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BSA twin motors in general

BSA twin motors in general

Postby seattle##gs » Wed Sep 06, 2017 11:32 am

I don't mean to offend all the twin owners but I have a question that I have never really been able to solve. I have ridden several A-10 and A-65 bikes in good mechanical shape and in good tune and I have always felt a real lack of power, as though they were running 7 : 1 compression instead of 9:1. No punch at all to the motors, they are real grampa's bikes. They look good but no zip to them. What gives? A 650 Triumph would run away from them easily. Sorry to offend.

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Re: BSA twin motors in general

Postby grandpaul » Wed Sep 06, 2017 2:04 pm

With proper tune and gearing, they are every bit a match for Triumph 650s.

Many time, the "sluggishness" is too-tall gearing.
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Re: BSA twin motors in general

Postby RoadScholar » Wed Sep 06, 2017 6:28 pm

The A65 engine is one of the few British twins that is actually over square, as such it has a tendency to want to make its' power at higher revs than a Triumph, which is under square. The real down side is that BSA supplied the A 65 series with an engine that has a bronze timing side bush, that doesn't need much of an excuse to wear quickly. On top of that most British motorcycle manufactures did not dynamically balance the rotating/reciprocating assemblies, even their static balancing techniques, such as matching the weight of the piston assemblies and the rod assemblies could have greatly benefited by even a modicum of QC.

My point is that most solid mounted British twins vibrate so violently that the power they make (could make) is unusable, or is seriously constrained by imbalance. Motorcycle Classics magazine ran an article on a service that resto-mods Triumphs and are claiming 65 HP from a single carb TR6; these guys pay close attention to detail

But, stay tuned, I have a 1970 A65 Lightening and plan to clearance it, dynamically balance it, and replace the timing side bush with an Alpha roller bearing, but not change its state of tune (stock cam, stock headers, stock valves and stock CR). Once broken-in it my expectation is that it will rip to its red line, it may well vibrate some, but not enough to break headlight bulbs or to tear sheet metal, my 1970 Triumph Bonneville did both in 1970.
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Re: BSA twin motors in general

Postby Triton Thrasher » Wed Sep 06, 2017 10:43 pm

In general, A10s are slower than Triumphs, but honestly- who cares! Is there a race?
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Re: BSA twin motors in general

Postby grandpaul » Thu Sep 07, 2017 5:54 am

Remember that A10s are pre-unit, so best to keep the comparisons to pre-unit Triumphs as well (T110, 6T, etc.)

A65 (unit) = TR6 & T120 (63 and later)

Still, the relative comparison doesn't change a lot. A really well-sorted and maintained (not modified) A65 can hold it's own against the Bonnie & Trophy on an afternoon's ride through varied terrain and road types.
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Re: BSA twin motors in general

Postby Onder » Thu Sep 07, 2017 7:15 am

BSA 650 twins vibrate and some vibrate badly. That is factory stock ones.
I think that if you did a rebuild very carefully and had it dynamically balanced
you would find it quite good. QC must have been pretty poor at the end of
production.
The bush is not a problem if you keep the oil clean but it wont last like a roller.
Keep an eye on the end play.

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Re: BSA twin motors in general

Postby frankdamp » Thu Sep 07, 2017 7:39 am

I had an A7 (the 500cc twin) for a coupe of years. It vibrated pretty badly. A friend's Gold Flash 650 was even worse. Even my company-provided Norton 650SS was less than smooth, but was a blast to ride.

I was living about 45 miles from the N-V factory when I started with them and it was two bus rides and a train ride, over 90 minutes each way, so my boss arranged for the loan of the bike. According to the odometer, it had over 130,000 miles on it, but the only incident I had was a blown head gasket which I fixed while at work the morning it happened. My ride to work was about 45 miles, all on country back roads. It really set up the day and was relaxing going home again.
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Re: BSA twin motors in general

Postby Onder » Thu Sep 07, 2017 9:20 am

Gee I dont know. Arriving exhausted at work and near death after the home run.
Not to mention the gentle hand of Old Man Winter in the dimsy as well.
Tough men in those days!

