Engines of Yore: Part 1
Rudge Ulster 4-valve created 20 April 1992
by Dave Williams [email protected]
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Our first look will be at the 499cc Rudge Ulster four-valve. This was
a four-valve single back when four valves were almost unheard of. At
the time the original article was written, Rudge was the only motorcycle
manufacturer building a four-valve engine. Not only that, but the Rudge
used radially canted valves, a concept Honda "invented" in the late '70s.
Rudge's valves were pushrod operated and the valve gear was consequently
much simpler than Honda's overhead cam layout. Rudge used a single
rocker to operate both intakes, with a train of three rockers operating
the two exhausts. The Honda used a similar multiple-rocker layout.
The intake valve was a nail head, the exhaust tuliped, and they were retained two-piece keepers in the valve spring cap. The Rudge used conventional coil valve springs (many of its contemporaries used hairpin springs). The only oddity was the keepers didn't grab a conventional groove in the valve; they grabbed a taper on the valve instead.
The head casting was in two pieces; the bottom holding the chamber, fins, and ports, the top "tray" forming the oil returns, rocker pivots, etc., similar to the "cam tray" of a Cosworth BDA. Rudge's intake valves were parallel and the exhausts were splayed. This layout was covered by a patent, now long expired, of course. Rudge called their combustion chamber shape "pent-roof" and the plug was in the middle. The two intake ports were siamesed, also not unusual for four-valve practice even today.
The two-lobe camshaft sat on the right, with rocker arm followers. Older British designers must have distrusted the common cylindrical followers which are almost universal now; most of the engines of the time used rockers on the cam. In this case, the Rudge used aluminum pushrods running through a tube on the right. An unusual feature was a gland nut and gasket in the tube to allow for differences in length due to expansion.
The engine was separate from the transmission as per normal practice, with vertically split crankcases and roller bearings. The rod was a one piece steel part with roller bearings, with a built-up crankshaft held together with nuts. The crank was disassembled if the big-end bearings needed service. Per conventional '50s practice, the Ulster used a plunger-type oil pump and a dry sump. The plunger pump's output was negligible by modern standards (1/2 pint per minute at 5,000 RPM) but roller bearings don't need pressure feed.
The crankcase was aluminum, the barrel was cast iron, and the cylinder head was aluminum-bronze on early models, plain aluminum on later ones. The barrel attached to the crankcase with short studs and double-ended nuts. The head attached with five oddly-spaced long bolts going up from the bottom, through the barrel, into threaded inserts in the head, a most peculiar practice. The drawing shows one bolt going through to the head and one double-ended stud, one end screwed into the head, the other screwed into one of the double-ended barrel retainer nuts. There might be some artistic license or an error here, as it looks like it would be impossible to assemble the latter. I can't think of any reason why Rudge didn't just run the bolts all the way down to the crankcase like most modern engines do, or bolt the head to the barrel as the conventional practice was then.
The piston was a full-skirted type, and the pin was retained by bronze thrust buttons instead of the more common press fit or snap rings. The Rudge used two compression rings and no oil ring. They specified the ring width as "1-1/2 millimeters", a peculiarity in an industry that was staunchly set on Imperial Standard inch measurements. Rudge also specified the valve lift in millimeters but the lash in decimal inches.
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