The Squashed Inlet Valve
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Gold Star Shakedown II
Awakening a hibernating BSA DBD 34 Gold Star is not without its problems.
Over the past few weeks I have been eager to find out what the Gold Star mystique is all about.
Well, I can tell you that the bike handles like a dream, as well as any Norton featherbed I’ve had the pleasure of knowing. The engine seems to offer an endless and flat torque curve that makes it a real joy to wind through the twisties without having to constantly play with the gears.
The Good and the Bad of having a Rev Counter
Big singles are deceptive. It is difficult at first when learning an engine to tell how
many rpms one is really hitting. The rev counter (tachometer for us Yanks) was not functioning. I spent a weekend cleaning and oiling the chronometric tach; the insides are a clockwork (see photo below). Unlike a sweeping modern magnetic tach, chronometrics jump between increments. Its a very sexy thing...brings me back to the days of Ferrari Barchettas.
However, if you don't look down at just the right time, one could miss
an over-rev. In any case, it was not until I repaired the instrument that I was able to truly run the engine up to its proper speed.
Once I had a functioning tach, I was surprised to see that I was way off from where I thought I was in revs. Chasing Skip on the Triton, I opened the Goldie
up at what I thought was at least 5500 rpm. It turned out that I was at about 4000.
With this new found cache of power, I went crazy last weekend. With all the primary and clutch issues tightened up, and a new set of magneto points, I set off on a very spirited run on Long Island's worst and best local roads. I finally experienced the thrill behind the Gold Star's reputation....pulling up next to R-1 and GXSR kids, blipping the throttle to egg them on.
As expected, I blew them off the line only because they were
dumbfounded as to what the hell that was with the chrome tank, and an old guy in ripped Wranglers next to them.... making more noise than a 440 Olds with open pipes.
And then it happened.....
On the final stretch home, the engine rolled easily past the 6 grand mark. The
vibration was less than that of a parallel twin, and the big single begged for
more...she had finally awakened. The huge fins kept her cool as a cucumber.
And then it happened; quite a similar sound to when I blew the bottom of the
crank case on my TR6R back in the 80s. The sound was a soft thud and a free
spinning engine. As I coasted to the side of the road, I thought the worst. I
jumped off the machine and immediately checked the cases; they were fine.
I stepped on the starter and kicked it over gently. Pressure came back through
the carb. This meant an open valve. Could it be stuck open....or even worse?
It was Mother's Day, and after 33 years of marriage and bikes, my lovely wife
knew the routine...bring the trailer, and get the team back to the pits.
I rolled the bike into the shop. The bike looked good, but I knew that the
potential damage could be in the thousands. A used Gold Star head goes
for well over a grand and a half. I pulled the plug and saw the inlet (intake for us Yanks) valve clearly in line with the plug hole. This was alarming; the valve should be no where near it. I gave up for the day and celebrated with the wife and kids.
Monday was spent speculating. My good Goldie friends in the UK, Ian from
the Goldie Club, and Len Haggis the Gold Star specialist, both had encouraging
but cautious words. By Tuesday night I was ready to check it out. I came home from work and rushed into the shop. Ginger, my Corgy, watched intently as I disassembled the big single's head. Like a real thoroughbred, Goldies come apart quicly….. in less than 20 minutes. These bikes are a joy to work on; designed to be most accommodating to the club racer and home mechanic.
The photo below shows what happened. The aluminum valve spring collar snapped in half. The part that holds the cotter halves is shown sitting within the springs. This allowed the inlet valve to drop. At about 6200 rpm the piston smacked into the valve, bending it. Now the head had to be removed so I can see if the season was over for the bike.
More detail of the fractured valve spring collar. So much for race lightened
aluminum parts. I am looking to replace these with steel since I am not going
to push her past 6000 rpm, even though my Gold Star friends tell me she
will be very happy at 7000 on the open road.
Photo below shows how convenient it is to work on big singles.
The moment of truth came as I flipped the cylinder head around to take a look.
The valve was squashed nearly flat against the dome. I used a drift to push it
out. Sweat dripped onto the aluminum as the hot shop lamp illuminated the cavity. I wore my best reading glasses and explored every square millimeter with great care. I could not believe my eyes......
Remarkably the bronze valve guide took the brunt of the impact. The top of the
piston had a small but harmless dent from the impact. The fact that the valve
slipped down so far must have allowed the piston to have the correct angle of
leverage to bend it neatly like an accordion.
Parts are on order already from the motherland. We’ll be back on the road in a couple of weeks.
By Armand (Brit Iron Rebels #173)