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

My A10 shown above had a Mustang tank that was popular in the USA years ago..Stripped down to look like a drag bike ....I don't remember the actual gearing but it vibrated less than many at 4500 rpm in high gear....After 1-1/2 hours or so riding any bike I'm ready to take a short break so fuel capacity isn't an issue.
I sold it to a guy who owned a seafood joint in Mississippi in 2005...That A10 is the only bike I ever sold that I want back....

My A10 was bought in boxes for 25 quid and came home on a double decker bus.
3 guys gave me a hand and the conductor allowed us to stand the frame on the rear open entry area of the bus.
It never looked very sexy but it did go well. It went to the elephentreffen (elephant rally) in germany a couple of times
with a sidecar on it too. At one time I had a steib sidecar on it which was stolen, they were quickly detachable and some bugger did!

The stock 650 Yamaha head had valves at 76degree, the OW72 had steeper valve angles at 56degree. Yamaha spent millions on a head to get into the 80hp region.
Does anyone know what A65s are? I think they may be around 60degree?
They seem to be referring to the angle between the valves.
And Triumph?

The A65 has 37 degree valve angles or 74 degree included. To reangle the valves to 54 degrees the chamber would have to be much flatter. I have 35/41mm valves in an 80mm bore with 35 degree valve angle and the chamber is 1.126" deep. Changing to 26 degree the chamber is 0.107" shallower and the valves are really close to each other and the cylinder walls.
I think the 35 degree valve angle is what I measured off the Wiseco XS750 piston.

A TSS style head would be a nice thing to have cast. In the dreams of many I suppose though.

I drew plans for a 4 valve but there was little interest. A proper two valve head is cheaper and has at least some chance of running in the historic races. Why they allow a four valve Triumph but not a four valve BSA just because the year of manufacture differs is beyond me.
Mark - Here is the OW72 intake port, something like yours?
https://thexscafedotcom.files.wordpress.com/2017/12/ow72-10.jpg?w=1000

Dave, I don’t remember your plans for the 4valve per chamber head. It’s sometjing I’ve fancied the idea of for a long time, but it’s a lot of work and changes in rocker geometry. Any Movement with the 5 spd box?

When the classing is policed, i have no objection to allowing 3 cylinder motors or 8 valve twins in the applicable periods.
What is wrong is things like allowing 900cc weslakes and 920 triples and 1200cc hondas in pre 72 racing, they didn't exist in 1972.
Rickman sold an 8 valve kit for triumphs in 69 or 70 so perfectly legitimate. Norton Commando/atlas cranks were around and people used them,
not 1 piece billet machined en40 things or belt drives and Mikuni flat slide carbs. etc etc.
Why not just enter a new Ducatti as a Vincent? it's a v twin so must be the same eh?
If you had done the 4 valve head for an a65 in 1971 it would be allowed in that period/racing class now. Unfortunately, you did it in 2016 so that's
when it's eligible for classic racing.
Go race a modern bike if you want to stay up to the minute. My 2c.

Hard to see what that OW72 port does Dave. I copied the XR750 port. My vacuum cleaners say 200cfm @ .410 valve lift @28"w. Hp calculator says 95hp at the crank, from a Street/strip engine 114hp Super stock engine. Which I guess is just a hotter version. On a 750 that means 10,000rpm, on the 883 it means 8,300rpm estimated rpm. Mine made 97hp @ 7780rpm but was not being revved enough for the graph to go over and start falling off. It was too lean by miles, had restrictive mufflers and a spark advance that was guessed at. With the mixture in the ballpark and better mufflers plus the ignition optimized I expect it would have better power. A 750 can rev more though I don't think we have revved one past 9,000.

This is the port on the 883 which probably has more flow than needed, which I guess doesn't matter as the thing has very strong bottom end and midrange anyhow. The 750 is more or less the same but slightly smaller and less radical for almost the same flow. The new 4V Triumph heads flow 180cfm by comparison.

Whats bolted onto that sexy flange? Round to oval?

The transition to oval is in the bolt on manifold, yes.

I was just testing a Thunderbolt head, minus the manifold, the port is shorter than a stock Lightning and only 27mm but it flows better. I doubt it would with the manifold on. But the port is drilled a bit better. It's a bit of a wake up call really. Cannot judge what a port will flow by basic specs of valve size and diameter. Measuring flow only really measures how easy air can flow through a port, so air goes through the manifold less Thunderbolt head easier than the Lightning, and faster. what happens with carb added changes the equation though. And carb size matters.

