Sugarcube petcocks fail

[kidsmoke]

PSA

My G5 came to me after being in Chucks care for a couple/3 years. During that time he had need to replace the petcocks and opted for the 'sugarcube ' style. They're pricy, machined, shiny, and, petcocks. Not too much goin on, right?
They both failed. One after perhaps 1000 miles and the other with less than 4000 miles.

The culprit is the black gasket material. It is not flat, but has raised 'lips' that are to keep it aligned with the three internal holes. Something causes the rigidity of these lips to suffer, and they move with the normal operation of the petcock, fouling the flow of fuel. This has been confirmed by replacing them with new 'old style' petcocks, 1/3 rd the cost of the sugarcubes, and the bike is back to normal.

My curiosity lies in the cause. What is it about the fuel that these gaskets couldn't stand up to? Knowing they will fail, you can keep a few on hand for a quick rebuild, but if they fail while traveling...Is the intent to rebuild the petcock every season? It's a simple task, but that doesn't seem right.



the link to replacement gaskets: https://www.mgcycle.com/index.php?main_page=product_info&cPath=379&products_id=5462

you can see in this pic that the holes are oblong, not round, since this gasket had moved and was jammed in there in some other position than intended.



While i was at it I thought I'd try the smaller pod filters, and replace the inlet screens on the carbs. So as of today everything going into the VHB30's is about as clean as it can be. I may decide the larger K&N's allow more air, but it's a simple swap. Anyone with anecdotes on that front?

[Kiwi_Roy]

A bout 10 years ago when I restored my loop I bought rebuild kits for the sugar cubes, they have never leaked and I run any old gas in it.
I seem to recall I got the kit from John Chicone but i'm not good at writing stuff down,
I'm pretty sure there were no springs in the kit just a bunch of different elastomers, fibre washers of different thicknesses and the filters.
https://www.thisoldtractor.com/moto_guzzi_loopframe_petcock_repair.html
I'm sure Charlie will be along shortly.

[kidsmoke]

A bout 10 years ago when I restored my loop I bought rebuild kits for the sugar cubes, they have never leaked and I run any old gas in it.

Haven't seen a 'kit' Roy. What aside from the gasket is in there? It occurs to me the spring plays a role. Do they replace that?

The G5 get's either non-E/89 or E10/93 in my care. I believe Chuck has a station that sells non-E/90, and I assume when travelling he buys E10/93, so the fuel has been pretty consistent. And Sta-bil in winter.

[Antietam Classic Cycle]

There is no kit to successfully rebuild those newer production sugar cubes - they will always be crap. The original 'cubes had extensions machined into the body that poked through the seal to keep it from turning and that works well. Old 'cubes are rebuildable, not those though.

Filters: I run these on my 'Vert: https://www.mgcycle.com/index.php?main_page=product_info&cPath=164_166&products_id=1907 over the original "air inlet tubes"/velocity stacks.

[blackcat]

The cubes on my 76 LeMans do not leak but I'm guessing that these gaskets won't work according to their list of bikes.

https://www.mgcycle.com/index.php?main_page=product_info&cPath=379&products_id=5462

[Antietam Classic Cycle]

The cubes on my 76 LeMans do not leak but I'm guessing that these gaskets won't work according to their list of bikes.

https://www.mgcycle.com/index.php?main_page=product_info&cPath=379&products_id=5462

John Chicoine and/or Bruce Giller can likely supply gaskets for yours. Harper's has several different varieties as well.
https://www.harpermoto.com/two-hole-fuel-tap-gasket-petcock-rebuild-kit.html
https://www.harpermoto.com/fuel-tap-gasket-petcock-rebuild-kit.html
https://www.harpermoto.com/four-hole-fuel-tap-gasket-petcock-rebuild-kit.html

[blackcat]

Thanks Charlie.

[Turin]

After going through 2 sets of the sugarcubes I fitted a kit to convert my Ambo to the newer style petcocks.

[Antietam Classic Cycle]

After going through 2 sets of the sugarcubes I fitted a kit to convert my Ambo to the newer style petcocks.

Yep, have done the conversion to at least three customer's Loops. Works well. Unfortunately, the original owner of my '69 Ambo tapped the tank bungs out to 1/4 NPT. 

[dguzzi]

 Looks like a split pin would hold the rubber in place. Correctly sized of course, and positioned to allow flow.  But if the 'rubber is wrong for gasoline then crap is crap....