Britbike forum Forums British Motorcycle specific Brands Bsa bulletin board The what if A65 67hp challenge.

Interesting thoughts here and makes me wish for another unit BSA twin.
Some time ago for my own amusement I wrote an "alternative history" essay in which AMC revived the Porcupine and gave two motors and spares to Eric Oliver in about 1955. By 1960 they were so developed that BMW rennsports were entirely outclassed and it was not until 1965, in my "history", that two-strokes came along.
Yes, dry sump, low c-of-g, and a motor that was at the beginning of its potential developement, as opposed to the RS. "By 1962", I wrote. "a four valve head was in the development sshop but not needed"...
Fun to make up a history in which one's favorites win.

I've driven Holdens with LS engines, not the blown one nor the LS7 427, but mostly at my work it was the Hemi in Jeeps and Chryslers . Highway patrol here now have the Holdens BMW and Hemis.

Didn't drive the Holdens much because we worked on the Toyata/Jeep side of the dealership. The hemi sounded much better to everyone, never saw anyone come back from driving one without a big grin, but we didn't pay for fuel I guess.

There's a good film on youtube of A70s being raced, they were definitely finding good hp. Just listen to Aldana's BSA. I think low 70s is what they had at the wheel, the F750 works 3s I think the best tested had 73rwhp. The best I've seen for a 3 was a 930cc at 87rwhp and that was following exhausting dyno tuning, which I guess is necessary to find the best settings, but you need money for that. The works Commando raced by Peter Williams around 1972-73 had 76 at the crank 67rwhp.

https://www.youtube.com/watch?v=fehu0WaPE6A&t=620s

While we are at it Peter Williams, brilliant guy in so many ways.

https://www.youtube.com/watch?v=a-SOXVVdIZ4&t=19s

I lived around the corner from 'crasher Croxford' for a while, used to see him about on his Guzzi.
Bloody nutter. Mick Hemmings rode that norton well too.

This brings up the question of what breaks next? At 40 HP the A65 was fairly reliable. With over 50% increase you have to start looking at all the failings of the design. You need RPM to make that power. Brings to mind Elvis Presley - "Shake, baby, shake!". The two bearing crank is going to need more support. The clutch hanging way out from the gearbox bearing needs support and the clutch itself with the basket supported by one row of rollers inboard and the pressure plate outboard is not up to the task. Valve train mass is going to be limiting.
Still your miles (kilometers?) off from the 90HP of the OW72 Roberts bike.

I hear it all the time, "Car engines used bushings on the crank."
The only one with which I am familiar enough to comment is the air-cooled VW. Yes, it used a bushed crank. No, it did not feed oil through the bush! It had oil feeds at two places along the crank. And, it was a wet-sump engine. And, if you wanted to rev it past about 4500rpm you had to dowel the crank so it wouldn't beat the bearings to death. Oddly enough, those engines could be built to deliver twice the HP and still be reliable.
BTW: My mid-71 A65 came with the crap-metal oil pump and alloy rod caps. Too little, too late.
There's a tale from Healy in Vintage Bike. They disassembled the first Trident they got at his shop and found casting sand inside the engine. So much for the artisans at Small Heath.

Automotive engines, auto/trucks/Diesels, use split plain bearings on all crankshaft journals.....Maybe some think those are bushings..The BSA crank bushing is rather wide and a small diameter, in comparison to other plain bearings that have a much greater diameter than width.
My first bike was a 1965 BSA 650 bought in 1972...I got it because it was much less expensive than a used Triumph because of the poor BSA reputation at that time..Same was true of British cars in the USA . American car industry and Harley was also suffering poor build quality for all the well discussed reasons...

Loved that Aldana video, thank you.

OW72, what an interesting bike. So the standard Yamaha was stuck in the mid 70s hp wise, 75-76hp, they needed 80+ to be in the race with the XR750s. The limitation was the head, it needed a new one that could flow more air, one with big valves 43 and 37mm with altered casting and altered valve angles. Yamaha spent money time and effort and built them.

https://www.mecum.com/lots/LV0116-228305/1976-yamaha-ow72-eddie-lawson-racer/

What I did with my A65 was to address its breathing limitation, but it doesn't need a new casting, though modification to the patterns, or even a non machined casting would allow even better breathing. I use 44.5mm inlets and 38-39mm exhausts. To improve the XR 750's 350 Gold Star based head, very clever tuners developed the oval port XR head. The same port I copied into my A65. It's a bit much for a 650, unless you were actually aiming for 10,000+ rpm but its great on the 883 and seems fine on the 750 though the head on our 750 flows a little less at around 190cfm rather than 200cfm which is a bit more involved to do.