And to add to that is is boring for the spectators particularly when you are watching something that you know could not be made to perform that well in it's day make real period racre bikes of that period look stupidly slow.
Back in the 80's we tried really hard to get Bantam racing established as an introduction to historic racing.
Don Nolan worked for Telstra and was always up bush so he dug out a lot of old time race bikes & the bloke who rode them in the 50's & 60's but it fell flat on its face because of all of the clowns with massive egos who spent $ 30,000 grafting most of a TZ into a Bantam case and ended up with a bike that dope burning Manx Nortons could not catch . If there was money to be made you could understand it but all you got was a trophy with was usually a period trophy repurposed.
Thus the category died and historic ( now called period ) racing has been going backwards ever since.

I see your point that my 750cc 90 degree XS crank with CR500 rods A65 would not be period correct. According to your rules, Mark's port would be illegal since it was not done back then either, nor Hill's 750cc aluminum cylinder and five speed gearbox. Where is the line is drawn, what was done, could have been done or something done to one make applied to another? If the rules are kept strict you end up with one make racing, whichever was the winning bike back then would be the bike to have.
I know someone who maintains circle track cars. Only very rich people race them now because unless you have the latest trick parts you are not competitive.
The four valve A65 head was to get more performance, not necessarily for racing although since Rickman already applied it to the Triumph T120 they could have easily applied it to the A65. An alternative is a better breathing two valve, cheaper to produce (within the realm of specialty parts) and (hopefully) more commercial interest. Since I want it to be a 750cc it needs a new 80mm cylinder and to keep it together, the four outer base studs are brought up through the head.
Allan, the five speed is on hold at the moment because I have to get the Wenco racer together for the Cachuma rally. Rather than having the gear shop dive in on ten or so sets of gears I am going to make the first set in aluminum to thoroughly check it out then make them in steel myself. Their setup costs are a bit high and since I have the machines to do it I might as well try. They did not sound completely confident about the special addendum gears and with the wider ratio set you wanted there are more of them.

Advantage with the 4 valve is the ability to use lighter valves, possibly also valves with slimmer stems (standard Brit ones are quite meaty compared to some Japanese valves, the TSS also looks to maintain 5/16” stems. This will effect flow, even tapered after the valve guide would be an improvement I would think.

Most Japanese engines have a bucket or something taking the side load off the stem. You would have to compare a Japanese rocker operated valve engine to see what stem size was engineered to work with a rocker setup. My Rickman four valve had stout 7mm stem valves. I changed them to XR200 5.5mm stem valves and roller rockers.
5/16" stems were the standard before any real engineering went into the valve train parts.

I don't think how you port a standard head would breach any rules for classic racing. It's what people did. And it's also what makes using these old things rewarding. Anyone can go spend money and buy a 200mph bike. Changing a crank to 90degree is something that could have been done, and gives quite an advantage in respect to rpm, smoothness reliability and performance, but it seems to be quite acceptable. If people race an old bike it's way better if they can do it with out breaking stuff, especially cranks. Also better for spectators at events if the bikes you went to see keep running. 5 speeds were also available for A65s back in the day, so it shouldn't be a drama to use one today, even if the ratios are better and the clutch hub is splined. The spline doesn't make the thing faster but it means the bike won't be sidelined with a spun taper and sheared key.

Mark's port work would not be illegal, many blokes used weird and wonderful techniques on performance bikes back then.
You could have used a 1972 xs crank if you had one with corrillo rods, though in an a65 i doubt the work would be worth the effort.
Devimead were producing 750 and 850 kits so Johns barrel would be ok. Several blokes fitted 5 speed quaife boxes too.
My outfit had a 6 speed shaflightner box in it with a morgo pre-unit triumph in 1974, before i bought it.
Anything that was available at that time may be used. You probably could get away with your cylinder head if it looked more home made,
but they were not a commercially available item back then. I raced against plenty of 750 Weslakes in 75-76 and a few 850's, at that
time they were not fantastic and blew up as often as other engines back then. We beat plenty of them on the old Morgo thing.
It's only when the jap tz's came in that it became a race of one type. They just killed the sport completely.
Look at the winning results for the classic series in the NZ. They police the rules properly, all sorts of genuine period bikes compete.
If you turn up with a 9 stud triumph and it's a pre-58 race you'll be allowed to race but will be given no placing. If you try getting
away with using a 5 speed box in a pre unit, you'll be pinged. Admittedly, you can't stop the Titanium rodded $2,000,000 Manxes
and G50's etc but generally they have a very good system. When i started racing 'Classic' sidecars in 1990 i was amazed that so
much non period gear was allowed, it got worse and ended up with the, 'he who has most money wins' thing.
Many of the racers don't prepare their own bikes anymore, it's gone away from the whole concept of club level racing, which was
what it was supposed to be about. If you look back at the 60's all the makes had their victories at one class or another so i disagree
with your 'one bike would be the winner' thing.

