From: hotrod@dixie.com (The Hotrod List)
Subject: Engines of Yore #1
Date: Sat, 09 Jan 93 05:03:31 GMT
Organization: Dixie Communications Public Access.  The Mouth of the South.
To: hotrod@dixie.com
Reply-To: hotrod@dixie.com
Posted-Date: Saturday, Jan 09 00:03:23
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 Some years ago I purchased an 8-1/2x11 booklet from a used book store.
Titled "Britsh Motorcycle Engines", it was published by Floyd Clymer
Publications in the USA, and sold for $1.50.  There is no publication
date, but from the engines and machines described I believe it to date
from the mid-1950s.

 The booklet is a set of interviews with the design staff of the various
companies plus typical exploded-view drawings.  At random intervals I
will select one of the articles and compare the engine described within
to modern design practice.  I hope this will give a view of the past to
some of the readers here.

           ===================================================

 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.

-30-
                                                                                                  

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Posted by: emory!chaos.lrk.ar.us!dave.williams (Dave Williams)
Newsgroups: alt.hotrod,wiz.hotrod