Dimensions for O-ring grove in 964 Case - 109mm spigots

[Bergan01]

Hi all,

I am building a 4.0L Engine from a 3.6 964.
Will use the GT3 80.4 crankshaft.

In relation to cylinders I need to machine the bore of my engine case to accept 109mm cylinder spigots.
As I want to incorporate the 110.72 x 3.53 mm O-ring in the case bores, Im very interested in the machining dimension needed for the groove.

Also I know that in some builds these grooves has been staggered to not comprimize the wall thickness between the cylinders in the case more than needed.

Have been searching high and low for the specific positions and dimension of this groove, if anybody has information on this subject to share that would be greatly appreciated.

Being located in Norway, its to-three times the price of the actual machine work at Turbokraft or LN to ship the case.

Thanks in advance for any help

Picture from a build thread on this forum:

[JoeMag]

I’ll measure mine this weekend. Factory machined.

[dannobee]

O-ring groove depths and widths are based on the cross section of the o-ring and are standardized. Any competent machinist will very very likely have a book such as the Parker O-Ring Handbook.

3.53mm is 0.139" cross section. A very common size.

https://www.theoringstore.com/store/index.php?main_page=page&id=39

[Bergan01]

Thanks for the replies!

As the new block is a quite expensive bit, I would like to be 100% certain on position (location in bore, width and depth) before commencing this process.

Thanks a lot for measuring Joe!

[JoeMag]

Here's measurements I got. Case is 993Cup. I did not have a gauge to get the depth directly so I used a small screw with a nut: nut on bore over groove and put screw in until it hit bottom of groove and measured length of screw sticking out of nut.

Depth of groove: 2.84mm


Groove width:



Location of groove. Deck to "top" of groove:

[Bergan01]

Hi Joe, sorry for the late reply. Thanks a lot for checking, great value for me to get these measurements.

Best Regards, Bo

[Bergan01]

One additional question regarding this O-ring that I am having trouble getting my head around:

The lower part of the cylinders that will go into the case is apprx. 109mm OD, just under based on my remembrance when I measured them.
The O-rings I have understood that is used in the machined groove of the case is the 110.72 x 3.53 mm quad ring - 999 705 023 41
As O-ring measurements are given in ID x Thickness, I do not understand how this will be able to provide any sealing as the ID is much larger than the OD of the barrels?