The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: anjimehra on 18.01. 2017 05:53
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Hi
Any idea when the large journal cranks were introduced on the super rockets. Also, whether the big end bolt dimensions for large & small were identical
Thanks
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The BB crank was introduced on the Road Rocket in 1954 then was adopted by all A10's in1958. The small journal and large journal bolts differ slightly as they have different part numbers. I think the large journal bolts are a couple of mm. longer.
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Thanks Beezermacc. So its safe to assume all A 10's after 1958 were large journal. Would I have to specifythis when ordering big end bolts or it will be undrstood if I state the year of manufacture
take care
Anji
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You will need to know which crank you have, as they can be swapped between the crankcases, so it is possible for a later engine to have an early crank and vice versa.
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Hi Anji,
Be wary of some big end bolts that are on the market, they have turned and not forged heads and cut not rolled threads
To the best of my knowledge the only quality big end bolts available are the ARP products
John
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Andrew,
I think that you will find that the Road Rocket in 1954/5 had the small journal crank and thin flange barrels.
I have been told that 1955 Rockets had the heavy L.J. crank but this needs confirmation.
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My understanding is that the 56/57 road rockets originally had what is often called either a transitional or heavy crank: this has a very small sludge trap arrangement and the flywheel is not removeable. the webs are also a different shape and it is solid through the centre. This is also a large journal.
As mentioned after 50-65 years anything is possible and until its apart you will be guessing. There was I recall an article about an A10 owner who realised many years later that the replacement crank in his A10 (that he had fitted) was an A65 crank and the pistons didn't even get to the top of the bores!
I understand the 54 road rockets had a polished crank and were hand assembled by the comp shop and dyno'd like the goldies.
In theory all the Super Rockets "should" have the final LJ crank, but I'm actually running a transitional crank in mine. They are lovely and smooth running.
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It would be interesting to see how you could fit an A65 crank into an A10 the primary sides are totally different, the A65 has a triplex chain sprocket and also an alternator you would not be able to fit the cush drive.