|Norton Featherbed/Commando AHRMA Road Racer|
Text and Photos: Gary
In the beginning I lusted for a Commando powered featherbed
street cafe type bike after riding one belonging to a friend. I built one back in
'88 and lo it was fun. Some friends were racing regularly at Firebird Raceway
with the AMA/CCS club which had a couple of vintage classes.
My best seasons so far have been '95 and '96 when both time
and budget allowed me to attend the AHRMA races at Daytona and at least one midwest
National in addition to several western state Nationals. I finished fourth in AHRMA's
Formula 750 national points in '96 competing in about half of the available nationals;
the guys finishing ahead of me ran in all of the nationals.
The swingarm is special in that it is much wider than standard featherbed to allow the use of modern race tires and I got it from Mick Hemmings Racing Equipment. I use Avon race tires with 130/65/VB18 rear and a 110/80/VB18 on the front. In addition to using an 18 inch rim on the front instead of the original 19 inch, I also use Works Perfomance aluminum body shocks that are 3/4 inch longer than standard Atlas. This combination raises the rear of the bike while dropping the front and nicely sharpens up the already good featherbed steering. The longer shocks also give better ground clearance, an important factor when I feel inspired enough to use all of the outstanding grip from the Avon race rubber. Avon really makes some great race tires in vintage race bike sizes and I continue to be amazed at what kind of stresses the featherbed frame can take without any problems.
The front fork is standard Atlas with updated springs, a
stout fork brace and a Commando disc slider added. The front brake is Norvil type floating
rotor and AP Lockheed caliper with race pads. Master cylinder is a Lockheed Racing
adjustable ratio item and this combo works well. Well enough to cook normal DOT 3/4 brake
fluid on some of the really tight and twisty venues. I use DOT 5 silicone fluid to avoid
this situation. The rear brake is standard Atlas with the exception of having a special
one-piece axle instead of the original axle/dummy axle set-up which breaks when stressed.
Ready to race with one gallon of gas the bike weighs about 350 pounds.
The oil pump is modified per the Dunstall Tuning Notes, i.e. use pump body with narrow feed gears from early Domi twin and then machine the body on the return side for the wider Commando scavange gears. This alters the feed/scavange ratio enough to prevent wet sumping under sustained high speed running. The crankcase breather has been relocated to the timing chest 850 style.
Pistons are GPM 10:1 and the head is shaved to give total compression of 11:1. The head is from Mick Hemmings and has larger (40mm) re-angled intake valves. Stock valve springs are used with titanium collars and pushrods.
The camshaft is also from Hemmings and is the PW3 item,
supposedly identical to what the Peter Williams racers used. The carbs are Amal 34mm MK 2
items. All the above makes a fairly flat power band, flat enough that I have never felt
the need for a 5 speed trans. It starts making good power at 4.5K rpm. My trans is
standard 4 speed with just the normal mods for reliability. I check the internals
regularly and have never had any problems with it but I am a smooth if not particularly
fast rider and I am always aware of that weak link and try to be easy on it. The belt
drive primary has also been reliable and I have only shredded one belt so far.
Link to Photo Feature page for this Bike