5 : 1 for the later Super Rockets. This lower compression ratio will help to minimise the risk of barrel failure.
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63a10r is correct re the bore size: the parts book lists a maximum piston oversize of one miilimeter (.040 inches). If you want to go to .060, you should have the barrel radiographed in the base flange region to make sure there's no incipient problems such as casting voids/inclusions and wall thinning. You'll probably be OK, particularly if the engine isn't pushed hard and you have the headstays and engine plates good and tight.
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My A10 had +60 pistons when I got it and worked ok although it had sidecar gearing and does have thick flange barrels also the pistons were 6.5:1
+80 pistons are available so I would consider +60 safe enough, however when I eventualy needed a rebore I went for liners to bring it back to standard
All the best - Bill