Alrighty, I've been doing some tootling around the forums regarding which front cover gaskets work where and which is best for avoiding the run away o-ring. I'm making this thread mainly to confirm my findings with you folks, but also to have a consolidated thread on the matter within the first gen section - I was only able to find a few in the second and third gen tech forums, none referencing the 12A (surprise surprise ).

I'll begin by asking anyone to please correct me if I'm wrong here. What I am writing below is the conclusions I've come to based on reading a number of other threads, and not first hand experience. To anyone looking through this in the future, I suggest reading down at least a few posts to make sure I'm not off my rocker.


Cutting to the chase, the '90-95 Cosmo gasket is the best option for all [?] engine combinations, part number N390-10-502. It is a metal gasket and uses no o-ring (or Teflon washer for '86+ 13Bs), so there is no concern for the o-ring squishing out under pressure due to front cover deflection. The bolt hole on the upper right is unused for earlier engines, and the gasket will fit the smaller 12A o-ring land as well as the larger 13B (late casting S4+) lands. In all applications, neither the o-ring or Teflon washer are used in conjunction with this gasket.

The next alternative is the early ('04-08) RX8 gasket, part number N3H1-10-502B. The gasket is functionally the same as the Cosmo gasket, requiring no o-ring or Teflon washer. However, the water pump gasket is now integrated and the top left front cover bolt hole will no longer line up with any pre-Renesis engine. The top right bolt is the same case as with the Cosmo gasket.

Beyond that, we have the stock 12A paper gasket with an o-ring. Some folks choose to run without the gasket in order to apply a little bit extra clamp load to the o-ring, although it seems the effectiveness is debated. A metal gasket with no o-ring is still preferable in my mind.


In summary, the Cosmo gasket is the best all around option, albeit the most costly as well. The RX8 gasket costs less but requires more work from the user and doesn't fit up quite as well. Lastly we have the stock gasket with o-ring, or alternatively, no gasket and just an o-ring. The reasoning behind not using the stock arrangement is to reduce the likelihood of the o-ring escaping leading to a loss of oil pressure, particularly of concern when oil pressure is raised above stock. I'm looking into this presently since my current build will be using a 90psi regulator. Once again, please do not hesitate to correct any inaccuracies I may have conveyed.

Cheers!

 

I have not done it, but have read to use the RX-8 gasket and cut off the incompatible portions.

 

it cuts quite nicely, i've used it a couple of times.

 

I have used the entire gasket on multiple 12A-based 13Bs with zero drama. You can cut the water pump housing section off or use it as-is.

If you use it as-is then you don't need the little water pump spacers, as the only reason for those is to simulate the thickness of the gasket. The RX-8 gasket has material there already.



I do not use an O ring at all, just to clear any confusion. My current 13B (with FC cover and 12A end housings) makes 60psi of oil pressure at 2500rpm hot and 80 at 4000rpm, with a 12A pump, so I know it is not bypassing