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Help building A65 road racing bike for 2021?
#800833 03/12/20 2:52 am
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Hi everyone,

Im trying to get some info, input or suggestions for building a race bike to race in the period 4 (up to 1972)Formula 750 class.(Australia) never done anything like this before so Im sure Ill have more questions as the build progresses. Dad(Marky Parky) will be helping(alot hopefully) with the build.
I have a 1971 oil in frame frame. Is there anything I should be aware of using this frame. Its sure to handle different to the RGV250 frame the motor is currently in.
My questions so far are these
-when the rules say reproduction of period parts does that mean for example that a 38mm fork from a bike made in the 1980s will be allowed? They all look a bit old to me.

-any recommendations for the following parts, fork, hubs, rims, swingarm, brakes. Ive spent a bit of time checking out other bikes racing in the class it appears that twin disc front ends are ok but drum brakes only on the rear. Brembo F08 callipers seem popular.

-high pressure oil line fittings? Where do you get those from?

Hopefully it will be ready for the 2021 season

Donations to the cause are also welcome. If you have any parts that would be suitable let me know

Thanks in advance

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Re: Help building A65 road racing bike for 2021?
Ben P #800845 03/12/20 6:31 am
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Triumph used a disc on the rear in 1970, it should be allowable. I think I have a Rickman hub. Rickman used 41.2mm forks and all round discs quite early.[Linked Image from i.postimg.cc]

Last edited by Mark Parker; 03/12/20 6:47 am.

mark
Re: Help building A65 road racing bike for 2021?
Ben P #800851 03/12/20 8:01 am
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All i can suggest is read the regs. Then if you get the chance talk to some guys who are already racing in that class.
It all depends on what class you want to run in. Post classic is up to 72. But they've made several classes of that now.
Apparently you can run any non-pumper carbs. (stupid really as i used a webber and that has accelerator pumps, and
was completely eligible. Made since 1958) I think it's all about the 'Power-jet' thing. Most blokes are cheating like all
buggery anyway. Just keep it 'visually compatible' and it'll be fine.

Re: Help building A65 road racing bike for 2021?
Ben P #800855 03/12/20 8:32 am
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TMs? They should make an exception on the pumper thing, even in era delortos had that. Plus it doesn't give an unfair advantage. TMs would be good, save buying more carbs. Lectrons flow better but are expensive.

There is a Rickman '1969' with 3 discs and A65 head on an A10.

Looking at carbs Delortos are expensive 260+ pound each, MK2 smoothbores also expensive, plus not listed as available, yet these Koso Chinese carbs are probably less than $100 each, or we have the TMs also fairly cheap, plus we have them and jets. Ben needs to download what's useable.


[Linked Image from i.postimg.cc]

[Linked Image from i.postimg.cc]

Last edited by Mark Parker; 03/12/20 9:34 am.

mark
Re: Help building A65 road racing bike for 2021?
Ben P #800858 03/12/20 9:50 am
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So Ive been looking at the rules last week or so. Forks 38mm max. No rear discs. Mikuni VM any size.
Ive been checking what these guys do. Same class.

http://old.xs650.org.au/Club%20Racer%20Stuff/Club%20Racer.htm

Re: Help building A65 road racing bike for 2021?
Ben P #800959 03/13/20 12:16 am
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The swinging arm connection to the oil spine could be beefed up, Triumph guys weld struts or angle iron to brace the pivot connections, my frame cracked near around the TS rear motor mount to the spine, fixed it with a weld repair, been OK since( I have not braced it). Worth a check, seal the oil spine inlets, outlets, and add air pressure via the breather connection, should hold about 15 psi. Do the soapy water thing round all welds. The rear hub is pretty heavy, maybe look for something lighter off an MX bike with a drum brake. Flanged alloy rims are strong, mine have stood up to several beatings. Maybe go for an 18 on the front , better rubber choice.
I am Confused ,is Marky Parky the same person as Mark Parker, or is this a weird near coincidence amongst A65 owners down under.?


71 Devimead, John Hill, John Holmes A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
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Re: Help building A65 road racing bike for 2021?
Ben P #800963 03/13/20 12:38 am
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Gavin is spot on with the spine thing.

