Never saw one that didn’t unless it was new

If they have a bad o-ring.

12 hours ago, Captain Obvious said:

So the O-ring for the early 2400 valve covers. Anyone got a source for those?

Fits in this groove as pictured above:

I assume it would be easy to measure the size and find a suitable replacement, but I also assume someone has already done that work so I don't have to do it again?

I have 99 on hand - Oil-Resistant Buna-N O-Rings!  I had to buy 100 to get the right thing.  Give me an address and cover shipping - I'll send you one.

Edited February 11Feb 11 by inline6

@inline6 my 78's valve cover doesn't have a groove for an o-ring but impressive you were able to find one that works!

 

9 hours ago, inline6 said:

I have 99 on hand - Oil-Resistant Buna-N O-Rings!  I had to buy 100 to get the right thing.  Give me an address and cover shipping - I'll send you one.

I figured that somebody went through that. I sent you PM. Thanks for the help!  

9 hours ago, chaseincats said:

my 78's valve cover doesn't have a groove for an o-ring

The grooved valve covers designed for an O-ring were only the early valve covers "2400" style. The later style design had the seal as part of the cap like your car.

Edited February 11Feb 11 by Captain Obvious

16 minutes ago, Captain Obvious said:

The grooved valve covers designed for an O-ring were only the early "2400" style. The later style design had the seal as part of the cap like your car.

Interesting!  My valve cover is the later "Nissan OHC" type but has the groove.  VIN 35883 - 6/1971

21 minutes ago, inline6 said:

Interesting!  My valve cover is the later "Nissan OHC" type but has the groove.  VIN 35883 - 6/1971

Oops. Probably my mistake. I knew it was just the "early" valve covers, and I assumed that "early" meant "2400". I may have been a little to confining with that.

Here are the measurements of the O-ring groove from #957's 2400 valve cover. It uses a true metric O-ring, not SAE.

Groove OD = 1.860" (47.24mm)

Groove ID = 1.604" (40.74mm)

Depth =  0.095" (2.41mm)

O-ring ID = 1.551" (39.40mm) uninstalled

O-ring C/S = 0.122" (3.10mm)

Definitely metric as expected. The closest SAE size is a 3/32" O-ring that has a cross-section (C/S) of 0.103" (2.61mm).

The O-ring in my car has a small stretch fit on the ID of the groove. I can't confirm that it is actually correct but it is a good fit. Here's a few pics:

 

Here is some info on JIS true metric O-rings that I googled. I believe the correct size is G40

https://www.globaloring.com/jisb-2401-metric-orings-2/

 

Edited February 11Feb 11 by CanTechZ

The one I used:

 

On 4/19/2023 at 7:55 PM, chaseincats said:

old rock hard one and being sandwiched between the oil cap and valve cover until I can find a replacement.

ZCD has them.  Cheap.  No idea of quality.

https://zcardepot.com/products/oil-cap-gasket-seal-240z-260z-280z-280zx?_pos=7&_sid=5b8d04292&_ss=r

5 hours ago, Zed Head said:

ZCD has them.

I think those are for after they went away from the grooved valve cover and moved the seal to the cap.