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#854125 07/19/21 10:57 pm
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I am wanting to build a stroked A65 so I am maximize all the cc's in the 750 class that I'll be racing at bonneville.

I am looking for an A10 crank is usable condition and am located in Oregon, USA

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bones_bir #854133 07/19/21 11:55 pm
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You would be better off sticking with the standard crank and putting decent rods and pistons in.
Any a10 crank will now be 60+years old and an instant rev limiter. As a 650 with good work on the head
and good compression you'll have a motor that will certainly be up there with most opposition.
The short stroke of the a65 allows revving to 8k which would be a benefit on a solo.
Failing that a 750 big bore kit is a great way to go with these engines. Just money........
Putting an a10 crank in involves doing all the bottom end work, end feed etc plus the drive side must
be machined for the smaller ID bearing. Easier to just do the standard crank up with an end feed and
start from there.
Having seen a few broken a10 cranks in these conversions over the years, if you do go that way, keep
it under 6800rpm.
Just my 2c.

Nick

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bones_bir #854134 07/20/21 12:07 am
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Thank you for your input, but you completely missed the point. Sometime you just have to do something completely ridiculous

Everything you have said is 100% correct, and I am not disputing a word.

However Landspeed racing is about putting HP to the ground. You can do that with revs, or you can do that with the brute force of the stroke.

Running with the throttle pinned for 1.5 miles is brutal on the engine. I do not want an 8000 rpm engine, I want a 6500 rpm engine that puts out that same power.

bones_bir #854137 07/20/21 12:21 am
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This one's a 740 with a10 crank, goes very well.
https://www.facebook.com/matthew.tyson.5621/videos/1672662059601228

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bones_bir #854140 07/20/21 12:34 am
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[Linked Image from images.i.thechive.com]

Last edited by bones_bir; 07/20/21 12:34 am.
bones_bir #854176 07/20/21 11:41 am
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Do you have a link to this article? Looks an interesting read, I have seen photos of this bike posted elsewhere too.


Now let’s all have a beer beerchug

68’ A65 Lightning “clubman”
71’ A65 823 Thunderbolt (undergoing restoration)
67’ D10 sportsman (undergoing restoration)
68’ D14 trials (undergoing transformation)

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Look in Canada, the northern border states & UK where thye don't ride that much or that far.
Southern states and places like NZ & OZ are very short of good cranks because they are all high milages by now and every one I had had anything to do with in the past 5 years was badly cracked.
You might even be better off with a new hand forged crank
You don't want it it fly apart at 150 + mph when you are lying prostrate over the top of it .


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Allan G #854192 07/20/21 2:31 pm
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It is just a photostrip that I put together, no article.

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I may have one sourced in Montana, we shall see.

I agree, I am not trying to build a grenade.

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Originally Posted by BSA_WM20
Look in Canada, the northern border states & UK where thye don't ride that much or that far.

Yes, because the British don’t take their bikes and ride across Europe or the full length of the country 🙄

Trying to find a decent A10 large journal crank isn’t easy, trying to find one that is of a price that doesn’t make you think of buying a complete A10 just for the crank is even harder still.

Occasionally they crop up for a few hundred notes or less but that’s not often.

Have you looked into having a crank made? There’s a few companies that claim to do them but not in the uk.


Now let’s all have a beer beerchug

68’ A65 Lightning “clubman”
71’ A65 823 Thunderbolt (undergoing restoration)
67’ D10 sportsman (undergoing restoration)
68’ D14 trials (undergoing transformation)

Allan G #854196 07/20/21 2:44 pm
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A custom crank, yes, that is certainly on the table. But if I can source one then I'll likely go that route.

Allan G #854211 07/20/21 4:56 pm
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........................
Originally Posted by Allan G
Originally Posted by BSA_WM20
Look in Canada, the northern border states & UK where thye don't ride that much or that far.

Yes, because the British don’t take their bikes and ride across Europe or the full length of the country 🙄


Of course us Brits don't stray far from home with our leaky old BSA clunkers ohno or do we ?


Truck stop I79 North PA

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clap laughing beerchug

Last edited by BeezaBryan; 07/21/21 1:15 pm.

