1972 "Family Racer"
Christine Seifert, Automotodrom Grobnik, Rijeka
Over twenty Racing Seasons under about a dozen Riders!
The Family Racer started life as a normal Commando, bought as a derelict reimport from the States in the early 1990s. Around the time we started vintage racing for fun the idea was to enter the 750cc class on a Commando. Rudi Kolano built the engine. Gearbox was at first a standard 4-speeder, primary is triplex chain with a tooth more on the engine sprocket and an aluminium clutch basket left over from some project bike once bought and re-sold. So is the twin-disc setup that was taken off another bike many years ago- must have been a very early Hemmings product, as Mick Hemmings made the first left hand/caliper at front sliders. The factory used the "one in front, one at rear" setup with the same slider used on both sides. Clutch runs in ATF oil, using the standard fibre and steel clutch plates and the standard clutch spring.
Engine started out as an unmodified but rebuilt "Combat" type crankcase, very much butchered around the l.h. main bearing, more anon. Using high-compression GPM pistons, standard Andover Norton Commando valves, Hyde valve springs, lightened rockers and cam followers, a PW3 cam, and TLC for the ports, breathed on by two 932 Amal carbs, rubber-mounted on longer inlet tracts, the bike exhales through two hacked and re-welded Roadster pipes out of shortened Roadster silencers on the r.h. side, similar to the works production racers. This, together with a modified outer primary, possible through leaving the alternator out, gives more ground clearance for cornering.
Ignition is now a Pazon Surefire. A dry battery provides the current.
One of our Andover Norton 750cc cylinder barrels that are made along the lines of the 850 barrel was fitted (part#06-1705) to give more stability to the crankcase as well as beefing up the flange area of this powerful 750cc engine. Original 750 barrels, when they crack, tend to crack at the base. We have yet to see an 850 barrel cracking, or one of these 745cc "850 lookalike" ones.

Over the many years this bike has now been on the track- or been thrown off the track at high speeds- it had various petrol tanks, starting with a Roadster one, via an English, highly polished Proddy Racer lookalike that fell apart at the seams that had been polished paper thin, through a rather agricultural but better-lasting German copy to the ex-Manx-Short Circuit tank it currently has.

Gearboxes progressed from standard, the ratios of which are not really suited for track work, to an English offering, a close-ratio 4-speeder that was right in principle but had the highly dangerous habit of gears splitting in half. This due to the fact the manufacturer- whose name I decline to mention- hardens his gears through, so making them brittle as glass. After the second failure the bike now sports a Quaiffe 5-speeder, purchased from Mick Hemmings, that so far has given no problems.

Rear whell is 18", not because we are fans of that, but because we run our bikes on Avon racing tires and there was no real choice for 19" rears in that weight and speed class. The bike weighs 175kg, so is no lightweight. It actually weighs as much as our original 1970 Proddy Racer- we had them on the same scales side by side.

In the first meeting, two problems arose- first, the "Combat type crankcase problem" in that the bike threw all the oil out of the breather. Secondly, after fitting no end of oil bottles in succession to no avail, the tone changed and on looking down the rider noticed the driveside crankcase had developed a grin around the main bearing and was only held together by the primary chaincase that was bolted to it. This led to a Steve Maney crankcase half for the drive side to which it was near-impossible to fit the inner primary- hence the modifications to it. Today, we would use one of the Andover Norton crankcases that are stronger than the OE ones anyway, and we believe the chisseling around the main bearing our American predecessors had administered did not help the integrity of that crankcase half.

In the rebuild the breathing system was modified as recommended and the breather has not been a problem ever since.

Rear suspension started out with DOT units that were clapped eventually, so other units were ordered from Holland which have been in the bike ever since. Front forks are back to standard dampers after experiments with other damping systems that proved unsatisfactory.

The bike has been in continuous use for at least 25 seasons, under 6 different regular riders, often one handing it straight over to the next in a three-day meeting, with two engine problems- first, Tim Seifert experienced a timing side crankshaft fracture, then, three years later, a drive side one.
Nothing is known about the previous life of the crankshaft, and secondhand part were used to repair the damage every time. On the plus side it must be mentioned Tim realized something was wrong immediately, and both times brought the bike in from the track with no further damage, i.e, apart from the crankcheek and bearing shells nothing needed to be replaced.

The bike was on the brake once when it was to get a new exhaust. The exhaust manufacturer put it on the rolling road, got the performance figures and rang immediately, asking us to collect the bike. He admitted with the figures he got out no way could he hope to get more power out of the bike with his new exhaust. Suffice to say power is in the region of the best JPN factory engines and torque is more than impressive. Which makes it the perfect beginners bike- whatever gear or revs you are in, it gives power. Katrin and Christine like to ride the bike on track though, these days, they race only occasionally, which proves the point.
left: 2nd stage, 2004, Joe S.
underneath: current state, Tim S.
right: Christine S. in her first track year, aged 15

phone: +44 (0) 1264 359 565 | telefax: +44 (0) 1264 748 409 |

Web shop order questions or Retail sales, Trade Sales, Delivery queries:

Technical advice, parts queries:

Andover Norton International Ltd | Unit 6 Wooler Park
North Way | ANDOVER SP10 5AZ England

Imprint/Contact | Shipping | Data Privacy | Terms of Use | Return Policy

© 2024 Andover Norton International Ltd.