O-ring sizes, as promised.

[robertbarr]

First, the intakes. These are ALWAYS Viton. Anything else will burn.

These are known as 'dash' sizes, an AS-568 sizing scheme. It does keep things simple...

28mm = -122 aka 'Dash 122'. And so on.
30mm = -123
32mm = -125
38mm = -128
40mm = -130

Metric sizes: Are specified by INNER DIAMETER by CROSS SECTION. You'll find them listed the other way around. To avoid confusion, we won't do that here.

All O-rings from here on are Buna, a pretty common and useful material, and a hardness of 70 (Durometer).

For the CV carbs:

Interconnecting fuel tubes use the 'Dash 10' or -010.
Choke assembly uses 10mm x 1.5mm
CV bleed screw (the tiny one) uses 2.5mm x 1.2mm
CV inlet uses 'dash 903'. This category of AS568 is known as a 'boss'; that might help.

For the VM carbs, I'll add my diagram at the end because I name them A through F. This image is hosted on my website, which will be SHUT DOWN SOON, so download this image!!

VM 'A' use 2.8mm x 1.6mm.
VM 'B' use 3.8mm x 1.25mm.
VM 'C' use Dash 9 (-009).
VM 'D' use 5.1mm x 1.6mm. This is the drain screw o-ring that also fits the CV carbs.
VM 'E' use 8.5mm x 1.5mm.
VM 'F' use Dash 11 (-011)

Happy hunting.

RB

 

[chuck hahn]

Saved in my documents. Thanks Robert

 

[Rob S.]

Thanks much.

 

[alke46]

Thank you Robert.

 

[hank2]

Thank you for this!

 

[salty_monk]

You're a good man Robert! Hope you're doing as well or better than can be expected

 

[93Bandit]

Thank you Robert! Prayers for a speedy recovery

 

[Guest]

Thank you Robert! Prayers for a speedy recovery

Thanks for the info sheet and thanks Robert. Will print this off and keep it handy

 

[650Skull]

Thumbs up. Cheers robertbarr

 

[bwringer]

Interesting how some ended up with "dash" sizes. Measuring, especially for smaller o-rings, is a maddening process because there are important differences between nominal and actual sizes, as well as manufacturing tolerances.

Plus, there are many oddball metric sizes that were used but not actually a standard manufactured size. The whole thing takes a lot of patience, conversion, and experimentation; sometimes o-rings that should work on paper don't have quite the correct fit in reality.

I found the same dash sizes for intakes years ago, when metric Viton o-rings in these sizes were unobtainable. They're actually very slightly "fatter" in cross-section than the OEM intake o-rings, which I think slightly improves the sealing. Viton is also a fair bit harder than the OEM o-rings, but that doesn't seem to matter much, and Viton intake o-rings work perfectly. I've had them in place on my bike and many others for a long time, and they were pretty inexpensive in bags of 25 from McMaster-Carr.

As Robert states, Buna-N is the correct material for the carb o-rings. Viton is a bit harder, and that makes a difference in many places, especially sealing around threaded jets and needle adjusters.

Robert, many thanks for your hard work and for sharing the data!

 

[eil]

Well now I feel bad that I don't check the forums nearly as often as I should. I hear about these things way too late.

Best wishes for a speedy recovery, Robert. And thank you for sharing your knowledge. Yet another reason why I love this community.