Maybe we weren't so stupid using the t'bolt heads eh?
We also had better results years ago on the morgo triumph using the T110 head with stubbs rather than the splayed port t120 one.

I just added 12cfm to the Thunderbolt port and its still 27mm,with no fill on the floor. I think the best stock Commando heads are around 123cfm, without checking calibration this is probably better. I hope your welded on stubs are not too long Nick.

Added another 11cfm by egging the port out, its still very small with stock valve. And it is not smooth nor has it any fill on the floor. It needs another 15cfm. Easy port to work on.




So I opened the seat area a little for a 42mm valve and reshaped a little which netted about 1cfm. So I tried a bellmouth on the port, It is bigger than the port, even squashed a little to match the oval, but it still leaves a step. Another 15cfm or so. So what goes on the port makes a difference. If it doesn't lose flow with manifold and carb on a race engine with high compression and decent exhaust 80hp might be possible. The port is still relatively small 28X32.5 it could be made a bit bigger. I need to re-calibrate the rig, to get exact figures, but it seems better by around 44cfm, though I didn't have the bell on the stock port, which would mean about 30cfm. I'll fill the floor a little and see what a better bottom radius does.

Mark, try if you can to get hold of a small port lightning head and check the values, unlike the later leads there is already a better turn radiusnonly the valve. It would be a good comparison against that thunder bolt head?

The stubbs are about 2 inches long, they have to splay out a few degrees too.
https://imgur.com/KyvNtrX
https://imgur.com/279izLk
https://imgur.com/Os6M7gB
https://imgur.com/wq18HiQ
https://imgur.com/TjD7SHJ
https://imgur.com/b5g7CwX

As i said, it's as rough as guts at the moment, i've just had the stubbs welded on and made a start hacking the roof away. Brutal i know.......
The mating part of the manifold will be another couple of inches long, this will give about 300mm from bellmouth to valve.
Old school thinking i suppose, but it can change if you think it would be better. I was just going along the lines of my old ones.
https://imgur.com/LEQRzc1

Ok, is he using alcohol (in the bike)? What I have at the moment is a small high speed port, if it stays small it should pull from lower rpm and if it flows good with the carb it should pull to around 8,000. Not sure what a hotter than 473 cam will do though. Except if the port is small it will get velocity earlier to overcome reversion of a late closing inlet and or big bore headers.

No methanol, i don't want to go that way with a standard A10 crank, i don't think
it's up to it and i have no experience using alcohol, i always ran petrol. Much to
many people's disgust.
The cam is not one i'm familiar with so until i clock it up, i can't comment.
As it's one of Ivan's i suspect it uses similar to chevy profiles, he grafted one of
those onto the inlet of my old one. I can't ask him now as he died a few years ago.
The head that's on it responded well to decreasing the port size and raising the floor,
with the motor as is, a 650. The proposed blood line is around 6800 rpm with the
a10 crank. If and when he uses the offset norton one it can go up a bit, maybe 7500
but i always got better lap time with earlier changes, around 6800-7000. The cam
has loads of overlap so mid range is very good and it's late i/l closing so he has a
revlimiter set at 7250 at the moment otherwise it just keeps pulling, and he's overdone
that a couple of times with the consequent result. I've only been involved with it for the
last year or so, so i've had to get the thing reliable and sort out heaps of other stuff.
He's a good rider and the thing handles well, the makings of a very good package.
In the last year he's done very well and is keen to step up a little. As a 750 it should
be more up to the task of winning the aussie title, he needs more corner exit grunt etc.
The small motor needs to buzz a bit too much which costs him traction. Not much i can
do about that so a little bigger we go. (it's like deja-vu for me)

I think it may be an idea to send you down the carb and inlet manifold setup when i've got it
finished as well, that way you can see how the setup works. (Or fails to work!!!)

I may try putting a large allen bolt through the crank to stiffen it up a bit
something i did with the old triumph years ago. Any extra strength there
is worth a go. Offsetting is the better way to go though, i know.

Can you get the radiuss on the crank rolled anywhere up there? This little port is looking like it would be good, not that I've ever run a motor with this small a port. If it's 160cfm it shouldn't run out of breath with a 473 cam till probably 8,000 depending on the pipes. The manifold would be good to have, the carb maybe doesn't matter so much because its what it is, we could try different venture sizes and see what they do on the bench for curiosity. The Thunderbolt port goes into the bowl area better than the Lightning, its smoother. I wonder what the difference is between a stock Thunderbolt and Lightning on a dyno, I know the factory claim different power for them, but I put a Thunderbolt motor in my plunger A10 and latter switch to a Lightning head without noticing much, if any difference. What was a huge difference was between the A10 and the A65. The A10 was a lovely thing but threw a rod and I couldn't get bits.

Allan I don't have one of those heads, it would for sure be very interesting to test one.