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I have several but I'm on the east coast. PM me if interested.
Miike G


1960 BSA A10
2007 Suzuki Bandit
1957 A10
(Used to be a Triumph here)
71 Norton Commando
17 Triumph Bonneville

MikeG #854243 07/21/21 12:07 am
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Thanks

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If you have one made, do it 90degree, it's around 45% less dynamic load, and maybe that much stronger, the way I work stuff out. But then 74mm is probably better and smoother than 84, or you can fit a Commando crank, 89mm and that's easy to make 90degree though lots of machining and it will vibrate. I'd still use 74mm.

An A10 needs a modified A65 flywheel and something like MAP rods and A70 or B44 pistons.

There is something to be said for running a stock size 650, and making hp from it, a 360 degree needs re-balancing for rpm, strong rods, outrigger bearing on clutch door and crank and efficient head and carbs and exhaust. And oil gauge and end feed is preferable. When it goes fast it's not attributed to size but in spite of size. Drone along at 8000 or more if necessary. The factory ran 500s to 9,000.

A big tuned engine to get hp will still want to rev, You can build for it but the cases will be more stressed.


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Kevin on this site knows a firm in the states that has several special 10 cranks for sale.
They were done for a65 conversions for dirt track work.
Hillbilly bike knows who i mean.
Rodi engineering i think the name was. They are a lovely job but not cheap.
Failing that, you can press a made up thick wall tube through the centre hole and have the crank
nitrided etc. it will better the odds.
Either way you must pay attention to the bottom end, fit 3/8 studs, end feed etc.
Using a Norton Commando crank is stronger but will take the displacement out to 800cc+ so may
preclude you from the class. It also involves more work fitting etc.
an offset crank is definitely the best bet as far as strength and balance are concerned.

By the way, putting horsepower to the ground on a65's is something i've been pi$$ing about with
for thirty odd years and i'm still a beginner.

Last edited by NickL; 07/21/21 7:42 am.
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bones_bir #854268 07/21/21 11:54 am
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OP, Nick could be referring to E&V Engineering in Michigan...give them a call. I have a bike that that ran 133 mph at the LSR track in Maine in the 650 modified production class.It made 57-58 rear wheel hp on the dyno at 7050 rpm, never turns over 6900 rpm at the track, not a radical engine...unfortunately it is a Triumph grin I'm just a shade tree mechanic but found parts that like each other and a guy who knows modern theories on head porting. Pushrod Tom's A65 bike has cracked 130 hp...
Spending a ton of money does not guarantee a ton of power...


79 T140D, 96 900M Ducati ,61 A10 .On a bike you can out run the demons.."I don't know what the world may need
But a V8 engine is a good start for me
Think I'll drive to find a place, to be surly"
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I would be more inclined to go along the big bore route.
For a given BHP at lower rpm you will need to make more torque thus more cylinder pressure. This will put additional strain on head bolts, flange bolts, bearings and clutch.
RPM puts little additional stress on the engine if the crank is well balanced (dynamically)
I would use a 750 alloy cylinder as it is stronger in tension than the iron one, Carillo or similar rods and a Newby or NEB belt and clutch


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It's a frequent topic in high performance engine discussions if high rpm or more cylinder pressue at a lower rpm is more stress... It's the opinion that high rpm is more stressful...The business of reciprocating loads increasing exponentially as rpm is increased


79 T140D, 96 900M Ducati ,61 A10 .On a bike you can out run the demons.."I don't know what the world may need
But a V8 engine is a good start for me
Think I'll drive to find a place, to be surly"
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Originally Posted by Hillbilly bike
It's a frequent topic in high performance engine discussions if high rpm or more cylinder pressue at a lower rpm is more stress... It's the opinion that high rpm is more stressful...The business of reciprocating loads increasing exponentially as rpm is increased

And I agree. Salt is a far different environment than dirt or runways. Not better or worse, just different. I have found that higher RPM floats the valves, slips the clutch and generally does not help when you are wide open throttle for over a mile. not to mention traction, which slips unpredictable on the salt and spikes rpm, so for me, more power at lower rpm is better than spinning faster.

