Norton Featherbed/Commando   AHRMA Road Racer

Text and Photos:  Gary Slabaugh     
Owner-Builder-Rider                 

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. 

Soon enough I was talked into joining them (yeah, sure... editor) and my street cafe bike became a race bike. About this same time AHRMA began to get big enough to hold a  few regional and national races per year at Firebird and also Las Vegas. 

 

 

 

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.

I am now forced into semi-retirement due to the fact that AHRMA now has no interest in putting on any nationals or regional races near my home (Tucson).  The closest one is Willow Springs and that is always fun to attend if  the wind is not too bad. Also, the CCS crowd at Firebird and Las Vegas banished the vintage classes several years ago to make room for more modern bike classes. I still go up and compete occasionally in the modern twins class when I feel like eating humble pie. When we go out and practice with all the experts at the CCS races, there is nothing quite like being passed at the end of the long Firebird straight by a  an open piped, open displacement bike with about 50-60 mph more top speed! On the other hand, when they combine classes on the grid, it is also fun beating green slow kids with novice plates on bikes 45 years newer than my featherbed Norton design.

The slimline featherbed (Atlas) frame was purchased for $100.00. The motor and trans are from a '72 Combat, purchased at a swapmeet for $175.00 in '88.  The center mount oil tank and motor mounting plates are from Unity Equip in England. Originally the bike had a large Manx style tank and seat but I didn't like the rearward riding position that the long tank forced, so I put on the current Atlas tank and seat (homemade) which for me is much more confidence inspiring as it allows more body weight to be placed on the front tire.

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 motor is 72 Combat and has changed a lot over the years. I originally used a lightened and re-balanced standard crankshaft with standard Combat head and camshaft. Vibration was the major problem and I took the crankshaft to several crankshaft balancing experts both static and dynamic but I could not get the thing to be smooth enough above 6K rpms. At one time it was so bad that it was actually hurting lap times by not allowing me to concentrate on just trying to go fast.  I gave up on trying to get a stock crank to be smooth and bought a Nourish Racing Engines billet one piece job and have never been bothered by vibration since. I occasionally buzz it to 8K rpm without realising it. It has standard rods that have been crack tested and polished.

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.

All welding and machine work was done by my friend Jim Nichols at Star Cycle in Tucson, and assembly done by myself.

 

Link to Photo Feature page for this Bike              

 

 

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