Rebuilding the fuel Petcock from a CB900

Having tried unsuccessfully for ages to access the authoritive source
on this subject at http://www.magpage.com/~bschnick/MC/workbench/

petcock_restore/pet.html, I could wait no more, and decided to
jump right in and do it. It's not complicated, and can be done in less
than half-an-hour.

The first step is to drill out the two rivets holding the cover plate
to the body. Rather than take them back flush to the surface of the body,
I left mine flush with the cover plate. This left enough material to act
as locator pins when I put it back together.

Gently pry the cover away, taking care not to distort it. When this has
been removed, you can take out the tap and two washers. This will expose
the rubber seal. Take note of which side is facing you, because we need to
flip it over when we re-assemble the petcock.

Just for reference, this is the order of re-assembly

If your O-ring is beyond repair (and they're not available from Honda
anymore), a fellow hondacb900cb1000 member suggested that the O-ring from a
73 CB750 might work (part no. 16955-268-020). It looks a
little smaller diameter and slightly thicker, but when it's all together
it works. Thanks Mike :)

Another reader (thanks Rick) tried this solution on his 82 model, but
found the replacement washer was in fact too small (20mm as opposed to
27mm original), and was never going to fit well enough to seal properly.
The chamber may be a different size on the later model bikes (mine is an
80), but I don't have two to compare. I know the mounting nut varies in
size but I thought the actual mechanisms were the same. Maybe not? The
other option is to fabricate a replacement from 3/32" Neoprene.

Drill the pilot hole for the new screws that will hold the plate on
when we've finished. I used a 2.5 mm drill that would tap a 3 mm thread
for the screws I had. If you have a drill press, fine, but I managed to do
mine with a hand drill, making sure I had the bit perpendicular to the
workpiece.

Tap the thread in the pilot holes.

Original (82) versus #16955-268-020. Thanks for the pic
Rick.

Give the two washers a good clean. I used some 0000 steel wool on the
metal 'wave' washer.

Give the underside of the tap a polish to make sure the
contact surface is a smooth as you can make it. I had some 1500 grade wet
and dry I placed on a sheet of 6mm glass I had lying around to give me a
flat surface.

Re-assembly

1. Re-assemble the petcock by placing the
rubber seal back in, taking care to reverse it. (No, that's not rust
on the rubber, merely a colour-cast from the flash :)

2. Sit the tap on top of it, in the 'on'
position.

3. Work the wave washer over the tap

4. Next the fibre washer.

5. Place the cover plate back on, making sure
the stamped 'on' position is at the top. You might need to 'click'
it in to place if you're using the 'locating pin' system I've done.
Screw the cover plate on with your shiny new 3x12mm stainless steel
screws, or whatever you have handy that will fit :)

6. You may need to find a new O-ring to seal
the unit against the fuel tank when it is fixed in position.

Please let me know if you
spot any glaring errors.

Ian Fox http://www2.deakin.edu.au/studio/bikes/default.htm

July 27, 2006 11:05 AM