Search Messages

Search Start Date:
Search End Date:
Sort Order
Sources to include:
OR Message ID:

Display Mesage #95107

Looking for Mr T (Keith) // front fender mod on 1990 PC
Written by spacetiger_j... on 7/18/2010 at 09:15 pm

Troy - Thanks for the heads up.

A bit more info on how I resolved this - I think.

The ST1100 right leg employs a cartridge vs. a damper pipe (rod) for the PC800.
For each application there is a different oil lock piece and a difference in the
way the bottom of the fork leg is machined to accept the cartridge or damper

Since I planned on using the ST1100 fork (lower part) and PC800 damper pipe and
stanchion (upper part), I had to resolve this issue. I had developed 3 options:
1. Have a machine shop to cut and re thread the ST1100 right stanchion and
shorten the cartridge to match the PC800 left leg length. It would be
expensive, perhaps 3 hours labor @$90/hr. The positive side would be a far
superior front suspension with greater adjustability.
2. Source out another Honda upper fork leg that would match the right ST1100
lower. Turns out the CBR600 F3 model looked promising. It used the same
diameter 41mm stanchion and employed a cartridge in the right leg. The F1 and
F2 models are similar to the PC800 forks. This surprised me as it showed the
ST1100 had a more sophisticated suspension over the CBR600. The F3 model came
out in 95, 4 years after the ST1100 appeared. The only question was how long
were the CBR stanchions. A quick check on eBay confirmed CBR forks are made of
unobtanium meaning the cost to go this route woulbe be in the $250 range...
3. The third option turned out to be the best as it was free. IN measuring all
of the PC800 right leg dimensions and the same for the ST1100, I found the oil
lock piece for the ST1100 matched the diameter of the machined portion of the
PC800 leg. The only issue was the length - it was about 5/8" too long. All I
had to do was cut the top done. Now, I just have to mount up both oil lock
pieces as shown in the pic I posted. The cutdown ST1100 will fit nicely into
the ST1100 fork and the PC800 damper pipe can still use the original oil lock

Some of you will note the PC800 damper pipe is displaced 5/8" up from the fork
bottom on the right. This means the spring will have some preload on it where
the left side does not have this. I plan on cutting a 5/8" spacer to place at
the bottom of the spring on the left, so both sides will have the same amount of
preload on the springs. In addition, I will have to use longer hex bolts than
the PC800. In the pic I left a ST1100 and 1 PC800 hex bolt in the pic so you
can see the length difference.

No, it just waiting for the brake discs and polished components to come in...


--- In, "Jerry" <sanae.ej@...> wrote:
> Okay,
> You have my attention. Do you know the functionality of the pieces well
enough to explain them?
> Here is how I was looking at the matter. The PC oil lock piece is a snug fit
to the damper rod. The damper rod is bolted to the bottom of the fork leg.
When the fork is in compression oil moves through the holes in the stanchion and
damper rod. The fork leg is machined so that the tip of the damper rod fit
nicely in a machined space. About an inch from the tip are 2 holes. The oil
lock piece does not cover these holes. The machined portion at the bottom
inside the fork is wide enough to leave maybe 1/4" clearance for the oil to flow
out of the 2 holes. As the stanchion bottoms out, the oil lock piece on the
damper rod goes into the stanchion. Any oil coming out the 2 holes has to go up
and outside the stanchion. Tough flowing. Perhaps it is this function that
keeps the fork from bottoming out?
> The ST1100 oil lock piece has the diameter of the machine wall in the PC800.
Since the damper rod is bolted to the fork, this means the ST1100 oil lock piece
is functioning like the inside wall of the PC fork lower. Oil can still come
out the 2 holes at the bottom of the damper rod like before. As the stanchion
gets near bottoming the ST1100 oil lock piece also fits into the stanchion.
Oddly enough, the damper rod has a very small lock ring that will not let the
stanchion compress any further using all PC components. When you use the ST1100
oil lock piece, the lock ring bottoms out just before the stanchion can bottom
out against the ST1100 oil lock piece. As near as I can tell the flow of oil
has almost no place to go at the very end. Up until that point, the oil will
flow from the bottom 2 holes in the damper rod through the gap between the
damper rod and ST1100 oil lock piece then up around the stanchion. I think it
will still function okay.
> In any case, I figured we are talking about a bottoming out with about 5" of
compression. I didn't think I would experience this very often + the right leg
is still functioning the same... so I wasn't going to sweat it. Should I?
> If this turns out to be a bigger deal, I suppose I have the [expensive] option
of having the machine shop cut down the ST1100 stanchion and re thread it at the
top. Then, I could use the ST1100 internal components and they would match up
directly with the ST1100 fork leg.
> Jerry
> --- In, "Tosh" <troy.ohio_pc800@> wrote:
> >
> >
> > ["...I find I can use the ST1100 small aluminum piece on the end of the PC
internal valving stem. Although it is not an exact fit on the stem, it will be
held in the center by the bolt...Jerry"]
> >
> > If the piece in question is called "oil lock piece" (a long hollow cone) it
needs to be a tight fit since it's the anti-bottoming valve. A loose fit on the
damper rod means it won't be able to work properly.
> >

Message Thread for message #95107