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Re: BSA twin motors in general

Postby worntorn » Sun Sep 10, 2017 8:05 am

seattle##gs wrote:I don't mean to offend all the twin owners but I have a question that I have never really been able to solve. I have ridden several A-10 and A-65 bikes in good mechanical shape and in good tune and I have always felt a real lack of power, as though they were running 7 : 1 compression instead of 9:1. No punch at all to the motors, they are real grampa's bikes. They look good but no zip to them. What gives? A 650 Triumph would run away from them easily. Sorry to offend.


You have to remember that BSA stands for "Boring Standard Apparatus" , not Birmingham Small Arms as most assume.
I have a 63 West Coast Super Rocket, so it is as wild as the production A10 motors ever got, same engine as the RGS, 9 to one and Spitfire cams.
It's not that wild. The 650SS runs away from it, however in fairness, that bike also runs away from 650 Triumph Bonnevilles.
I do like the BSAa lot, it's very comfortable, has decent torque to pull up a long hill and is relatively smooth running at 65 mph. Not bad for an old 650 but not the crackerjack 116 mph machine that magazine roadtests raved about ( lied about) back in the day.

Glen

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Re: BSA twin motors in general

Postby frankdamp » Sun Sep 10, 2017 3:22 pm

Actually, Onder, the ride was quite a good one both ways and most of the time I was doing it was spring and summer. Once we started the Command endurance testing, I got more road miles than I was comfortable with (2500 a week!) so the 45 miles each way commute was a bit of a strain. Fortunately, not long after the endurance miles started, we moved to a small village just north on Wolverhampton, so my 45 mile commute changed to about 7 miles.
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Re: BSA twin motors in general

Postby mxman1 » Sun Sep 10, 2017 4:38 pm

I have a well sorted 1967 BSA Lightning. Dynamically balanced crank on a Stewart-Warner Machine. Roller bearing conversion (EdV), JE pistons with angled domes from EdV (no pinging problem running premium), SRM oil pump, slightly ported head. Stock cam, 21 tooth sprocket.Amal premieres, altair ignition. (Stock timing) It pulls really hard (and I'm a big guy) and when the cams kick in (and it does kick around 4500rpm) it will beat many Triumph 650 Bonnevilles. It's a great motor, vibes are there but not buzzy...no numb hands to be had and I can ride it all day. BSA's like to be revved. And when well sorted, are one of the most fun and comfortable rides from that era. IMOA
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Re: BSA twin motors in general

Postby Fast Eddie » Mon Sep 11, 2017 12:16 am

seattle##gs wrote:I don't mean to offend all the twin owners but I have a question that I have never really been able to solve. I have ridden several A-10 and A-65 bikes in good mechanical shape and in good tune and I have always felt a real lack of power, as though they were running 7 : 1 compression instead of 9:1. No punch at all to the motors, they are real grampa's bikes. They look good but no zip to them. What gives? A 650 Triumph would run away from them easily. Sorry to offend.


That's why TriBsa's were invented...
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Re: BSA twin motors in general

Postby Fast Eddie » Mon Sep 11, 2017 12:18 am

worntorn wrote:
seattle##gs wrote:I don't mean to offend all the twin owners but I have a question that I have never really been able to solve. I have ridden several A-10 and A-65 bikes in good mechanical shape and in good tune and I have always felt a real lack of power, as though they were running 7 : 1 compression instead of 9:1. No punch at all to the motors, they are real grampa's bikes. They look good but no zip to them. What gives? A 650 Triumph would run away from them easily. Sorry to offend.


You have to remember that BSA stands for "Boring Standard Apparatus" , not Birmingham Small Arms as most assume.
I have a 63 West Coast Super Rocket, so it is as wild as the production A10 motors ever got, same engine as the RGS, 9 to one and Spitfire cams.
It's not that wild. The 650SS runs away from it, however in fairness, that bike also runs away from 650 Triumph Bonnevilles.
I do like the BSAa lot, it's very comfortable, has decent torque to pull up a long hill and is relatively smooth running at 65 mph. Not bad for an old 650 but not the crackerjack 116 mph machine that magazine roadtests raved about ( lied about) back in the day.

Glen


I thought it stood for Bloody Sore Arse!

Although some say it's Buy Spares Aplenty ...

Or...??
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Re: BSA twin motors in general

Postby mxman1 » Mon Sep 11, 2017 3:01 am

Bastard Stopped Again
69 Commando S
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67 Triumph Bonneville

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Re: BSA twin motors in general

Postby trident sam » Tue Sep 19, 2017 7:42 am

Bits stuck anywhere

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