The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: blackiston on 10.10. 2012 01:28
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Frame Vin: ZA7S 12480
Motor Vin: Za10 2384 HC
Transmission has AD stamped in it
To my understanding I'm working with a 1950 plunger frame, with a 1950 a10 motor. What does HC stamped below the crankcase vin mean? The transmission shifts top to bottom; 1,2,3,N,4..I've been told that is not normal, the PO said he had put a couple hundred miles on it that way. If I am correct on the motor being a 1950 a10, is it advisable to run valve clearance at .015 intake and exhaust? I have read 2 different specs in different locations of the haynes manual for this motor.
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Hi blackiston, Correct on 1950 plunger (frame S designation) A10, HC usually means High Compression (actually not really that high: probably 7.5:1). The early A7 Star twins (A7S motors) had HC on them, but others will shortly reply with details of models & gearboxes, Gavinoz
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G'day blackiston, welcome to the forum.
yep 1950 A10 plunger.HC = high comp = 7.25:1. gears are from neutral up to 1st,down to 2nd, down to 3rd, down to 4th, with the gear lever pointing forward. If it's opposite you must have a reverse cam plate in there, or rear set pegs with the lever pointing backwards. Not sure if they did them for plunger box's. 15thou is right for 1950 tappets.
Cheers
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Blackiston & Musky,
A10 didn't have .015" clearance.
According to Bacon, 1950 had .010" & .010" and all others had .010" & .016", with the 334 cam, of course.
Service sheet 216 shows .010" & .016" for the A10 (Flash) until the 356 cam was fitted when the clearances were changed to suit. (1958)
Trev.
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G'day Trev,
Baconed again maybe. BSA Twins & Triples page 163 A10 '50 - '54 10 & 10 except '50 was 15. *dunno*
Cheers
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Thanks for the help, bike seems to run well at .015 disregarding the tappet noise. Any clarification on whether .010 or .015 is the route to go? Does Bacons manual trump haynes?
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BSA service sheets trump them both!
See previous.
Trev.
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Just to be difficult I thought I would throw in a bit more information.
Service sheet 216 does indeed show .010" and .016" for the A10.
However I have quite a lot of other genuine BSA information and all of that including the 1950 handbook shows .010" for both inlet and exhaust.
I live in a hot climate, in summer I ride on plus 40° C days and I have always run all my A twins with .010".
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I imagine that the 1950 book shows both settings at .010 as that was the first year of A10 production but possibly experience in the field with valve clearances tightening led to the higher clearance.
The same thing with the 356 cam, the exhaust clearance was increased.
Trev.
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Could be Trev but the 1954 service sheet 701 also shows .010" for both valves. Thats from August 1954. You would think they would have corrected the info by then if there was a problem.
Looking through all my service books its only sheet 216 that gives the .016".
In Munro's book of BSA twins he says .008" is the acceptable clearance.
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Lucky that's sorted then??
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Yeah, clear as mud *dunno*
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Thanks for all the advice, I'll give .010 inlet and exhaust a try and keep an eye out for overheating.