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Fuel petcock flange o-ring specifications and recommendations


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My garage smells of gas and it looks like it is attributed to a leaky flange o-ring on the manual petcock.

Does anyone know the size/specifications of the o-ring, part no. GU90706116?

Also is it recommended to install a new one dry or with some kind of gasket sealer?

I was hoping to get one from a local autoparts supplier or fastener supplier so I could fix it today rather than ordering it from an online shop.

Thanks

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7 hours ago, antmanbee said:

My garage smells of gas and it looks like it is attributed to a leaky flange o-ring on the manual petcock.

Does anyone know the size/specifications of the o-ring, part no. GU90706116?

Also is it recommended to install a new one dry or with some kind of gasket sealer?

I was hoping to get one from a local autoparts supplier or fastener supplier so I could fix it today rather than ordering it from an online shop.

Thanks

This flange gasket almost never leaks, its some sort of hard plastic material. Its not an oring BTW but a square section and around 2mm thick. I've had them on and off many times with the same gasket used and never an issue. Check to make sure your fuel tap body isn't cracked. I had a new fuel tap body leaking in the open position and thought it was the seals. Turned out to be a hairline crack in the body itself. The crappy Nitrile seals swell so much that eventually opening and closing them with pliers with the seals half jamming cracks the body as the body is less than 1mm wall section in some places. This cracked tap was fine until I closed it and then months later refitted the tank opened the valve and its leaking.

ciao

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Thanks guys,

I have ordered some 16OD x14ID x2mm o-rings. They should show up later today. I think the 2mm thickness will compress and seal the flange.

Phil, I have read your posts on the rebuild of the valve. I'm sure it is the best way to get a reliable valve. This is the first time I have shut the valve since I got the bike and I hope to not have to use it much, otherwise it will most likely necessitate your repair.

Regarding the o-ring, do you think a dressing with some kind of sealer is adviseable?

The ones I ordered are, Buna-N - Standard Nitrile Butadiene Rubber.

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I think you're right. The 1.78 is the thickness.

I just got my o-rings and they measure exactly 2mm but with a round section rather than square like Phil mentioned for the OEM ones.

I put it back together and it appears to be no leaks so far. Success!!

I did not use any sealer of any type with assembly, just the o-ring with a tiny amount of grease to hold it in place.

Thanks

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3 hours ago, antmanbee said:

Thanks guys,

I have ordered some 16OD x14ID x2mm o-rings. They should show up later today. I think the 2mm thickness will compress and seal the flange.

Phil, I have read your posts on the rebuild of the valve. I'm sure it is the best way to get a reliable valve. This is the first time I have shut the valve since I got the bike and I hope to not have to use it much, otherwise it will most likely necessitate your repair.

Regarding the o-ring, do you think a dressing with some kind of sealer is adviseable?

The ones I ordered are, Buna-N - Standard Nitrile Butadiene Rubber.

If you are referring to the seal between the tap and the adapter on the tank then an oring is not appropriate. This particular seal is as I said some sort of square section plastic material as it has no compression control when tightened. If you use an o ring there it will just get crushed when you tighten the tap body nut. No sealer is required when using the std square section plastic/Teflon seal and it survives multiple fitments just fine.

Buna -n seals or Nitrile aren't recommended in gasoline, they swell, however having said that as long as its a stationary seal then that can still work. In addition Nitrile seals come in quite a few subtle variations and some swell more than others. Problem is when you undo the joint the swollen oring is now unable to be re fitted. Viton or FKM are totally fuel proof and what I recommend. As I said though a rubber O ring is the wrong seal in the tap to adaptor location. The std seal is what it is for a reason.

Ciao 

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1 hour ago, Rolf Halvorsen said:

I think the 16x1,78 means Ø16mm inside diameter with thickness 1,78mm.

Rolf

Std o ring measurement is defined by ID and cross section.

Ciao

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I am referring to the flange on the fuel tap that is attached to the underside of the plastic tank that is retained by 2 allen head cap bolts. The o-ring is slid over the fuel strainer and then rests in a circular channel in the face of the flange. The channel is about 1mm deep and the o-ring protudes 1mm above the surface of the flange and is then compressed against the flat plastic of the tank when both the cap head bolts are tightened.

I hope to not have to remove it again, but I got 9 spares.

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51 minutes ago, antmanbee said:

I am referring to the flange on the fuel tap that is attached to the underside of the plastic tank that is retained by 2 allen head cap bolts. The o-ring is slid over the fuel strainer and then rests in a circular channel in the face of the flange. The channel is about 1mm deep and the o-ring protudes 1mm above the surface of the flange and is then compressed against the flat plastic of the tank when both the cap head bolts are tightened.

I hope to not have to remove it again, but I got 9 spares.

Oh ok sorry I've missed something in the previous posts. Yes you can get away with a nitrile o ring there but a Viton or FKM would be better. I use Viton/FKM wherever possible on everything now. As I mentioned the material is totally unaffected by fuel and also has better heat tolerance. Nitrile has maximum temperature threshold of 100 deg C where Viton is somewhere around twice that. There are many areas where you engine sees temps in excess of 100 deg C and this is why old head o rings for example go hard and leak. Viton seals stay flexible in these conditions. Guzzi has superseded some o rings with Viton over the years, such as the orings that go around the cylinder studs on the Daytona engines. 

BTW look after that tank flange adapter, they are unobtainable now.

Ciao

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