What you can and can't change/get away with depends on the class you are entering.
(also on whether the scrutineers know what their looking at.............)
I've seen blokes go out with such blatant class deviations that it's a joke. But they need
to fill grids at the ever shrinking amount of tracks available now.
Just go out and ride/have a good time, you can't win any sheep stations anyway, you can buy
better plastic trophies with your entry money than you can win.

Re: Help building A65 road racing bike for 2021?
Ben P #801023 03/13/20 12:15 pm
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This should be a good thread!! We only have to go fast. RR includes turns and stopping! PRT

Last edited by pushrod tom; 03/13/20 12:19 pm.
1 member likes this: Allan G
Re: Help building A65 road racing bike for 2021?
Mark Parker #801029 03/13/20 12:54 pm
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Originally Posted by Mark Parker
Triumph used a disc on the rear in 1970...
On which model? I thought '78 was the first year for rear disc...


GrandPaul (does not use emoticons)
Author of the book "Old Bikes"
Too many bikes to list, mostly Triumph & Norton, a BSA, & some Japanese
"The Iron in your blood should be Vintage"
Re: Help building A65 road racing bike for 2021?
Ben P #801095 03/13/20 8:10 pm
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Are we talking "production" racing or factory racers? Both the '71 "highboy" and '72 "lowboy" had rear discs. The comical hub can be lightened. Several pictures around the web of holy hubs.

Re: Help building A65 road racing bike for 2021?
Ben P #801137 03/13/20 11:46 pm
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Looking at the rules some stuff if original fitment is allowed like rear disc, but not on an OIF BSA. Carbs can be 38VM, probably the cheapest of whats ok. Nicks webber would be ok, they are talking power jets before the carbs, and not carbs available then. A factory 3 would probably be eligible but not titanium bolts and axles.

The articles Ben posted on the Yamaha racer are good. They built a 90degree 750, dynode rich it was 62hp and they get nearly 200kph at the Island. They do a lot of work, and fix stuff a fair bit frown

Same one Gav.


mark
Re: Help building A65 road racing bike for 2021?
Ben P #801271 03/14/20 8:46 pm
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The front end from an MZ 250 with its single 10 inch disc is very light, comes with a nice ally top yoke, MZ copied a decent Italian brembo 2 pot alloy caliper, I think the forks were a Paoli copy ,loads lighter than the Brit stuff, you will need to play with steering stems and fork lengths. The MZ stem is too fat for the OIF bearings.
I have the twin disc T style front end, it slowed the steering flickability down noticeably, try to keep the front light.
Consider keeping the air box, my bike runs much better with the air box than without it, you may need to open it up a bit for bigger carbs.
I dunno how tall you are, if you are shorter than 5 ten, then consider moving the seat rails down the frame spine an inch or two, later OIFs after 73 had this. I am 5 ten and enjoy the leg room, rear sets somewhere around the swing arm spindle but a bit lower is comfy, for the rear brake it may be a good idea to convert to cable to give max adjustability of foot rest position.

I shortened my front suspension by 2 inches, that is a good thing, the stock front is too high and the bike doesnt need 6 and a 1/2 inches of travel. Side bonus , shorter legs are stiffer.
The swinging arm could be stiffer, longer ( not much) and lighter, tapered tubes with a U brace and struts would be an improvement. At 56 inch the wheel base is very user friendly, fairly flicky, much longer and it will get more ponderous.
Forkwise
If you want to keep it Brit , Norton forks had the 2nd fattest stanchions, roadholders can be made to work very well, and if you have deep pockets all sorts of brake upgrades are possible, Rickmans were far fatter still and probably the best option if you can get them.
Sounds like a great project , with one of MPs breathed on motors , a load of fun.

Oil volume,
the spine only holds 3.5 pints I have measured it, ( the manual lies about 5 pints), although it is a fairly effective cooler I dont think thats enough for racing ( manx N has a 1 gallon oil tank), a large capacity return line filter holding another pint or two would be a significant boost. I have heard of folk moving the filler cap up the frame spine to near the headstock, without putting baffles in the top spine I think thats probably a bad idea, even at the low stock level I see oil coming from the breather at the frame neck after heavy braking especially.
. For sustained thrashing a wee oil cooler on the feed to the rockers will keep temps down a little, Citreon Deux Chevaux style.


