[C320-list] Deck filler O-rings

[Dennis Cookson]

Thanks to both Johns for the replies. I think these rings would break if I removed them, they look very old and rather fragile!  But I found this useful list of O-ring standard sizes used in the US, as defined by Aerospace Standard AS568B:

https://www.sealanddesign.com/page/o-ring-size-as568b <https://www.sealanddesign.com/page/o-ring-size-as568b>

If we can assume that Perko used a US standard size O-ring on these deck fillers, at the risk of answering my own question the most likely suspect seems to be AS568B -222, which has a nominal ID of 1.5” and cross section of 1/8”.   The actual ID is 1.484” and actual cross section is 3.53mm.  

The other possibility is AS568B -128, which has the same ID but a nominal cross section of 3/32”, and an actual cross section of 2.62mm. However this appears to be a bit thinner than my existing rings, especially given it would be thinner still when stretched.

John S - do you think that the 1/8” cross section would be too large for the diesel/water filler caps?

Dennis Cookson
#577



> On 1 Sep 2020, at 12:29, John Stetson <jbstetson721 at gmail.com> wrote:
> 
> I just replaced ours.  After a little trial and error, the correct sizes
> are:
> 
>   - Water and Diesel - 1-1/2" by 3/32"
>   - Waste - 1-3/4" by 1/8"
> 
> West Marine did not have the right sizes, but the local hardware store did.
> 
> 
> John Stetson
> Hull #578
> 
> 
> On Tue, Sep 1, 2020 at 5:16 AM Dennis Cookson <dennis at cooksons.net> wrote:
> 
>> I need to replace the o-rings in all my deck filler caps, and I can see
>> that many owners have done this, but I can’t see any info on the size/spec
>> of the replacement ring.  Does anyone know the exact spec, especially for
>> the ring fitted to the diesel filler cap on a 1999 vintage 320?   I
>> measured the outer diameter of the filler cap threads at about 41.3mm
>> (1.625”) so presumably the o-ring inner diameter needs to be a little
>> smaller for a snug fit, perhaps 1.6” or even 1.5”?  The cross section
>> diameter appears to be 1/8”.
>> 
>> Are the diesel and water filler caps sizes identical?
>> 
>> Dennis Cookson
>> #577