Early Bouncing Pins

This page shows a few of the instruments which have developed
to measure detonation in the octane engine.


Before the Knock Meter.
A Gas Evolution Burette was used
with the early Bouncing Pin and
was incorporated with the first CFR
units in the 1920's.
Light knock would result in low current
flow through the sulfuric acid,
generating a small amount of hydrogen
gas. As the knock increased, the gas
volume increased.
( and you thought octane rating
was difficult today!)
The knock meter (Weston) was not
conceived & designed until 1929.

The pictures below are from a Ethyl Corp.
Knock Engine Manual dated May 1942.

The first Bouncing Pin may go back to the
20's, when Dr. H.C. Dickinson described
a " diddle pin" (not shown) he used to detect
whether an airplane engine was knocking.

The diddle pin was simply a free pin
held loosely in a guide with it's lower
end resting on the engine cylinder surface.
The pin vibrated during normal combustion
but bounced violently when knock occurred.

At right: An experimental Bouncing Pin.


24kb The Bouncing Pin was steadily improved
through changes that came from many sources.
Bouncing Pins remained standard instrument
of knock intensity until 1948.

Left: Leverage Bouncing Pin

27kb The Bouncing Pin and the characteristics
of the knock intentsity signal it produced
were, and continue to be an integral
component of the complex collection of
factors that define octane numbers that as
measured by Research & Motor Methods.

Left: Plungerless Bouncing Pin.

Right: Electro Magnetic Knock Indicator --->

Not really a bouncing pin, but an early type
of "Pickup". It uses a diaphragm exposed
to the combustion chamber like todays
knock sensors. It has an electro-magnetic
coil that can be adjusted with relation to
the diaphragm by means of the screw
on the top. The electro-magnetic does
not rest on the diaphragm but is separated
from it by a small gap. The reluctance
of the magnet field in the region of the
gap is altered by each detonantion and
this effect is amplified and damped to
indicate the amount of knock.

20 kb

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Page Created November 6, 2000

Updated 03/03/2007