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That's interesting, power production is quite variable in some respects. I was surprised bigger carbs and more flow through slightly bigger valves actually increased midrange on a stock Firebird. If I understand correctly what is happening if the ports are only around 15-18% bigger but the flow increase is around 50% which means the gas speed in the port is much higher. Even at lower test pressure. I can measure the speed roughly on the bench and measure vacuum in the port with a probe. Then convert inches of water to speed on a chart, provided I'm testing at 28"w. If you can follow that. A porting book has a chart reading to 38"w which equals 400fps. 320fps is what they have you aim for, but: A fully ported high precision cast port as with cars is 320fps for peak power, 330fps in race spec of a production head, cnc ported non production head 340-360fps. F1 style 4valve 380-400fps. So this head in the centre of the port is pulling 46"w and more nearer the valve though it has a hose stuck in it. It's at least 420fps the limit is around Mach 0.5 or 580-640fps after 0.65 power generally drops.

On the bike what that means is response and power even at lower rpm, why that is is because even at lower rpm gas speed is higher as you open the throttle the higher speed has kinetic energy push the charge into the cylinder even after the piston passes bdc forcing more air and fuel into the cylinder before the valve shuts, then a 335cc cylinder can fire 335cc + quantity of charge. Just like having a small blower. You can possibly get the same flow from a much bigger port but it does not work the same because it doesn't have speed and the rising piston can push intake out if it's not pushing in.

The A65 outfit Nick's talking about is making power sufficient to beat 840 920 and 1200cc engines running on methanol with a 750 not revving past 6,800. It no doubt can rev higher but it doesn't need to yet. BSA ran A50s at 9,000 so rpm isn't particularly limited by valve gear. C/molly pushrods are good but I'm not sure what Nick uses. But you need possibly 1000rpm over rev ability so stuff doesn't fail. When that dyno time on the 750 happens we can see the power curve and see where it's going.

With a Norton 89mm crank my road bike was not going over it's peak at nearly 8,000 and it was way off with mixture reading far too lean on the main jet.

I drew my rwhp on this graph for comparison but I expect those bikes were tested at their best.

[Linked Image from i.postimg.cc]


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So how many ride John'O'Grotes to Lands end, all 603 miles of it in winter ?
Where as we do ride MElbourne to Brisbane , 854 miles in winter

How many months do you ride a year ?
comparred to sunny climates like California / Texas or OZ where most ride all year round
And how many ride all over Europe comparred to the number who just rode to & from work which was not likely to be more than 20 miles each way.

Boy you lot get touchy.
I did notice at the National at Halls Gap a lot of people complaining the Saturday ride was way too long where most locals considered it too short.
For 2 years I rode 75 mies each way to & from work every single day and there were people who rode / drove further than me.
Back in the 60's 30,000 miles was considered the AVERAGE distaance ridden yearly in NSW and was a consistant complaint because most vehicles only came with a 12/12 warranty ( 12 months or 12,000 miles ) which regularly ended up being less than 6 months till the Japanese imports went 12/12 what ever came last .
Add to that the larger numbers of A10's in the UK comparred to OZ there is a much better chance of finding a good crank there, or Canada or US border states than here .

So yes some do big miles but there would be a lot more who do very little where as down here it is the other way round and the only chance of getting a good crank is a bike some one pulled down to restore 30 years ago then never got around to finishing it .

Last edited by BSA_WM20; 07/22/21 5:05 am.

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And because I can be just as narky

from the T140 Tyre Balance? thread on the British motorcycles in general forum

Post by Steve Jonesz

Quote
OK an update, missed the white spot on the VEE RUBBER tyre, I have now lined the white spot on the VEE RUBBER tyre with the valve and rebalanced, sorted, vibration gone, smooth at any speed! I contacted Avon and received an EMAIL back saying there tyres do not use a balance spot, they should work in any position, this was from the technical department. So I have a front Avon tyre which is four years old with about 200 miles on it, and it seems to be faulty as I could not get it to work in any position on the rim. Never fitted a VEE RUBBER tyre before but it seems to be grippy and stable, how it wears I shall find out in due coarse!

I think that works out to be 50 miles a year for whatever bike the Avon is fitted to .


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Hi Trevor

Think you should have started a new post, regarding the distance of your rides over the year etc. Rather than join this post which the topic was about engine power

My tuppence worth

John

Last edited by JER.Hill; 07/22/21 6:22 am. Reason: correction
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Actually the topic was about sourcing an A10 crank for a racebike engine build.

I did not come on here to start an internet fight.

