lets go racing

acadian

acadian

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Decided to put my spares to use and start a race bike build, beginning with the frame, my goal is to have a rolling chassis by winter, then work on engine through the snow months. Starting modestly, and strategically directing funds. Will be based on the spare 750 lump that's been sitting on my bench for years. Lots of head work, likely a molnar steel crank, short stroke build with JS bits. Standard tranny as I can't budget for a TTI box.

Spent the past couple of weeks straightening and reinforcing the frame, swingarm and cradle, spray bombed it and just got the bits together. Next up will be fitting a T140 rear hub.

Swingarm straightening
IMG_4700.jpeg


blasted and painted frame

IMG_4704.jpeg


SA and cradle reinforced, new verniers installed

IMG_4705.jpeg


assembled

IMG_4706.jpeg


my version of the valve spring/engine support bracket, this has a 7/16-20 bolt threading into a valve cup from the bottom

IMG_4707.jpeg
 
Fantastic… gotta love an interesting build thread like this !

Looking great so far.

Ref the gearbox (sorry, can’t bring myself to say tranny)… I ran a stock box in my hot Rodded 850 without issue. I’m convinced that minimising the weight on the mainshaft is a big help, so a belt drive with alloy drum and lightweight plates (like Barnet and plain plates with the middle removed) help a LOT.

Also, raising the primary gearing takes stress off the gearbox. Last I looked Steve Maney still had belt kits, they’re very good and reasonably priced. IMHO you don’t need the 40mm race kit, a 30mm ‘Road’ belt will be perfectly fine.

Final gearbox point from me: the stock box does appear to respond very well to a ‘mechanically sympathetic’ rider.

One thing I learnt (as is oft stated by others) is the importance of the good head work. My V1 build had JS cam, raised CR, FCRs, etc, but nothing done to the head, and was very healthy indeed I thought. HOWEVER, on the V2 build, I had sir Comnoz do the head, with everything else the same, this gave an additional 9 (yes NINE) rwhp ! I would suggest that the more you do to these engines in terms of tuning, the bigger the impact head work will have, ie on a stock motor, it’s probably barely noticeable but on a tuned motor a stock head is really going to be the bottleneck in the system and unblocking it could well give you as much gain as all other work combined !

So if I were you, I’d search a head guy (Comnoz would be my first port of call) and get him working on the head now whilst you’re working on the chassis etc.

Anyway, enough from me, your build is the most interesting thing on the forum currently so please keep us updated at every step and turn, we’re all rootin’ for yer !
 
Last edited:
Fast Eddie said:
Fantastic… gotta love an interesting build thread like this !

Looking great so far.

Ref the gearbox (sorry, can’t bring myself to say tranny)… I ran a stock box in my hot Rodded 850 without issue. I’m convinced that minimising the weight on the mainshaft is a big help, so a belt drive with alloy drum and lightweight plates (like Barnet and plain plates with the middle removed) help a LOT.

Also, raising the primary gearing takes stress off the gearbox. Last I looked Steve Maney still had belt kits, they’re very good and reasonably priced. IMHO you don’t need the 40mm race kit, a 30mm ‘Road’ belt will be perfectly fine.

Final gearbox point from me: the stock box does appear to respond very well to a ‘mechanically sympathetic’ rider.

One thing I learnt (as is oft stated by others) is the importance of the good head work. My V1 build had JS cam, raised CR, FCRs, etc, but nothing done to the head, and was very healthy indeed I thought. HOWEVER, on the V2 build, I had sir Comnoz do the head, with everything else the same, this gave an additional 9 (yes NINE) rwhp ! I would suggest that the more you do to these engines in terms of tuning, the bigger the impact head work will have, ie on a stock motor, it’s probably barely noticeable but on a tuned motor a stock head is really going to be the bottleneck in the system and unblocking it could well give you as much gain as all other work combined !

So if I were you, I’d search a head guy (Comnoz would be my first port of call) and get him working on the head now whilst you’re working on the chassis etc.

Anyway, enough from me, your build is the most interesting thing on the forum currently so please keep us updated at every step and turn, we’re all rootin’ for yer !
Click to expand...
Thanks Eddie,

I have a maney belt in my road bike and will be using the same in this, though good to know the 30mm should suffice, other options (Molnar and Newby) are beautiful but very spendy. I've emailed Jim about the head work already, hopefully he has the bandwidth to take the job on. Re. rear hub, I'm going with a drum T140 rear rather than disc, so the absence of a cush is a errr... problem. I am fairly conservative in my riding and have a good sense of what the "machine" I'm sitting on is telling me so as not to abuse her
 
acadian said:
Thanks Eddie,

I have a maney belt in my road bike and will be using the same in this, though good to know the 30mm should suffice, other options (Molnar and Newby) are beautiful but very spendy. I've emailed Jim about the head work already, hopefully he has the bandwidth to take the job on. Re. rear hub, I'm going with a drum T140 rear rather than disc, so the absence of a cush is a errr... problem. I am fairly conservative in my riding and have a good sense of what the "machine" I'm sitting on is telling me so as not to abuse her
Click to expand...
Personally, I’d always fit a cush drive wherever possible. However, that’s often not been the case and I’ve had several bikes without a cush.

I honestly never noticed or experienced a down side to not having one.
 
is this road or race bikes? I have a lightweight rear wheel & disc from a motocrosser which I would really like to try to use on my 850, but am a bit worried about the lack of a cush drive on a (mainly) road bike.
 