71 Devimead, John Hill, John Holmes A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
Re: Help building A65 road racing bike for 2021?
Ben P #801272 03/14/20 8:53 pm
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High pressure Oil fittings, Dave Madigan did some fancy stuff for an A65 oil to motor connection.
Do you really need them , rules? non of the lines are under any significant pressure, not what I would call HP.
To further ramble about oil volume, modify the spine oil connections and go up a size, more oil in the pipes adds useful volume without being too obtrusive.

To keep the bike crashtastic, use a rigid LHS footrest ( if rules allow) , mounted to a sacrificial 10 mm thick ally plate, make spare plates!, this will help save the primary side when dropped, another bung at the front would save it entirely. Find a cheap source of control levers and base cabling around easily replaceable cheap spares. Try to get a clutch lever that has a 7/8" pivot to nipple centre, most of the copies are over an inch , this leads to a heavier than necessary feel.

Last edited by gavin eisler; 03/14/20 9:04 pm.

71 Devimead, John Hill, John Holmes A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
Re: Help building A65 road racing bike for 2021?
Ben P #801278 03/14/20 9:12 pm
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may i politely request that anybody who posts in here please double the information that you put into your posts?

you may think what you have to say is casual but that is not the case.

this stuff is priceless and i would like to read more of it.

thank you.


every day you do not take a chance is a day of your life that you will never get back.
Re: Help building A65 road racing bike for 2021?
Ben P #801288 03/14/20 10:11 pm
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More ramblings about carbs and airboxes and cables and oil volume.
I have rubber mountings for the carbs, if MP is doing this you will too probably, with the stock tank you quickly run out of cable space as the carbs move back, with no airbox i found the carbs drooped on the rubbers very quickly causing them to split, with the airbox and T140 rubbers to the airbox the carbs dont droop and the rubbers dont split. If building from scratch make sure the rear of whatever tank you choose leaves space for a clean cable run.
As well as making life hard for the cables, moving the carbs back also causes huge headaches with the fuel tap location, , ideally the fuel taps should be moved forward and away from the carb. All this hassle comes with the 4 gallon breadbox tank, smaller T peanut tanks have similar fuel tap issues , better cable clearance.
My bike came with an alloy tank, it split, dont bother. On a vibrating brit twin ally is trouble metal. Use a steel tank.


71 Devimead, John Hill, John Holmes A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
Re: Help building A65 road racing bike for 2021?
gavin eisler #801290 03/14/20 10:14 pm
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Thats some great info Gavin.

Re: Help building A65 road racing bike for 2021?
Ben P #801293 03/14/20 10:28 pm
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If I was building the ideal fuel tank for an A65 OIF race bike it would be shorter, with more seat, the taps would be 4 inches or more forward and at the lowest point, , the bollock area would be padded over the tank hump. the tank would have an arched tunnel rather than the splitty square section, and the front would have wide deep pannier sides with an air guide flair to the head , knees would be out of the wind behind scallops.

The motor is under finned , do anything you can to improve airflow around the top, oval down tubes even.


71 Devimead, John Hill, John Holmes A65 750
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MZ TS 250
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Re: Help building A65 road racing bike for 2021?
gavin eisler #801295 03/14/20 10:38 pm
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So some more info. A couple of years ago I bought the frame and swingarm. Thats all I got. So its a blank canvas. Im 5’11 so the standard height should be ok unless lower changes handling for the better. The RGV frame is just amazing, its low, stable and very easy to change direction. There are many other factors however such as the somewhat steeper head angle and long swingarm can cause this not just weight distribution and centre of gravity.

Not much in the budget for anything thats not easy and readily available. So probably not too many exotic parts. I plan on using a different rear hub, to allow some variation in sprocket sizes and to lighten it up a bit. I originally bought the frame to build a street tracker so did some research on swingarms and found the gs500 swing arm could be made to fit and is 3-4 inches longer than stock. Im just not sure how it would go passing the log book stage. So i might keep it stock and change it later if I feel it will help.

Ive read a few mixed reports regarding oil volume and temperature etc. Racing will definitely be different to road riding.

I need to check further regarding the oil lines etc. Its still not clear. Ill find the rules and screen shot some.

Re: Help building A65 road racing bike for 2021?
Ben P #801306 03/14/20 11:14 pm
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'High pressure oil hoses', some bikes have them. the Yamaha has one at the front to the head - there are replacements, swaged fittings. BSA std arrangement are low pressure.