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Originally Posted by BSA_WM20
So how many ride John'O'Grotes to Lands end, all 603 miles of it in winter ?
Where as we do ride MElbourne to Brisbane , 854 miles in winter

How many months do you ride a year ?
comparred to sunny climates like California / Texas or OZ where most ride all year round
And how many ride all over Europe comparred to the number who just rode to & from work which was not likely to be more than 20 miles each way.

Boy you lot get touchy.
I did notice at the National at Halls Gap a lot of people complaining the Saturday ride was way too long where most locals considered it too short.
For 2 years I rode 75 mies each way to & from work every single day and there were people who rode / drove further than me.
Back in the 60's 30,000 miles was considered the AVERAGE distaance ridden yearly in NSW and was a consistant complaint because most vehicles only came with a 12/12 warranty ( 12 months or 12,000 miles ) which regularly ended up being less than 6 months till the Japanese imports went 12/12 what ever came last .
Add to that the larger numbers of A10's in the UK comparred to OZ there is a much better chance of finding a good crank there, or Canada or US border states than here .

So yes some do big miles but there would be a lot more who do very little where as down here it is the other way round and the only chance of getting a good crank is a bike some one pulled down to restore 30 years ago then never got around to finishing it .

Which year? The present year or back when I was at home a lot more to ride the bike? At around 30,000 driving miles a year it doesn’t give me much time to spend it with family.
I used to ride a bantam for about 1000 miles over a British winter period, and I used to ride all year, mostly because it was cheaper than putting fuel in the car (back when I was poorer) Each weekend doing 150-200, easily 200 miles a week if I was riding to work as well.
I’m more a fair weather biker these days and I’d much prefer to ride the European motorways than the British ones.
I was not one of those that complained about the distance of the halls gap rides, might of complained about the heat, we pommies complain when it gets above 28°c in the uk as we’re not used to it, so for us it was hot but we would rather ride as the riding kept us cool. There were also some fantastic riding to be had on those routes and the bike Shane kindly loaned me was perfect for the task. It was also a fantastic rally!!

Not being touchy though. It was meant as a joke. You might get a better crank in the UK, but they still dont come up for sale often and many have been left to rot in damp sheds.


Now let’s all have a beer beerchug

68’ A65 Lightning “clubman”
71’ A65 823 Thunderbolt (undergoing restoration)
67’ D10 sportsman (undergoing restoration)
68’ D14 trials (undergoing transformation)

bones_bir #854417 07/22/21 11:32 pm
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Peeing matches aside, areas with shorter distances and shorter riding seasons should give a better chance of a big journal A10 crankshaft which isn't cracked.
There was also a tendency in quite a bit of the US to buy a new bike after a couple of years and stick the old one in the shed or basement. One of those would have an even better chance of having a good crankshaft, but is also likely to still be in such good shape that you wouldn't want to cannibalise it.
I've bought a few low mileage US bikes over the years which fall into this category.

The bottom line is that decent A10 crankshafts are becoming as rare as hens teeth.

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The mob i mentioned that make cranks in the 'states are not e+v.

They made the crank for Kevins bike (a triumph) and he actually posted that
they have a few 84mm a65 cranks on the shelf they would like to move.
Can't remember their damned name now........... At the time, i had a look and
they were a nice job, they've been at it for years.

Nourish used to be the goto place in the uk but they are gone now. They made loads of
85mm and 90mm offset and standard ones for srm etc.


At the time a10's were being sold in the uk, blokes that bought them would be riding them
to and from work and most would be thrashing the daylights out of them in the evening
and at weekends, certainly most of the ones i knew anyway. Me included. The a10 crank i've
just stuck in an a65 race engine is at -10 and i had my reservations about using that.
A redline of 6850 is set on a rev-limiter and a large red led indicates slightly before that,.
I can check how many times it's got there and kick the rider in the bum if i think it's too often.

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Originally Posted by NickL
The mob i mentioned that make cranks in the 'states are not e+v.

They made the crank for Kevins bike (a triumph) and he actually posted that
they have a few 84mm a65 cranks on the shelf they would like to move.
Can't remember their damned name now........... At the time, i had a look and
they were a nice job, they've been at it for years.
I'd be quite interested if you remember the details as well.

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Tony, Hillbilly Bike, you know Kevin, who made his crank?

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Matt said he was revving the 650 to what he thought was 6,600 is that really all? You definitely have that little motor going well. Shift lights are great just shift when it blinks.