So the stock A65 head can be modified to flow well enough for at least 85rwhp as I have with the 883. The 750 should be able to approach that as well though at higher rpm. The 750 could be running 12-1 compression when at the moment it's around 10-1. I ran the 883 at just over 12-1 for a while, I didn't realize that's what it was, its now 11-1 because even though it was ok with higher compression on pump gas it made me nervous.

The 90 degree configuration is like running a 46% stronger crank because that is the load reduction on it. The crank is supported on 3 bearings the 3rd is outside the alternator stopping deflection and primary misalignment, it also has an extra bearing behind the clutch to prevent the main-shaft deflecting. It's more difficult for the centre of a crank to flex when the extreme end is held, if you put a piece of wood between two bricks and push it the overhanging ends move up when the centre flexes down, clamping an end makes bending it in the middle more difficult. The A65 valve gear seems good at least to 9,000. The stock 473 cam profile retarded a little, to square it up, works really well, and it doesn't need excessively strong valve springs. An A65 like this with 190cfm heads running 12-1 compression according to a hp calculator should be able to make about 98hp at the flywheel at somewhere around 9000-9,500. Something might break, but the 883 doesn't break stuff anymore at that power level. (not that it's being raced)

With this small oval port head I was just wondering what it would do on an otherwise stock motor.

Might have missed something earlier Mark (or dementors is setting in which is possible) so your now flowing a 30mm head? Not one that’s been opened up like on the 883?

Yea a little version of the bigger oval port, I had it at 30mm with stock valve flowing around 143cfm now its 32mm with 42mm valve around 160cfm but the carb restricts it to 145cfm, a flatslide with smooth bore would give better flow. But I can use these 32VM round slides to see how it works, its a small port with higher velocity. Just need to build the bike.

Wonder what you would get on cfm on the small port head, flowed, I've found that to give me the best power on the 650's

The British bike industry was much more adventurous in what they made before the war. After the war Britain was skint and reverted to making singles, parallel twins, and villiers engined ring-dingers for people to get to work on. The shareholders wanted their dividends and refused to reinvest money when it was really needed, leading to 30hp twins being stretched by crude tuning to fragile leaky 50+ hp machines.

Doug Hele, who was a good engineer, had the triple ready to rock in the early 1960's, but the money men said no as the Bonneville was selling like hot cakes and they didn't want to rock the boat. It was a real missed opportunity imho. By the time the triple was needed, the money to build it was not there any longer.

What Mark is doing with his twin, Bsa could have done 50 years ago, Developement rather than ever wilder cams and higher compression ratios, and hoping the main bearings don't fail, the crank doesn't break, or the engine doesn't start throwing rods.

Mark.
I am doing the engine prep work on a 650/750 a65 for an outfit at the moment, it goes well for what it is.
He's just won the Queensland title on it and came 2nd last year in the aussie championship as a 'worked' standard 650.
He was only beaten by a 920 norton (totally illegal really) But, it made a lot of blokes look silly.
The 'new' motor will have an a10 crank in it, end fed etc.
As he has to comply with pre-63 regs he must use a modified single carb head which we have done, (a65 'Star' was around in 62)
he will be running a dcoe40 carb, so i've had stubbs welded on. He can run main venturis up to 34mm but i have 33's so we'll use those.
Up to now we have run a pair of 30mm or 32mm standard carbs, but he wants to use the weber as do i. It complies and i have experience with them.
I have a set of large inlet valves for it. (modified velo ones, they are quite nice)
Do you fancy doing the head up for me? No money in it as i do it for love! Classic racing is like that i'm afraid.
Just tell me to pi$$ off if your not interested. LOL.

Many blokes are riding their standard setup a65's quite happily, me included, with alley rods and a standard timing side bush. I certainly don't 'baby' my road bikes and i know
the racing outfit i prepped last year (also standard) gets used to 7-7500 often. I really think you suffer from a phobia about beezers. As i've said before, why not just sell it? (and buy another vw)
The artisans at beezer were renowned for 'doing the dirty' on triumphs wherever possible, human nature towards the competition i suppose. Chances are, the blokes at triumph would have done the same.
The bearing used on the a65 timing side is very similar to a car main with the exception of it not being split. Only aftermarket bearings were in fact a bronze bush. Either type work well if
installed correctly. Look at the racing history of bsa during the '50's when they produced the goldie if you need proof they could get a proper production bike to go, it won everything.

