E
Ed Price
Guest
So I'm having a close look at my 40-year-old front shocks. I decided to remove
the spring from around the shock, and found out several interesting things:
1. The spring has no "pre-load", that is, with the shock off the Amphi, the
spring pushes the shock rod out to full extension. But at full extension, there
is no more "push" (compression) left in the spring.
2. The "eye" mount at the top is just threaded onto the male-threaded shock rod.
Once you can get a vise-grip pliers in through the spring coils, and grab the
shock rod, you can unscrew the eye off of the rod. The upper spring seat, and a
somewhat conical locating stub then will just slip off the shock rod, followed
by the spring.
3. You can thus take this whole thing apart, without fear that the spring will
hop across your garage or modify your hairline. Note that the vise-grip will
likely score the polished rod, so this is really a one-way operation. You don't
want to use a shock that has a scored or burred rod!
4. My shock had a layer of rust on the top 2/3 or so of the rod length. That
tells me that the bottom 1/3 was within the shock when my Amphi sat for all
those years. That tells me my Amphi normally compresses the spring only about an
inch.
5. Now here, things get weird. The Amphi spring is 15 turns of 0.365" diameter
steel wire, which forms a coil 10.25" long with an OD of 2.5". When you plug
these values into the engineering spring equation, you get a calculated spring
rate of 180 pounds per inch. (That means that it takes 180 pounds to compress
the spring one inch; a load of 360 pounds will compress it two inches, etc.)
6. But the Amphi specs say that the front wheel loading is 564 pound (curb
weight) or 438 pounds (empty weight). Even 438 pounds loading would just about
squash a 180 pound 3.5" spring down all the way. Either the spring rate, or the
loading, isn't accurate. If my Amphi actually puts maybe 450 pounds on a front
wheel, this implies that my spring rate is really much more like 400 pounds per
inch.
7. I had bought a pair of the Maeco PK22K1 shocks from Surplus Center (see
previous posts). These shocks have been reported to work well on the Amphi
front, despite their having a spring which is 12 turns of 0.312" diameter wire
forming a 10.25" long, 2.25" OD coil. (Their rated spring rate is 200 pounds,
but I calculate only 150 pounds.) But a loaded Amphi would put 564 pounds on
this spring, and even with a 200 pound rate, it would squash it down 2.8" of the
available 3.5" of travel. And that's not good; hit a moderate bump, and you'll
bottom out on the spring.
I'm going to measure the spring rate, now that I have the coil handy. I'll let
you know what comes out of this obsession, but meanwhile, has anybody actually
weighed each corner of their Amphi?
Ed
El Cajon
67 Rust Guppy
[Non-text portions of this message have been removed]
the spring from around the shock, and found out several interesting things:
1. The spring has no "pre-load", that is, with the shock off the Amphi, the
spring pushes the shock rod out to full extension. But at full extension, there
is no more "push" (compression) left in the spring.
2. The "eye" mount at the top is just threaded onto the male-threaded shock rod.
Once you can get a vise-grip pliers in through the spring coils, and grab the
shock rod, you can unscrew the eye off of the rod. The upper spring seat, and a
somewhat conical locating stub then will just slip off the shock rod, followed
by the spring.
3. You can thus take this whole thing apart, without fear that the spring will
hop across your garage or modify your hairline. Note that the vise-grip will
likely score the polished rod, so this is really a one-way operation. You don't
want to use a shock that has a scored or burred rod!
4. My shock had a layer of rust on the top 2/3 or so of the rod length. That
tells me that the bottom 1/3 was within the shock when my Amphi sat for all
those years. That tells me my Amphi normally compresses the spring only about an
inch.
5. Now here, things get weird. The Amphi spring is 15 turns of 0.365" diameter
steel wire, which forms a coil 10.25" long with an OD of 2.5". When you plug
these values into the engineering spring equation, you get a calculated spring
rate of 180 pounds per inch. (That means that it takes 180 pounds to compress
the spring one inch; a load of 360 pounds will compress it two inches, etc.)
6. But the Amphi specs say that the front wheel loading is 564 pound (curb
weight) or 438 pounds (empty weight). Even 438 pounds loading would just about
squash a 180 pound 3.5" spring down all the way. Either the spring rate, or the
loading, isn't accurate. If my Amphi actually puts maybe 450 pounds on a front
wheel, this implies that my spring rate is really much more like 400 pounds per
inch.
7. I had bought a pair of the Maeco PK22K1 shocks from Surplus Center (see
previous posts). These shocks have been reported to work well on the Amphi
front, despite their having a spring which is 12 turns of 0.312" diameter wire
forming a 10.25" long, 2.25" OD coil. (Their rated spring rate is 200 pounds,
but I calculate only 150 pounds.) But a loaded Amphi would put 564 pounds on
this spring, and even with a 200 pound rate, it would squash it down 2.8" of the
available 3.5" of travel. And that's not good; hit a moderate bump, and you'll
bottom out on the spring.
I'm going to measure the spring rate, now that I have the coil handy. I'll let
you know what comes out of this obsession, but meanwhile, has anybody actually
weighed each corner of their Amphi?
Ed
El Cajon
67 Rust Guppy
[Non-text portions of this message have been removed]