It's the750 going on the dyno is it? The factory ran one past 7,000 where it was peaking, it would be interesting to compare them. They used an engine dyno but we can convert it fairly accurately. And if you have the curve you can see where it's going without revving more than you want. The Norton F750 was tested on both; 67rwhp and 76hp at the engine.

Aldana seems to be using rpm on his A70.



Put head phones on and go to 14.31.


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The 650 was being used to 7200. (different ignition unit)
I didn't tell Matt............
The 750 is the one going on the dyno.
Looking like the aussie titles will be cancelled again this year, bollocks!

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For LSR a new strong 84mm crank would be the thing.

Just finished the seats on a head this morning, calibrating using a head with big 44.5 valve and 38mm port that I know flows 158cfm against the 34mm that flows more. And stuck the speed probe in both in the middle of the port the 38mm is 26" the 34mm around 40". They are different depending where you put the hose but it gives an idea. 26" is fast enough but on a small motor esp with big bore headers it will get reversion and there would be more time spent waiting to get revs up when the other one would be long gone.

I've seen LSR bikes doing this, trying to get on the cam and pull the tall gears, finally get going and change gears and try to pull out of the hole again.

It would be interesting to see what hp the 650 has as well if the dyno shop was sponsoring and not charging. The factory got 66hp from one, which would be 58.18 @ the wheel.

Tom might tell us his best? I think it's more.


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This chap makes various cranks up.
He's not the one i mentioned earlier though.

https://offsetcrank.com/history/

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One of our club members has one of his offset A10 crankshafts.

He modifies existing crankshafts rather than making them from scratch, and apparently is finding usable big journal A10 crankshafts difficult to source as well.

From what we've seen, they either crack radially around the drive shaft, or crack through a big end journal at a web. It may be possible for a much better welder than me to repair a radial drive side crack, but as far as I know a crack though a big end journal turns them into expensive paperweights.

It may be feasible to turn up a crankshaft from billet using a suitable grade of steel, but that is similarly beyond my current abilities.

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Hi

Offsetcranks are made by Geoff Collins in Canada. The 84mm 90 degree crank he made me is fine, dynamically balanced, heat treated after welding to stress relieve it. Its 7.25kg while a standard A65 74mm stroke is 10.6kg, going 90 degrees allows you to loose a lot of weight off the crank.

John

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Originally Posted by Mark Parker
Aldana seems to be using rpm on his A70.


Put head phones on and go to 14.31.
That might have still been an A65 at the 14:31 section, because it was June 1971. I'm not sure that the BSA team had the A70s that early, and they probably hadn't been homologated. The last batch of the 201 was built in August.

That was an interesting film, for an "On Any Sunday" wannabe. The interview with Dave and Bart at the end was cool, and it was nice that they both rated Dick Mann so highly.

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They made 101 A70s in June '71. But cranks were in the states long before complete bikes. They started using A10 cranks I believe, but that one has the A65 size bush. The maximum capacity allowed was 750, It's hard to imagine them not being on it. Imagine if they had rubber mounted these engines and built them to be totally bullet proof. They knew how.

Maybe Peter's next book will tell us all about the flat trackers.

Meanwhile finishing some heads. They all seem about the same. This has good low lift flow with the seats cut. Cannot really do that till the guides are done and the valve aims where it will. I possibly should have narrower seats because they will work harden a bit. I bought some stones and stuff off ebay which are the best I've used. No point lapping valves.

It really stuffs you up when people use modern seat cutters on them and sink them back with a ridge around them. The one I'm half way through the valves are sunk a bit. Flows ok but it lowers compression a little.

[Linked Image from i.postimg.cc]

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Back "in the day" many A10s in UK were used to power road sidecar outfits.
Many of them big "family" outfits.
The engines saw lots of lugging and not many oil changes.
I remember growing up in a working class neighborhood in the industrial West Midlands.
In a typical street of say 20 houses only 2 or 3 would have cars.
There would be maybe half a dozen with solo bikes and 10 with outfits. The remainder used bicycles.
Those outfit engines had a hard life.
Crankshaft fatigue life is not measured in miles but a combination of force and the number of cycles.
Typically the guy would be latre for work--so no gently warming up the oil but start the bike, into gear, maximum throttle when cold to get to work qick so as not to be late and be docked his wages. Short ride of just a few miles--oil never got hot then repeat at the end of the day.
Then once a year load up the outfit with luggage, wife and two kids and ride the fully laden bike for 120 miles to get to the seaside for a one week family holiday.
Not an easy life for a crankshaft!
No wonder so many had fatigue failure!
Back in the day I had an A7 Shooting Star and that threw a rod through the primary side crankcase.
When stripped the crank had fatigued across the primary side big end journal.
If I was going to use an A10 crank for serious racing then I would dig deep in my rear pocket and get a new one made.
Just my two cents worth of course.

