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 :)

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

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.

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 fibre washer over the tap
4. Next the wave washer. The images have been taken in the wrong order, but the fibre washer goes on fist, with the wave washer providing the pressure between the body and the valve. 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.

Update!

Potentially exciting news! I managed to track down a possible replacement O-ring from Mikes XS site. About half-way down the page. 

It's not an exact match, but fits in all the right places. I've been using one for nearly a year now with no trouble. 

 

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