Gregory Bender

Petcock repair

Moto Guzzi V700, V7 Special, Ambassador, 850 GT, 850 GT California, Eldorado, and 850 California Police models



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My petcocks started leaking / weeping and rather than replacing them, I decided to attempt a repair. The leaking / weeping problem is usually not the washer between the tank and the petcock - which is an easy fix anyway. Rather, the leak is usually caused by a worn out rubber gasket inside the petcock.

There was a tip in the Moto Guzzi National Owners Club (MGNOC) newsletter submitted by Bruce Giller suggesting that 116 inch and 332 inch thick Viton be used as a replacement material. Viton is expensive and I couldn't easily find any locally. So I decided to try Neoprene.

The aluminum Orlandi petcocks use 332 inch material. I found a 7 34 inch diameter disc of 332 inch thick Neoprene at my local Ace Hardware store (enough for lot's and lot's of petcocks). It was in the plumbing section...I have no idea what it is normally used for.

The chrome plated brass petcocks use 116 inch material. I found a very large 116 inch thick Neoprene washer in the plumbing section of my local Menards home improvement store Danco Company, Stock Number 61808B, UPC Code 0 37155 61808 8). The washer is 1 12 inch diameter and has a 316 inch hole in the center. The remaining material leaves sufficient room to create 3 gaskets..

I stuck the Neoprene in a can of gas for about 24 hours and didn't see any deterioration; none of the material came off when I rubbed it vigorously with my thumb. So, I figure that it is pretty safe to use, although I'm certain Viton would be better.

Making the gasket and repairing the petcock is not difficult, just follow these steps:

  1. Remove the tank from the bike.
  2. Remove the petcock from the tank.
  3. Place the petcock in a vice so that the front (where the handle is located) is sticking straight up. I used two pieces of wood to sandwich the petcock so as to avoid damage.
  4. Unscrew the handle. I was able to use a pliers to grip it firmly. This technique left only very small marks on the handle for me. It is possible to disassemble the petcock without removing the handle, but reassembly can be more difficult as the spring-loaded bolt will be cockeyed.
  5. Using a wrench or a socket, unscrew the bolt from the face of the petcock. There is a spring under there, so be careful not to let things fly across the garage.
  6. You should now see the rubber gasket. I used a small pick to remove it. You will notice that each hole in the body of the petcock (one hole connects to the fuel tank, one hole connects to the fuel line) has a very small pipe that extends partway through the two corresponding holes in the rubber gasket. This construction prevents the rubber gasket from turning, thus alleviating any need for an adhesive to hold the rubber gasket in place.
  7. With the gasket removed, you can now make and install the replacement. I used a hollow punch set to create my holes. I purchased the set from a tool tent sale a number of years ago. Harbor Freight sells a similar 9 piece set (Harbor Freight item number 3838).
    • Aluminum Orlandi petcocks: Use the 332 inch material. For the outer diameter, I used a 34 inch hole punch. For the two holes inside the gasket, I used a 316 inch or a 732 inch hole punch.
    • Chrome plated brass petcocks: Use the 116 inch material. For the outer diameter, I used a 58 inch hole punch. For the two holes inside the gasket, I used a 316 inch hole punch.
  8. Assembly is pretty much the reverse of disassembly, except for the following tips:
    • I made sure that the surfaces that come into contact with the rubber gasket were free from nick, burrs, etc.
    • I put grease on all the parts before reassembly. Some of it will definitely wash off, but hopefully some will remain to help lubricate things.
    • Getting the bolt started into the face of the petcock can be challenging because the spring is working against you. I used a box-end wrench for the bolt and pressed down with a small deep-well socket on the bolt itself. I found this method very effective.
    • I used a little bit of thread locking compound on the handles. I've heard that they have a tendency to rattle loose and fall off if they are not secured well.
  9. Before mounting the tank back on the bike, I installed each petcock and tested for leaks with the handle turned in all directions, both with fuel flowing freely from the fuel line and with the fuel line plugged to provide a little back pressure.

So far, my repair seems to be working out well (repair made ). If the status changes, I'll post that information here.

Gregory Bender's thoughts:

My petcocks started leaking again only a few short months after I replaced the gaskets with neoprene. I contacted Bruce Giller and he sold me several of his Viton gaskets. They installed very well and are working great. They also have a better feel than the neoprene. Contact Bruce Giller to get your own set.

The Gnome Viton Workshop. Loop tested.
The Gnome Viton Workshop. Loop tested.

Photo courtesy of Bruce Giller.