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I bought A10 engine parts for my recent bike build from a hoarder friend...He had four crankcase sets, all had welded repairs on the left side....I found a really nice set on Ebay for reasonable money
Had a half dozen connecting rods, all were junk..Bought a set of R&R alloy rods...The are made from Triumph 650 rod blanks so the are .040 longer than stock A10 rods. This presented no problems other than checking valve to piston clearance. Using flat top pistons it raised the compression from 7.25 to about 7.8 or so...No biggie..
The valve work including replacing recessed exhaust seats was done on a Newan single axis machine. Does really nice valve work and minimal valve runout allows tight stem to guide clearances without possible galling..
The engines runs nicely...with the 357 cam it idle fairly smooth, has good power over 3500 rpm.
The engine is balanced to 64%....the vibration subdued and doesn't not get worse at higher rpm..


79 T140D, 96 900M Ducati ,61 A10 .On a bike you can out run the demons.."I don't know what the world may need
But a V8 engine is a good start for me
Think I'll drive to find a place, to be surly"
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At this point I am more interesting in doing a straight A10 crank conversion than going with an offset crank.

As I said, I have two engines to rebuild. More likely one will be for LSR salt duty (Stroker) and the other for road racing (higher RPM).

but these tech tips are great and a pleasure to read, so thank you for that.

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Originally Posted by NickL
Tony, Hillbilly Bike, you know Kevin, who made his crank?
I texted Kevin, waiting for his reply


79 T140D, 96 900M Ducati ,61 A10 .On a bike you can out run the demons.."I don't know what the world may need
But a V8 engine is a good start for me
Think I'll drive to find a place, to be surly"
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I found Kevin's crank maker.... Ro-Dy in Plymouth Michigan...


79 T140D, 96 900M Ducati ,61 A10 .On a bike you can out run the demons.."I don't know what the world may need
But a V8 engine is a good start for me
Think I'll drive to find a place, to be surly"
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Originally Posted by bones_bir
At this point I am more interesting in doing a straight A10 crank conversion than going with an offset crank.

As I said, I have two engines to rebuild. More likely one will be for LSR salt duty (Stroker) and the other for road racing (higher RPM).

but these tech tips are great and a pleasure to read, so thank you for that.


I contacted Ed V on the back of this conversation. He does have some A70 end fed cranks that he has had made.


Now let’s all have a beer beerchug

68’ A65 Lightning “clubman”
71’ A65 823 Thunderbolt (undergoing restoration)
67’ D10 sportsman (undergoing restoration)
68’ D14 trials (undergoing transformation)

Allan G #854503 07/23/21 9:22 pm
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Originally Posted by Allan G
Originally Posted by bones_bir
At this point I am more interesting in doing a straight A10 crank conversion than going with an offset crank.

As I said, I have two engines to rebuild. More likely one will be for LSR salt duty (Stroker) and the other for road racing (higher RPM).

but these tech tips are great and a pleasure to read, so thank you for that.


I contacted Ed V on the back of this conversation. He does have some A70 end fed cranks that he has had made.
La la la la la; I can't hear you.


A new crankshaft would be the a more practical approach. The only problem is that the 85mm stroke takes the capacity to 751cc with the standard 75mm A65 bore. BSA managed to use a loophole in the rules to get away with that, but the LSR bike might need to be sleeved slightly undersize.

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That was anticipated and is planned for. Re-sleeve to accommodate triumph pistons that are slightly smaller.

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I got some -20 (undersize) JE pistons made from Ed a few years ago (A70) with a crazy high compression. The idea at the time was to use them on a long rod A65 650 motor. If I remember right I have some Total Seal rings with them too.