Maybe they should have opened the R&D shop in Oz instead of Slumberglade.
You blokes seem to be able to tweek anything. Toss another crank on the barby, mate.

No rocket science David, just a sense of humour and time.

Never tried the crank on the barby though hmmmmmmmmmm

BTW i'm still classed as a pommie, iv'e only been here 20 years!

Nick so he's ok using an A10 crank but not a twin carb head, they make ridiculous rules. Are you sure twin carb heads were not available as a competition option? But yea I'd love to look at that head.

Don't know about the crank on a barbie , but I did know a bloke who had a goldie rod on his power hacksaw .

Around 2000 I bought a 55 BSA A10 basket case on Ebay... Disassembling the engine it had a brand new crank , the "better " A10 rods and GMP pistons of about 10-1 compression..I got on this site to read about A10's and there was a lot of discussion on oil pumps and poor oil pressure when warmed up..I found a nice cast iron pump and carefull checked bearings clearances on the timing side bushing and rods...I drilled a passge and tapped it for a remote oil pressure gauge...Added a "357" cam , found a decent head and has the magneto rebuilt....Had a bit of a tuning issues with the cam but got it to run well except for a bit reversion around 4500 rpm. It always had good oil pressure when warmed up even at lower rpm's..I like to say it was one of the best Brit bikes I owned...

That's great Mark, thanks very much, i'll pm you and send it down. There's no panic, he won't be out again until Feb/March time.

The a10 crank is perfectly legitimate, the a10 had been produced since mid 50's. The a65 wasn't used in competition much until 64/65 anyway.
The twin carb head did not come about until 63/64 it was never available for the 'star twin'
which was the first a65 to launch and the only one in 1962.
I have no problems with sticking to the rules. i wish others would though. The 'norton atlas' that won the aussie title
was built using a set of those new cases that are about an inch thick etc etc. About as much an atlas as a gs1000.

Tony, i had an a10 super rocket as a kid and loved it, thrashed the living daylights out of it, never had any serious problems.
That had 10.5s-1's TT carb sweptback pipes with small bore goldie silencers etc etc. Great old iron.

it looked like this...best Triumph I ever owned, lol Hot rod 37 Chevy truck in background.

The picture of the A10 reminded me of a conversation I had with one of our colleagues about petrol tank size in the American market. Large country with long distances yet we loved those tiny fuel tanks. Only Norton offered a touring size tank.

I think several issues are at play here:
1) Vibration limited the ability of most people to ride an A65 for hundreds of miles non-stop. 2 gallon fuel tanks forced one into taking regular breaks (& most were surely grateful for it). It also forced the rider into giving the engine a break as well.
2) Engine displacement has always been a sales factor for Americans. The small fuel tank makes the engine appear as large as a Sportster.

Perhaps it's fortunate that the A65 died so suddenly. The T140 died many deaths before it's last.

I don't know really Ray, my old crate does vibe a bit but i was out last week and rode it at 70-80 mph for around 200 miles with only one stop for a quick leak. (me, not the bike.)
Bursts up to 90+ indicated, the only thing that slowed me was one front turn indicator rotated on it's stem.......... i think
the late ones with the scalloped flywheel were better balance wise, they were supposed to be 'dynamically balanced' in the factory
but i doubt that. I don't think it's any worse than my t120 at that sort of speed, maybe a little more 'tingly' but you don't have to grip the bars that hard.
Maybe when i strip it again i'll have the crank 'dynamically balanced' as everyone seems to think it makes a marvellous improvement, i only did mine statically on knife edges.
I don't like small tanks, when i go for a ride i don't want to be stopping every 100 miles for fuel it would stop me riding on the best bike roads here.

I very much doubt it as well. The clue to whether a crank's been dynamically balanced is whether there are any holes drilled asymmetrical to the centre line of the flywheel. The attached photo of a late 'scalloped' crank shows all the holes are drilled symmetrically, including interestingly, the side cheeks which you don't often see. One thing that is in the favour of the later crank's balance, is that it has been machined all over the side cheeks, thereby giving greater control of any out of balance asymmetric forces.

The scalloped flywheel is new to me ,didnt know that, my 71 has the full circle, since it was dynamically balanced 6,000 miles ago there have been no light bulb failures so it might be worth the bother Nick.