Shop Fabricated Substitute Gaskets

You will notice many motorcycle engines, particularly the vintage
air-cooled types, are "stacked." That is, you may have a separate
crankcase, cylinder block, cylinder head, and rocker boxes, all bolted
together, with various gaskets sealing the various parting lines.

There is a problem with this arrangement, particularly since the valve
train spans all these bolt-together components. Gaskets are inherently
compressible, notably those of fibrous composition. With heating and
cooling cycles and the mandatory "retorquing," valve clearances will
decrease markedly, even within the first hour of operation. Zero or
negative clearance is a distinct possibility with attendant engine
malfunction.

There is a remedy to the inherent dimensional instability of the stacked
assembly: Substitute sheet copper gaskets for the factory composition
types. Use the fiber gasket as a pattern and cut and punch copper sheet of
similar thickness or one grade thinner as copper will compress to a lesser
extent. You need not worry about the few thousanth's difference in the
final assembly as adjustment will accommodate any tolerance in this regard.

Apply Permatex #2 to both sides of the copper sheet gasket to affect a
perfect seal. Copper will not conform as well as fiber, but the coating of
sealant will compensate. The final assembly should be so rigid as no
further adjustment of the valve train need be done except for routine
scheduled maintanence.

Some valve train wear will take place as valve faces recede into their
seats, and some rocker arm-valve stem wear occurs as well. This wear is
nominal and as a rule of thumb, check the clearance every 1000 hours of
operation.

This is an original post and has not appeared anywhere on the net.

Nomen the Megaposter

 

A quick Google search shows that aftermarket copper cylinder base
gaskets are available for
old Triumph/BSA triples.
http://www.triples.demon.co.uk/products/gaskets/index.htm

They seem to have been developed because the cylinders moved around too
much on the crankcases and fiber gaskets began to leak.

Copper gaskets were also used on Porsches and model airplane engines.

 

This is bull. Torque heads, adjust valves, ride. Repeat at the
specified intervals your service manual calls for. WTF
kind of machine have you seen this on ?

If you're having problems with valve clearances on an older
bike, more likely the seats are receding and the clearances
tightening up because they were originally designed for leaded
gasoline.

 

I'm still trying to figure out how any gaskets in my engine are going
to affect my screw-and-locknut rocker arm adjustments. Should I be
putting copper gaskets between the screw end and the valve stem? Or is
it put some copper sheet stock between the rocker pad and the cam lobe?
I'm confused by all this. I think I'll just see what my factory
service manual recommends.

Later,

Charlie

 

Head and possibly base gasket in a pushrod engine.

My boxer engine gets a periodic head torque followed
by a valve adjustment. Base is metal to metal with
Hylomar and O rings. Torqued cold to about 28 -30 ft/lb
followed by a valve adjustment.

Oddly enough, the correct proceedure is all called out in
the service manual and works exactly as promised. How
astonishingly clever of the manufacturer to have figured
this all out ahead of time. Who woulda thunk it ?

As I suggested before, if the valve clearances are diminishing,
it's most likely recession caused by valves and seats which
were not designed for leaded gasoline. I've heard this complaint
occasionally. Copper gaskets for valve recession seems just
amazingly clueless.

 

The real advantage to using a copper cylinder base gasket had nothing
to do with changes in valve clearances. It's difficult to locate a
separate cylinder block and keep it from moving around. Connecting rod
angularity and the resulting sideways thrusting of the piston is what
makes a cylinder rock on its base and that erodes the gaskets. So, in
the early 1980's, Honda began offering engines with no separate
cylinder block that could rock back and forth as the pistons went up
and down and the rods pushed from side to side.

 

If the cylinder is bolted at the base, this should keep it from moving also.
I possibly see some movement if the head bolts also held the cylinders...

Les

 

Some engineers had a solution to cylinder block movement that turned
out to be a nightmare for home mechanics.

Suzuki's GT-750 had base bolts to help locating the cylinder block, but
even that wasn't adequate when they decided to eliminate the usual
large copper plated washers in the pressed up crankshaft in favor of a
new system, called "overhead guidance".

Cyclical reversals of rotational direction direction on the copper
plated washers was causing the washers to heat up and that would
vaporize any oil that was on them. The hot washers were causing
connecting rod seizures and rod breakage.

So Suzuki eliminated the washers and machined the piston pin boss to
allow precision
locating washers to be inserted at the small end of the rod, where
there was much less fretting motion.

Now the piston was locating the position of the big end of the rod,
keeping it from touching the crankshaft wheels. That's where the term
"overhead guidance" came from.

But Suzuki engineers decided that the cylinder block had to be more
precisely located
so the new system of guidance would work better.

So they increased the diameter of two of the large studs that passed
through the cylinder block. The cylinder block could not move around on
the studs.

It couldn't move up or down, either, after the studs rusted and the
aluminum block corroded to the studs. It took me weeks of struggling
with penetrating oils, heat and caustic liquids to get the cylinder
blocks off of two Water Buffalo engines.

 

Airhead BMWs have a cylinder/head stack with pushrods
and mechanical lifters. Even the oilhead boxers aren't
really overhead cam.

Some years have problems with valve seat recession. Not
even the dimmest of owners try to solve these problems with
copper gaskets. The agreed on cure is seats and valves more
suited to unleaded gasoline.

Seems reasonable to expect that other older bikes of the same
design would be fixed the same way.

Next tech tip please .

 

Nomen - The King of Bullshit postings.

How he comes up with such bullshit is beyond me.

pierce