Topic: Honda o-ring size format confirmation

[davis96]

When Honda lists an o-ring in this format, it is indicating ODxID correct?

So in this example, the o-ring is 6mm outer diamter, 3mm inner diameter, making the cross-section 1.5mm?

Thanks,
Davis

[davis96]

Anybody? I'm pretty sure I'm right but it'd be nice to get confirmation before I place my o-ring order from generic o-ring supplier.

[HondaMan]

No, the larger number is the ID, the smaller one is the cross-section of the rubber itself. That's the industry-standard method. In the Orient, they tend to list the large number first, small second: in the US it is opposite, but is the same part.

Also: Honda lists the MINIMUM size that will seal, based on the machined well that the O-ring fits into. Often, you can go slightly thicker, or use a slightly larger ID value, to reach it from a standard Japanes part. For example, the fuel tees in the carbs are listed as 1.9x7.9mm size: the 2.0x8.0mm is easier to find here, but it may require that you lube it prior to installation to prevent shearing. But, it will fit, and work fine. Another: the 1.9x5.9 head oil jet O-rings in the 750K1-K8 engines (and "F" series) can directly take the 2x6 instead.

[davis96]

No, the larger number is the ID, the smaller one is the cross-section of the rubber itself. That's the industry-standard method. In the Orient, they tend to list the large number first, small second: in the US it is opposite, but is the same part.

Also: Honda lists the MINIMUM size that will seal, based on the machined well that the O-ring fits into. Often, you can go slightly thicker, or use a slightly larger ID value, to reach it from a standard Japanes part. For example, the fuel tees in the carbs are listed as 1.9x7.9mm size: the 2.0x8.0mm is easier to find here, but it may require that you lube it prior to installation to prevent shearing. But, it will fit, and work fine. Another: the 1.9x5.9 head oil jet O-rings in the 750K1-K8 engines (and "F" series) can directly take the 2x6 instead.

Thanks! Just the answer I was looking for. The orings I'm looking for are the 2 on each side of the cb500 head cover (#20) in this diagram:

Do you think I could get away with 1/4" ID 1/8" cross section orings? The ID would be a tiny bit small, but the cross section be tiny bit big so it might work out?

-Davis

[davis96]

No, the larger number is the ID, the smaller one is the cross-section of the rubber itself. That's the industry-standard method. In the Orient, they tend to list the large number first, small second: in the US it is opposite, but is the same part.

Also: Honda lists the MINIMUM size that will seal, based on the machined well that the O-ring fits into. Often, you can go slightly thicker, or use a slightly larger ID value, to reach it from a standard Japanes part. For example, the fuel tees in the carbs are listed as 1.9x7.9mm size: the 2.0x8.0mm is easier to find here, but it may require that you lube it prior to installation to prevent shearing. But, it will fit, and work fine. Another: the 1.9x5.9 head oil jet O-rings in the 750K1-K8 engines (and "F" series) can directly take the 2x6 instead.

Thanks! Just the answer I was looking for. The orings I'm looking for are the 2 on each side of the cb500 head cover (#20) in this diagram:

Do you think I could get away with 1/4" ID 1/8" cross section orings? The ID would be a tiny bit small, but the cross section be tiny bit big so it might work out?

-Davis

[bryanj]

6 x 3 is the size

[HondaMan]

6 x 3 is the size

If 6x3 is the size: the .250"x.125" works out to 6.35 x 3.18mm. This yields a squish seal of:
(3.18/2.54)-1 = .25 (i.e., 25%).
Honda used 15%-18% for most of their squish-seal fits is oil pressure was involved. If you squish an O-ring more than 25%, they can split under pressure, unless it is Viton. So, if you want to sub in one that is that much more thick, see if you can find a Viton one instead.

On the other hand, a 6x3mm O-ring is easy to come by at any seal shop. I have a bunch of them, as Honda uses them everywhere. I think they cost about $.40 each in lots of 50.