SteveBorland said:
is this road or race bikes? I have a lightweight rear wheel & disc from a motocrosser which I would really like to try to use on my 850, but am a bit worried about the lack of a cush drive on a (mainly) road bike.
Click to expand...
PM sent so as not to derail this good thread with long and futile chain vs belt, cush vs none, diatribe that will no doubt ensue otherwise…
 
SteveBorland said:
is this road or race bikes? I have a lightweight rear wheel & disc from a motocrosser which I would really like to try to use on my 850, but am a bit worried about the lack of a cush drive on a (mainly) road bike.
Click to expand...
The OP, acadian, mentioned not having a cush in his rear hub for this build so talking about it is OK in my book.

Rather than rattle on with my no cush story I'll repeat what FF said

"I honestly never noticed or experienced a down side to not having one."
 
@acadian there are several (many) forms of racing. What TYPE of racing will this bike be built for?

Circuit/Roadracing, I hope...
 
My 70 model year, like all the early bikes, had no cush drive from the factory. Of course once I found out, I obsessed about it and when it came time to buy new tires some years ago, I adapted yamaha cast alu wheels to my bike which do have a modern cush drive. Cast wheels are probably not as light as alu rimmed spoke wheels, but they are more rigid. My wheels in particular have the drum brake on the timing side of the hub and a sprocket carrier on the primary side so you can change ratios by just changing the rear sprocket. In fact, you can buy "split" rear wheel sprockets which can be changed without removing any parts besides the sprocket, allowing for quick ratio adjustments. If you want to explore that route, just shoot me a message, and I would be glad to give you the run down on that modification. Since someone already dropped Jim Comstock's name in this thread, he had commented that he saw no correlation between "no cush drive" rear wheels and gearbox issues in all his years of experience, so maybe having pneumatic tires does enough to compensate for shock loads on the gearbox. I think the stock norton cush drive is kind of pathetic anyway, so how much difference could having a cush drive commando rear wheel actually make??

Cool project, thanks for sharing it here.
 
Acadian
One too look for if you would like a cush drive is anything from the Honda CB350 250 360 rs250 range. Cheap & lines up, small enough that you can have a bigger range of sprockets. You will have to get them made as 520 & make a small spacer.
lets go racing
 
When you are building a race bike, two things are critical - the front brake and the gearbox. You can only race as fast as you can stop, and with wide ratio gears you will need much more power. A Manx gear cluster costs about $700 Australian, and the Commando first gear will fit for clutch starts. If you try the Commando cluster then fit the Manx cluster you will notice the difference. It reduces the need for a lot of motor development. When you first ride the bike, enter a corner in the middle of the road and gas the bike while it is on a lean. If you are leaning in a corner and the bike turns in the direction of the lean when you gas it, you are in business.
 
Chris said:
Acadian
One too look for if you would like a cush drive is anything from the Honda CB350 250 360 rs250 range. Cheap & lines up, small enough that you can have a bigger range of sprockets. You will have to get them made as 520 & make a small spacer.View attachment 115093
Click to expand...
Great photo there Chris, but how did you setup the rear brake? There's a cable running from the brake lever upwards, but I don't see how this works the rear brake on the other side?
 
Hi Steve yes it's an easy option. I've got the boys 350k4 bikes still, so have ended up collecting a few lol. I have one that's been milled, lots of holes & slots. Scaloping around the spoke flange. When I end up showing bikes I will fit it. The only problem I have ever had has been with the 960. Loose spokes once & I've had a warped rim. Not sure if that's the torque but have put heavy duty spokes in the latest rim.
 
grandpaul said:
@acadian there are several (many) forms of racing. What TYPE of racing will this bike be built for?

Circuit/Roadracing, I hope...
Click to expand...
Closed circuit, period 2 heavyweight vintage

Chris said:
Acadian
One too look for if you would like a cush drive is anything from the Honda CB350 250 360 rs250 range. Cheap & lines up, small enough that you can have a bigger range of sprockets. You will have to get them made as 520 & make a small spacer.
Click to expand...

Thanks Chris, going without a cush for now and will be using a T140 drum rear hub, less worried about shock loading the gearbox, but I am keen on supporting the mainshaft, and since Maney outriggers aren't available any longer I have plans to manufacture something myself

I've shipped the head off to Comnoz for a big valve race conversion, and I have a set of aluminium bodied Ikons on the way, once I get the wheels laced up that will finish up most of the back end , then I'll be moving to the front end

In the meantime I got the early central mount oil tank installed, I made up a platform that sits the tank low and much further rearwards, it sits on two vibration mounts between the frame gussets, and one at the front gusset arm

IMG_4710.jpeg
 
acadian said:
my version of the valve spring/engine support bracket, this has a 7/16-20 bolt threading into a valve cup from the bottom

View attachment 115058
Click to expand...
Please forgive my ignorance on this subject, but what is the scientific reason for the spring under the front engine mounting and does it replace the front isolastics or just increase the vertical stiffness?
 
hybridracer said:
Please forgive my ignorance on this subject, but what is the scientific reason for the spring under the front engine mounting and does it replace the front isolastics or just increase the vertical stiffness?
Click to expand...
Provides additional vertical support to the motor, gives the front ISOs an easier time. I've not tried it myself but figured it was worthwhile to add the bracket while prepping the frame. The idea was pioneered, I believe, by Jim Comstock who has many miles on his reporting good results.

www.accessnorton.com

New use for a Kibblewhite Performance valve spring (2013)

Getting ready for my upcoming 4-5000 mile road trip and thought I would play with reducing vibration on the road. The iso rubbers were replace a couple years ago but with heavy 880 pistons and steel rods the bike has never been as smooth as it was originally. Now after a couple years the...
www.accessnorton.com www.accessnorton.com
 
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