It’s been a while since I looked at the rules for Bonneville but I do recall allowing one oversize. So you could easily do 751 or even a standard A65 I believe.

I’m interested in one of these myself, though at the moment I’ve been advised to hold back on bike spends by SWMBO as I’ve just done quite an expensive OIF build.


Now let’s all have a beer beerchug

68’ A65 Lightning “clubman”
71’ A65 823 Thunderbolt (undergoing restoration)
67’ D10 sportsman (undergoing restoration)
68’ D14 trials (undergoing transformation)

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I previously ran in M-CG, which is a production engine class. yes you can overbore by one size, but because the baseline capacity is 654cc, it is already out of the 650 class. A production A70 is also the same, being the baseline is out of class, rendering to overbore rule moot.

Next outing I will likely be running in an altered class anyway. For me it is not about winning races or making records, rather it is about building and running old bike and hanging out on the paddock with friends.

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Originally Posted by Hillbilly bike
I found Kevin's crank maker.... Ro-Dy in Plymouth Michigan...


Ahhh, thanks Tony i got the name correct just the spelling wrong!!

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According to Peter's book A70 cranks should be in two sizes 85 and 84.5mm stroke. Though I'm sure an 80x74 is a better base. It's all dependent on how they are tuned. And the bigger bore means better breathing area.


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Originally Posted by Tridentman
If I was going to use an A10 crank for serious racing then I would dig deep in my rear pocket and get a new one made.
Just my two cents worth of course.


As you know Richard, i don't take anything on these old crates seriously anymore.

bones_bir #854530 07/24/21 12:15 am
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Hi Nick--yes-- I know what you mean.
The older I get the more perverse pleasure I get from doing things that I make work that everybody else says is wrong and loudly tut tut.
I guess I am just an obstinate individualistic old bastard-- at least that is what my wife tells me!

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The intent is to build an engine with a A10 85mm stroke and a 74.5mm bore which adds up to a 741cc. That also leaves me room for later oversizing pistons and staying within class.

there are a number of pistons that can drop into that bore size, depending on fuel and purpose.

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The A10 had an 84mm stroke, so using an A10 crankshaft in an A65 gives you around 742cc as opposed to 751cc with the A70's 85mm stroke.

Using the 74.5 x 85 should work well, if you can get hold of a crankshaft.
If you're feeling really adventurous (masochistic?), it might be possible to modify things to fit a T140 crankshaft.

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That being the case, I can keep the standard bores and pistons I have and not have to resleeve. (75mm x 84mm x 2 = 742cc)

I may have a line on a crank, we will see. If so, I may proceed this winter with an engine build.

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Originally Posted by Shane in Oz
The A10 had an 84mm stroke, so using an A10 crankshaft in an A65 gives you around 742cc as opposed to 751cc with the A70's 85mm stroke.

Using the 74.5 x 85 should work well, if you can get hold of a crankshaft.
If you're feeling really adventurous (masochistic?), it might be possible to modify things to fit a T140 crankshaft.

Load of hassle to fit a weaker crank with a shorter stroke...... (T140=82mm)
Unless you can get a TSS crank, then it's better, still 82 but a lot stronger. BUT = hens teeth.
Also means special rods.

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Originally Posted by NickL
Load of hassle to fit a weaker crank with a shorter stroke...... (T140=82mm)
I'm learning lots of new things on this thread.
To hear the Triumph blokes, you'd think that Triumph cranks were the strongest thing ever made. Well, apart from the TSS which is even more unbreakable.

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It all depends, BSA 74mm cranks do not have the breakages of the Triumphs. Unless it's A65hp combined with A10 cranks, intensified by rpm. If you go on XS650 forums they bemoan the weakness of the XS cranks. Norton's replace flywheels with steel. But they can shear the primary side shaft. There is might and there is will. Triumphs are predictable with hp level.

You can press a tight steel rod into cranks. But dynamically 360s want to flex in proportion to rpm. If the bearing filets are rolled and compressed it makes it much more difficult to fail . 90s seem more robust as dynamic load is reduced by around 45%.

BSA cranks are very tough if anyone has hacked one up, This 90 has a large flange area and trues up as it fits neatly into the new steel flywheel. It has lots of h/tensile bolts including a big one into each crank pin. It gets a bit thin in places but neither one in use has failed yet, and smoothness is vastly improved.

