Author Topic: Crankcase dates  (Read 943 times)

Offline Nourish

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Crankcase dates
« on: 09.12. 2013 18:40 »
Should the dates on the two crankcase halves match? The crankcases I've mentioned elsewhere have the dates - 1 10 52 on the drive side (although the 5 is upside down!) and the timing side is stamped 25 9 52 - only 6 days apart. The barrel base surface is a good match - ie no step.
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Online bsa-bill

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Re: Crankcase dates
« Reply #1 on: 09.12. 2013 19:28 »
some random thoughts
I think they should match as I believe they are machined as a pair, as well as the cylinder base the chamfers would be mated.
However I reckon if you removed the alignment pins/tubes you could mate them with a bit of very fine grinding paste -  usual meticulous cleaning required after

might be as they are only days apart date wise that they were done on the same machine, maybe not how many  machines would BSA have had ?.
lot of work putting it all together to find it leaks, maybe bolt it up and shine a torch in it in a dark room.

alignment for the crank - probably line boring would cure any mismatch

Think I'll shut up now before the engineers amongst you have coronaries  *smiley4*
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All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Offline muskrat

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Re: Crankcase dates
« Reply #2 on: 09.12. 2013 19:44 »
In a perfect world the cases should be kept as pairs, but.
The main crank bush will need to be line reamed as well as the cam bushes. Hopefully this won't alter the idler center distances and create binding or backlash. Then the deck will need to be true and square to the crank. The crank will need to be shimmed as normal.
There's a bit in it but a very good result can result if done right.
Golden rule - measure 10 times ___ machine,grind,cut,weld or bash once.
Cheers
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'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
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Online trevinoz

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Re: Crankcase dates
« Reply #3 on: 09.12. 2013 19:56 »
I think that it is normal for plunger cases to have different dates.

Trev.
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Online Brian

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Re: Crankcase dates
« Reply #4 on: 09.12. 2013 20:44 »
The dates dont really matter.

On the front of the cases on one of the lugs there should be two corresponding numbers, if those numbers are the same the cases should be a pair.
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Online bsa-bill

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Re: Crankcase dates
« Reply #5 on: 09.12. 2013 21:35 »
Quote
if those numbers are the same the cases should be a pair.

Good point Brian but if the dates are different what are the chances of the numbers being the same - comes back to how many machines they had, I have no idea
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All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Offline Rocket Racer

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Re: Crankcase dates
« Reply #6 on: 09.12. 2013 23:44 »
While as mentioned factory matched cases have a common number on the front, and typically a date stamp consistent with the engine number, my super rocket cases have a date stamp from 1967, which had me wondering if it was a factory replacement engine.
I've only seen a single date stamp on the various sets of swing arm cases in my man cave.
These bikes have seen so much history I try not to get hung up with numbers as they can be messed with but would be interesting to know what the date stamp actually meant originally.  
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A good rider periodically checks all nuts and bolts with a spanner to see that they are tight - Instruction Manual for BSA B series, p46, para 2.
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Offline Nourish

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Re: Crankcase dates
« Reply #7 on: 10.12. 2013 23:12 »
I finished vapour blasting the cases and polished them up with a wire brush on a spindle and now that they look like freshly cast casings I can see the stamping on the lips of the casings at the front - they are both stamped 920 and a small round stamp that covers both halves on the cylinder base gasket face lines up - so although the dates stamps don't match they still appear to be a matched pair.
Cheers
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