Maybe one of the first things is to dyno the thing. With legal carbs might be worth while. Comparative power in 2nd gear, can anyone workout what goes better? Remembering Bens 2nd is C/R.

https://www.youtube.com/watch?v=oBD2g_bBog4
38mm VM carbs. 8500 about. Pretty bad flat spot till after 4,500-5000. Firebird style pipes with 'X'.

https://www.youtube.com/watch?v=8OOw26Fbe1A
38mm flat slide TM very little flat spot. Under the bike 'X'.


mark
Re: Help building A65 road racing bike for 2021?
Ben P #801316 03/15/20 12:28 am
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The high pressure oil hose thing was something we had to comply with when racing in
'forgotten era' stuff in the uk, so we did it. Complete rubbish really but it's in the regs.
They will also cane you with a nappy for engine oil content.
Opening the primary to engine breathing is a good mod the extra volume also works as
a cooler. Most races are sprints these days so massive oil cooling/quantity is not needed.
Same with fuel, 4 litres is all you'll ever need. Big tanks look nice but that's all.
Gavin is correct regarding the heating thing, run a couple of tubes to the front of the head
to direct air. The a65 when tuned gets very hot exhaust valve wise. Mod the oprv to direct oil to
the head rather than back to the tank, it all helps.
You can smoothbore a pair of 32mm mk1 amals to 33mm that works well on a 750 a65 and
is eligible for pre-72. Not that difficult to do just have to re-drill the pilot holes.
You'll be clutch starting so the tall cr 1st will be fine and will give you a usable low gear for
hairpins etc, standard 1st is a bit low and makes the 1-2 gap too wide, standard 3rd is good.
Brakes, well i like hydraulics myself so i would be looking at converting either your drums
or fitting eligible discs , the old mini wheel cylinders were popular as a starting point but there
are probably loads of options around now.

Last edited by NickL; 03/15/20 1:11 am.
Re: Help building A65 road racing bike for 2021?
Ben P #801318 03/15/20 12:55 am
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use the nappy to your advantage, a belly pan cuts CoD, always a good thing, the A65 motor itself is very aero, use that, make a belly pan that works with the motor shape , its free power.
Do what Nick says .


71 Devimead, John Hill, John Holmes A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
Re: Help building A65 road racing bike for 2021?
Mark Parker #801323 03/15/20 1:16 am
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Originally Posted by Mark Parker
Looking at the rules some stuff if original fitment is allowed like rear disc, but not on an OIF BSA. Carbs can be 38VM, probably the cheapest of whats ok. Nicks webber would be ok, they are talking power jets before the carbs, and not carbs available then. A factory 3 would probably be eligible but not titanium bolts and axles.

The articles Ben posted on the Yamaha racer are good. They built a 90degree 750, dynode rich it was 62hp and they get nearly 200kph at the Island. They do a lot of work, and fix stuff a fair bit frown

Same one Gav.


Funny really as the accelerator pump jets in a dcoe webber actually function as 'power jets' at higher gas speeds anyway.
If you read some of Passini's stuff he highlights that on several occasions.
The best carb of the era with no doubt.

Re: Help building A65 road racing bike for 2021?
Ben P #801324 03/15/20 1:23 am
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Don't go mad lightening everything, i've seen so much lightened 'performance' gear break.
use a little discretion and look at stress factors.

To win you must finish, no use being the fastest for one lap only.

Re: Help building A65 road racing bike for 2021?
Ben P #801329 03/15/20 2:04 am
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The CB750 disc was used on the rear of US factory triples. Can you use parts off another manufacturer? VM's were not on BSA's so why not CB discs?
If you need to keep the drums they can be hydraulically actuated to give better mechanical advantage.
Dirt track hubs are a good choice for mounting discs and sprockets. You can bolt them on instead of knock-offs for more security.
Using AN fittings on the engine and tank makes servicing simpler.
Adding a scoop to direct air to the tunnel between the exhaust valves will help cooling.
You may have to close off the timed breather or put a hose connection on it to keep oil from escaping. Another possibility is to plug the external hole and drill through into the primary so the timed breathing goes into there then a breather port can go from the primary to a catch tank.

Re: Help building A65 road racing bike for 2021?
DMadigan #801354 03/15/20 3:25 am
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Great comments guys. The class has a blanket no rear disc rule. I can use any parts from the period from any manufacturer or parts that look like they are from the period but with limits eg fork diameter 38mm, minimum 18” WM4 wheels.

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