[Linked Image from i.postimg.cc]

I also have good rods for it or the 360 in the Firebird which needs balancing better for rpm. Not sure which crank to fit. The problem with the 90 it invites speed the stock brakes and stuff will find difficult.

[Linked Image from i.postimg.cc]


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One of our pals, known here as Blown Income, has a long stroke A-65 for the 750 class. It has seen some development and he hopes to run it next year.

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Originally Posted by Mark Parker
......This 90 has a large flange area........It gets a bit thin in places but neither one in use has failed yet........
Thanks Mark for posting that photo. I find this fascinating and have been dreaming of doing this sort of thing for years. It's great to see someone actually doing it.

But a couple of questions.
Is it essentially an original BSA crank, sawn in two and bolted together Norton fashion at 90deg?

Is there any particular reason for phasing the drive side ahead of the timing side?

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By phasing the drive ahead of the timing side it just means good SRM ready made cams do not fit. It can be done either way and I have cams made this way with stock 68-473 profile which I retard a little for valve piston clearance mainly but it delays the shutting of the inlet valve to allow better cylinder filling with the heads I use. Not that that is noticeable really.

The Norton crank aligns on a pin, This one aligns on the flywheel fit already machined on the crank. We gave this drawing to the machinist doing the first one in the 1990s. It's been in use since with no problems. It's had new B44 pistons a few years ago but the bottom end hasn't been apart.

[Linked Image from i.postimg.cc]

This is it some years ago, this is with 20-40t.

Second is 8,500 on that dial.


Last edited by Mark Parker; 07/24/21 11:39 pm.

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So riddle me this one there smart peoples

What connecting rods are you using? Triumph 6.5"? Something else?

What about push rods? I see the bore kits come with longer pushrods, but does anyone sell them individually?

Lastly, I know that I will need to figure out extending the cylinders out. my thought was an 8mm spacer under barrels.

I tend to make a lot of what I need, or draft it out and send it to local machine shops for fabrication.

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Bore kits generally use B44 pistons with a shorter pin height. And the block is shortened to suit, so often kits comes with shorter pushrods. Though you can buy C/molly pushrods from K/white. Or blanks to set your own length. I made some out of a broken Ford set. Alloy cyls and C/molly push rods means zero tappet settings because what you end up with with a hot motor is important, and the metals expand differently.

Using a longer stroke 84-85mm crank means A70 pistons and stock length cyl though you may have to shorten it a little for A10's and the 84mm stroke. T140 pistons are about the same as A70, but naturally the valve cut outs are wrong for an A65, and high spec A70 pistons are readily available and far better.

You cannot just lift the cylinder block with a spacer because it has cam followers that need to stay in their little block.

MAP make the high spec steel rods as pictured above, at a very reasonable price. Alloy are available but have a shorter fatigue life.

The problem we had with the bike above was primary chain. If you do that to it, it pulls on the clutch basket, the more power the worse it is. This one had no bearing between the clutch basket and the front 20t drive sprocket, it must have one or the primary will fail. What happens, and you can test it easily by pushing on the primary and watching the secondary chain tighten or vice versa. Because the shaft deflects. When it does under power the sprockets go out of line then they strike and run against the side plates and depending on chain type push them off the rivets, then they start coming apart and breaking, until it lets go punches a hole like a Falcon cam chain and locks the wheel.

Laverda ran the same spec chain on their 3cyls up to 1200cc, but it must stay in line, so I fit two extra bearing to ensure that, one behind the clutch and one outside the alternator.

This picture of a 5speed shows a door with bearing, it needs a thinner series bearing and a proper seal, as bearing dust seals will not hold oil if you are running a chain. Especially with that case breathing.

[Linked Image from i.postimg.cc]

Having the breather blocked off and breathing through the primary case like a T140 means the primary always has oil and you never run it dry nor have to check it.


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MAP will cut and insert a bearing into a sprocket cover. I had one done when I put a MAP big bore kit on my T120, so I can get that covered and I agree, that is a key weakness that needs addressed.

My Primary is sealed, separate from the sump and has it's own breather. I run ATF to lubricate the chain.so I also get that those seals also need to be up to the task.

Thanks for the info. this should be a fun winter. I have a ZB33 engine on the bench and this bit of craziness. should be a hoot.

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