Author Topic: big end shells A7 52 star twin  (Read 587 times)

Offline KeithA

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big end shells A7 52 star twin
« on: 31.12. 2015 03:40 »
Can any-one advise on how I interpret the numbers on these big end shells I removed from my engine.
My crank is worn 0.023" so I will require a set of 0.030" undersize shells with a regrind.
Any advise regards suppliers of quality parts eg shells, lead bronze timing side bush, cam bushes, gearbox bushes? D/fly, SRM, Degroot, British only Au.
Thanks in advance.
Keith


Offline terryk

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Re: big end shells A7 52 star twin
« Reply #1 on: 31.12. 2015 17:12 »
Get your bigends ground first to see if they both clean up at -30 otherwise you may buy shells only to find that it doesn't quite clean up at -30 and you have to go to -40.
Also with the timing side journal just get it ground to clean up don't worry about the size because you can get the bush made to fit. Eg you don't need to grind to -20 just because its worn 9 thou from STD just get it ground to whatever it cleans up at eg 12 thou then get the bush made to fit. These cranks are getting very hard to find these days so preserve any life in them that you can.
1950-53 A10 rigid/plungers, 1958-61 A10 super rockets, 1947-50 A7 longstrokes, 1949 Star twin,
1951-54 A7 plungers, 1940s M21, WDM20s,
1948-50s B33s rigid/plunger/swingarm, 1948-50s b31s rigid/plunger/swingarm

Offline KeithA

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Re: big end shells A7 52 star twin
« Reply #2 on: 01.01. 2016 12:17 »
Thanks for your reply.
After much careful measuring, I cant detect any oval wear more than 2 or 3 tenths.
I think I have more of an issue with the journals being parallel.
I'll take it to the local engine reconditioner, and see if he can clean it up at 030"
Also I will be able to line bore a timing side bush like you suggest, with just cleaning it up.
Yes these flywheel forgings are a work of art no doubt, and have to be preserved.
What is the recommended brand of shells to buy for a standard engine rebuild intended for moderate highway use.
Thanks
Keith


Offline terryk

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Re: big end shells A7 52 star twin
« Reply #3 on: 07.01. 2016 15:04 »
I have a number of different brands for BSAs so I don't think it matters unless other members have had trouble with a particular brand. I don't know if the Indians are making these but I would steer clear of them. If the shells are from a reputable source then they should be fine.
1950-53 A10 rigid/plungers, 1958-61 A10 super rockets, 1947-50 A7 longstrokes, 1949 Star twin,
1951-54 A7 plungers, 1940s M21, WDM20s,
1948-50s B33s rigid/plunger/swingarm, 1948-50s b31s rigid/plunger/swingarm

Online KiwiGF

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Re: big end shells A7 52 star twin
« Reply #4 on: 07.01. 2016 21:05 »
New Zealand

1956 A10 Golden Flash (1st finished project)

1949 B31 rigid “400cc hot rod” (2nd finished project, + favourite bike)

GL1800 Goldwing, well, the wife likes it

KTM 950 ADV, cos it’s 100% nuts

1952 Armstrong Siddeley Whitley for rainy days (with wife)