tech9

Your neighbor invites you over and you discover an extremely dusty BSA
A65 , or any other vintage motorcycle for that matter, lurking in the
shadows of his garage. When questioned he answers: 1) "I lost interest
when the now teenagers were born and other responsibilities invaded on
my free time" or 2) "This guy gave it to me because his wife was tired
of tripping over it" or 3) "It broke years ago and I have never gotten
around to fixing it". In any case the poor thing has sat there unused
and is now begging you to get it back on the road. This is where the
pitfalls start. It seems so easy to clean it up and try to get it
running but that's probably the worst thing you can do for it.

While it sat there for years several things happened to it. First the
fuel evaporated out of the carburetor but the leaky fuel petcock
continues to supply more, resulting in a form of distillation process
where the gaseous products plate out on the interior of the rest of
the carb and the solid particles become just that, solid and clump up
blocking internal passages. I have seen carbs that required drilling
out of the internal passages to clear them. The next thing that
happens is that constantly changing temperatures in the storage area
cause condensation inside the motor. That leads to rusting of
unprotected metal parts. Most of the engine parts eventually become
unprotected as the oil film, over time, slides off their surfaces
revealing bare metal. The oil turns to something other than oil, God
only knows what, and thickens and clumps blocking oil passages.
Someone pulls the spark plugs out of bike stored outside, forgets to
reinstall them, and it rains creating pools of water on the top of
the pistons. The rings then rust to the bore. I had one engine where I
had to drive the pistons out of the cylinder with a wooden stick the
entire length of the bore. The bore was so eroded that a two oversize
rebore job still left minor eroded away spots.

Still another problem is the bike that was stored because it was
broken. Sometimes it passes through several owners and the failure is
forgotten. One motor I rebuilt had a broken outer race on the
crankshaft main roller bearing. What if that motor had been started?
How long would it have been before something inside really broke?

As for our beloved BSA A65 motor of which I am most familiar, it can
be a time bomb waiting to explode. The problem is that BSA designed in
an Achilles heel: the plain bush on the timing side coupled with the
use of thin shims for end play adjustment. A scenario for catastrophic
failure goes like this. The end play is suppose to be shimmed at
engine build time to less than 0.002 inches using thin shim washers.
All of the end thrust of the crank is absorbed by the shim, which will
eventually tear increasing the end play beyond the 0.002 inch
specification. Now the crank bangs back and forth, sideways, hammering
the plain bearing end surface which is not design to absorb the
pounding. End play continues to increase. If the crank moves enough it
significantly shrouds the oil transfer holes in the timing side plain
bearing, starving the rod journals for oil. Then the rod bearing
farthest from the oil supply, the left rod, overheats causing either
the piston to seize, if you're lucky, or the rod journal bearing to
seize breaking the rod and ultimately the cases. This can be avoided
if you regularly check crankshaft end play and tear down the engine at
the first sign of a change in the build specification.

The key to motor performance is the head. Leaky or burnt valves can
significantly effect performance. Thirty year old valve spring are
almost always sacked out and need replacement. Old valves can get work
hardened and the heads break off creating massive engine damage. And
old head gaskets are just as likely to leak as not, effecting
performance and, if sever enough, seizure of the pistons. My BSA A65
had a head gasket leak between cylinders not found until increasingly
poor running dictated an inspection. No wonder the intake tract always
had carbon deposits in it!

An A65 tear down engine inspection on a motor long out of service is
almost mandatory. Other manufacture's motors require the same if you
expect any kind of reliability from the completed motorcycle. All such
motorcycles should have the motor torn down, internal parts inspected
and measured, and replace parts that are worn out. Of course, the
seals, gaskets, o-rings, copper washers, etc. need to be renewed as
well. Don't forget to clean out the crankshaft oil sludge trap. No
matter what the previous owner said about the engine "status", what do
you really know for absolute truth about the engine's condition
without the tear down inspection?

This seems to be and can be expensive. If you do the work yourself as
much as possible, most large displacement twin rebuilds run $500 to
$1000. Just factor that into the cost of the motorcycle when you are
deciding to take on the project. Skimp a little on the chrome and
paint and spend the money to make the motor reliable. But don't just
get it running or you may destroy a perfectly good core motor.

The Achilles heel of the A65 can be fixed! SRM in England developed a
replacement combination roller and ball bearing for the timing side,
coupled with feeding oil through the end of the crank. Apparently it
is also being done here in the US. I have been given a contact name
who has lined up the bearings and is able to do the machine work to
the disassembled cases. I have no personal knowledge of this person's
work but if you contact me I'll give you his name and phone number.

Do yourself a big favor and take the time to correctly prepare your
new found vintage treasure. You may avoid spending money by starting
out "right" and you will save yourself the grief and concern of a
stoppage along the side of the road. Have you ever had to beg a ride
for you and your bike back to the start? I have and it is humiliating
and probably not necessary if you do your homework. A final bit of
advice: find the people and shops that know your make of bike. They
can make or break your engine rebuild. If you want a few
recommendations contact me.