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Ruby Racer: Excelsior OHC Motor (Oct. 2011)


My race motor is very similar to the boardtracker motor, except for  12.5:1 pistons, Spanish Amal carb, electronic ignition, and tuned  pipes. On the dyno it had 70.9 rear wheel HP at 6000 rpm. This is likely 85 engine HP.

I had a lot of grief with the lubrication system. It worked fine bench  testing on the milling machine, even 15 continuous minutes on the dyno, but would stop scavenging on the track. I would come home, strip it down, modify, improve, and test again. I think that, if someone were to ride Excelsior 004 down a road and back again, for example, the lubrication system  would probably work just fine. With no brakes you would be careful, and the single speed wouldn’t allow huge acceleration. You would be duplicating the dyno, basically.

The oil passages are in the crankcase walls, to keep the historic external look. I made them almost 1/4″, but they need to be bigger for racing. With transmission, brakes and a clutch, I can get some G-forces to move the oil around inside the crankcase on a racetrack.  This is where the stock scavenge system can’t keep up. The photo (of  my race bike motor) shows the bevel drive, oil pumps, oil filter, and  a small part of the external oil line to the squirters. At the bottom of the crankcase is the “oil well” and external scavenge line. This is what I arrived at after two seasons of development. It scavenges very well, and oil pressure is usually 40-50 lbs using 10/40 oil.

This is Ruby Racer. Basically, the oil from the tank flows down, enters the oil pump, is pressurized, and immediately leaves the engine case, where it goes to either the oil filter or the pressure relief valve (safety wired to the filter). If it goes through the filter, an external oil line takes it up to the squirters that will never plug up. Oil going through the pressure relief valve is sent back to the upper oil tank. There is less oil to scavenge. The pressure relief valve is adjustable; even while the motor is running! This system works very well.

Last race of the season at Seattle in 750 Vintage, I got the holeshot (there were 4 of us) and led for almost a lap until the head gasket let go. The rear cylinder rear studs are slowly pulling out of the barrel. I will install Timeserts, and solve that problem too! I’m really excited about next season. I think Ruby Racer is going to do really well.  Watch me Go!


Ruby Racer Excelsior motor

Ruby Racer Excelsior motor


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