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BSA A65 stroker

BSA A65 stroker

Postby Andy55 » Mon Nov 09, 2015 1:06 pm

HI guys new to this forum so first thanks for accepting me. I would like to start with a question please. I have a 1969 BSA A65 Lightning rolling chassis and would like to build up a stroker motor for it. I understand that the BSA A10 crankshaft can be persuaded to fit and have also heard of people fitting a Norton Commando crank, any of you guys out their have any first hand knowledge of what is involved? I have previously built a 750 motor using the SRM big bore kit(not available at present) but I went too far with the mods, race cam, big valve head, 34mm carbs etc and produced a motor that liked to rev but had little bottom end. I sold it to a guy who wanted to go racing. Thanks in advance. Apologies if this has been covered before, I did search the forum before posting and could not get a match.

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Re: BSA A65 stroker

Postby Bernhard » Tue Nov 10, 2015 5:20 am

There are different ways of doing it, I ‘ve heard of at least one big 800cc BSA twin which was owned by a London dispatch rider who only brought it out on sunny days, he got through a least 2 gearboxes;


http://victorylibrary.com/brit/BSA-c.htm

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Re: BSA A65 stroker

Postby Mark F » Thu Dec 03, 2015 3:36 am

See modified BSA A65 below.
Lots done to this bike .
'74 Roadster
'65 Lightning Rocket
'52 Goldstar
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Re: BSA A65 stroker

Postby J. M. Leadbeater » Sat Jan 23, 2016 2:21 pm

Decades ago people would take 89mm stroke Norton cranks and machine the big ends to 1 5/8 dia to accept BSA / Triumph rods........
Personally before even thinking of using or modifying a second hand or new crank I would 1. check the D.S. crank half does NOT have a stress raiser inside directly beneath the big ends outer stress REDUCING 90 thou radius. (The idiots in the factory often during machining left a stress raiser inside directly beneath the 90 thou radius so the crank would break more easily at this point of very high stress concentration) and 2. have the D.S. crank x rayed / crack tested before doing anything as it could well already be on its way to failure and when the crank becomes 4 piece it gets rather expensive. A friend and I had a few D.S. halves checked and two were thrown straight in the scrap bin not that we could visually see the fault although I can assure you one can see it very easily when the crank has failed big time...some of us learnt about stress raisers the expensive way....Some people reckon Nortons were built to teach Engineering to those capable of learning.
Friends sidecar scramble big A65s and even fit 79mm bore B44 pistons and they seem to stay in one lump even though well abused......mind you they do have a dry running diaphragm spring clutch belt system fitted that does NOT slip when fully engaged and which is easily operated with two fingers.....which makes getting off the line a lot easier and normally results in them being first into the first bend. Of course it helps if the friendly starter holds everyone on the line so the competition are suffering left arm and wrist ache long before the flag drops!!!
Suggest you attend a few pre 65 scrambles meetings and talk to a A65 owners. Try pulling a few clutch levers at the same time...its good for a laugh...especially B50 ones! How some people free off their clutches is beyond me unless they use both hands or have super human strength......or trained on T140s or 820 Commandos....

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Re: BSA A65 stroker

Postby J. M. Leadbeater » Sun Jan 24, 2016 2:35 pm

Have just had a word with frame maker/ big A65 sidecar scrambler friend...
Both their engines employ A10 cranks which with B44 pistons give something like 840cc. only police a10s had alternators. I assume?? that one could do a Triumph and screw an extension into the end of the crank for the alternator?? Others use Norton cranks ending up with somewhere around 900cc motors but all depend on how much meat there is in the barrel and the bores are often offset to take 79mm pistons. Apparently there is a Triumph pisaton with a bore size midwayish between std A65 and B44 that some use.
Of course one could always have a crank manufactured............. Have fun playing.

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Re: BSA A65 stroker

Postby grandpaul » Tue Jan 26, 2016 7:31 am

Mark's bike is not to shabby...

modified-bsa-a65-t22989.html
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Re: BSA A65 stroker

Postby Matt Spencer » Sun Feb 05, 2017 1:12 pm

What you Need is a A 70 crank & T 140 Rods ( as Theyre A70 Rods , actually )

Image

Image

Image

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:D :lol: :(

haveareadoffthis : http://www.britbike.com/forums/ubbthrea ... ber=574703
Last edited by Matt Spencer on Sun Feb 05, 2017 1:43 pm, edited 1 time in total.
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Re: BSA A65 stroker

Postby Matt Spencer » Sun Feb 05, 2017 1:18 pm

CHEAPEST'd just be a pair of stickers ! .

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or a poster . ( Trackmaster ) was intresting McM articles on Chris Vincent & Devimead , back in the day . Component Pictures ' notes ' .

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750 Devimead Beeza - Image TEST .

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If your well heeled , theyred be ' off the shelf ' coustom crankshafts . For a mere pittance , in comparison to a Rolls Royce Merlin .
Last edited by Matt Spencer on Sun Feb 05, 2017 1:31 pm, edited 1 time in total.
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Re: BSA A65 stroker

Postby grandpaul » Sun Feb 05, 2017 1:25 pm

That drawing is beautiful.
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