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.
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.
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.
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..
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.
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 .
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 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...
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.
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.
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!
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.
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.
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.
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.