1974 CR250M fork emulators?

 

Does anyone know if a 1974 Honda CR250M came from the factory with fork
emulators? I am in the process of changing the seals on my Vintage MX
bike and noticed something "new to me" in the forks. A web search found
they are emulators. My intentions were to braze one or two of the inner
tube holes closed to slow down the dampening, but that has already been
done. I'm wondering just how much work has been done to these forks.
Regardless, new seals and oil will help a bunch. They both leaked, and
only had about 2 ounces of oil in them.


"War is an ugly thing, but not the ugliest of things; the decayed and
degraded state of moral and patriotic feeling which thinks nothing is
worth a war, is worse." --- John Stuart Mill: 

 

On Sep 28, 4:31�pm, AWR7MM...@webtv.net (Mike Corey) wrote:

Do your "emulators" sit under the fork springs and have an adjustment
bolt sticking up on top

My 1973 CR250M had plain old damper rods in the forks.

An emulator is a device which emulates, or behaves like, the flexible
shim stack in a cartridge fork.

Race Tech's simple Gold Valve Emulator is an adjustable spring-loaded
round plate which relieves excess pressure on rapid compression.

The basic problem with damper rods is that they have fixed orifice
holes in the side of the tube, and a certain weight of oil can only
pass through a hole of a particular size at a certain speed in order
to achieve the desired rebound damping.

Riders who want more rebound damping will use a heavier weight oil and
when the fork stroking speed doubles, the damping force quadruples.

At some speed the hole damper rod is just too small to allow the
passage of significant amounts of oil, and the fork becomes very
harsh, it can't compress fast enough because the oil won't flow
through the hole.

The Gold Valve Emulator blows off the excess pressure through the top
of the damper rod to the upper fork chamber.

My old 1968 Yamaha 250 Single Enduro had a sort of foot valve on the
damper rod.

Shock absorbers have foot valves under the piston to relieve excess
pressure on compression and they close again on rebound to slow the
flow of oil.

The damper rod in a fork has the piston on top, the damper rod is
upside down compared to a normal shock absorber, so a foot valve on a
damper rod would be on top and could be thought of as an "emulator"...

My Yamaha's foot valve had thin wave washers that acted as springs to
control the foot valve motion. The wave washers broke after a few
thousand miles and Yamaha couldn't sell them to me separately, they
wanted to sell me a whole new damper rod assembly.

Yamaha's racing engineer showed me the simple 1969 damper rod with
holes and no moving parts and told me that it was "improved"...